Process for preparing a photographic silver halide photosensitive material

Abstract: A silver halide photosensitive material is subject to J-band spectral sensitization in the infrared range such that it has a sensitization maximum at a longer wavelength than 730 nm and the sensitivity at the spectral sensitivity maximum wavelength is higher by a factor of at least 4.5 than the spectral sensitivity to light having a wavelength 30 nm longer than said spectral sensitivity maximum wavelength and higher by a factor of at least 2 than the spectral sensitivity to light having a wavelength 30 nm shorter than said spectral sensitivity maximum wavelength. The photosensitive material has high sensitivity to light in a specific wavelength range such as semiconductor laser light, but low sensitivity to light in other wavelength ranges and experiences a minimal lowering of sensitivity during storage.

Description: TECHNICAL FIELD This invention relates to a process for preparing photographic silver halide photosensitive materials which are spectrally sensitized in the infrared region, and more particularly, photographic silver halide photosensitive materials of J-band spectral sensitization type which are intensely sensitized only in a necessary wavelength region in the infrared spectrum and are low sensitive in other wavelength regions. BACKGROUND OF THE INVENTION One known exposure method of photographic photosensitive material is an image forming method including scanning an original to derive image signals and subjecting photographic silver halide photosensitive material to exposure in accordance with the image signals, thereby forming a negative or positive image corresponding to the image of the original, which is known as the scanner system. There are available a number of recording apparatus utilizing an image forming method of the scanner system. Glow lamps, xenon lamps, mercury lamps, tungsten lamps, light-emitting diodes and the like were used as light sources for the recording apparatus of the scanner system. All these light sources have the practically undesirable drawbacks of a low power and a short lifetime. To eliminate these drawbacks, some scanners use coherent laser light sources such as Ne-He laser, argon laser, and He-Cd laser as the scanner system light source. These light sources offer increased outputs, but have several drawbacks that they are expensive, require modulators, and use visible light which limits the safe light of photosensitive material and renders handling difficult. In contrast, semiconductor laser has several advantages including compactness, low cost, ease of modulation, a longer lifetime than the aforementioned lasers, and emission of infrared light which allows the use of bright safe light when photosensitive material having sensitivity in the infrared region is used, leading to ease of handling. Nevertheless, there are few photosensitive materials which have high sensitivity only in the infrared region as well as shelf stability. Thus the superior properties of the semiconductor laser have not been utilized. Among a number of known techniques for the manufacture of photographic photosensitive materials is a spectral sensitization technique of expanding the sensitive wavelength region to a longer wavelength side by adding a certain cyanine dye to a photographic silver halide emulsion. This spectral sensitization technique is known to be applicable to not only the visible region, but also the infrared region. For spectral sensitization in the infrared region, sensitizing dyes having absorption relative to infrared light are used, which are described in Mees, "The Theory of the Photographic Process, Third Edition, MacMillan (1966), pages 198-201. It is desired that the spectral sensitivity, that is, the sensitivity to light in the desired infrared region is high and that the sensitivity experiences little change during shelf storage of photosensitive material and even in a liquid stage in the form of a silver halide emulsion during the preparation process. A number of sensitizing dyes have been developed. They are described in, for example, USP Nos. 2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921, and 3,582,344. The sensitizing dyes described in these patents are far from satisfactory in sensitivity and shelf stability. It is known that by adding a spectral sensitizer dye and a second specific organic compound to photosensitive materials, spectral sensitivity is markedly increased. This phenomenon is known as supersensitization. As to supersensitization in the infrared region, JP-A 191032/1984, 192242/1984, and 80841/1985 describe combinations of infrared sensitizing dyes (e.g., tricarbocyanine dyes and 4-quinolinedicarbocyanine dyes) with cyclic onium salt compounds or certain heterocyclic compounds. These known techniques, however, are not successful in achieving satisfactorily high sensitivity. Since laser beams including semiconductor laser beams have a predetermined wavelength of emission, it suffices that sensitization be made only at a characteristic wavelength matching with the oscillation wavelength of laser. Differently stated, it is often preferred that the sensitivity in wavelength regions other than the oscillation wavelength of laser is as low as possible because a wide range of safe light is available and color mixing in multilayer color photosensitive materials for conventional wet development systems and heat development systems is prevented. "Nikkei New Material", September 14, 1987, pages 47-57 describes an image recording system of the construction that a light source in the form of an assembly of three light emitting diodes of near-infrared (800 nm), red (670 nm) and yellow (570 nm) combined is used for the exposure of a color photosensitive material having three layers which are spectrally sensitized in infrared, red and yellow regions. Some systems are commercially practiced. JP-A 137149/1986 describes a recording system which uses a light source in the form of an assembly of three semiconductor lasers emitting at 880, 820 and 760 nm combined for recording an image on a color photosensitive material having three photosensitive layers having spectral sensitization at the respective wavelengths. Also JP-A 197947/1988 describes a recording system which uses a light source in the form of an assembly of three semiconductor lasers emitting at 810, 750 and 670 nm or 830, 780 and 670 nm combined for recording an image on a color photosensitive material having three photosensitive layers having spectral sensitization matched to the respective wavelengths. In general, multilayer color photosensitive materials are designed such that yellow, magenta and cyan colors are developed by exposing them to three mutually different spectral regions. When a semiconductor layer (LD) as mentioned above is used as an exposure light source, there is no design other than that three spectral sensitivities are positioned in a narrow spectral range of from red end to infrared. Then it is a key for improvement in color separation how to minimize the overlap between the respective spectral sensitivities. Heretofore available sensitizing dyes covering the near infrared to infrared region have a very broad range of spectral sensitivity so that there often occurs the overlap between the respective spectral sensitivities, resulting in low color separation. For ensuring color separation, it is known to sequentially increase sensitivity toward a shorter wavelength side or to provide a filter layer as disclosed in USP No. 4,619,892. The sequentially increasing sensitivity toward a shorter wavelength side can invite an increase of fog and deteriorate live storage stability. Live storage stability is inherently poor in the case of infrared sensitization. It is difficult to achieve high sensitivity in the case of infrared sensitization. The technique of providing intense sensitization only at a specific wavelength thus enabling light exposure in a narrow range without color mixing is known as J-band sensitization in the photographic silver halide emulsion spectral sensitization technique. The J-band results from the formation of a special associated product designated J-aggregate which has a very high absorbance and exhibits a steep absorption peak having a narrow half-value width. There also appears a sharp spectral sensitivity distribution spectrum reflecting this absorption characteristic. This J-band sensitization is now an essential spectral sensitization technique in the manufacture of full color photosensitive materials. Although many practical examples are known as to the spectral sensitization in the visible light region, only a few examples are known in the infrared light region. As long as the inventors know, brief descriptions are found only in A.H. Herz, Photogr. Sci. Eng., Vol. 18, No. 3, 323-335 (1974) and H. Kampfer, Proceedings of ICPS, pp 366-369 (1986). No example is found as to spectral sensitization in the co-presence of dye-providing substances such as color couplers. More particularly, the above-cited publications refer to the formation of J-band. As seen from the description that a very broad spectral sensitivity distribution spectrum is obtained with silver iodobromide and silver chlorobromide emulsion predominantly based on silver bromide, this spectral sensitization is deemed to be a mixture of M-band type spectral sensitization due to molecular state molecules of the sensitizing dye and J-band type spectral sensitization due to the J-aggregate of the sensitizing dye. Since laser exposure, handling under safe light, and application to full color photosensitive material were not taken into full account, it was not acknowledged to suppress sensitivity in unnecessary regions. J-band sensitization was achieved, but it was insufficient for practical use because predominant J-band type spectral sensitization having a narrow spectral sensitization distribution was by no means established. Therefore, there is a need for the development of an infrared region J-band sensitization technique having improved safe light availability and color separation and a photosensitive material utilizing the same technique. In infrared sensitized systems having maximum sensitization on a longer wavelength side than 730 nm, significant desensitization occurs when the amount of a sensitizing dye added is increased (see USP 4,011,083). This desensitization is well known as inherent desensitization caused by the sensitizing dye itself. It is also known that dyes of longer wavelength absorption give rise to more desensitization. Since the above-mentioned infrared region sensitizing dyes have a broad spectral sensitivity distribution based on molecular state absorption and induce a substantial amount of such desensitization, the surface coverage of silver halide grains with the sensitizing dye is generally limited to about 10 to 20%. This naturally results in a low percent light capture and a very low spectral sensitivity as compared with the spectral sensitivity available in the visible region. Therefore, there is a need for a sensitization method capable of J-band sensitization to provide a high spectral sensitivity matched with the infrared region, especially the wavelength of semiconductor laser light while minimizing sensitivity in unnecessary regions. To provide spectral sensitization at a longer wavelength than 730 nm, the spectral sensitizing dye used is that capable of efficiently absorbing the longer wavelength light. Infrared sensitizing dyes are disclosed in JP-A 137149/1986, 197947/1988, 13505/1980, 191032/1984, 192242/1984, and 80841/1985. For such M-band type spectral sensitization, dyes having a long conjugated methine chain are used to provide absorption in the infrared region. The dyes having a long conjugated methine chain are deemed quite difficult to form J-aggregates on silver halide grains to achieve predominant J-band sensitization. They are known to provide less sensitization due to their not so basic reduction potential and to possess less stability against wet heat and oxygen due to their basic oxidation potential as compared with visible region dyes. This propensity becomes more outstanding in the co-presence of dye providing substances such as color couplers which are needed to provide full color images and various compounds used in photosensitive materials of the multilayer full color heat developable system as described in USP 4,500,626, 4,483,914, 4,503,137, and 4,559,290, JP-A 149046/1983, 133449/1985, 218443/1984, and 238056/1986, EP-A 220,746 A2 and 210,660 A2, Technical Report 87-6199, etc. In order to consistently manufacture silver halide photosensitive material on a large scale at low cost, it sometimes occurs that a silver halide emulsion which has been spectrally sensitized by adding spectral sensitizing dyes must be stored in solution state for several hours. A substantial lowering of sensitivity in such a state due to the infrared region sensitizing dye as mentioned above is a serious problem in the large scale manufacture. Moreover, a lowering of sensitivity and an increase of fog during a period from the end of manufacture to use are also serious problems. Some of currently commercially available infrared-sensitive silver halide photosensitive materials and even black-and-white infrared-sensitive silver halide photosensitive materials which are free of color couplers have to be stored in refrigerators prior to use because otherwise they lose capability. There exist a need for improvement in this respect. The processing speed is now increasing with the advance of automatic processors. As a result of such speedup, there is left a short time for discoloration during treatment of dyes so that residual color associated with the sensitizing dyes becomes noticeable. There is a need for a sensitizing system having minimized residual color. EP-A-244 184 discloses a light sensitive silver halide photographic material. EP-A-368 356 discloses a silver halide color photographic material comprising specific spectrally sensitizing compounds. EP-A-276 319 discloses a silver halide color photographic material comprising specific couplers. US-A-5,296,343 discloses a silver halide photographic emulsion spectrally sensitized in the wavelength range longer than 730 nm. EP-A-342 553 discloses a heat developing color photosensitive material. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a process for preparing a photographic silver halide photosensitive material having high sensitivity to infrared light, which is a rapidly processable photographic silver halide photosensitive material having high spectral sensitivity in a desired wavelength region and minimized spectral sensitivity in unnecessary wavelength regions, more specifically having high spectral sensitivity to semiconductor laser light and fully low spectral sensitivity to light other than the semiconductor laser light, which preferably is a very rapidly processable photographic silver halide photosensitive material in which an emulsion during storage in solution state prior to coating and the photosensitive material during shelf storage after coating are minimized in lowering of photographic sensitivity in the infrared region and increase of fog density, which preferably is a photographic silver halide photosensitive material having high sensitivity to infrared light and leaving minimized residual color in rapid processing, and which preferably is a photographic silver halide photosensitive material for use in wet and heat development systems having improved color separation upon exposure to semiconductor laser having a longer wavelength than 730 nm, high sensitivity, and improved live storage stability. This object of the present invention is achieved by the process defined in claim 1 and claim 2, respectively. Prefered embodiments are defined to the subclaims. The at least one photographic silver halide emulsion layer is spectrally sensitized with at least one spectral sensitizer such that the layer has a sensitization maximum at a longer wavelength than 730 nm and the sensitivity at the spectral sensitivity maximum wavelength is higher by a factor of at least 4.5 than the spectral sensitivity to light having a wavelength 30 nm longer than said spectral sensitivity maximum wavelength and higher by a factor of at least 2 than the spectral sensitivity to light having a wavelength 30 nm shorter than said spectral sensitivity maximum wavelength. The spectral sensitizer used herein has a polarographic half-wave reduction potential at values ≤ -1.26 V or at a value of -1.26 V or more negative and a polarographic half-wave oxidation potential at values ≥ 0.38 V or at a value of 0.38 V or more positive relative to the saturated calomel electrode. The spectral sensitivity distribution spectrum of a photographic silver halide emulsion does not precisely coincide with the absorption on silver halide of the sensitizing dye used to provide spectral sensitization, but reflect the latter. Therefore, the object of the present invention is also achieved by a process as defined above wherein a silver halide photosensitive material comprises a support and at least one layer of a photographic silver halide emulsion thereon, wherein the at least one photographic silver halide emulsion layer is spectrally sensitized with at least one spectral sensitizer such that said layer has a sensitization maximum at a longer wavelength than 730 nm, and the light absorption due to said spectral sensitizer satisfies both the requirements of formulae (1) and (2): Abs(peak wavelength)/Abs(peak wavelength + 30 nm) ≥ 4.5 Abs(peak wavelength)/Abs(peak wavelength - 30 nm) ≥ 2 DETAILED DESCRIPTION OF THE INVENTION The main object of the present invention is achieved by preparing the silver halide emulsion layer possessing a sensitization maximum at a longer wavelength than 730 nm and meeting the specific spectral sensitivity ratios and/or optical density ratios as defined in the claims. It is difficult to provide satisfactory sensitization simply by adding a spectral sensitizing dye to a silver halide emulsion. The above-specified spectral sensitivity ratio and/or optical density ratio can be met by adding 6.2x10 -7 mol to 2.7x10 -6 mol, preferably 9.3x10 -7 to 2.1x10 -6 mol, more preferably 1.1x10 -6 mol to 1.9x10 -6 mol of a spectral sensitizing dye per square meter of silver halide grain surface area to a silver halide emulsion and aging the emulsion at a temperature of 40 to 90°C, preferably 50 to 80°C, more preferably 60 to 70°C for at least 15 minutes, preferably at least 30 minutes. It is to be noted that 6.2x10 -7 mol of the spectral sensitizing dye corresponds to a coverage of slightly less than 40% of the grain surface, provided that one molecule of the sensitizing dye occupies an area of 106 square angstrom and silver halide grains adsorb all the sensitizing dye added as a mono layer. Whether or not the above-specified sensitivity ratios are met may be determined by exposing a film coated with a silver halide emulsion layer having a spectral sensitizing dye added thereto to light through a wedge in a equal-energy spectral exposure apparatus, developing the film, and comparing sensitivity at different exposure wavelengths. The sensitivity is an inverse of an exposure which provides a density equal to a fog density plus 0.2 in the case of black-and-white development, an inverse of an exposure which provides a density equal to a fog density plus 0.5 in the case of color development, and an inverse of an exposure which provides a density equal to a fog density plus 1.0 in the case of heat development color systems. In the absence of a color coupler, the film was developed with a developer having the following composition at 20°C or lower for 10 minutes (or 5 minutes when silver chlorobromide containing 80% or more silver chloride or silver chloride is used), followed by stopping, fixation and water washing. Black-and-white developer composition Metol 2.5 g L-ascorbic acid 10.0 g Potassium chloride 1.0 g Navox 35.0 g Water totaling to 1000 ml pH (20°C) 9.8 In the presence of a color coupler, color development was carried out in accordance with the following procedure. Step Temp. Time Replenishment Tank volume Color development 35°C 45 sec. 161 ml 17 l Bleach-fix 30-35°C 45 sec. 215 ml 17 l Rinsing (1) 30-35°C 20 sec. - 10 l Rinsing (2) 30-35°C 20 sec. - 10 l Rinsing (3) 30-35°C 20 sec. 350 ml 10 l Drying 70-80°C 60 sec. The respective processing solutions had the following compositions. Color developer Tank Replenisher Water 800 ml 800 ml Ethylenediamine-N,N,N',N'-tetramethylene phosphonic acid 1.5 g 2.0 g Triethanol amine 8.0 g 12.0 g Sodium chloride 1.4 g - Potassium carbonate 25.0 g 25.0 g N-ethyl-N-(b-methanesulfonamide-ethyl)-3-methyl-4-aminoaniline hydrogen sulfate 5.0 g 7.0 g N,N-bis(carboxymethyl)hydrazine 5.5 g 7.0 g Brightener (WHITEX 4B) 1.0 g 2.0 g Water totaling to 1000 ml 1000 ml pH (25°C) 10.05 10.45 Blix solution (tank solution = replenisher) Water 800 ml Ammonium thiosulfate (70%) 100 ml Sodium sulfite 17 g Iron (III) ethylenediaminetetraacetate ammonium 55 g Disodium ethylenediaminetetraacetate 5 g Ammonium bromide 40 g Water totaling to 1000 ml pH (25°C) 6.0 Rinsing water (tank solution = replenisher) Deionized water (calcium and magnesium contents less than 3 ppm) The heat development was carried out in accordance with the procedure of Example 5 which is described later. Whether or not the above-specified optical density ratios or absorbance ratios are met may be determined by measuring the absorbance of a film coated with a silver halide emulsion layer having a spectral sensitizing dye added thereto using a spectrophotometer with integrating sphere (for example, spectrophotometer model U-3410 by Hitachi, Ltd.). The wavelength region on measurement ranges from a wavelength 30 nm longer than the peak wavelength to a wavelength 30 nm shorter than the peak wavelength in the infrared region. Measured are an absorbance (Abs) at the peak wavelength, an absorbance (Abs) at a wavelength 30 nm longer than the peak wavelength, and an absorbance (Abs) at a wavelength 30 nm shorter than the peak wavelength. Their ratios are then calculated in accordance with formulae (1) and (2). In a preferred embodiment, in addition to meeting the above-specified sensitivity ratios, the sensitivity at the spectral sensitivity maximum wavelength is higher by a factor of at least 3 than the spectral sensitivity to light having a wavelength 20 nm longer than said spectral sensitivity maximum wavelength. In order to provide a photographic silver halide photosensitive material in which an emulsion during storage in solution state prior to coating and the photosensitive material during shelf storage after coating are minimized in lowering of photographic sensitivity in the infrared region and increase of fog density in accordance with the object of the present invention, it is desired that the spectral sensitizer used herein has a polarographic half-wave reduction potential at values ≤ -1.26 V and a polarographic half-wave oxidation potential at values ≥ 0.38 V relative to the saturated calomel electrode (SCE). The spectral sensitization efficacy and polarographic half-wave reduction potential of spectral sensitizing dyes are related such that the more basic the half-wave reduction potential, the higher becomes the efficacy, as described in T. Tani, T. Suzumoto, K. Ohzeki, Journal of Physical Chemistry, Vol. 94 (1990), page 1298. Most of conventional sensitizing dyes providing molecular type spectral sensitization as described in the patents relating to infrared sensitization have a half-wave reduction potential of -1.1 to -1.25 V vs SCE, which is not so negative that their sensitization efficacy is very low as compared with visible region sensitizing dyes having a more negative half-wave reduction potential. The present invention which is successful in infrared sensitization by J-band sensitization enables the use of sensitizing dyes having a polarographic half-wave reduction potential at values ≤ -1.26 V vs SCE and a higher sensitization efficacy therewith. For enhancing spectral sensitivity, it is desired that the sensitizing dye used have a polarographic half-wave reduction potential at values ≤ -1.26 V vs SCE. On the other hand, most of conventional sensitizing dyes providing molecular type spectral sensitization as described above have an oxidation potential less than 0.40 V vs SCE, and some have an oxidation potential less than 0.30 V vs SCE. The oxidation potential of this level is considerably little as compared with visible region sensitizing dyes. The less the oxidation potential, the more susceptible to oxidation is the sensitizing dye. Therefore, infrared photosensitive materials which have been sensitized with such conventional molecular type spectral sensitizing dyes having a less oxidation potential experience a noticeable loss of sensitivity during shelf storage. We have found that the stability during shelf stability is substantially improved by effecting J-band sensitization with a sensitizing dye having an oxidation potential at values ≥ 0.38 V vs SCE. In order that an emulsion during storage in solution state prior to coating and the photosensitive material during shelf storage after coating be minimized in lowering of photographic sensitivity in the infrared region and increase of fog density in accordance with one of the objects of the present invention, it is desired that the sensitizing dye used have a polarographic half-wave oxidation potential at values ≥ 0.38 V vs SCE. The polarographic half-wave potential may be measured in accordance with the phase-discriminating second harmonic AC voltammetry described in T. Tani, K. Ohzeki, K. Seki, Journal of the Electrochemical Society, vol. 138, pages 1411-1415 and J. Lenhard, Journal of Imaging Science, vol. 30, pages 27-35. In the formula, Z 1 and Z 2 , which may be identical or different, represent a sulfur atom or a selenium atom. Y 1 and Y 4 each represent a hydrogen atom. In addition, Y 1 may represent a methyl, ethyl, hydroxyl or methoxy group where Y 2 is not a hydrogen atom, and Y 4 may represent a methyl, ethyl, hydroxyl or methoxy group where Y 5 is not a hydrogen atom. Y 2 and Y 5 are independently selected from the class consisting of a hydrogen atom, substituted or unsubstituted alkyl group having up to 3 carbon atoms (preferably, for example, methyl, ethyl, propyl, methoxymethyl and hydroxyethyl groups), hydroxyl group, chlorine atom, bromine atom, methoxy group, ethoxy group, monocyclic aryl group (preferably, for example, phenyl, tolyl, anisil, 2-pyridyl, 4-pyridyl, 2-thienyl and 2-furyl groups), acetylamino group, and propionylamino group. In addition, Y 2 and Y 1 taken together may form a methylenedioxy, trimethylene or tetramethylene group, and Y 5 and Y 4 taken together may form a methylenedioxy, trimethylene or tetramethylene group. Y 3 and Y 6 each represent a hydrogen atom. In addition, Y 3 and Y 2 taken together may form a methylenedioxy, ethylenedioxy, trimethylene, tetramethylene or tetradehydrotetramethylene group, and Y 6 and Y 5 taken together may form a methylenedioxy, ethylenedioxy, trimethylene, tetramethylene or tetradehydrotetramethylene group. R 1 and R 2 , which may be identical or different, are a substituted or unsubstituted alkyl or alkenyl group, preferably having up to 10 carbon atoms in total. Preferred substituents on the alkyl and alkenyl groups include a sulfo group, carboxy group, halogen atom, hydroxy group, alkoxy group having up to 6 carbon atoms, substituted or unsubstituted aryl group having up to 12 carbon atoms (e.g., phenyl, tolyl, sulfophenyl, carboxyphenyl, naphthyl, 5-methylnaphthyl, and 4-sulfonaphthyl groups), heterocyclic group (e.g., furyl and thienyl groups), substituted or unsubstituted aryloxy group having up to 12 carbon atoms (e.g., chlorophenoxy, phenoxy, sulfophenoxy, hydroxyphenoxy and naphthyloxy groups), acryl group having up to 8 carbon atoms (e.g., benzenesulfonyl, methanesulfonyl, acetyl and propionyl groups), alkoxycarbonyl group having up to 6 carbon atoms (e.g., ethoxycarbonyl and butoxycarbonyl groups), cyano group, alkylthio group having up to 6 carbon atoms (e.g., methylthio and ethylthio groups), substituted or unsubstituted arylthio group having up to 8 carbon atoms (e.g., phenylthio and tolylthio groups), substituted or unsubstituted carbamoyl group having up to 8 carbon atoms (e.g., carbamoyl and N-ethylcarbamoyl groups), acylamino group having up to 8 carbon atoms (e.g., acetylamino and methanesulfonamino groups), acylaminocarbonyl group having up to 8 carbon atoms (e.g., acetylaminocarbonyl and methanesulfonylaminocarbonyl groups), and ureido group having up to 7 carbon atoms (e.g., 3-ethylureido and 3,3-dimethylureido groups). More than one substituent may be present on the alkyl and alkenyl groups. R 3 and R 5 represent a hydrogen atom. In addition, R 3 and R 1 taken together may form a five- or six-membered ring, and R 5 and R 2 taken together may form a five- or six-membered ring. R 4 is a hydrogen or a substituted or unsubstituted lower alkyl group. R 6 is a hydrogen atom, methyl group, ethyl group or propyl group. R 7 is a substituted or unsubstituted lower alkyl group or substituted or unsubstituted phenyl group. X is a counter ion necessary to neutralize the electric charge. Letter n is equal to 0 or 1, n being 0 in the case of an intramolecular salt. As seen from formula (I), Z 1 and Z 2 form nitrogenous heterocyclic nuclei with adjacent carbon and nitrogen atoms. Examples of the nitrogenous heterocyclic nucleus include benzothiazole, 5-methylbenzothiazole, 5-ethylbenzothiazole, 5-propylbenzothiazole, 5,6-dimethylbenzothiazole, 5-methoxybenzothiazole, 5-ethoxybenzothiazole, 5,6-dimethoxybenzothiazole, 5-methoxy-6-methylbenzothiazole, 5-phenylbenzothiazole, 5-p-tolylbenzothiazole, 5-acetylaminobenzothiazole, 5-propionylaminobenzothiazole, 5-hydroxybenzothiazole, 5-hydroxy-6-methylbenzothiazole, 5,6-dioxymethylenebenzothiazole, 4,5-dioxymethylenebenzothiazole, 5,6-trimethylenebenzothiazole, naphtho[1,2-d]thiozole, 5-methylnaphtho[1,2-d]thiazole, 8-methoxynaphtho[1,2-d]thiazole, 8,9-dihydronaphthothiazole, benzoselenazole, 5-methylbenzoselenazole, 5-ethylbenzoselenazole, 5-methoxybenzoselenazole, 5-ethoxybenzoselenazole, 5,6-dimethylbenzoselenazole, 5-hydroxybenzoselenazole, 5-hydroxy-6-methylbenzoselenazole, naphtho[1,2-d]selenazole, etc. Examples of the group represented by R 1 and R 2 include methyl, ethyl, propyl, allyl, pentyl, hexyl, methoxyethyl, ethoxyethyl, phenethyl, tolylethyl, phenoxyethyl, phenoxypropyl, naphthoxyethyl, sulfophenethyl, 2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, carbamoylethyl, hydroxyethyl, 2-(2-hydroxyethoxy)ethyl, carboxymethyl, carboxyethyl, ethoxycarbonylmethyl, sulfoethyl, 2-chloro-3-sulfopropyl, 3-sulfopropyl, 2-hydroxy-3-sulfopropyl, 3-sulfobutyl, 4-sulfobutyl, 2-(2,3-dihydroxypropyloxy)ethyl, 2-[2-(3-sulfopropyloxy)ethoxy]ethyl, acetylaminoethyl, methylsulfonylaminoethyl, methylsulfonylaminocarbonylethyl, acetylaminocarbonylethyl groups, etc. Preferred examples of the substituted or unsubstituted lower alkyl group represented by R 4 include methyl, ethyl, propyl and benzyl groups. Preferred examples of the substituted or unsubstituted lower alkyl and phenyl groups represented by R 7 include methyl, ethyl, propyl, butyl, benzyl, phenyl, p-methoxyphenyl and p-tolyl groups. Examples of the counter ion represented by X 1 include cations, for example, alkali metal ions such as potassium and sodium, ammonium ions such as triethylammonium and N,N-dimethylbenzylammonium, and immonium ions such as pyridinium and anions, for example, halide ions such as chloride ion, bromide ion and iodide ion, sulfonate ions such as p-toluenesulfonate and benzensulfonate, and carboxylate ions such as acetate. Preferred among the sensitizing dyes of formula (I) are those wherein at least one of Z 1 and Z 2 represents a sulfur atom. More preferably, Y 1 and Y 4 represent hydrogen atoms, Y 2 and Y 5 represent a hydrogen atom, methyl, ethyl, propyl, methoxymethyl, hydroxyethyl, hydroxy, methoxy, ethoxy, phenyl, or acetylamino group, Y 2 and Y 3 taken together and Y 5 and Y 6 taken together represent a methylenedioxy, tetramethylene or tetradehydrotetramethylene group, R 1 and R 2 represent a sulfo, carboxy, alkoxy, hydroxy, alkylacylamino, alkylacylaminocarbonyl group, alkyl group optionally having a monoalkyl-substituted ureido group and having up to 6 carbon atoms in total, or aryloxyalkyl group having up to 12 carbon atoms in total, and R 6 represents a hydrogen atom. Several illustrative, non-limiting examples of the sensitizing dye of formula (I) are given below. Among these dyes, anionic sensitizing dyes are especially preferred since they are likely to exhibit sharp spectral sensitivity probably because of their good adsorptivity and are stable during aging in solution state in a coating emulsion having added thereto a gelatin dispersion containing a dye-providing substance because of their low solubility in oil. Also for unknown reasons, the anionic dyes are improved in live shelf stability as compared with cationic dyes. The sensitizing dyes of formula (I) used herein are known compounds. They may be synthesized in accordance with the techniques described in JP-A 104917/1977, JP-B 25652/1973, JP-B 22268/1982, F.M. Hamer, The Chemistry of Heterocyclic Compounds, Vol. 18, The Cyanine Dyes and Related Compounds, A. Weissberger ed., Interscience, New York, 1964, D.M. Sturmer, The Chemistry of Heterocyclic Compounds, Vol. 30, A. Weissberger and E.C. Taylor ed., John Willy, New York, page 441, and Japanese Patent Application No. 270164/1990. The cyanine dye of formula (I) may be introduced in the silver halide emulsion according to the present invention by directly dispersing the dye in the emulsion. It is also possible to dissolve the dye in a solvent and then add the solution to the emulsion. The solvents used herein include water, methanol, ethanol, propanol, acetone, methylcellosolve, 2,2,3,3-tetrafluoropropanol, 2,2,2-trifluoroethanol, 3-methoxy-1-propanol, 3-methoxy-1-butanol, 1-methoxy-2-propanol, and N,N-dimethylformamide alone or in admixture of two or more. Several alternative methods are available as disclosed in USP 3,469,987 wherein a dye is dissolved in a volatile organic solvent, the solution is dispersed in water or hydrophilic colloid, and the dispersion is added to an emulsion; JP-B 24185/1971 wherein a water-insoluble dye is dispersed in a water-soluble solvent without dissolution, and the dispersion is added to an emulsion; JP-B 23389/1969, 27555/1969 and 22091/1982 wherein a dye is dissolved in an acid and the solution is added to an emulsion or a dye is dissolved in water to form an aqueous solution in the co-presence of an acid or base and the solution is added to an emulsion; USP 3,822,135 and 4,006,025 wherein an aqueous solution or colloidal dispersion of a dye in the co-presence of a surfactant is added to an emulsion; JP-A 102733/1978 and 105141/1983 wherein a dye is directly dispersed in hydrophilic colloid and the dispersion is added to an emulsion; and JP-A 74624/1976 wherein a dye is dissolved with the aid of a red-shifting compound and the solution is added to an emulsion. Ultrasonic may also be utilized to dissolve the dye. In the practice of the present invention, the sensitizing dye may be added to the silver halide emulsion at any stage of emulsion preparation which has been recognized to be significant for spectral sensitization in accordance with the claims. For example, the dye may be added during the step of forming silver halide grains, at a stage prior to desalting, during desalting, or at a stage after desalting, but prior to the onset of chemical ripening or any combination thereof as disclosed in USP 2,735,766, 3,628,960, 4,183,756, and 4,255,666, JP-A 184142/1983 and 196749/1985, or immediately before or during the step of chemical ripening. Furthermore, as disclosed in USP 4,255,66 and JP-A 7629/1983, a single compound alone or compounds of different structures separately or in admixture may be added entirely in one step, or added as divided portions during different steps, for example, during the grain formation step and during or after the chemical ripening step, or before, during and after the chemical ripening step. In the case of addition of divided portions, the type and combination of compounds may be altered between the divided portions. It is also acceptable to add the dye in the silver halide grain formation step by mixing it with a water-soluble halide necessary for grain formation or to add the dye in the chemical ripening step by mixing it with a chemical sensitizer. A predetermined amount of the dye may be added within a short time or continuously over a long time, for example, over a period associated with the grain formation step covering from the end of nucleus formation to the completion of grain formation or during most of the chemical ripening step. More preferably, the dye is added at any stage from the end of nucleus formation in the grain formation step to an early half of the chemical ripening step. The temperature is preferably from 50 to 80°C, more preferably 60 to 70°C. After the sensitizing dye has been added, the emulsion is preferably ripened at the temperature for at least 15 minutes, more preferably from 30 minutes to 10 hours. The silver halide used herein includes silver chloride, silver bromide, silver iodide, silver chlorobromide, silver chloroiodide, silver chloroiodobromide, and silver iodobromide. The silver halide emulsion used herein may be an emulsion containing grains of such a silver halide alone or a mixture of silver halides. The silver halide grains include grains having different phases between the core and shell, grains of multiphase structure having a junction, grains having a localized phase on the grain surface, and grains of totally homogeneous phase, and mixtures thereof. The silver halide grains preferably have a mean particle size of 0.1 to 2.2 µm, more preferably 0.1 to 1.2 µm, most preferably 0.1 to 0.8 µm. The silver halide grains may be either mono-dispersed or multi-dispersed. As to shape, the grains may have a regular crystal form such as cube, octahedron, and tetradecahedron (14 sided), an irregular crystal form or a composite form of these crystal forms, or a mixture of different crystal form grains. Also acceptable are plate grains. An emulsion in which plate grains having an aspect ratio of at least 5, especially at least 8 occupy at least 50% of the entire projected area of grains is preferred. The aspect ratio is a ratio of diameter to thickness wherein the diameter of a grain is the diameter of a circle having an area equal to the projected area of the grain and the thickness is the distance between two approximately parallel major surfaces. An emulsion containing a mixture of grains of different crystal forms is also useful. These emulsion may be either of the surface latent image type wherein latent images are predominantly formed at the surface or the internal latent image type wherein latent images are formed in the grain interior. The photographic emulsion used herein may be prepared by any conventional technique as disclosed in P. Grafkides, "Chimie et Physique Photographique", Paul Montel (1967), G.F. Duffin, "Photographic Emulsion Chemistry", Focal Press (1966), V.L, Zelikman et al., "Making and Coating Photographic Emulsion", Focal Press (1964), F.H. Claes et al., The Journal of Photographic Science, (21) 39-50, 1973, F.H. Claes et al., The Journal of Photographic Science, (21) 85-92, 1973, JP-B 42737/1980, USP 4,400,463, 4,500,626, 4,628,021, 4,801,523, JP-A 218959/1987, 25159/1987, 213836/1988, 218938/1988, Japanese Patent Application No. 291487/1987, and Research Disclosure, No. 17029 (1978). More particularly, acidic, neutral and ammonia methods may be used. The mode of reacting a soluble silver salt with a soluble halide may be single jet, double jet or a combination thereof. It is also employable to form grains in the presence of excess silver, which is known as reverse mixing method. One special type of the double jet technique is by maintaining constant the pAg of a liquid phase in which silver halide is created, which is known as a controlled double jet technique. This technique results in a silver halide emulsion of grains having a regular crystalline form and a nearly uniform particle size. Also employable are emulsions prepared by the conversion technique including the step of converting a once formed silver halide to a silver halide having a lower solubility product before the completion of a silver halide grain formation step, and emulsions in which similar halogen conversion is carried out after the completion of a silver halide grain formation step. In the preparation of silver halide grains according to the present invention, silver halide solvents may be used. Examples of the silver halide solvent which are often used include thioether compounds (for example, USP 3,271,157, 3,574,628, 3,704,130, and 4,276,347), thion compounds and thiourea compounds (for example, JP-A 144319/1978, 82408/1978, and 77737/1980), amine compounds (for example, JP-A 100,717/1979), and thiocyanates. Ammonia may also be used in an amount not giving adverse effect. Further, nitrogeneous compounds may be added at the stage of silver halide grain formation as disclosed in JP-B 7781/1971, JP-A 222842/1985 and 122935/1985. In preparing silver halide grains according to the present invention by adding a silver salt solution (e.g., silver nitrate solution) and a halide solution (e.g., sodium chloride solution), grain growth can be accelerated by increasing the flow rate, amount and concentration of the solutions with time. For this acceleration technique, reference may be made to British Patent 1,335,925, USP 3,672,900, 3,650,757, and 4,242,445, JP-A 142329/1980, 158124/1980, 113927/1980, 113928/1983, 111934/1983, and 111936/1983. In the step of forming or physical ripening silver halide grains, any desired salt may coexist, for example, cadmium salts, zinc salts, potassium salts, rhenium salts, ruthenium salts, thallium salts, iridium salts or complex salts, rhodium salts or complex salts, iron salts or complex salts, chromium salts or complex salts, and nickel salts or complex salts. Preferred are rhenium salts, iridium salts, rhodium salts and iron salts. These salts are generally added in amounts of about 10 -9 to 10 -3 mol per mol of silver, but may be added in larger or less amounts as necessary. For example, iridium salts (e.g., Na 3 IrCl 6 , Na 2 IrCl 6 , and Na 3 Ir(CN) 6 ) are added in amounts of 1x10 -8 to 1x10 -5 mol per mol of silver and rhodium salts (e.g., RhCl 3 and K 3 Rh(CN) 6 ) are added in amounts of 1x10 -8 to 1x10 -3 mol per mol of silver. In the preparation of a silver halide emulsion according to the present invention, a desalting step may be carried out for removing the excess salt. The desalting step may be by the old well-known noodle washing method of gelling gelatin or by flocculation methods using inorganic salts of polyvalent anions, for example, sodium sulfate, anionic surfactants, anionic polymers (e.g., polystyrenesulfonic acid), and gelatin derivatives (e.g., fatty acid acylated gelatin, aromatic acid acylated gelatin, and aromatic acid carbamoylated gelatin). The excess salt removal may be omitted in some cases. Alternatively, excess salt may be removed by ultrafiltration means as disclosed in USP 4,758,505 and 4,334,012, JP-A 113137/1987, and JP-B 43727/1984. In the preparation of the silver halide emulsion according to the present invention, gelatin is advantageously used as protective colloid and as a binder for other hydrophilic colloids. Besides, the use of hydrophilic colloids is also acceptable. Useful are gelatin derivatives, graft polymers of gelatin with other polymers, proteins such as albumin and casein; cellulose derivatives such as hydroxyethylcellulose and cellulose sulfate ester, sodium alginate and starch derivatives; and various other synthetic hydrophilic polymers such as polyvinyl alcohol, polyvinyl alcohol partial acetal, poly-N-vinyl pyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinylimidazole, and polyvinylpyrazole, alone or copolymers thereof. Examples of the gelatin used include lime treated gelatin, acid treated gelatin, and enzyme treated gelatin as described in Bull. Soc. Sci. Phot., Japan, No. 16, p 30 (1966) as well as hydrolyzed and enzymatically decomposed products of gelatin. The silver halide emulsion used herein may be used without chemical sensitization although it is advantageous to chemically sensitize the emulsion for enhancing the sensitivity thereof. For chemical sensitization purpose, there may be employed gold sensitization using gold compounds (see USP 2,448,060 and 3,320,069), noble metal sensitization using iridium, platinum, rhodium, palladium or the like (see USP 2,448,060, 2,566,245, and 2,566,263), sulfur sensitization using sulfur compounds (see USP 2,222,264), chalcogenide sensitization using chalcogenides such as selenium and tellurium compounds, and reducing sensitization using reducing agents such as tin salts, thiourea dioxide, and polyamides (see USP 2,487,850, 2,518,698 and 2,521,925), and combinations thereof. For the silver halide emulsion of the invention, gold or sulfur sensitization or a combination thereof is preferred. Preferably, the gold or sulfur sensitizing agent is added in amounts of 1x10 -7 to 1x10 -2 mol, more preferably 5x10 -6 to 1x10 -3 mol per mol of silver. When gold and sulfur sensitization combination is desired, the gold and sulfur sensitizing agents are preferably mixed in a molar ratio of from 1:3 to 3:1, more preferably from 1:2 to 2:1. In order to carry out effective chemical sensitization, the temperature may range from 30°C to 90°C and the pH may range from 4,5 to 9.0, preferably from 5.0 to 7.0. The time for chemical sensitization may vary depending on the temperature, type and amount of chemical sensitizer, pH and other factors and generally ranges from several minutes to several hours, often from 10 to 200 minutes. In the practice of the invention, sensitizing dyes may be used in addition to the sensitizing dye of formula (I). For enhancing adsorption of the sensitizing dyes to silver halide and formation of a J-aggregated product for achieving higher spectral sensitivity, selected salts, for example, water-soluble iodide salts such as potassium iodide, water-soluble bromide salts such as potassium bromide, water-soluble thiocyanate salts such as potassium thiocyanate, and calcium chloride may be used in combination with the sensitizing dyes as often used in conventional silver halide emulsions. The water-soluble bromide salts and water-soluble thiocyanate salts are more effective when applied to silver chlorobromide having a higher silver chloride content. For very rapid processing allowing a development time of only less than 30 seconds, a high silver chloride emulsion having a silver chloride content of at least 50 mol% is advantageous. To this end, since iodide ion is development suppressive as is well known in the art, the iodide ion including the above-mentioned water-soluble iodide salt should preferably be limited to 0.05 mol% or lower per mol of silver. For preparing a silver halide photosensitive material adapted for very rapid processing, a high silver chloride emulsion having a silver chloride content of at least 80 mol% is more advantageous. In such an emulsion, the additional use of a water-soluble bromide salt and/or water-soluble thiocyanate salt as mentioned above is effective for enhancing formation of a J-associated product and achieving higher spectral sensitivity while these salts are preferably added in amounts of 0.03 to 3 mol%, more preferably 0.08 to 1 mol% per mol of silver. Preferred among high silver chloride grains having a silver chloride content of at least 80 mol% are high silver chloride grains containing a localized phase therein as disclosed in JP-A 248945/1990 because they have advantages of higher sensitivity and stability, especially latent image stability when subject to infrared region spectral sensitization. As disclosed in JP-A 248945/1990, the localized phase should preferably have a silver bromide content in excess of 15 mol%, more preferably 20 to 60 mol%, most preferably 30 to 50 mol% with the balance of silver chloride. The localized phase may be disposed in the interior, on the surface or at the sub-surface of silver halide grains, or both in the interior and on the surface or at the sub-surface of silver halide grains. The localized phase in the interior or on the surface may form a laminar structure enclosing silver halide grains or have a discontinuous or discrete structure. One preferred exemplary arrangement of a localized phase having a higher silver bromide content than the surrounding is represented by silver halide grains having a localized phase having a silver bromide content of at least 15 mol% locally and epitaxially grown on the surface thereof. The silver bromide content of the localized phase may be analyzed by X-ray diffractometry (as described in the Chemical Society of Japan, "New Experimental Chemistry Series No. 6, Structural Analysis", Maruzen, for example) or XPS (as described in "Surface Analysis - Application of IMA, Auger Electron and Photoelectron Spectroscopy", Kodansha, for example). The localized phase is preferably formed from 0.1 to 20%, more preferably 0.5 to 7% of silver based on the total silver amount of silver halide grains. Either a definite phase boundary or a narrow transition region where the halogen composition gradually varies may be present between the localized phase having a high silver bromide content and the surrounding phase. Any of various known methods may be used to form a localized phase having a high silver bromide content. For example, a localized phase may be formed by reacting a soluble silver salt with a soluble halide salt by the single jet or double jet technique. A localized phase may also be formed by the conversion technique including the step of converting a once formed silver halide to a silver halide having a lower solubility product. Alternatively, a localized phase can be formed by adding silver bromide fine grains to silver chloride grains and causing silver bromide to recrystallize on the silver chloride grains. In the practice of the invention, photosensitive silver halide is preferably coated in a weight of 0.2 to 10 grams calculated as silver per square meter of photosensitive material (0.2 to 10 g/m 2 ). In combination with the photosensitive silver halide, an organic metal salt may be used as an oxidizing agent. Preferred organic metal salts are organic silver salts. Exemplary organic silver salts are those obtained from benzotriazoles, fatty acids and other organic compounds as disclosed in USP 4,500,626, col. 52-53. Also useful are silver salts of carboxylic acids having an alkynyl group such as phenylpropiolic acid as described in JP-A 113235/1985 and acetylene silver as described in JP-A 249044/1986. A mixture of two or more organic silver salts may also be used. The organic silver salt is preferably used in an amount of 0.01 to 10 mol, more preferably 0.01 to 1 mol per mol of photosensitive silver halide. The total coverage of photosensitive silver halide plus organic silver salt may range from 50 mg/m 2 to 10 g/m 2 calculated as silver. For further enhancing the benefits of the present invention, the sensitizing dye is incorporated in the silver halide emulsion in combination with a tetraazaindene compound of the following general formula (II) or (III). In the formulae, R 21 , R 22 , R 23 and R 24 , which may be identical or different, each represent a hydrogen atom, substituted or unsubstituted, linear, cyclic or branched alkyl group having 1 to 20 carbon atoms in total, substituted or unsubstituted, monocyclic or bicyclic aryl group, substituted or unsubstituted amino group, hydroxy group, alkoxy group having 1 to 20 carbon atoms in total, alkylthio group having 1 to 6 carbon atoms in total, carbamoyl group which may have an aliphatic or aromatic substituent, halogen atom, cyano group, carboxy group, alkoxycarbonyl group having 2 to 20 carbon atoms in total, and heterocyclic group containing a 5- or 6-membered ring having a hetero-atom such as a nitrogen, oxygen and sulfur atom. R 21 and R 22 taken together or R 22 and R 23 taken together may form a 5- or 6-membered ring. At least one of R21 and R23 represents a hydroxy group. Examples of the unsubstituted alkyl group include methyl, ethyl, n-propyl, i-propyl, t-propyl, n-butyl, t-butyl, hexyl, cyclohexyl, cyclopentylmethyl, octyl, dodecyl, tridecyl, and heptadecyl groups. Examples of the substituent on the alkyl group include monocylic or bicyclic aryl groups, heterocyclic residues, halogen atoms, carboxy group, alkoxycarbonyl groups having 2 to 6 carbon atoms, alkoxy groups having up to 19 carbon atoms, and hydroxy group. Then exemplary substituted alkyl groups include benzyl, phenethyl, chloromethyl, 2-chloroethyl, trifluoromethyl, carboxymethyl, 2-carboxyethyl, 2-(methoxycarbonyl)ethyl, ethoxycarbonylmethyl, 2-methoxyethyl, hydroxymethyl, and 2-hydroxyethyl groups. Examples of the unsubstituted aryl group include phenyl and naphthyl groups. Examples of the substituent on the aryl group include alkyl groups having up to 4 carbon atoms, halogen atoms, carboxy, cyano, alkoxycarbonyl groups having up to 6 carbon atoms, hydroxy, and alkoxy groups having up to 6 carbon atoms. Then exemplary substituted aryl groups include p-tolyl, m-tolyl, p-chlorophenyl, p-bromophenyl, o-chlorophenyl, m-cyanophenyl, p-carboxyphenyl, o-carboxyphenyl, o-(methoxycarbonyl)phenyl, p-hydroxyphenyl, p-methoxyphenyl and m-ethoxyphenyl groups. Examples of the substituent on the substituted amino group include alkyl groups (e.g., methyl, ethyl and butyl groups) and acyl groups (e.g., acetyl, propionyl, benzoyl and methylsulfonyl groups). Then exemplary substituted amino groups include dimethylamino, diethylamino, butylamino and acetylamino groups. Examples of the alkoxy group include methoxy, ethoxy, butoxy and heptadecyloxy groups. Examples of the alkylthio group include methylthio, ethylthio and hexylthio groups. The carbamoyl group may have one or two substituents selected from alkyl groups having up to 20 carbon atoms and monocyclic or bicyclic aryl groups. Exemplary substituted carbamoyl group include methylcarbamoyl, dimethylcarbamoyl, ethylcarbamoyl and phenylcarbamoyl groups. Examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl and butoxycarbonyl groups. Examples of the halogen atom include fluorine, chlorine and bromine atoms. The heterocyclic residue may be monocyclic or a fused ring of two or three rings, and examples thereof include furyl, pyridyl, 2-(3-methyl)benzothiazolyl and 1-benzotriazolyl groups. In the substituted alkyl groups mentioned above, the substituent on the substituted alkyl group represented by R 24 can be a heterocyclic residue. Preferred are substituents of the general formula (IV). In formula (IV), R 21 , R 22 and R 23 are as defined above, and n is equal to 2, 3 or 4. In the practice of the invention, the tetraazaindene compound of formula (II) or (III) may be added in an amount of 1x10 -5 to 0.2 mol, preferably 3x10 -4 to 0.02 mol per mol of silver halide. It is desired that the amount of the tetraazaindene compound added be selected optimum depending on the grain size and halogen composition of the silver halide emulsion, type and degree of chemical sensitization, relationship of the emulsion layer according to the invention to other emulsion layers, type of antifoggant, and the like. Experimentation for such selection is well known to those skilled in the art. The compound of formula (II) or (III) may be incorporated into the silver halide emulsion according to the present invention in a manner similar to the addition of the cyanine dye of formula (I), for example, by directly dispersing the compound in the emulsion, or dissolving the compound in a water-miscible organic solvent to form a solution, dissolving the compound in water to form a solution if the compound is water soluble, or dispersing the compound in a hydrophilic colloidal solution, all followed by addition to the emulsion. The tetraazaindene compound of formula (II) or (III) is incorporated into the silver halide emulsion at any stage from the silver halide grain forming step so that chemical sensitization (according to JP-A 255159/1987) is carried out in the presence of the tetraazaindene compound. Also a spectral sensitizer may be added at any stage from the silver halide grain forming step in accordance with the claimed process, for example, at the onset, midway or end of silver halide grain formation, or at the onset, midway or end of desalting, or at the time of gelatin re-dispersion, or at the onset, midway or prior to the end of chemical sensitization. The tetraazaindene compound and the spectral sensitizer coexist for at least a portion of the chemical sensitization step. In one mode, the tetraazaindene compound and the spectral sensitizer may be simultaneously added. In another preferred mode, the amount of the tetraazaindene compound added is divided into two or more portions. A first appropriate portion of the tetraazaindene compound which is up to 3x10 -3 mol per mol of silver and which is selected in accordance with the type and grain size of silver halide (such that the absorption intensity of the sensitizing dye may not be lowered or may rather be increased to a sharp one) is added prior to the addition of the spectral sensitizer. The remaining portion or portions are added prior to the onset of chemical ripening. This divided addition procedure is more effective for suppressing fog and increasing sensitivity therewith. In the invention the tetraazaindene compound and the spectral sensitizer are simultaneously added in the form of a mixture of these compounds or the compounds may be added separately. Moreover, these compounds may be added as a mixture thereof with another compound or compounds such as chemical sensitizers and alkali halides which are necessary for chemical sensitization or preparation of silver halide grains or silver halide emulsion. Several illustrative, non-limiting examples of the compounds of formulae (II) and (III) are given below. The silver halide emulsion prepared in accordance with the present invention may contain a methine dye other than the cyanine dyes of the present invention and/or a supersensitizer for the purposes of expanding the photosensitive wavelength range and effecting supersensitization. Where silver halide grains other than the silver halide grains according to the present invention are contained in the same or different layer, the other silver halide grains may be spectrally sensitized with the cyanine dyes according to the present invention as well as other methine dyes and supersensitizers. The dyes useful for spectral sensitization include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxonol dyes. Particularly useful dyes among them are cyanine, merocyanine, and complex merocyanine dyes. To these dyes, any nuclei generally utilized for cyanine dyes can be applied as basic heterocyclic ring nuclei. For example, applicable are pyrroline nuclei, oxazoline nuclei, thiazolin nuclei, pyrrole nuclei, oxazole nuclei, thiazole nuclei, selenazole nuclei, imidazole nuclei, tellurazole nuclei, pyridine nuclei, tetrazole nuclei, etc.; and nuclei of the foregoing nuclei having cycloaliphatic hydrocarbon rings fused thereto and nuclei of the foregoing nuclei having aromatic hydrocarbon rings fused thereto, such as indolenine nuclei, benzindolenine nuclei, indole nuclei, benzoxazole nuclei, naphthoxazole nuclei, benzimidazole nuclei, naphthoimidazole nuclei, benzothiazole nuclei, naphthothiazole nuclei, benzoselenazole nuclei, naphthoselenazole nuclei, quinoline nuclei, benzotellurazole nuclei, etc. These nuclei may be substituted on a carbon atom(s). For the merocyanine and complex merocyanine dyes, those nuclei generally used for merocyanine dyes are applicable as a nucleus having a ketomethylene structure, for example, 5- or 6-membered heterocyclic nuclei such as a pyrazolin-5-one nucleus, thiohydantoin nucleus, 2-thiooxazolidin-2,4-dione nucleus, thiazolidin-2,4-dione nucleus, rhodanine nucleus, thiobarbituric acid nucleus, 2-thioselenazolidin-2,4-dione nucleus. These sensitizing dyes may be used alone or in combination. Combinations of sensitizing dyes are often used particularly for the purpose of supersensitization. Typical examples are found in the following patents. USP 2,688,545 2,977,229 3,397,060 3,522,052 3,527,641 3,617,293 3,628,964 3,666,480 3,672,898 3,679,428 3,703,377 3,769,301 3,614,609 3,837,862 4,026,707 UKP 1,344,281 1,507,803 JP-B 4936/1968 12375/1978 JP-A 110618/1977 109925/1977 Typical examples of the supersensitizer are the bispyridinium salts described in JP-A 142541/1984, stilbene derivatives described in JP-B 18691/1984, water-soluble bromides described in JP-B 46932/1974, aromatic compound-formaldehyde condensates described in USP 3,743,510, cadmium salts, and azaindene compounds. These methine dyes may be added to the silver halide emulsion at any stage of emulsion preparation which is known to be effective for the purpose. The addition mode and the amount of the methine dye added may be selected from the modes and amounts which are known to be effective. For example, the stage, mode and amount of methine dye addition may follow those previously described for the cyanine dyes of formula (I). The infrared sensitizing dyes often cause fog under certain addition conditions. The addition of the compounds of formula (II) or (III) is effective for preventing such fog as previously described and thus preferred in this respect too. There are many other compounds which can suppress such fog and provide supersensitization, for example, azoles and azaindenes as described in RD 17643 (1973), pages 24-25, nitrogenous carboxylic acids and phosphoric acids described in JP-A 168442/1984, mercapto compounds and metal salts thereof described in JP-A 111636/1984, and acetylene compounds described in JP-A 87957/1987, benzothiazole quaternary salts, and compounds of the following general formula (VI). These compounds may be added at any stage after the addition of the sensitizing dye of the present invention, and if chemical sensitization is carried out, from a later stage of the chemical sensitization step to the emulsion coating step. The amount of these compounds is preferably about 0.3 to 10 equivalents relative to the sensitizing dye of the present invention. (VI) Z 61 -(V 61 ) m61 In formula (VI), Z 61 is an azole ring (e.g., imidazole, triazole, tetrazole, thiazole, oxazole, selenazole, benzimidazole, benzindazole, benzotriazole, benzoxazole, benzothiazole, thiadiazoleoxadiazole, benzoselenazole, pyrazole, naphthothiazole, naphthoimidazole, naphthoxazole, azabenzimidazole, and purine), pyrimidine ring, triazine ring, pyridine ring, or azaindene ring (e.g., triazaindene and pentaindene). V 61 is a hydrogen atom or a substituent. Exemplary substituents include substituted or unsubstituted alkyl groups (e.g., methyl, ethyl, hydroxyethyl, trifluoromethyl, sulfopropyl, di-propylaminoethyl, adamantyl, benzyl, p-chlorophenethyl, ethoxyethyl, ethylmercaptoethyl, cyanopropyl, phenoxyethyl, carbamoylethyl, carboxyethyl, ethoxycarbonylpropyl, and acetylaminoethyl), substituted or unsubstituted alkenyl groups (e.g., allyl), substituted or unsubstituted aryl groups (e.g., phenyl, naphthyl, p-carboxyphenyl, 3,5-dicarboxyphenyl, m-sulfophenyl, p-acetamidophenyl, 3-caprylamidophenyl, p-sulfamoylphenyl, m-hydroxyphenyl, p-nitrophenyl, 3,5-dichlorophenyl, p-anisil, o-anisil, p-cyanophenyl, p-N'-methylureidophenyl, m-fluorophenyl, p-tolyl and m-tolyl), substituted or unsubstituted heterocyclic residues (e.g., pyridyl, 5-methyl-2-pyridyl and thienyl), halogen atoms (e.g., chloro and bromo), mercapto group, cyano group, carboxy group, sulfo group, hydroxy group, carbamoyl group, sulfamoyl group, amide group, nitro group, substituted or unsubstituted alkoxy groups (e.g., methoxy, ethoxy, 2-methoxyethoxy and 2-phenylethoxy), substituted or unsubstituted aryloxy groups (e.g., phenoxy and p-methylphenoxy), acyl groups (e.g., acetyl, benzoyl and methanesulfonyl), acylamino groups (e.g., acetylamino, caproylamino and methylsulfonylamino), substituted amino groups (e.g., diethylamino and hydroxyamino), alkyl- or arylthio groups (e.g., methylthio, carboxyethyl and sulfobutylthio), alkoxycarbonyl groups (e.g., methoxycarbonyl), and aryloxycarbonyl groups (e.g., phenoxycarbonyl). Letter m61 is a positive integer of up to 5, which means that two or more substituents represented by V61 may be present as a mixture of identical or different types. Preferred among the compounds of formula (VI) are mercapto-substituted azole ring compounds. In the practice of the present invention, the photosensitive material or dye fixing element may contain a binder in its emulsion or intermediate layer. Hydrophilic binders are preferred, for example, such as described in JP-A 253159/1987. More specifically, transparent or semi-transparent hydrophilic binders are preferred, for example, proteins such as gelatin and gelatin derivatives; cellulose derivatives; natural compounds like polysaccharides such as starch, gum arabic, dextran and pluran; and synthetic hydrophilic polymers including polyvinyl alcohol, polyvinylpyrolidone and polyacrylamide. Also useful are the hygroscopic polymers described in JP-A 245260/1987, which include a homopolymer of a vinyl monomer having -COOM or -SO 3 M wherein M is a hydrogen atom or alkali metal, or copolymers of the vinyl monomer with another vinyl monomer (e.g., sodium methacrylate, ammonium methacrylate and Sumicagel L-5H by Sumitomo Chemical K.K.). These binders may be used in admixture of two or more. Examples of the gelatin used herein include lime-treated gelatin, acid-treated gelatin, and low molecular weight gelatin. For the preparation of gelatin, reference is made to Arthur Vice, The Macromolecular Chemistry of Gelatin, Academic Press, 1969. In a system wherein a minor amount of water is fed to allow for heat development, the use of hygroscopic binders as mentioned above is effective for promoting water absorption. Also, if a hygroscopic polymer is used in a dye fixing layer or a protective layer therefor, it is effective for preventing the once transferred dye from retransferring from the dye fixing layer to another layer. Preferably the binder is coated in an amount of up to 20 g/m 2 , more preferably up to 10 g/m 2 , most preferably up to 7 g/m 2 . In a layer (inclusive of a back layer) of the photosensitive material or dye fixing element, various polymer latexes may be contained for the purposes of improving dimensional stability and preventing curling, sticking, crazing and pressure sensitization/desensitization. Any of the polymer latexes described in JP-A 245258/1987, 136648/1987 and 110066/1987 may be used. It is particularly effective to add a polymer latex having a low glass transition temperature (below 40°C) to a mordant layer since the mordant layer is prevented from crazing and to add a polymer latex having a high glass transition temperature to a back layer since anti-curling effect is exerted. In the heat development system prepared according to the present invention, there may be used any of the reducing agents which are known in the field of heat development photosensitive materials. Also included are dye providing substances having reducing nature as will be described later (in this case, another reducing agent may be additionally used). Also useful are reducing agent precursors which themselves have no reducing nature, but exert reducing nature under the action of nucleophilic reagents or heat during development step. Examples of the reducing agent and precursor are described in the following patents. USP 4,500,626 4,483,914 4,330,617 4,950,152 JP-A 140335/1985 40245/1982 138736/1981 178458/1984 53831/1984 182449/1984 182450/1984 119555/1985 128436/1985 128437/1985 128438/1985 128439/1985 198540/1985 181742/1985 259253/1986 244044/1987 131253/1987 131254/1987 131255/1987 131256/1987 EP-A 220746 A2 Also useful are combinations of reducing agents as disclosed in USP 3,039,869. Where a non-diffusion reducing agent is used, an electron transfer agent and/or an electron transfer agent precursor may be used for promoting electron transfer between the non-diffusion reducing agent and developable silver halide, if desired. The electron transfer agents and precursors thereof may be selected from the above-mentioned reducing agents and precursors thereof. The electron transfer agent or precursors thereof should preferably have greater mobility than the non-diffusion reducing agent (electron donor). Useful electron transfer agents are 1-phenyl-3-pyrazolidones and aminophenols. The non-diffusion reducing agent (electron donor) which is combined with the electron transfer agent may be selected from those of the above-mentioned reducing agents which are substantially immobile in a layer of photosensitive material, preferably hydroquinones, sulfonamidophenols, sulfonamidonaphthols, and the compounds described as the electron donor in JP-A 110827/1978, and dye providing substances having non-diffusion and reducing properties to be described later. In the photosensitive material for the heat development system prepared according to the present invention, the reducing agent is generally added in an amount of 0.01 to 20 mol, preferably 0.1 to 10 mol per mol of silver. In the practice of the invention, color couplers may be used in the photosensitive material of the conventional wet development system. Preferred are non-diffusion color couplers having a hydrophobic group known as a ballast group in a molecule and polymerized color couplers. The couplers may be of either 4 or 2 equivalents relative to the silver ion. Also included are colored couplers having color correcting effect and couplers capable of releasing development inhibitors with the progress of development (known as DIR couplers). Furthermore, colorless DIR couplers which form colorless products as a result of coupling reaction and release development inhibitors are also useful. Exemplary magenta couplers include 5-pyrazolone couplers, pyrazolobenzimidazole couplers, pyrazolotriazole couplers, pyrazolotetrazole couplers, cyanoacetylcumarone couplers, open chain acylacetonitrile couplers, etc. Exemplary yellow couplers include acylacetamide couplers (e.g., benzoylacetanilides and pivaloylacetanilides). Exemplary cyan couplers include naphthol couplers and phenol couplers. Preferred cyan couplers are phenol couplers having an ethyl group at the meta position of a phenol nucleus, 2,5-diacylamino substituted phenol couplers, phenol couplers having a phenolureido group at the 2-position and an acylamino group at the 5-position of a phenol nucleus, and couplers having a sulfonamide, amide or similar group at the 5-position of naphthol for the advantage of image fastness as described in USP 3,772,002, 2,772,162, 3,758,308, 4,126,396, 4,334,011, 4,327,173, 3,446,622, 4,333,999, 4,451,559, and 4,427,767. Preferred examples of the color coupler are also found in JP-A 248,945/1990. Two or more color couplers may be added in a common layer or the same color coupler may be added to two or more different layers for meeting the characteristics required for photosensitive material. Preferably, the color couplers are used in amounts of 0.1 to 1.0 mol, more preferably 0.1 to 0.5 mol per mol of silver halide in a silver halide emulsion layer serving as a photosensitive layer. The color couplers may be added to the photosensitive layer by any of various well-known techniques. Often an oil-in-water dispersion technique well known as an oil protect technique is used to add color couplers by dissolving them in a solvent and then emulsion dispersing it in a gelatin aqueous solution containing a surfactant. Alternatively, water or gelatin aqueous solution is added to a coupler solution containing a surfactant and phase conversion is effected to produce an oil-in-water dispersion. In the case of alkalisoluble couplers, a Fischer dispersion technique may be used. The coupler dispersion is removed of the low-boiling organic solvent by distillation, noodle washing or ultrafiltration before it is mixed with a photographic emulsion. As the dispersion medium for such couplers, high-boiling organic solvents having a dielectric constant of 2 to 20 at 25°C and an index of refraction of 1.5 to 1.7 at 25°C or water-insoluble polymers or both may be used. Preferred examples of the high-boiling organic solvent are described in JP-A 248945/1990 and 215272/1987. Also, the couplers may be used by impregnating loadable latex polymers (see USP 4,203,716) with the couplers in the presence or absence of the high-boiling organic solvent or by dissolving the couplers in water-insoluble, organic solvent-soluble polymers and emulsion dispersing the solution in a hydrophilic colloid aqueous solution. Preferably, the homopolymers and copolymers described in WO 88/00723 are used, with the use of acrylamide polymers being most preferred for color image stability. In a photosensitive material of the heat development system according to the present invention, there may be contained a compound which, when the photosensitive silver halide or silver ion is reduced into silver at elevated temperatures, produces or releases a mobile or diffusible dye in direct or inverse proportion to the reaction. These compounds are simply referred to as dye-providing compounds or substances. Typical of the dye-providing substance are compounds capable of forming dyes through oxidative coupling reaction (or couplers). The couplers may be either 4 or 2 equivalent couplers. Useful are 2 equivalent couplers having a non-diffusion group as a splittable group and capable of forming a diffusible dye through oxidative coupling reaction. The non-diffusion group may form a polymeric chain. Illustrative examples of the color developing agents and couplers are described in, for example, T.H. James, "The Theory of the Photographic Process", 4th Ed., pages 291-334 and 354-361, and the following Japanese laid-open specifications . JP-A 123533/1983 149046/1983 149047/1983 111148/1984 124399/1984 174835/1984 231539/1984 231540/1984 2950/1985 2951/1985 14242/1985 23474/1985 66249/1985 Another class of dye-providing substances includes compounds having the function of releasing or diffusing a diffusible dye imagewise. The compounds of this type may be represented by the following formula [L I]: [L I] (Dye-Y) n -Z wherein Dye represents a dye group, a temporarily wavelength shortened dye group or a dye precursor group; Y represents a single bond or a connecting linkage; and Z represents a group which, in correspondence or counter-correspondence to photosensitive silver salt having a latent image distributed imagewise, produces a difference in diffusibility of the compound represented by (Dye-Y) n -Z or releases Dye, the diffusibility of Dye released being different from that of the compound represented by (Dye-Y) n -Z; and n represents an integer of 1 or 2, when n=2, the Dye-Y's may be the same or different. Illustrative examples of the dye providing compound of formula [L I] are given below as classes (1) to (5). It is to be noted that the compounds of classes (1) to (3) are those forming a diffusible dye image (positive dye image) in counter proportion to the development of silver halide and the compounds of classes (4) to (5) are those forming a diffusible dye image (negative dye image) in proportion to the development of silver halide. Class (1): Dye developing reagents in the form of a hydroquinone-type developing reagent having a dye moiety attached thereto are disclosed in USP 3,134,764; 3,362,819; 3,597,200; 3,544,545; and 3,482,972. These dye developing reagents are diffusible in an alkaline environment and become non-diffusible upon reaction with silver halide. Class (2): Non-diffusible compounds which release diffusible dyes in an alkaline environment, but lose the ability upon reaction with silver halide are described in USP 4,503,137. Examples are substances which release a diffusible dye through intramolecular nucleophilic substitution reaction as disclosed in USP 3,980,479, and substances which release a diffusible dye through intramolecular rewind reaction of an isooxazolone ring as disclosed in USP 4,199,354. Class (3) includes compounds which release a diffusible dye through reaction with the reducing agent which has left non-oxidized by development as disclosed in USP 4,559,290 and 4,783,396, EP 220746 A2, and Technical Report 87-6199. Examples are compounds which release a diffusible dye through intramolecular nucleophilic substitution reaction after reduction as disclosed in USP 4,139,389 and 4,139,379, JP-A 185333/1984 and 84453/1982; compounds which release a diffusible dye through intramolecular electron transfer reaction after reduction as disclosed in USP 4,232,107, JP-A 101649/1984 and 88257/1986, RD 24025 (1984); compounds which release a diffusible dye through cleavage of a single bond after reduction as disclosed in German Patent 30 08 588A, JP-A 142530/1981, UPS 4,343,893 and 4,619,884; nitro compounds which release a diffusible dye upon receipt of an electron as disclosed in USP 4,450,223; and compounds which release a diffusible dye upon receipt of an electron as disclosed in USP 4,609,610. Preferred examples are compounds having a N-X bond wherein X is an oxygen, sulfur or nitrogen atom and an electron attractive group in a molecule as disclosed in EP 220746 A2, Technical Report 87-6199, USP 4,783,396, JP-A 201653/1988 and 201654/1988; compounds having a SO 2 -X bond wherein X is as defined above and an electron attractive group in a molecule as disclosed in Japanese Patent Application No. 106885/1987; compounds having a PO-X bond wherein X is as defined above and an electron attractive group in a molecule as disclosed in JP-A 271344/1988; and compounds having a C-X' bond wherein X' is the same as X or -S02- and an electron attractive group in a molecule as disclosed in JP-A 271341/1988. Also useful are compounds which release a diffusible dye through cleavage of a single bond after reduction due to p-bond conjugated with an electron accepting group as disclosed in Japanese Patent Application Nos. 319989/1987 and 320771/1987. More preferred are the compounds having a N-X bond and an electron attractive group in a molecule, with examples being described in EP 220746 A2 or USP 4,783,396 as compounds (1)-(3), (7)-(10), (12), (13), (15), (23)-(26), (31), (32), (35), (40), (41), (44), (53)-(59), (64), and (70) and in Technical Report 87-6199 as compounds (11) to (23). Class (4) includes couplers having a diffusible dye as an eliminatable group and thus releasing a diffusible dye through reaction with an oxidant of a reducing agent, known as DDR couplers, as described in British Patent No. 1,330,524, JP-B 39165/1973; USP 3,443,940, 4,474,867 and 4,483,914. Class (5) includes compounds (DRR couplers) which themselves have reducing nature to silver halide or organic silver salts and release a diffusible dye upon reduction of the silver halide or organic silver salts. Without a need for an extra reducing agent, the DRR couplers eliminate the serious problem that an image can be contaminated with oxidation decomposition products of a reducing agent. Typical examples are described in the following patents. USP 3,443,939 3,725,062 3,728,113 3,928,312 4,053,312 4,055,428 4,336,322 4,500,626 JP-A 65839/1984 69839/1984 116537/1983 179840/1982 3819/1978 104343/1976 Examples of the DRR compound are described in USP 4,500,626, columns 22-44, with preferred ones being identified as compounds (1)-(3), (10)-(13), (16)-(19), (28)-(30), (33)-(35), (38)-(40), and (42)-(64). Also useful are those described in USP 4,639,408, columns 37-39. There are available dye providing compounds other than the aforementioned couplers and compounds of formula [L I]. Such additional dye-providing compounds include dye-silver compounds in which an organic silver salt is combined with a dye (see Research Disclosure, May 1978, pages 54-58); azo dyes useful in heat development silver dye bleaching process (see USP 4,235,957 and Research Disclosure, April 1976, pages 30-32); and leuco dyes (see USP 3,985,565 and 4,022,617). Hydrophobic additives like dye-providing compounds and non-diffusible reducing agents may be introduced into a layer of photosensitive material by any desired method, for example, by the method described in USP 2,322,027. Use may be made of high-boiling organic solvents as described in JP-A 83154/1984, 178451/1984, 178452/1984, 178453/1984, 178454/1984, 178455/1984, 178457/1984, optionally in combination with low-boiling organic solvents having a boiling point of 50 to 160°C. The amount of the high-boiling organic solvent used is generally up to 10 grams, preferably up to 5 grams per gram of the dye-providing compound and up to 1 cc, preferably up to 0.5 cc, more preferably up to 0.3 cc per gram of the binder. A dispersion method using a polymer as disclosed in JP-B 39853/1976 and JP-A 59943/1976 may be used. In the case of substantially water-insoluble compounds, they may be dispersed in a binder as fine particles although any of the aforementioned addition methods may be used. In dispersing hydrophobic compounds in hydrophilic colloids, a variety of surfactants may be used. Examples are found in JP-A 157636/1984. The photosensitive material prepared according to the invention may further contain a compound capable of activating development and stabilizing an image at the same time. Examples are found in USP 4,500,626, columns 51-52. In the system of forming images through diffusion transfer of dyes, a photosensitive material is used incombination with a dye fixing element. There are generally two typical forms, one form having photosensitive material and dye-fixing element separately applied on two separate supports and another form having both photosensitive material and dye-fixing element applied on a common support. With respect to the relation of the photosensitive material and the dye-fixing element to one another, to the support, and to a white reflective layer, reference may be made to USP 4,500,626, col. 57. The dye-fixing element preferably used in the present invention has at least one layer containing a mordant and a binder. The mordant may be selected from those known in the photographic art, for example, the mordants described in USP 4,500,626, col. 58-59 and JP-A 88256/1986, pages 32-41; and the compounds described in JP-A 244043/1987 and 244036/1987. Also useful are dye accepting polymers as disclosed in USP 4,463,079. If desired, the dye-fixing element may be provided with any auxiliary layer, for example, a protective layer, peeling layer, and anti-curling layer, in addition to the above-mentioned layers. Provision of a protective layer is especially effective. One or more layers of the photosensitive material and dye-fixing element may contain a plasticizer, lubricant, or high-boiling organic solvent as an agent for facilitating stripping of the photosensitive material from the dye-fixing element. Examples are found in JP-A 253159/1987 and 245253/1987. Moreover, various silicone fluids may be used for the same purpose as above. The silicone fluids include dimethylsilocone fluid and modified silicone fluids of dimethylsiloxane having organic groups incorporated therein. Examples are the modified silicone fluids described in "Modified Silicone Oil Technical Data", Shin-Etsu Silicone K.K., pages 16-18B, especially carboxy-modified silicone (trade name X-22-3710). Also useful are the silicone fluids described in JP-A 215953/1987 and 46449/1988. The photosensitive material and dye-fixing element prepared according to the present invention may further contain a color fog restrainer which is generally selected from hydroquinone derivatives, aminophenol derivatives, gallic acid derivatives and ascorbic acid derivatives. Various anti-fading agents may be used in the photosensitive material according to the invention. Organic anti-fading agents for cyan, magenta and/or yellow images include hydroquinones, 6-hydroxychromans, 5-hydroxycoumarans, spiro-chromans, p-alkoxyphenols, hindered phenols such as bisphenols, gallic acid derivatives, methylenedioxybenzenes, aminophenols, hindered amines, and ether or ester derivatives of the foregoing compounds wherein a phenolic hydroxyl group is silylated or alkylated. Also useful are metal complexes as typified by (bissalicylaldoximato)nickel complex and (bis-N,N-dialkyldithiocarbamato)nickel complex. Examples of the organic anti-fading agent are found in the following patents. For hydroquinones, reference is made to USP 2,360,290, 2,418,613, 2,700,453, 2,701,197, 2,710,801, 2,728,659, 2,732,300, 2,735,765, 2,816,028, 3,982,944 and 4,430,425, and UKP 1,363,921. For 6-hydroxychromans, 5-hydroxycoumarans, spiro-chromans, reference is made to USP 3,432,300, 3,573,050, 3,574,627, 3,698,909 and 3,764,337, and JP-A 152225/1977. For spiro-indanes, reference is made to USP 4,360,589. For p-alkoxyphenols, reference is made to USP 2,735,765, UKP 2,066,975, JP-A 10539/1984 and JP-B 19765/1982. For hindered phenols, reference is made to USP 3,700,455 and 4,228,235, JP-B 72224/1977 and 6223/1977. For gallic acid derivatives, methylenedioxybenzenes, aminophenols, reference is made to USP 3,457,079 and 4,332,886 and JP-B 21144/1981. For hindered amines, reference is made to USP 3,336,135 and 4,268,593, UKP 1,326,889, 1,354,313 and 1,410,846, JP-B 1420/1976, JP-A 114036/1983, 53846/1984 and 78344/1984. For metal complexes, reference is made to USP 4,050,938, 4,241,155, 4,245,018 and 4,254,195, UKP 2,027,731 (A), JP-A 174741/1987, 88256/1986, 199248/1988, 75568/1989 and 74272/1989. To achieve their purpose, these anti-fading agents are added to a photosensitive layer by forming an emulsion together with corresponding dye-providing compounds such as color couplers while using the anti-fading agents in an amount of 5 to 100% by weight based on the dye-providing compounds. For preventing degradation of cyan dye images by heat and especially light, it is effective to introduce a UV absorber in a cyan color developing layer, a dye-fixing layer and contiguous sandwiching layers. The UV absorbers include aryl-substituted benzotriazoles (e.g., those described in USP 3,533,794), 4-thiazolidones (e.g., those described in USP 3,314,794 and 3,352,681), benzophenones (e.g., those described in JP-A 2784/1971), cinnamates (e.g., those described in USP 3,705,805 and 3,707,395), butadienes (e.g., those described in USP 4,045,229), and benzooxidoles (e.g., those described in USP 3,700,455). Also useful are UV absorbing couplers (e.g., a-naphthol series cyan dye forming couplers) and UV absorbing polymers. These UV absorbers may be mordanted in a particular layer. Preferred among these UV absorbers are aryl-substituted benzotriazoles. Together with the aforementioned couplers, especially pyrazoloazole couplers, the following compounds are preferably used. Useful are a compound (F) which chemically bonds with the aromatic amine color developing agent which is retained after color development, thereby forming a chemically inert, substantially colorless compound and a compound (G) which chemically bonds with the oxidant of aromatic amine color developing agent which is retained after color development, thereby forming a chemically inert, substantially colorless compound. Compounds (F) and (G) may be used alone or in admixture for preventing stain generation or other side effects due to a color developing dye formed by reaction of the coupler with a residual color developing agent or oxidant thereof retained in the film during shelf storage after processing. Preferred compounds (F) are those capable of reacting with p-anisidine at a secondary reaction rate constant k2 of 1.0 to 1x10 -5 l/mol·sec. in trioctylphosphate at 80°C. It is to be noted that the secondary reaction rate constant is measured in accordance with the method of JP-A 158545/1988. If k2 exceeds this range, the compounds would be unstable and decompose through reaction with gelatin and water. If k2 is below the range, the compounds would react very slowly with a residual aromatic amine color developing agent and as a result, fail to prevent the side effect of the residual color developing agent. More preferred examples of compound (F) are represented by the following formula (F-I) or (F-II). (F-I) R 101 -(A) n101 -Y 101 In the formulae, R 101 and R 102 each are an aliphatic, aromatic or heterocyclic group. Letter n101 is equal to 0 or 1. A is a group which reacts with an aromatic amine developing agent to form a chemical bond therewith. Y 101 is a group which is split off upon reaction with the aromatic amine developing agent. B is a hydrogen atom, aliphatic, aromatic, heterocyclic, acyl or sulfonyl group. Y 102 is a group which promotes addition of an aromatic amine developing agent to the compound of formula (F-II). Note that R 101 and Y 101 taken together and Y 102 and R 102 or B taken together may form a cyclic structure. Typical of the mode of chemically bonding with a residual aromatic amine developing agent are substitution reaction and addition reaction. Illustrative examples of compounds of formulae (F-I) and (F-II) are found in JP-A 158545/1988 and 283338/1987, Japanese Patent Application No. 158342/1987, EP-A 277,589 and 293,321. Preferred examples of the compound (G) which chemically bonds with the oxidant of aromatic amine color developing agent which is retained after color development, thereby forming a chemically inert, substantially colorless compound are represented by the following general formula (G-I). (G-I) R 103 -Y 103 In the formula, R 103 is an aliphatic, aromatic or heterocyclic group and Y 103 is a nucleophilic group or a group which decomposes in a photosensitive material to release nucleophilic group. Preferred are those compounds of formula (G-I) wherein Y 103 is a group having a Pearson's nucleophilic CH 2 I value of at least 5 or a group derived therefrom (see R.G. Pearson, et al., J. Am. Chem. Soc., 90, 319 (1968)). Illustrative examples of the compound of formula (G-I) are found in EP-A 255,722, 277,589 and 298,321, JP-A 143048/1987, 229145/1987, 2042/1989, 230039/1989 and 57259/1989. For the detail of the combination of compounds (F) and (G), reference is made to EP-A 277,589. In the photosensitive material prepared in accordance with the present invention, colloidal silver or dyestuffs may be used for the purposes of preventing irradiation, preventing halation, especially separating the spectral sensitivity distributions of the respective photosensitive layers of full color recording material, and insuring safety against safe light in the visible wavelength region. Some examples of the dyestuffs include oxonol, hemioxonol, styryl, merocyanine, cyanine, and azo dyestuffs. Preferred among them are oxonol, hemioxonol and merocyanine dyestuffs. As the red end or infrared dyestuffs, discolorable dyestuffs as disclosed in JP-A 3250/1987, 181381/1987, 123454/1987 and 197947/1988 and dyestuffs as disclosed in JP-A 39682/1987, 123192/1987, 15877/1987 and 174741/1987 may be used optionally after a water-soluble group which will flow out during processing is introduced into the dyestuffs. The infrared dyestuffs used herein may be colorless ones exhibiting no substantial light absorption in the visible wavelength region. If the infrared dyestuff is mixed with a silver halide emulsion which has been spectrally sensitized in the red end or infrared wavelength region, there can occur desensitization, fogging, or even adsorption of the dyestuff itself to silver halide grains which induces weak broad spectral sensitization. Therefore, it is preferred that the infrared dyestuff be contained substantially solely in a colloidal layer other than the photosensitive layer. To this end, the dyestuff may be introduced into a predetermined colored layer in a non-diffusible state. First, the dyestuff can be non-diffusible by introducing a ballast group therein. The first means often leaves problems of residual color and processing stain. Secondly, the anionic dyestuff is mordanted using a polymer or polymer latex presenting a cation site. Thirdly, a dyestuff which is insoluble in water at pH 7 or lower and discolored and dissolved out during processing is used in the form of a dispersion of fine particles thereof. To this end, the dyestuff is dissolved in a low-boiling organic solvent or solubilized with a surfactant, and dispersed in a hydrophilic protective colloid aqueous solution such as gelatin. Preferably, the dyestuff in solid state is kneaded together with an aqueous solution of surfactant, thereby mechanically milling the solid into fine particles, which are dispersed in a hydrophilic colloid aqueous solution such as gelatin. Fluorescent brighteners may be used in the photosensitive material and dye-fixing element prepared according to the present invention. Preferably, the brightener is incorporated in the dye-fixing element or supplied thereto from the exterior such as the photosensitive material. Exemplary brighteners are described in K. Veenkataraman, "The Chemistry of Synthetic Dyes", Vol. V, Chap. 8, and JP-A 143752/1986. Illustrative examples include stilbene compounds, coumarin compounds, biphenyl compounds, benzoxazolyl compounds, naphthalimide compounds, pyrazoline compounds, and carbostyryl compounds. The brightener may be combined with the anti-fading agent. The photosensitive material and dye-fixing element prepared according to the present invention may contain an inorganic or organic hardener in a photographic emulsion layer or any other hydrophilic binder layer. Useful hardeners are described in USP 4,678,739, JP-A 116655/1984, 245261/1987, and 18942/1986. Illustrative examples include aldehyde hardeners (e.g., formaldehyde), aziridine hardeners, epoxy hardeners, vinylsulfon hardeners (e.g., N,N'-ethylene-bis(vinylsulfonylacetamide)ethane), N-methylol hardeners (e.g., dimethylol urea), and polymeric hardeners (e.g., the compounds described in JP-A 234157/1987). The photosensitive material and dye-fixing element may contain a surfactant in any layer thereof for various purposes including coating aid, stripping aid, lubrication, antistatic, and development acceleration. Useful surfactants are found in JP-A 173463/1987 and 183457/1987. The photosensitive material and dye-fixing element may contain an organic fluorine compound in any layer thereof for various purposes including lubrication, antistatic, and stripping aid. Useful organic fluorine compounds are the fluoride surfactants described in JP-A 9053/1982, 20944/1986 and 135826/1987, and hydrophobic fluorine compounds oily fluorine compounds such as fluoro-oil, solid fluorine compound resins such as tetrafluoroethylene resin. The photosensitive material and dye-fixing element may contain a matte agent in any layer thereof. Exemplary matte agents include silicon dioxide, polyolefins, polymethacrylate and other compounds as described in JP-A 88256/1986, and beads of benzoguanamine resin, polycarbonate resin, AS resin or the like as described in JP-A 274944/1988 and 274952/1988. The photosensitive material and dye-fixing element may contain thermal solvents, defoaming agents, antifungal and antibacterial agents, colloidal silica or the like in any layer thereof. These additives are described in JP-A 88256/1986. An image formation promoter may also be used in the photosensitive material and/or dye-fixing material in the practice of the present invention. The image formation promoters have the functions of promoting such reaction as redox reaction of a silver salt-oxidizing agent with a reducing agent, formation of a dye from a dye-providing substance, decomposition of a dye or release of a mobile dye, and promoting transfer of a dye from a photosensitive material layer to a dye-fixing layer. From their physical-chemistry, they may be classified into bases, base precursors, nucleophilic compounds, high-boiling organic solvents (oils), thermal solvents, surface-active agents, and compounds capable of interacting with silver or silver ion. It should be noted that these compounds generally have multiple functions and thus possess some of the above-mentioned promoting effects combined. For further detail, reference is to be made to USP 4,678,739, col. 38-40. Base precursors are preferably those precursors which undergo any reaction under heat to release a base, for example, organic acid-base salts which are decomposed or decarbonated upon heating, and compounds which are decomposed to release amines through such reactions as intramolecular nucleophilic substituting reaction, Lossen rearrangement, Beckman rearrangement, etc. Examples are found in USP 4,511,493 and JP-A 65038/1987. In a system wherein heat development and dye transfer are simultaneously carried out in the presence of a minor amount of water, the base and/or base precursor may be contained in the dye-fixing element because the photosensitive material is improved in shelf stability. Additionally, combinations of a difficultly soluble metal compound and a compound capable of reaction with a metal ion of said difficultly soluble metal compound to form a complex (complexing compound) as described in EP-A 210660 and USP 4,740,445 and compounds which generate bases through electrolysis as described in JP-A 232451/1986 may also be used as the base precursor. The former is particularly effective. Advantageously, the difficultly soluble metal compound and complexing compound are separately added to the photosensitive material and dye-fixing element. The photosensitive material and dye-fixing element prepared in accordance with the present invention may contain a development stopper for the purpose of providing consistent images at all times despite of variations in temperature and time of development. The development stopper used herein is a compound which quickly neutralizes a base or reacts with a base to reduce the base concentration in the film for terminating development or a compound which interacts with silver or a silver salt for suppressing development, both after optimum development has been done. Useful are acid precursors which release acids upon heating, electrophilic compounds which undergo substitution reaction with coexisting bases upon heating, nitrogenous heterocyclic compounds, mercapto compounds and precursors thereof. For detail, reference is made to JP-A 253159/1987. The full color photosensitive material prepared according to the present invention generally includes on a support a photosensitive layer (YL) containing a yellow dye-providing compound, a photosensitive layer (ML) containing a magenta dye-providing compound, a photosensitive layer (CL) containing a cyan dye-providing compound, a protective layer (PL), an intermediate layer (IL), and optionally, a colored layer which can be discolored during development, especially an anti-halation layer (AH). The layers YL, ML and CL have spectral sensitivities adapted to at least three luminous fluxes having different wavelengths. The main sensitivity wavelengths of layers YL, ML and CL are spaced apart at least 30 nm, preferably 50 to 100 nm. At the main sensitivity wavelengths of one photosensitive layer, there is a sensitivity difference of at least 0.8logE (light quantity), preferably at least 1.0logE, more preferably at least 1.21ogE between the one and other photosensitive layers. At least one of the photosensitive layers has sensitivity at a longer wavelength than 650 nm, and preferably t least two of the photosensitive layers have sensitivity in a longer wavelength region than 730 nm. For photosensitive materials of the conventional wet development system, the respective photosensitive layers may be arranged as follows. In connection with the respective photosensitive layers, R designates red sensitization, IR-1 and IR-2 designate spectral sensitization in first and second infrared wavelength regions. Sample 1 2 3 4 Protective layer PL PL PL PL Photosensitive YL=R YL=IR-2 YL=R ML=R layers ML=IR-2 ML=IR-1 CL=IR-1 YL=IR-1 Unit CR=IR-2 CL=R MR=IR-2 CL=IR-2 (AH) (AH) (AH) (AH) Support Sample 5 6 7 8 Protective layer PL PL PL PL Photosensitive CL=R CL=R CL=IR-2 ML=IR-2 layers YL=IR-1 ML=IR-1 ML=IR-1 CL=IR-1 Unit ML=IR-2 YL=IR-2 YL=R YL=R (AH) (AH) (AH) (AH) Support Sample 9 Protective layer PL Photosensitive ML=R layers CL=IR-1 Unit YL=IR-2 (AH) Support Not only the silver halide emulsion having spectral sensitivity maximum at a longer wavelength than 730 nm prepared according to the present invention, but also a silver halide emulsion which may be additionally used for a particular purpose without applying the present invention may further contain a dyestuff for the purposes of enhancing image sharpness and safe light stability and preventing color mixing. The dyestuff may be contained in a layer with or without the emulsion. Preferably it is fixed in a particular layer. To this end, the dyestuff is added to a colloid layer in a non-diffusible state such that it may be decolored during development. First, a dyestuff which is insoluble in water below pH 7, but soluble in water above pH 7 is used in the form of a dispersion of fine particles thereof. Secondly, an acidic dyestuff is used together with a polymer or polymer latex presenting a cation site. For the first and second modes, the dyestuffs described in JP-A 197947/1988 as having formulae (VI) and (VII) are useful. Dyestuffs having a carboxy group are particularly useful for the first mode. With respect to other additives to be added to photographic photosensitive materials no particular limit is imposed. Reference may be made to Research Disclosure, Vol. 176, Item 17643 (RD 17643), ibid., Vol. 187, Item 18716 (RD 18716), and ibid., Vol. 307, Item 307105 (RD 307105). The pages of RD 17643, RD 18716 and RD 307105 where additives are described are listed below. Additive RD 17643 18716 307105 1. Chemical sensitizer 23 648R 866 2. Sensitivity riser 648R 3. Spectral sensitizer/Supersensitizer 23-24 648R-649R 866-868 4. Brightener 24 647R 868 5. Antifoggant/stabilizer 24-25 649R 868-870 6. Light absorber/filter dye/UV absorber 25-26 649R-650L 873 7. Anti-staining agent 25R 650L-R 872 8. Dye image stabilizer 25 650L 872 9. Hardener 26 651L 874-875 10. Binder 26 651L 873-874 11. Plasticizer/lubricant 27 650R 876 12. Coating aid/surfactant 26-27 650R 875-876 13. Antistatic agent 27 650R 876-877 14. Matte agent 876-879 The support used in the photosensitive material and dye-fixing element prepared according to the present invention may be of any desired material which can withstand photographic processing. Such materials include paper, polymers (film), metals, fabric and glass. Particularly, transparent films for use in photographic photosensitive materials such as cellulose nitrate films and polyethylene terephthalate films and reflective supports are useful. The support preferably has a thickness of 10 to 350 µm, more preferably 30 to 250 µm. The support on the surface may be coated with a hydrophilic binder and an antistatic agent such as a semiconductive metal oxide (e.g., alumina sol and tin oxide) and carbon black. The "reflective support" used herein is a support which is increased in reflection so as to make clearer or sharper a dye image formed on a silver halide emulsion layer. The reflective supports include supports coated with a hydrophobic resin having a light reflective substance (e.g., titanium oxide, zinc oxide, calcium carbonate and calcium sulfate) dispersed therein for increasing the reflectivity in the visible wavelength region and supports formed of a hydrophobic resin having a light reflective substance dispersed therein. Exemplary supports include baryta paper, polyethylene-coated paper, polypropylene base synthetic paper, transparent supports having a reflective layer coated or reflective substance applied thereon, glass plates, polyethylene terephthalate film, polyamide film, polycarbonate film, polystyrene film, vinyl chloride resin and the like. A choice may be made among these supports depending on a particular purpose. Preferably, the light reflective substance is prepared by fully milling a white pigment in the presence of a surfactant. Pigment particles may be surface treated with di- to tetrahydric alcohols. The white pigment fine particles preferably have a coefficient of variation of the occupied area ratio (%) of up to 0.15, especially up to 0.12, which is defined as follows. The white pigment fine particles have an occupied area ratio (%) per unit area. The occupied area ratio (%) is determined by dividing an area under observation into adjoining unit areas of 6 µm x 6 µm, measuring the area occupied by fine particles, that is, the area of fine particles projected on the unit area, and calculating the percentage (R1 %) of the occupied area relative to the unit area. A coefficient of variation of the occupied area ratio (%) is determined as a ratio s/Rav wherein Rav is an average of R1 and s is a standard deviation of R1. Therefore, the coefficient of variation s/Rav is calculated according to the follow formula. Other useful light reflective substances are metal thin films, for example, alloys of aluminum or the like and metals having a mirror reflective or secondary diffusion reflective surface as disclosed in JP-A 118154/1988, 24247/1988, 24251/1988, 24253/1988 and 24255/1988. The photographic photosensitive materials prepared in accordance with the present invention may be embodied as, for example, picture-taking black-and-white and color negative films (general and motion picture), color reversal films (slide and motion picture), black-and-white and color print papers, color positive films (motion picture), color reversal print papers, heat developing black-and-white and color photosensitive materials, graphic printing black-and-white and color photosensitive materials (lithographic films and scanner films), medical and industrial black-and-white and color photosensitive materials, diffusion transferring black-and-white and color photosensitive materials (DTR), etc. For exposing the photosensitive material imagewise to record images therein, a variety of exposure methods are employable. For example, exposure may be done by directly taking pictures of objects using a camera or the like, exposing through a reversal film or negative film using a printer, enlarger or the like, scanning an original and exposing through a slit using an exposure unit of a duplicating machine, actuating a light emitting diode, laser or the like to emit light for exposure in response to electrical signals representative of image information, or outputting image information on a display such as a CRT, liquid crystal display, electroluminescent display and plasma display and exposing directly or through an optical system. A variety of light sources may be used for recording images in photosensitive material, for example, sunlight, tungsten lamps, light emitting diodes, laser light sources, CRT light sources and the like as described in USP 4,500,625, col. 56. The image information may be given in the form of image signals available from video cameras and electronic still cameras, television signals as represented by NTSC, image signals obtained by dividing an original into a multiplicity of pixels by means of a scanner, and image signals created by means of computers as represented by CG and CAD. Next, a luminous flux output mechanism for use in the practice of the invention will be described. The laser which can be used in the practice of the present invention is preferably a semiconductor laser, examples of which include those of In 1-x Ga x P (-700 nm), GaAs 1-x P x (610-900 nm), Ga 1-x Al x As (690-900 nm), InGaAsP (1100-1670 nm), and AlGaAsSb (1250-1400 nm). For light exposure to a color photosensitive material according to the invention, YAG laser (1064 nm) in which Nb:YAG crystal is excited by a GaAs x P 1-x light emitting diode may also be used as well as the above-mentioned semiconductor lasers. Preferably, a choice is made among semiconductor laser luminous fluxes of 670, 680, 750, 780, 810, 830 and 880 nm. A second harmonic generator (SHG) element may also be used in the practice of the invention. Utilizing a non-linear optical effect, the SHG element converts the wavelength of laser light to one-half. Elements using CD*A and KD*P as non-linear optical crystals are known (see Laser Associate of Japan, Laser Handbook, December 15, 1982, pages 122-139). Also useful are LiNbO 3 optical waveguide elements wherein an optical waveguide is formed in a LiNbO 3 crystal by ion exchange of Li + by H + (see Nikkei Electronics, July 14, 1986, No. 399, pages 89-90). An output apparatus as disclosed in JP-A 226552/1988 may also be used in the practice of the invention. for the photographic processing and applicable systems of the photosensitive material prepared according to the present invention, reference is made to the above-cited RD 17643, XIX-XXIV and RD 307105, XIX-XXIII. The photosensitive material and/or dye-fixing element prepared according to the present invention may have an electroconductive heat-generating layer as heating means for heat development or dye diffusion transfer. In this embodiment, transparent or opaque heating elements as disclosed in JP-A 145544/1986 may be used. It is to be noted that these conductive layers also serve as antistatic layers. In the heat development step, the heating temperature is about 50°C to about 250°C, preferably about 80°C to about 180°C. Dye diffusion transfer may be carried out effected at the same time as heat development or after the completion of heat development. In the latter case, the heating temperature in the transfer step may be from room temperature to the temperature used in the heat development, preferably from about 50°C to a temperature about 10°C lower than the heat development temperature. Dye transfer can be induced solely by heat although a solvent may be used for promoting dye transfer. It is also useful to heat in the presence of a minor amount of solvent (especially water) to carry out development and transfer simultaneously or sequentially as disclosed in JP-A 218443/1984 and 238056/1986. In this mode, the heating temperature is from 50°C to below the boiling point of the solvent, for example, from 50°C to 100°C if the solvent is water. Examples of the solvent which is used in order to promote development and/or allowing the diffusible dye to migrate to the dye-fixing layer include water and basic aqueous solutions containing inorganic alkali metal salts and organic bases (which may be those described for the image formation promoter). Also, low-boiling solvents and mixtures of a low-boiling solvent and water or a basic aqueous solution are useful. Surfactants, antifoggants, difficultly soluble metal salts, complexing compounds or the like may be contained in the solvents. The solvent is used by applying it to the dye-fixing element or photosensitive material or both. The amount of the solvent used may be as small as below the weight of solvent corresponding to the maximum swollen volume of entire coatings, especially below the weight of solvent corresponding to the maximum swollen volume of entire coatings minus the dry weight of entire coatings. Useful for applying the solvent to the photosensitive layer or dye-fixing layer is a method as disclosed in JP-A 147244/1986. It is also possible to seal the solvent in microcapsules and incorporate the microcapsules in the photosensitive material or dye-fixing element or both. To promote dye transfer, a hydrophilic thermal solvent which is solid at room temperature, but soluble at high temperature may be incorporated into the photosensitive material or dye-fixing element or both. The layer into which the thermal solvent is incorporated is not limited and may be selected from emulsion layers, intermediate layer, protective layer and dye-fixing layer. Preferably, the thermal solvent is incorporated into the dye-fixing layer and/or layers contiguous thereto. Examples of the hydrophilic thermal solvent include ureas, pyridines, amides, sulfonamides, imides, alcohols, oximes, and heterocyclics. To promote dye transfer, a high-boiling organic solvent may be incorporated into the photosensitive material or dye-fixing element or both. Heating required in the development and/or transfer step may be carried out by any desired means, for example, by contacting with heated blocks or plates, contacting with hot plates, hot presses, hot rollers, halide lamp heaters, infrared or far infrared lamp heaters, or by passing through a hot atmosphere. Pressure is applied in overlapping a photosensitive element and a dye-fixing element in close contact. Such pressure requirements and pressure application are described in JP-A 147244/1986. For processing photographic elements according to the present invention, there may be used any of various heat developing apparatus including those described in JP-A 75247/1984, 177547/1984, 181353/1984 and 18951/1985 and Japanese U.M. Application Kokai No. 25944/1987. EXAMPLE Examples of the present invention are given below by way of illustration and not by way of limitation. Example 1 A reactor vessel was charged with 1000 ml of water, 25 grams of deionized bone gelatin, 15 ml of 50% NH 4 NO 3 aqueous solution, and 7.5 ml of 25% NH 3 aqueous solution. With thorough stirring at 50°C, 750 ml of 1N silver nitrate aqueous solution and 1N potassium bromide aqueous solution were added to the solution while maintaining a silver potential at +50 mV relative to the saturated calomel electrode during reaction. The resulting silver bromide grains are cubic with a side length of 0.76±0.06 µm. The emulsion was cooled down and a copolymer of isobutene and mono-sodium maleate was added as a flocculant for allowing the salt to precipitate. The salt was removed by washing the emulsion with water. To the emulsion were added 95 grams of deionized bone gelatin and 430 ml of water. The emulsion was adjusted to pH 6.5 and pAg 8.3 at 50°C. Portions of each 50 grams were weighed from the emulsion. To each portion, 5 mg of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene was added and the sensitizing dye shown in Table 1 was then added. After ripening at 70°C for 30 minutes, sodium thiosulfate, sodium chloroaurate and potassium thiocyanate were added to the emulsion so as to provide optimum sensitivity, followed by ripening at 60°C for 45 minutes. The emulsion contained 0.74 mol of silver bromide per kg of the emulsion. To the emulsion were added 10 mg of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, 15 grams of 10% gel of deionized bone gelatin and 55 ml of water. The emulsion was coated on a cellulose triacetate film base. Coating was done to give a coverage: 2.5 g/m 2 of silver and 3.8 g/m 2 of gelatin. An upper layer in a coverage of 1.0 g/m 2 of gelatin was formed by concurrently coating an aqueous solution predominantly containing 0.22 g/l of sodium dodecylbenzenesulfonate, 0.50 g/l of sodium p-sulfostyrene homopolymer, 3.9 g/l of 1,3-bis(vinylsulfonyl)-2-propanol and 50 g/l of gelatin. The thus coated sample was measured for absorption spectrum by means of a spectrometer with integrating sphere, Model U-3410 manufactured by Hitachi Ltd. The sample was subject to spectral exposure through a wedge using an equal-energy spectral exposure machine. The exposed sample was developed with the previously formulated black-and-white developer, stopped, fixed, washed and finally dried. The sample was measured for sensitivity at the spectral sensitivity maximum wavelength, the spectral sensitivity maximum wavelength + 30 nm, and the spectral sensitivity maximum wavelength - 30 nm. The sensitivity was represented by an inverse of the exposure necessary to give an optical density equal to the fog density + 0.2. Table 1 shows the ratios of the sensitivity S(max) at the spectral sensitivity maximum wavelength to the sensitivity S(-30nm) at the wavelength 30 nm shorter than the spectral sensitivity maximum wavelength and the sensitivity S(+30nm) at the wavelength 30 nm longer than the spectral sensitivity maximum wavelength. Table 1 also shows the ratios of the absorbance Abs(max) at the longest wavelength absorption maximum wavelength to the absorbance Abs(-30nm) at the wavelength 30 nm shorter than the longest wavelength absorption maximum wavelength and the absorbance Abs(+30nm) at the wavelength 30 nm longer than the longest wavelength absorption maximum wavelength. Table 2 shows the sensitivity at the spectral sensitivity maximum wavelength (lmax) as expressed in relative value based on a sensitivity of 100 for sample No. 1-1. Table 2 also shows the polarographic half-wave reduction potential (Ered 1/2 ) and polarographic half-wave oxidation potential (Eox 1/2 ) of the respective spectral sensitizing dyes. Table 2 further shows the sensitivity of a coated sample which was stored for 6 months at room temperature, exposed at the spectral sensitivity maximum wavelength (lmax) and similarly developed. This sensitivity is expressed in relative value based on a sensitivity of 100 for the same coated sample which was stored for the same period in a refrigerator at -30°C. It is to be noted that the sensitizing dyes within the scope of the invention are identified by designations like I-8 previously appearing in the specification and those outside the invention are identified by designations R-1 to R-4 which are defined subsequent to Table 2. Example 2 (comparative process not within scope of the claims) A silver halide emulsion was prepared from several liquid parts. Part 1 Water 1000 cc NaCl 4.65 g Gelatin 22 g Citric acid 0.80 g Part 2 KBr 25.3 g NaCl 32.3 g K 2 IrCl 6 (0.005%) 11.2 cc Na 3 RhCl 6 ·2H 2 O (10 -5 mol/l) 18.9 cc Water totaling to 348 cc Part 3 AgNO 3 120.6 g Water totaling to 348 cc Part 4 KBr 30.0 g NaCl 48.7 g Water totaling to 552 cc Part 5 AgNO 3 176.3 g Water totaling to 552 cc To Part 1 which was heated at 50°C, 262 cc of Part 2 and 262 cc of Part 3 were concurrently added at a constant flow rate over 12 minutes. Then Parts 4 and 5 were concurrently added over 20 minutes. Over the later 10 minute period from 10 minutes after the start of addition of Parts 4 and 5 to the end of addition, a methanol solution of the sensitizing dye shown in Table 3 was concurrently added at a constant flow rate. Then the temperature was lowered and a copolymer of isobutene and mono-sodium maleate was added as a flocculant for allowing the salt to precipitate. The salt was removed by washing the emulsion with water. Water and deionized bone gelatin were added to the emulsion, which was adjusted to pH 6.1 and pAg 7.5. Then sodium thiosulfate, sodium chloroaurate and potassium thiocyanate were added to the emulsion to effect optimum chemical sensitization. There was prepared a mono-dispersed cubic silver chlorobromide emulsion having a grain size of 0.28 µm in average side length, a coefficient of variation of 0.08 (standard deviation divided by average side length, s/d), and a silver bromide content of 30%. To 1 kg of the emulsion were added 0.75 grams of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, 280 grams of 10% gel of deionized bone gelatin and 1040 ml of water. The emulsion was coated on a polyethylene terephthalate film base to give a coverage of 1.2 g/m 2 of silver in a similar manner to Example 1. As in Example 1, the coated sample was measured for absorption spectrum and sensitivity at the spectral sensitivity maximum wavelength, the spectral sensitivity maximum wavelength + 30 nm, and the spectral sensitivity maximum wavelength - 30 nm. Table 3 shows the relative sensitivity at the spectral sensitivity maximum wavelength (a relative value based on a sensitivity of 100 for sample No. 2-1), sensitivity ratios, and absorbance ratios. Example 3 A silver halide emulsion was prepared from several liquid parts. Part 1 Water 1000 cc NaCl 5.5 g Gelatin 32 g Part 2 Sulfuric acid (1N) 24 cc Part 3 1% 1,3-dimethylimidazolidine-2- thion solution 3 cc Part 4 NaCl 11.0 g Water totaling to 200 cc Part 5 AgNO 3 32 g Water totaling to 200 cc Part 6 NaCl 44.05 g K 2 IrCl 6 (0.001%) 4.54 cc Water totaling to 600 cc Part 7 AgNO 3 128 g Water totaling to 600 cc To Part 1 which was heated at 56°C were added Parts 2 and 3. Then Parts 4 and 5 were concurrently added over 10 minutes. Further, 10 minutes later, Parts 6 and 7 were concurrently added over 20 minutes. After 5 minutes from the completion of addition, the temperature was lowered and a copolymer of isobutene and mono-sodium maleate was added as a flocculant for allowing the salt to precipitate. The salt was removed by washing the emulsion with water. Water and deionized bone gelatin were added to the emulsion, which was adjusted to pH 6.2 and pAg 7.4. There was prepared a mono-dispersed cubic silver chloride emulsion having a grain size of 0.54 µm in average side length and a coefficient of variation of 0.09 (standard deviation divided by average side length, s/d). To the emulsion were added 2.5x10 -3 mol of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, 8x10 -3 mol of potassium bromide and the sensitizing dye shown in Table 4, per mol of silver. The emulsion was ripened at 60°C for 30 minutes. Then sodium thiosulfate was added to the emulsion to effect optimum chemical sensitization. Thereafter, 0.3 grams per kg of the emulsion of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene was added to the emulsion. The emulsion was coated on a polyethylene terephthalate film base. Coating was done to give a coverage: 1.6 g/m 2 of silver and 3.0 g/m 2 of gelatin. An upper layer in a coverage of 1.0 g/m 2 of gelatin was formed by concurrently coating an aqueous solution predominantly containing 0.1 g/l of sodium dodecylbenzenesulfonate, 0.22 g/l of sodium p-sulfostyrene homopolymer, 3.1 g/l of 2-hydroxy-4,6-dichloro-1,3,5-triazine and 50 g/l of gelatin. As in Example 1, the coated sample was measured for absorption spectrum and sensitivity at the spectral sensitivity maximum wavelength, the spectral sensitivity maximum wavelength + 30 nm, and the spectral sensitivity maximum wavelength - 30 nm. Table 4 shows the relative sensitivity at the spectral sensitivity maximum wavelength (a relative value based on a sensitivity of 100 for sample No. 3-1), sensitivity ratios, and absorbance ratios. Example 4 (comparative process not within scope of the claims) A silver halide emulsion was prepared by adding 3.3 grams of sodium chloride to 3% lime-treated gelatin aqueous solution and adding 3.2 ml of 1% 1,3-dimethylimidazolidine-2-thion aqueous solution. With vigorous stirring, an aqueous solution containing 0.2 mol of silver nitrate and an aqueous solution containing 15 µg of rhodium trichloride and 0.2 mol of sodium chloride were added to the solution at 56°C. Then, with vigorous stirring, an aqueous solution containing 0.780 mol of silver nitrate and an aqueous solution containing 0.780 mol of sodium chloride and 4.2 mg of potassium ferrocyanide were added to the solution at 56°C. Five minutes later from the composition of addition of the silver nitrate and sodium chloride solutions, with vigorous stirring, an aqueous solution containing 0.020 mol of silver nitrate and an aqueous solution containing 0.015 mol of potassium bromide, 0.005 mol of sodium chloride and 0.8 mg of potassium hexachloroiridate (IV) were added to the solution at 40°C. Thereafter, a polymeric flocculant was added, followed by precipitation, desalting and washing. Then 8x10 -3 mol per mol of silver of potassium bromide and the sensitizing dye shown in Table 5 were added to the emulsion, which was ripened at 60°C for 30 minutes. Then 90.0 grams of lime-treated gelatin and triethylurea were added to the emulsion which was ripened for chemical sensitization at 55°C to achieve a maximum sensitivity. To the emulsion was added 4.0x10- 4 mol per mol of silver of 1-(5-methylureidophenyl)-5-mercaptotetrazole. There was prepared an emulsion of cubic silver chlorobromide grains having a mean grain size of 0.52 µm with a coefficient of variation of 0.08. The grain size is expressed by the diameter of a circle equivalent to the projected area of a grain and the coefficient of variation is the standard deviation of grain size divided by average grain size. The silver halide grains were analyzed by X-ray diffractometry to determine the halogen composition thereof. Using a monochromatic CuK(a) ray as a ray source, the angle of diffraction was precisely measured from (200) plane. It will be understood that a diffraction line from a crystal having a uniform halogen composition has a single peak and a diffraction line from a crystal having a localized phase of a different composition has a plurality of peaks corresponding to the compositions. By calculating lattice constants from the angles of diffraction at the peaks on measurement, the halogen composition of silver halide of which the crystal is formed can be determined. As a result of analysis of the silver chlorobromide emulsion prepared above, there was observed a broad diffraction pattern which has a main peak corresponding to 100% silver chloride, a center at 70 mol% of silver chloride (30 mol% of silver bromide), and a skirt extending to 60 mol% of silver chloride (40 mol% of silver bromide). A paper support laminated with polyethylene on either surface was coated with the emulsion along with color couplers. The coating solution was prepared as follows. A mixture of 19.1 grams of a yellow coupler (Ex-Y), 4.4 grams of a color image stabilizer (Cpd-1) and 1.4 grams of a color image stabilizer (Cpd-2) was dissolved in 27.2 ml of ethyl acetate and 8.2 grams of a solvent (Solv-1). The solution was emulsion dispersed in 185 ml of a 10% gelatin aqueous solution containing 8 ml of 10% dodecylbenzenesulfonic acid aqueous solution. This emulsified dispersion was added to the previously prepared silver chlorobromide emulsion at 40°C, which was mixed for dissolution. In this way, there was prepared a coating solution having the composition shown below. A protective layer was formed as an upper layer. The gelatin hardener used in the respective layers was sodium salt of 2-hydroxy-4,6-dichloro-1,3,5-triazine. The composition of the respective layers was shown below. The coverage of substances is expressed in g/m2 and the coverage of silver halide emulsion is expressed by the weight of silver. Support Polyethylene-laminated paper (The polyethylene on the first layer side contains a white pigment (TiO 2 ) and a blue dye (ultramarine)). Silver chlorobromide emulsion layer (Yellow developing layer) Silver chlorobromide emulsion 0.30 Gelatin 1.86 Yellow coupler (Ex-Y) 0.82 Color image stabilizer (Cpd-1) 0.19 Color image stabilizer (Cpd-2) 0.06 Solvent (Solv-1) 0.35 Upper layer (Protective layer) Gelatin 1.33 Acryl-modified copolymer of polyvinylalcohol (modification 17%) 0.17 Fluid paraffin 0.03 The thus coated sample was measured for reflective absorption spectrum as in Example 1. The spectral sensitivity was measured after carrying out exposure and development as in Example 1 except that the development was carried out according to the color development procedure previously described in the specification. The sensitivity was represented by an inverse of the exposure necessary to give a color development density equal to the fog density + 0.5. Table 5 shows the relative sensitivity at the spectral sensitivity maximum wavelength (a relative value based on a sensitivity of 100 for sample No. 4-1), sensitivity ratios, and absorbance ratios. Example 5 The preparation of emulsion (1) is described. To a thoroughly agitated gelatin aqueous solution having the composition shown in Table 6, Liquids I and II shown in Table 7 were concurrently added over 18 minutes. After 5 minutes from,the completion of addition of Liquid I, Liquids III and IV shown in Table 7 were concurrently added over 42 minutes. The emulsion was desalted by adding a flocculant (P-1) of the formula: and washing with water. After 22 grams of gelatin was added to the emulsion at pH 4.1, an aqueous solution of NaCl and NaOH was added to the emulsion to adjust it to pH 6.1 and pAg 7.6 at 40°C for re-dispersion. Using triethylthiourea and 4-hydroxy-6-methyl-(1,3,3a,7)-tetraazaindene, the emulsion was chemically sensitized optimum at 60°C. The optimum implies the conditions under which maximum sensitivity is achieved without a fog. There was obtained 635 grams of a mono-dispersed cubic emulsion having a mean grain size of 0.26 µm and a coefficient of variation of 8.5%. Gelatin aqueous solution composition H 2 O 620 cc Gelatin 20 g KBr 0.03 g NaCl 2.00 g H 2 SO 4 (1N) 16 cc 1,3-dimethylimidazolidine-2-thion 0.015 g pH = 3.9 Temperature = 45°C Liquid I II III IV AgNO 3 30.0 g - 70.0 g - KBr - 13.7 g - 44.1 g NaCl - 3.6 g - 2.4 g K 2 IrCl 6 - - - 4.0x10 -5 Water (totaling to) 150.0 cc 150.6 cc 350.2 cc 360.1 cc Next, the preparation of a gelatin dispersion of a dye-providing substance is described. To 70 ml of ethyl acetate were added 14.64 grams of a magenta dye-providing substance (D-M), 0.81 grams of a reducing agent (Cpd-3), 0.20 grams of a mercapto compound (Cpd-4), 0.38 grams of a surfactant (Cpd-5), and 5.1 grams of a high-boiling organic solvent (2). The mixture was heated to about 60°C to form a uniform solution. This solution was mixed with 100 grams of 10% lime-treated gelatin solution and 60 ml of water. The mixture was subjected to dispersion by a homogenizer at 10,000 rpm for 10 minutes. This dispersion is designated a magenta dye-providing substance dispersion. To 50 ml of ethyl acetate were added 7.3 grams of a cyan dye-providing substance (D-C1), 10.6 grams of a cyan dye-providing substance (D-C2), 1.0 grams of a reducing agent (Cpd-3), 0.3 grams of a mercapto compound (Cpd-4), 0.38 grams of a surfactant (Cpd-5), and 9.8 grams of a high-boiling organic solvent (1). The mixture was heated to about 60°C to form a uniform solution. This solution was mixed with 100 grams of 10% lime-treated gelatin solution and 60 ml of water. The mixture was subjected to dispersion by a homogenizer at 10,000 rpm for 10 minutes. This dispersion is designated a cyan dye-providing substance dispersion. To 45 ml of ethyl acetate were added 18.75 grams of a yellow dye-providing substance (D-Y), 1.0 grams of a reducing agent (Cpd-3), 0.12 grams of a mercapto compound (Cpd-4), 1.5 grams of a surfactant (Cpd-5), 7.5 grams of a high-boiling organic solvent (1), and 2.1 grams of a dye (Cpd-6). The mixture was heated to about 60°C to form a uniform solution. This solution was mixed with 100 grams of 10% lime-treated gelatin solution and 60 ml of water. The mixture was subjected to dispersion by a homogenizer at 10,000 rpm for 10 minutes. This dispersion is designated a yellow dye-providing substance dispersion. High-boiling organic solvent (1): triisononylphosphate High-boiling organic solvent (2): trihexylphosphate Using the above-prepared components, a heat developable color photosensitive material No. 100 of the following formulation was prepared. It is to be noted that sensitizing dye (R-1) was added at the time of preparing a coating solution in an amount optimized to achieve the highest sensitivity. It will be understood that No. 100 was prepared as a reference sample which is outside the scope of the invention. Formulation of photosensitive material No. 100 Ingredient Amount (g/m 2 ) 7th layer: protective layer Gelatin 0.264 Matte agent 0.018 Zn(OH) 2 0.964 Surfactant (Cpd-7) 0.028 Surfactant (Cpd-8) 0.011 Water-soluble polymer (Cpd-13) 0.004 6th layer: intermediate layer Gelatin 0.762 Surfactant (Cpd-7) 0.007 Surfactant (Cpd-8) 0.022 Water-soluble polymer (Cpd-13) 0.016 5th layer: red (670nm) sensitive layer Emulsion (1) 0.321 (Ag) Sensitizing dye (R-5) 0.0013 Magenta dye-providing substance (D-M) 0.2845 High-boiling organic solvent (2) 0.100 Reducing agent (Cpd-3) 0.016 Mercapto compound (Cpd-4) 0.007 Gelatin 0.297 Antifoggant (Cpd-14) 0.003 Water-soluble polymer (Cpd-13) 0.007 4th layer: intermediate layer Hardener 0.058 Gelatin 0.629 Surfactant (Cpd-7) 0.009 Surfactant (Cpd-9) 0.046 Water-soluble polymer (Cpd-13) 0.012 3rd layer: near infrared (750nm) sensitive layer Emulsion (1) 0.320 (Ag) Sensitizing dye (R-1) 5.8x10 -5 Cyan dye-providing substance (D-C1) 0.132 Cyan dye-providing substance (D-C2) 0.193 High-boiling organic solvent (1) 0.178 Reducing agent (Cpd-3) 0.018 Mercapto compound (Cpd-4) 0.005 Surfactant (Cpd-5) 0.007 Gelatin 0.284 Mercapto compound (Cpd-10) 0.0003 Stabilizer (Cpd-12) 0.0043 Water-soluble polymer (Cpd-13) 0.010 2nd layer: intermediate layer Gelatin 0.629 Surfactant (Cpd-7) 0.006 Surfactant (Cpd-9) 0.057 Water-soluble polymer (Cpd-13) 0.009 1st layer: infrared (810nm) sensitive layer Emulsion (1) 0.340 (Ag) Mercapto compound (Cpd-10) 8.4x10 -4 Sensitizing dye (R-6) 1.1x10 -4 Yellow dye-providing substance (D-Y) 0.429 Dye (Cpd-6) 0.049 High-boiling organic solvent (1) 0.172 Reducing agent (Cpd-3) 0.023 Mercapto compound (Cpd-4) 0.003 Surfactant (Cpd-5) 0.034 Gelatin 0.338 Stabilizer (Cpd-12) 0.0054 Water-soluble polymer (Cpd-13) 0.014 Support Polyethylene-laminated neutral paper, 120 µm thick Surfactants (Cpd-7), (Cpd-8) and (Cpd-9), mercapto compound (Cpd-10), hardener (Cpd-11), stabilizer (Cpd-12), water-soluble polymer (Cpd-13), antifoggant (Cpd-14), sensitizing dyes (R-5) and (R-6) are identified below. For comparison purposes, a comparative photosensitive material No. 101 was prepared by the same procedure as No. 100 except that sensitizing dye (R-1) was omitted in the preparation of the emulsion coating solution for the third layer, and in the preparation of emulsion (1) for the third layer, sensitizing dye (R-7) was added after the addition of triethylthiourea and 4-hydroxy-6-methyl-(1,3,3a,7)-tetra-azaindene and the mixture was agitated for 30 minutes at 70°C. The sensitizing dye (R-7) was added in an amount to give a coverage of 5.0x10 -4 g/m 2 . Preparation of photosensitive materials within the scope of the invention A photosensitive material No. 102 was prepared by the same procedure as No. 101 except that sensitizing dye (R-7) was replaced by sensitizing dye (I-32) in the preparation of emulsion (1) for the third layer. The sensitizing dye (I-32) was added in an amount to give a coverage of 7.0x10 -4 g/m 2 . A photosensitive material No. 103 was prepared by the same procedure as No. 102 except that addition of sensitizing dye (I-32) was followed by agitation for 30 minutes and subsequent addition of triethylthiourea in the preparation of emulsion (1) for the third layer. A photosensitive material No. 104 was prepared by the same procedure as No. 101 except that emulsion (2) was used instead of emulsion (1) as the emulsion for the third layer. Emulsion (2) was prepared by the same procedure as emulsion (1) except that the completion of addition of Liquids III and IV was followed by heating to 75°C, addition of 4-hydroxy-6-methyl-(1,3,3a,7)-tetraazaindene, addition of 0.270 grams of sensitizing dye (I-32), and agitation for 30 minutes. A photosensitive material No. 105 was prepared by the same procedure as No. 102 except that sensitizing dye (I-32) was replaced by sensitizing dye (I-29) in the preparation of emulsion (1) for the third layer. The sensitizing dye (I-29) was added in an amount to give a coverage of 8.50x10 -4 g/m 2 . A photosensitive material No. 106 was prepared by the same procedure as No. 105 except that sensitizing dye (I-29) was replaced by sensitizing dye (I-14). The sensitizing dye was added in an amount to give a coverage of 8.50x10 -4 g/m 2 . A photosensitive material No. 107 was prepared by the same procedure as No. 102 except that sensitizing dye (I-32) was replaced by sensitizing dye (R-8) in the preparation of emulsion (1) for the third layer. The sensitizing dye was added in an amount to give a coverage of 8.5x10 -4 g/m 2 . A photosensitive material No. 108 comparative was prepared by the same procedure as No. 102 except that sensitizing dye (I-32) was added at the time of coating as in No. 100 and agitated for 45 minutes at 60°C. The sensitizing dye was added in an amount to give a coverage of 7x10 -4 g/m 2 . A photosensitive material No. 109 (comparison) was prepared by the same procedure as No. 101 except that sensitizing dye (R-7) was replaced by sensitizing dye (R-9) in the preparation of emulsion (1) for the third layer. The sensitizing dye was added in an amount to give a coverage of 8.50x10 -4 g/m 2 . A photosensitive material No. 110 was prepared by the same procedure as No. 109 except that sensitizing dye (R-9) was replaced by sensitizing dye (I-24) in the preparation of emulsion (1) for the third layer. A photosensitive material No. 111 was prepared by the same procedure as No. 110 except that sensitizing dye (I-24) was replaced by sensitizing dye (I-8) in the preparation of emulsion (1) for the third layer. It is to be noted that the amount of the sensitizing dye added in photosensitive material Nos. 101 to 111 is in the range of 50 to 100% of the adsorption saturation coating amount. Next, the preparation of a dye fixing material is described. A dye fixing material was prepared by coating a polyethylene-laminated paper support in accordance with the following formulation. Formulation of dye fixing material Ingredient Amount (g/m 2 ) 3rd layer: Gelatin 0.05 Silicone oil (Cpd-15) 0.04 Surfactant (Cpd-7) 0.001 Surfactant (Cpd-16) 0.02 Surfactant (Cpd-17) 0.10 Guanidine picolate 0.45 Polymer (Cpd-21) 0.24 2nd layer: Mordant (Cpd-19) 2.35 Polymer (Cpd-22) 0.60 Gelatin 1.40 Polymer (Cpd-21) 0.21 High-boiling organic solvent (3) 1.40 Guanidine picolate 1.80 Surfactant (Cpd-7) 0.02 1st layer: Gelatin 0.45 Surfactant (Cpd-17) 0.01 Polymer (Cpd-21) 0.04 Hardener (Cpd-20) 0.30 Support Polyethylene-laminated paper, 170 µm thick Back 1st layer: Gelatin 3.25 Hardener (Cpd-20) 0.25 Back 2nd layer: Gelatin 0.44 Silicone oil (Cpd-15) 0.08 Surfactant (Cpd-7) 0.002 Matte agent 0.09 Surfactant (Cpd-18) 0.01 Silicone oil (Cpd-15), Surfactants (Cpd-16), (Cpd-17) and (Cpd-18), mordant (Cpd-19), and hardener (Cpd-20) are identified below. Polymer (Cpd-21): vinyl alcohol-sodium acrylate copolymer (75/25 molar ratio) Polymer (Cpd-22): dextran (molecular weight 70,000) High-boiling organic solvent (3): Leophos 95 (manufactured by Ajinomoto K.K.) Matte agent: benzoguanamine resin containing 18 vol% of particles in excess of 10 µm Evaluation of these photosensitive materials was made by the following exposure and processing. Using a laser exposure apparatus as described in Japanese Patent Application No. 129625/1990, each photosensitive material was exposed under the following conditions. Exposure conditions Beam intensity on photosensitive material surface: 1 mW Beam diameter: 100±10 µm in main scanning direction 80±10 µm in subordinate scanning direction Exposure time: 0.9 msec./luster Exposure wavelength: 670, 750, 810 nm (laser light) Exposure quantity: a variation of 1logE/2.5 cm in subordinate scanning direction (maximum 80 erg/cm 2 , minimum 1.2 erg/cm 2 ) Exposure quantity control: light emitting time modulation After 12 cc/m 2 of water was supplied to the emulsion surface of the exposed photosensitive material by means of a wire bar, a dye fixing material was placed on the wet photosensitive material such that their effective surfaces contacted each other. Using a heating drum, the assembly was heated such that the water-absorbed coating reached a temperature of 90°C for 20 seconds. The dye fixing material which now born an image thereon was then stripped from the photosensitive material. Spectral sensitivity was measured by exposing each photosensitive material to monochromatic light for 5 seconds through a wedge and thereafter carrying out the same procedures as above. With respect to transfer density, fog and sensitivity (an inverse of the exposure providing a fog of +1.0) were measured using an auto-recording densitometer. Live storage stability was evaluated by comparing photographic properties between a photosensitive material immediately after coating and a photosensitive material which was stored for 3 days at 60°C and RH 60% after coating. A degree of color separation was evaluated, after exposure at 810 nm, in terms of the difference between an exposure quantity logE1 providing a density of (Dmax - 0.1) for yellow and an exposure quantity logE2 providing a density of (Dmin + 0.1) for cyan in color mix with the yellow, that is, logE = logE1 - logE2. In accordance with the above-defined procedures, photosensitive material Nos. 100 to 111 were measured for spectral sensitivity, sensitivity, fog, and degree of color separation of a cyan color developing layer. The results are shown in Table 8. Table 8 also reports the ratio of the sensitivity S(max) at a wavelength (λmax) at which the third layer provides a maximum spectral sensitivity to the spectral sensitivity S(+20nm) at a wavelength 20 nm longer than λmax, that is, S(max)/S(+20nm). Sensitivity is expressed in relative sensitivity based on a sensitivity of 100 for photosensitive material No. 1 immediately after coating. Additional photosensitive materials were prepared by the same procedure as photosensitive material No. 100 except that the stage of addition of sensitizing dye (R-1) in the third layer was changed in accordance with photosensitive material Nos. 101, 103 and 104. They were similarly processed and evaluated, with the results equivalent to those of photosensitive material No. 100. Further, additional photosensitive materials were prepared by the same procedure as photosensitive material No. 101 except that the stage of addition of sensitizing dye (R-7) in the third layer was changed in accordance with photosensitive material Nos. 103 and 104. They were similarly processed and evaluated, with the results equivalent to those of photosensitive material No. 101. As demonstrated in Examples, the present invention is successful in achieving J-band sensitization of a silver halide emulsion in the infrared region having longer wavelengths than 730 nm independent of the halogen composition of the emulsion. With respect to infrared sensitization with sensitizing dyes including those used for comparison purposes, molecular type spectral sensitization has heretofore been resorted and J-band sensitization has not been developed. Since most molecular type spectral sensitizing dyes for the infrared and red end regions have intense inherent desensitization, they should be added in as small an amount as possible in order to insure sensitivity. This is the reason why the amount of sensitizing dye added is small in Sample Nos. 1-1, 1-3, 1-5, 2-1, 3-1 and 4-1 as compared with the samples within the scope of the present invention. It is to be noted that the amounts of the sensitizing dyes added in these comparative samples are the amounts at which a maximum sensitivity is occasioned by the respective dyes. Among prior art known molecular type infrared sensitizing dyes, comparative dyes R-1 and R-2 are known to provide very high spectral sensitivity and experience a relatively less lowering of sensitivity during shelf storage. When these comparative dyes as well as comparative dye R-3 are added in an increased amount equal to the inventive samples, spectral sensitivity is extremely lowered and no J-band sensitization occurs. In contrast, the inventive samples are fully sharp in both absorption distribution and spectral sensitivity distribution as seen from Tables 1, 3, 4 and 5. The fact that the spectral sensitivity is reduced to below one-half of the maximum spectral sensitivity by shifting the wavelength only 30 nm shorter from the spectral sensitivity maximum wavelength implies that the safety of safe light is accordingly increased. It is not so rare in the present invention that the spectral sensitivity is reduced to below one-third of the maximum spectral sensitivity by such a wavelength shift. A sharper spectral sensitivity distribution implies that as the wavelength becomes shorter by more than 30 nm, there occurs a great lowering in sensitivity from the maximum spectral sensitivity as compared with the prior art molecular type sensitization. This enables the design of increasing sensitivity by a factor of 3 or more for the same level of safe light safety or of increasing the safe light safety by a factor of 3 or more for the same level of sensitivity. Since practical safe light is visible light, the safe light safety is extremely enhanced far beyond the differential sensitivity at the 30-nm shorter wavelength. Moreover, the J-band sensitization according to the invention is extremely sharper at a longer wavelength side. The spectral sensitivity is reduced to below 1/4.5 of the maximum spectral sensitivity by increasing the wavelength only 30 nm from the spectral sensitivity maximum wavelength, which differential sensitivity is approximately twice that of prior art molecular type sensitization. It is sometimes possible to provide a differential sensitivity of more than 10 times (S(max)/S(+30nm) > 10) as evidenced by sample No. 1-8 achieving a differential sensitivity of more than 100 times. This is very advantageous in the design of multilayer full color photosensitive material. For example, assume that it is desired to provide a magenta color developing layer which is to be exposed to laser light having a 30-nm shorter wavelength than a cyan color developing layer, and that both the layers have the same maximum spectral sensitivity. Then, the exposure energy width over which only the cyan layer is exposed without exposing the magenta layer (or without magenta color development) is expanded by a factor of 4.5 or more, and often by a factor of 10 or more by effecting J-band sensitization according to the present invention, in contrast to the prior art molecular type sensitization which allows the exposure energy width to be expanded only by a factor of about 2.5. It is desired to provide a sensitivity ratio of at least 6.5 for acceptable image reproduction, especially a sensitivity ratio of at least 10 for faithful image reproduction. If the spectral sensitivity maximum wavelengths of the two layers are spaced 50 nm, then even the prior art molecular type sensitization can provide a sensitivity ratio of 6.5 or more, but at most 10. The J-band sensitization according to the present invention provides a sensitivity ratio of more than 10 quite easily and often several ten times. On the other hand, the exposure energy width over which only the magenta layer at a shorter wavelength side is exposed without exposing the cyan layer is expanded by a factor of 1.5-1.85 in the molecular type sensitization and by a factor of 2 or slightly more in the J-band sensitization of the invention, which factor is not so high although a factor of 6.5 or more is sometimes possible. However, if the spectral sensitivity maximum wavelengths of the two layers are spaced 50 nm, then a great differential sensitivity on a longer wavelength wide allows for the design of increasing the sensitivity of the magenta layer at the expense of restraining the differential sensitivity of the cyan layer at the necessary level, or reducing the sensitivity of the cyan layer. In this way, the J-band sensitization of the invention allows such a great differential sensitivity to be easily imparted to even a magenta layer adapted for shorter wavelength exposure whereas the molecular type sensitization with a 50-nm spacing needs another means for providing differential sensitivity, for example, by adding a filter dye to a cyan layer to thereby reduce the sensitivity thereof at a 50-nm shorter wavelength from the spectral sensitivity maximum wavelength because the cyan layer has no margin for differential sensitivity. Even when such extra means is used, it is quite difficult to achieve a sensitivity ratio of 10 or more with the prior art molecular type sensitization. There occur some side-effects since the absorption of the filter dye itself is generally not so sharp. Not only the wavelength region where it is desired to reduce sensitivity is reduced in sensitivity, but also the wavelength region where exposure is desired are somewhat reduced in sensitivity. The technique of the present invention thus enables easy design and manufacture of a full color photosensitive material having an increased degree of freedom of choice of a semiconductor laser light source for exposure and improved color reproducibility. It is known that the spectral sensitization of silver halide becomes more effective with a sensitizing dye having a less reduction potential. On the other hand, for equal transition energy of absorption, the less the reduction potential, the less becomes the oxidation potential of a sensitizing dye. A dye having a less oxidation potential is more susceptible to oxidation so that it may be oxidized during storage, resulting in a lowering of sensitivity. If the reduction potential of a molecular type infrared sensitizing dye is made less for increasing sensitivity, then its oxidation potential becomes too negative to ensure stability. As shown in Table 2, with an oxidation potential at values ≤ 0.38 V vs SCE, the associated photosensitive material experienced a substantial lowering of sensitivity during storage. Most of molecular type infrared sensitizing dyes including those sensitizing dyes used in commercially available infrared photosensitive materials have a reduction potential of from -1.1 to - 1.25 V vs SCE and thus noticeably low spectral sensitivity as compared with visible region sensitizing dyes having a less reduction potential. Despite of low sensitivity, many such dyes also have an oxidation potential as negative as 0.4 V vs SCE or lower, some as negative as 0.3 V vs SCE or lower, leading to a substantial loss of sensitivity during storage. The sensitizing dyes which can be used in the present invention have a more basic reduction potential and yet a more noble oxidation potential comparable to those of visible region sensitizing dyes, and consequently provide high sensitivity and restrain the sensitivity from lowering during shelf storage as compared with those of prior art infrared sensitizing dyes providing relatively high spectral sensitivity. The J-band sensitization according to the invention is successful in increasing sensitivity by a factor of 10 or more, and sometimes 50 or more. It is quite unexpected that such a great sensitivity increase is achieved with a minimized loss of sensitivity during storage. The photosensitive material prepared in accordance with the invention is also effective in providing high sensitivity, live storage stability and color separation when it is applied to heat development systems of complex organization, as is evident from Example 5. Noteworthy are test results of further samples. Photosensitive material samples were prepared by the same procedure as in Example 1 except that octahedral and 14-sided silver bromide grains prepared by adjusting the silver potential during silver halide grain formation in Example 1 or plate silver iodobromide grains prepared in accordance with Example 4 of JP-A 131533/1985 were used instead of the cubic silver bromide grains, 80 mg per mol of silver of tetraazaindene compound (11-11) was used instead of the 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene added prior to the addition of the sensitizing dye, and the addition of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene after chemical ripening was omitted. Sensitizing dyes R-1, R-4, I-8, I-16 and I-18 were added to emulsions in amounts of 1.52x10 -6 mol per m 2 of silver halide grain surface area. These samples showed test results equivalent to those of sample Nos. 1-2, 1-6, 1-12 and 1-9 of Example 1.

Claims: A process for preparing a silver halide photosensitive material comprising a support and at least one layer of a photographic silver halide emulsion thereon, said at least one photographic silver halide layer being spectrally sensitized with at least one spectral sensitizer having a polarographic half-wave reduction potential at values ≤ -1.26 V and a polarographic half-wave oxidation potential at values ≥ 0.38 V relative to the saturated calomel electrode, characterized in that said sensitizer is present in an amount of 6.2 x 10 -7 mol to 2.7 x 10 -6 mol per square meter of silver halide grain surface area such that said layer has a sensitization maximum at a longer wavelength than 730 nm and the sensitivity at the spectral sensitivity maximum wavelength is higher by a factor of at least 4.5 than the spectral sensitivity to light having a wavelength 30 nm longer than said spectral sensitivity maximum wavelength and higher by a factor of at least 2 than the spectral sensitivity to light having a wavelength 30 nm shorter than said spectral sensitivity maximum wavelength; and in that said spectral sensitizer is a dicarbocyanine dye of the general formula (I): wherein Z 1 and Z 2 , which may be identical or different, are a sulfur atom or a selenium atom, Y 1 and Y 4 each represent a hydrogen atom, Y 1 where Y 2 is not a hydrogen atom and Y 4 where Y 5 is not a hydrogen atom may represent a methyl, ethyl, hydroxyl or methoxy group, Y 2 and Y 5 are independently selected from the class consisting of a hydrogen atom, substituted or unsubstituted alkyl group having up to 3 carbon atoms, hydroxyl group, chlorine atom, bromine atom, methoxy group, ethoxy group, monocyclic aryl group, acetylamino group, and propionylamino group, Y 2 and Y 1 taken together and Y 5 and Y 4 taken together may form a methylenedioxy, trimethylene or tetramethylene group, Y 3 and Y 6 each represent a hydrogen atom, Y 3 and Y 2 taken together and Y 6 and Y 5 taken together may form a methylenedioxy, ethylenedioxy, trimethylene, tetramethylene or tetradehydromethylene group, R 1 and R 2 , which may be identical or different, are a substituted or unsubstituted alkyl or alkenyl group, R 3 and R 5 represents a hydrogen atom, R 3 and R 1 taken together and R 5 and R 2 taken together may form a five- or six-membered ring, R 4 is a hydrogen or a substituted or unsubstsituted lower alkyl group, R 6 is a hydrogen atom, methyl group, ethyl group or propyl group, R 7 is a substituted or unsubstituted lower alkyl group or substituted or unsubstituted phenyl group, X is a counter ion necessary to neutralize the charge, and letter n is equal to 1 or 0 in the case of an intramolecular salt, comprising the step of chemically sensitizing the silver halide emulsion of at least one layer in the presence of at least one dicarbocyanine dye of formula (I) and at least one tetraazaindene compound. A process for preparing a silver halide photosensitive material comprising a support and at least one layer of a photographic silver halide emulsion thereon, said at least one photographic silver halide emulsion layer being spectrally sensitized with at least one spectral sensitizer having a polarographic half-wave reduction potential at values ≤ -1.26 V and a polarographic half-wave oxidation potential at values ≥ 0.38 V relative to the saturated calomel electrode, characterized in that said spectral sensitizer is a dicarbocyanine dye of the general formula (I): wherein Z 1 and Z 2 , which may be identical or different, are a sulfur atom or a selenium atom, Y 1 and Y 4 each represent a hydrogen atom, Y 1 where Y 2 is not a hydrogen atom and Y 4 where Y 5 is not a hydrogen atom may represent a methyl, ethyl, hydroxyl or methoxy group, Y 2 and Y 5 are independently selected from the class consisting of a hydrogen atom, substituted or unsubstituted alkyl group having up to 3 carbon atoms, hydroxyl group, chlorine atom, bromine atom, methoxy group, ethoxy group, monocyclic aryl group, acetylamino group, and propionylamino group, Y 2 and Y 1 taken together and Y 5 and Y 4 taken together may form a methylenedioxy, trimethylene or tetramethylene group, Y 3 and Y 6 each represent a hydrogen atom, Y 3 and Y 2 taken together and Y 6 and Y 5 taken together may form a methylenedioxy, ethylenedioxy, trimethylene, tetramethylene or tetradehydromethylene group, R 1 and R 2 , which may be identical or different, are a substituted or unsubstituted alkyl or alkenyl group, R 3 and R 5 represents a hydrogen atom, R 3 and R 1 taken together and R 5 and R 2 taken together may form a five- or six-membered ring, R 4 is a hydrogen or a substituted or unsubstsituted lower alkyl group, R 6 is a hydrogen atom, methyl group, ethyl group or propyl group, R 7 is a substituted or unsubstituted lower alkyl group or substituted or unsubstituted phenyl group, X is a counter ion necessary to neutralize the charge, and letter n is equal to 1 or 0 in the case of an intramolecular salt, such that said layer has a sensitization maximum at a longer wavelength than 730 nm and the light absorption due to said spectral sensitizer satisfies both the requirements of formulae (1) and (2): Abs(peak wavelength)/Abs(peak wavelength + 30 nm) ≥ 4.5 Abs(peak wavelength)/Abs(peak wavelength - 30 nm) ≥ 2 comprising the step of chemically sensitizing the silver halide emulsion of at least one layer in the presence of at least one dicarbocyanine dye of formula (I) and at least one tetraazaindence compound. The process according to any of claims 1 or 2, wherein in general formula (I) R 6 is a hydrogen atom. The process according to any of claims 1 or 2, wherein said silver halide photosensitive material includes at least three layers of silver halide emulsions having different spectral sensitivities and at least three layers containing dye providing compounds capable of releasing or generating dyes of different hues in proportion or counter proportion to the reduction of silver ion to silver at elevated temperature. The process according to claim 4, wherein the emulsion layers are spectrally sensitized such that the sensitivity at the spectral sensitivity maximum wavelength is higher by a factor of at least 3 than the spectral sensitivity to light having a wavelength 20 nm longer than said spectral sensitivity maximum wavelength. The process according to any of claims 1 or 2, wherein the silver halide emulsion layer has been aged with the spectral sensitizer at a temperature of 50 to 80°C for at least 15 minutes.

Inventors: HIOKI TAKANORI, IKEDA TADASHI, KATO TAKASHI, MIYAKE KIYOTERU, HIOKI, TAKANORI, IKEDA, TADASHI, KATO, TAKASHI, MIYAKE, KIYOTERU, HIOKI, TAKANORI, C/O FUJI PHOTO FILM CO., LTD., IKEDA, TADASHI, C/O FUJI PHOTO FILM CO., LTD., KATO, TAKASHI, C/O FUJI PHOTO FILM CO., LTD., Miyake, Kiyoteru, c/o Fuji Photo Film Co., Ltd.
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1992
Main classification: G03C1
IPC codes: G03C8, G03C1, G03C5