Tabular grain emulsions containing a restricted high iodide surface phase

A photographic emulsion is disclosed comprised of a dispersing medium and radiation-sensitive silver halide grains with greater than 50 percent of total grain projected area being accounted for by grains containing a host portion of a face centered cubic rock salt crystal lattice structure and a first epitaxial phase containing greater than 90 mole percent iodide. The host portion is tabular, being bounded by an exterior having first and second parallel major faces joined by a peripheral edge. The first epitaxial phase accounts for less than 60 percent of total silver, and the first epitaxial phase is restricted to a portion of the exterior of the host portion that includes at least 15 percent of the major faces.

FIELD OF THE INVENTION 
The invention is directed to an improvement in photographic emulsions 
containing radiation-sensitive intermediate and higher aspect ratio 
tabular grains. 
SUMMARY OF DEFINITIONS 
In referring to silver halide emulsions, grains and grain regions 
containing two or more halides, the halides are named in order of 
ascending concentrations. 
All references to the mole percentages of a particular halide in silver 
halide are based on total silver present in the grain, grain region or 
emulsion being discussed. 
The symbol ".mu.m" is employed to denote micrometers. 
The "equivalent circular diameter" (ECD) of a grain is diameter of a circle 
having an area equal to the projected area of the grain. 
The "aspect ratio" of a silver halide grain is the ratio of its ECD divided 
by its thickness (t). 
The "average aspect ratio" of a tabular grain emulsion is the quotient of 
the mean ECD of the tabular grains divided by their mean thickness (t). 
The term "tabular grain" is defined as a grain having an aspect ratio of at 
least 2. 
The term "tabular grain emulsion" is defined as an emulsion in which at 
least 50 percent of total grain projected area is accounted for by tabular 
grains. 
The terms "thin" and "ultrathin" in referring to tabular grains and 
emulsions are employed to indicate tabular grains having thickness of &lt;0.2 
.mu.m and &lt;0.07 .mu.m, respectively. 
The term "dopant" refers to a material other than silver or halide ion 
contained in a silver halide crystal lattice structure. 
All periods and groups of elements are assigned based on the periodic table 
adopted by the American Chemical Society and published in the Chemical and 
Engineering News, Feb. 4, 1985, p. 26, except that the term "Group VIII" 
is employed to designate groups 8, 9 and 10. 
The term "meta-chalcazole" is employed to indicate the following ring 
structure: 
##STR1## 
where X is one of the chalcogens: O, S or Se. 
All spectral sensitizing dye oxidation and reduction voltages were measured 
in acetonitrile against a Ag/AgCl saturated KCl electrode, as described in 
detail by J. Lenhard J. Imag. Sci., Vol. 30, #1, p. 27, 1986. Where 
oxidation or reduction potentials for spectral sensitizing dyes were 
estimated, the method employed was that described by S. Link "A Simple 
Calculation of Cyanine Dye Redox Potentials", Paper F15, International 
East-West Symposium II, Oct. 30-Nov. 4, 1988. 
The term "inertial speed" refers to the speed of a silver halide emulsion 
determined from its characteristic curve (a plot of density vs. log E, 
where E represents exposure in lux-seconds) as the intersection of an 
extrapolation of minimum density to a point of intersection with a line 
tangent to the highest contrast portion of the characteristic curve. The 
inertial speed is the reciprocal of the exposure at the point of 
intersection noted above. 
Speeds are reported as relative log speeds, where a speed difference of 1 
represents a difference of 0.01 log E, where E is exposure in lux-seconds. 
Research Disclosure is published by Kenneth Mason Publications, Ltd., 
Dudley House, 12 North St., Emsworth, Hampshire P010 7DQ, England. 
Background 
Maskasky U.S. Pat. Nos. 4,094,684, 4,142,900 and 4,158,565 (collectively 
referred to as Maskasky I) disclose emulsions in which silver chloride is 
epitaxially deposited on nontabular silver iodide host grains. These 
patents are generally credited as the first suggestion that a silver 
iodide phase can be relied upon for photon capture while a developable 
latent image is formed in an epitaxially joined lower iodide portion of 
the grain. When a photon is captured within the iodide portion of the 
grain, a hole (photohole) and a conduction band electron (photoelectron) 
pair are created. The photoelectron migrates across the epitaxial junction 
to form a latent image in the lower iodide portion of the grain. On the 
other hand, the photohole remains trapped within the silver iodide phase. 
Thus, the risk of dissipation of absorbed photon energy by hole-electron 
recombination is minimized. House U.S. Pat. No. 4,490,458 and Maskasky 
U.S. Pat. No. 4,459,353 (collectively referred to as House and Maskasky) 
later placed silver chloride epitaxy on silver iodide tabular grains to 
combine the advantages of Maskasky I with those known to flow from a 
tabular grain configuration. Although the Maskasky I and the House and 
Maskasky emulsions offer superior performance compared to emulsions with 
grains consisting essentially of a high (&gt;90 mole percent) iodide silver 
halide phase, the performance of none of these emulsions has been 
sufficiently attractive to lead to commercial use in photography. The 
ratio of iodide to the remaining halide(s) is unattractively high while 
photographic speed and developability, though superior to grains 
consisting essentially of a high iodide silver halide phase, are slow. 
Between the investigations of Maskasky I and those of House and Maskasky, a 
marked advance took place in silver halide photography based on the 
discovery that a wide range of photographic advantages, such as improved 
speed-granularity relationships, increased covering power both on an 
absolute basis and as a function of binder hardening, more rapid 
developability, increased thermal stability, increased separation of 
native and spectral sensitization imparted imaging speeds, and improved 
image sharpness in both mono- and multi-emulsion layer formats, can be 
realized by increasing the proportions of selected tabular grain 
populations in photographic emulsions. The tabular grains were initially 
selected to have a high (&gt;8) average aspect ratio or at least an 
intermediate (5-8) average aspect ratio. The tabular grains were those 
having a face centered cubic rock salt crystal lattice structure 
(hereinafter referred to as an FCCRS crystal lattice structure), which a 
high iodide silver halide composition does not form, except under extreme 
conditions having no relevance to photography. Silver chloride, silver 
bromide and mixtures thereof in all ratios form an FCCRS crystal lattice 
structure. An FCCRS crystal lattice can accommodate minor amounts of 
iodide. The highest reported levels of photographic performance have been 
obtained with tabular grain emulsions containing silver iodobromide 
grains. Early disclosures of high and intermediate aspect ratio tabular 
grain emulsions with FCCRS crystal lattices are illustrated by Kofron et 
al U.S. Pat. No. 4,439,520, Wilgus et al U.S. Pat. No. 4,434,226 and 
Abbott et al U.S. Pat. Nos. 4,425,425 and 4,425,426. 
Solberg et al U.S. Pat. No. 4,433,048 demonstrated that silver iodobromide 
high aspect ratio tabular grain emulsions with superior speed-granularity 
relationships can be prepared by increasing the iodide concentration in a 
region of the tabular grain laterally displaced from a central region. 
Solberg et al most extensively discussed and demonstrated the effect of 
gradually increasing the iodide concentration in the FCCRS crystal lattice 
of the tabular grain as lateral growth onto the edges of the tabular 
grains occurred. 
As an alternative, Solberg et al suggested abruptly introducing silver and 
iodide ions, preferably after 75 to 97 percent of the total silver forming 
the grain had been precipitated. Solberg et al reported that, in some 
instances, the edges of the grains appeared castellated following abrupt 
iodide addition. Abrupt iodide addition has subsequently come to be 
referred to in the art as "dump" iodide addition, which means simply that 
the iodide ion is added to the grains as rapidly as possible, as opposed 
to being introduced at an intentionally limited flow rate, referred to as 
a "run" iodide addition. 
It is generally understood that silver and iodide ions are concurrently 
introduced when iodide is being incorporated in the crystal structure of 
an intermediate or high aspect ratio tabular grain. If iodide ion alone is 
introduced into an intermediate or high aspect ratio tabular grain 
emulsion containing a FCCRS crystal structure, the effect is to destroy 
the tabular nature of the grains. Since iodide is a much less soluble 
compound than either silver chloride or silver bromide, the addition of 
iodide ion unaccompanied by silver ion results in the displacement of the 
previously incorporated halide ions. In other words, halide conversion 
occurs. Since silver iodide is a much larger ion than either chloride or 
bromide ion, a massive disruption of the crystal structure occurs, 
resulting in massive degradation or complete destruction of the tabular 
shape of the grains. Warnings against halide conversion in preparing 
tabular grain emulsions are provided by Wey U.S. Pat. No. 4,399,215 and 
Maskasky U.S. Pat. No. 4,400,463. Yamamoto et al U.S. Pat. No. 5,021,323, 
which prepares core-shell grains by the addition of potassium iodide alone 
to effect halide conversion for shell formation, teaches the selection of 
host grains having an aspect ratio of not more than 5. 
Piggin et al U.S. Pat. Nos. 5,061,609 and 5,061,616 teach the formation of 
silver iodobromide tabular grain emulsions that exhibit reduced pressure 
sensitivity as a result of forming laminae on the major faces of tabular 
grains. The laminae have a FCCRS crystal lattice structure and contain 
iodide in concentrations ranging from 10 mole percent, based on silver, up 
to the saturation limit (approximately 40 mole %) of iodide in the FCCRS 
crystal lattice structure. Piggin et al '609 forms the laminae by any 
convenient technique and then shells the laminae with silver bromide 
deposition within a specified pAg and temperature parameter boundary. 
Piggin et al '616 first adjusts a tabular grain emulsion to satisfy the 
same pAg and temperature parameter boundary of Piggin et al '609. This 
rounds the corners of the tabular grains. Silver iodide then deposits at 
the rounded corners of the tabular grains and can restore the corners to 
their original configuration. Thereafter, while still within the pAg and 
temperature parameter boundary, silver iodobromide is precipitated onto 
the major faces of the host tabular grains. Concurrently the previously 
precipitated silver iodide is redistributed and incorporated in the FCCRS 
crystal lattice structure of the laminae. 
Brust et al U.S. Pat. No. 5,314,798 discloses the preparation of high 
chloride {100} tabular grain emulsions in which the tabular grains are 
comprised of a core and a surrounding band containing a higher level of 
iodide ions and containing up to 30 percent of the silver in the tabular 
grains. Brust et al speculates in column 9, lines 10 to 16, that a 
separate silver iodide phase may form, but no separate silver iodide phase 
in the completed emulsions has been observed. A separate iodide phase has 
been observed at the edges of the tabular grains, but not on their major 
faces, during precipitation, but this separate silver iodide phase 
disappeared as precipitation continued. 
Suga et al U.S. Pat. No. 5,418,124 discloses an emulsion in which silver 
halide have been formed while iodide ions are rapidly being generated in a 
reaction vessel to form a silver iodide-containing region as an edge 
fringe portion that contains 10 or more dislocations per grain. The edge 
location of the silver iodide exhibits limited light absorption. 
Problem to be Solved 
Notwithstanding the many advances imparted to photographic imaging by 
silver iodobromide intermediate and high aspect ratio tabular grain 
emulsions, some shortcomings have been observed. Intermediate and high 
aspect ratio tabular grain emulsions work best when applied to minus blue 
(green and/or red) imaging, since they provide large surface areas in 
relation to grain volume for minus blue absorbing spectral sensitizing 
dyes. The silver halide itself lacks native minus blue sensitivity; hence 
reducing silver coating coverages while maintaining large surface areas 
for spectral sensitizing dye adsorption saves silver with little negative 
impact on imaging. 
By comparison, the application of intermediate and high aspect ratio 
tabular grain emulsions to forming blue exposure records has lagged. The 
reason is that traditionally the native blue sensitivity of silver 
iodobromide grains has been heavily relied upon for latent image 
formation, even when blue spectral sensitizing dyes have been employed in 
combination with the grains. Attempts to realize the silver savings in 
blue recording emulsion layers that are routinely realized in minus blue 
recording emulsion layers by employing intermediate and high aspect ratio 
tabular grain emulsions have resulted in speed penalties. The problem is 
exacerbated by the fact that, while daylight contains an equal amount of 
its total energy in the blue, green and red regions of the visible 
spectrum, blue photons contain more energy than either green and red 
photons; hence, daylight has available fewer blue photons than green or 
red photons for latent image formation. The problem cannot be corrected by 
simply increasing the levels of blue spectral sensitizing dye, since 
additional speed enhancement is not realized by dye additions beyond those 
that can be adsorbed to the grain surfaces. Kofron et al suggests 
increasing the maximum thickness of tabular grains from 0.3 .mu.m to 0.5 
.mu.m to enhance their blue absorption. In the highest speed multicolor 
photographic elements it is common for the fastest minus blue recording 
emulsion layers to be formed using tabular grain emulsions while the 
fastest blue recording emulsion layer employs nontabular grains. Since the 
highest speed blue recording layer is typically the first emulsion layer 
to receive exposing radiation, there is a significant negative impact by 
the nontabular grains on the sharpness of the images in all of the 
remaining emulsion layers. 
Another problem inherent in the conventional choices of silver iodobromide 
tabular grain emulsions is that the techniques disclosed by Maskasky I for 
photohole and photoelectron separation, with attendant reduction in their 
recombination, have been largely unrealized. Conventional tabular grains 
either contain no high iodide silver halide phase or have limited its 
extent to a small band at the edge of the tabular grain. 
SUMMARY OF THE INVENTION 
In one aspect the invention is directed to a photographic emulsion 
comprised of a dispersing medium and radiation-sensitive silver halide 
grains with greater than 50 percent of total grain projected area being 
accounted for by grains containing a host portion of a face centered cubic 
rock salt crystal lattice structure and a first epitaxial phase containing 
greater than 90 mole percent iodide, wherein the host portion is tabular, 
being bounded by an exterior having first and second parallel major faces 
joined by a peripheral edge, the first epitaxial phase accounts for less 
than 60 percent of total silver, and the first epitaxial phase is 
restricted to a portion of the exterior of the host portion that includes 
at least 15 percent of the major faces. 
The emulsions of the invention offer advantages that have heretofore been 
unrealized in providing intermediate and high aspect ratio tabular grain 
emulsions for photographic imaging. 
Restriction of the first epitaxial phase to a portion of the external 
surface of the host tabular grains allows latent image formation and 
development initiation at relatively low iodide sites on the surfaces of 
the grains. This translates into higher levels of photographic 
performance, particularly better utilization of the latent image. By 
leaving at least a portion of the tabular grain edge surfaces free of the 
first epitaxial phase, as is preferred, ideal, low iodide sites for latent 
image formation are provided. 
The location of the first epitaxial phase over at least 15 percent 
(preferably at least 25 percent) of the surface area of the major faces of 
the host tabular grains optimally positions this high iodide phase for 
absorption of short (400 to 450 nm) blue light. With only thin plates of 
the high iodide first epitaxial phase short blue absorptions far exceeding 
those attainable with adsorbed spectral sensitizing dye are realized. By 
combining the tabular grains of the invention with spectral sensitizing 
dye exhibiting blue absorption maxima (hereafter referred to as blue 
spectral sensitizing dyes) even higher blue speeds can be realized. By 
employing the tabular grain emulsions of the invention in combination with 
long (450 to 500 nm) blue absorption maxima spectral sensitizing dyes, 
increased levels of light capture over the entire blue portion of the 
spectrum can be realized. 
The tabular grain emulsions of the invention are, in fact, so efficient in 
blue absorption that it is possible to eliminate from a multicolor 
photographic element underlying blue filter layers customarily 
incorporated to protect minus blue recording emulsion layers from unwanted 
blue exposure, while still avoiding objectionable blue contamination of 
the minus blue recording records. 
Whereas, it has been frequently suggested to incorporate iodide in silver 
iodobromide tabular grain emulsions in concentrations up to iodide 
saturation, about 40 mole percent iodide, superior blue light absorption 
can be realized by the emulsions of the invention with lower overall 
levels of iodide. 
Yet another advantage of the emulsions of the invention is that sites are 
distributed over the major faces of the tabular grains for photohole 
capture and separation from photoelectrons. This reduces the risk of 
photohole-photoelectron recombination and increases latent image forming 
efficiency in both the blue and minus blue regions of the spectrum.

DESCRIPTION OF PREFERRED EMBODIMENTS 
At least 50 percent of the total grain projected area of emulsions 
according to the invention is accounted for by composite silver halide 
grains having two readily distinguishable portions, a host portion that is 
tabular and at least a first epitaxial phase restricted to only a portion 
of the host exterior, but overlying at least 15 percent (preferably at 
least 25 percent) of the major faces of the host tabular grains. The host 
tabular grains exhibit a face centered cubic rock salt crystal lattice 
structure (an FCCRS crystal lattice structure) while the first epitaxial 
phase forms a separate silver halide phase containing greater than 90 mole 
percent iodide, hereinafter referred to as a high iodide silver halide 
phase. The first epitaxial phase accounts for less than 60 (preferably 
less than 25) percent of total silver forming the composite grains. 
A typical composite grain structure 100 is schematically shown in FIGS. 1 
and 2. A host tabular grain portion 102 is bounded by an upper major face 
104 and a lower major face 106 joined by a laterally surrounding 
peripheral edge 108, schematically shown. Epitaxially grown on the major 
faces of the host tabular grain are discrete plates 110, shown to have 
triangular and hexagonal boundaries. The plates contain the first 
epitaxial phase. Notice that the plates overlie at least 15 percent of the 
surface area of the major faces of the tabular grain, yet are restricted 
in their areal extent so that portions of the tabular grain exterior 
remain free of the plates. 
As is well understood in the art, tabular grains are oriented with their 
major faces approximately normal to the direction of light transmission 
during imagewise exposure in a photographic element. When the grain 100 is 
exposed to light in the short (400 to 450 nm) blue region of the spectrum, 
photons are initially absorbed preferentially (and in some cases entirely) 
in the plates 110 on the major faces 104 and 106 of the host tabular grain 
portion 102. The plates on both the major face nearer to and farther from 
the source of exposing short blue light actively absorb short blue 
photons, since the host tabular grain portion cannot absorb more than a 
small fraction of the exposing short blue light and unabsorbed light is 
transmitted through the host tabular grain portion. 
Measured along the section line A--A, the plates as shown in FIG. 2 overlie 
35% of the upper major face and 48% of the lower major face. Notice that 
the plates on the upper and lower major faces are not aligned. At some 
points a short blue photon encounters no plate in passing through the 
composite grain, in other areas one plate, and in remaining areas two 
plates. As shown the upper and lower plates are positioned to intercept 
71% of photons incident along section line A--A. 
It should be noticed that location of the plates on the major faces of the 
host tabular grain portion is an ideal orientation for short blue photon 
absorption. In this orientation the plates present a maximum target area 
for the photons. If the plates were instead located entirely on the 
peripheral edge 108 of the host tabular grain portion, they would present 
a much smaller target area and fewer short blue photons would be absorbed. 
Although the ideal is to eliminate edge plates, as shown, it is recognized 
that in practice plates are usually located to some extent on both the 
edge and major face of the host tabular grain exterior. However, 
techniques are described below for minimizing the proportion of the plates 
located along the peripheral edge. 
If, instead of forming a high iodide silver halide phase on the surface of 
the tabular grain portion, the tabular grain portion is simply optimally 
sensitized with a spectral sensitizing dye having a short blue absorption 
maxima (hereinafter referred to as a short blue spectral sensitizing dye), 
the highest blue light absorption attainable without desensitization is 
still much less than that which can be obtained by employing the first 
epitaxial phase as described. Maximum light absorption by an optimally 
spectrally sensitized tabular grain is typically in the 10 to 15 percent 
range. By contrast, the epitaxial phase can produce short blue light 
absorptions in each grain that are well in excess of 50 percent. Since in 
emulsion coatings the path of exposing radiation intercepts a plurality of 
grains, it is appreciated that capture of short blue photons can approach 
100 percent when the emulsions of the invention are employed. 
Nevertheless, to reduce the amount of silver required in coating, it is 
specifically contemplated to employ an emulsion according to the invention 
in combination with one or more conventional short blue spectral 
sensitizing dyes. 
When a blue spectral sensitizing dye (a dye having an absorption maximum in 
the 400-500 nm spectral region) is selected for a conventional tabular 
grain emulsion, a theoretically ideal choice is a dye having a half-peak 
bandwidth (a spectral wavelength range over which it exhibits an 
absorption of at least half its maximum absorption) of 100 nm, extending 
from 400 to 500 nm. In practice, few spectral sensitizing dyes exhibit 100 
nm half peak bandwidths, nor are actual half peak bandwidths coextensive 
with the blue region of the spectrum. Typical blue spectral sensitizing 
dyes exhibit half peak bandwidths of less than 50 nm. 
In a specifically preferred form of the invention it is contemplated to 
employ emulsions according to the invention in combination with one or 
more spectral sensitizing dyes having an absorption maxima in the long 
blue (450-500 nm) region of the spectrum (hereinafter referred to as a 
long blue spectral sensitizing dye). The high iodide silver halide 
provided by the first epitaxial phase offers peak absorption near 425 nm. 
When this absorption is combined with that provided by a long blue 
spectral sensitizing dye, a higher blue absorption over the entire blue 
portion of the spectrum is realized. 
It is, of course, possible to employ combinations of short and long blue 
spectral sensitizing dyes with the tabular grain emulsions of the 
invention. Assuming dyes are selected of equal efficiencies, when this is 
undertaken, the proportion of total sensitivity provided by the 
combination of blue spectral sensitizing dyes is no higher and usually 
somewhat less than that which can be obtained by employing the long blue 
spectral sensitizing dye alone. 
When, in the absence of a spectral sensitizing dye, a short blue photon is 
absorbed by a plate, a photohole and a photoelectron pair are created. The 
photoelectron is free to migrate across the epitaxial junction into the 
host tabular grain portion. On the other hand, the photohole is trapped 
within the plate. What therefore occurs is separation of the photoelectron 
from the photohole, which in turn minimizes the risk of their mutual 
annihilation by recombination. Thus, the plates contribute to larger 
numbers of photoelectrons being available for latent image formation and 
enhance the overall sensitivity of the emulsion grains. 
When a spectral sensitizing dye of any absorption maxima is employed in 
combination with the composite grains of the invention, the high iodide 
silver halide phase still contributes to enhanced emulsion sensitivity. 
Longer wavelength photons are initially absorbed by the spectral 
sensitizing dye and the dye injects the absorbed energy into the plates 
directly or into the host tabular grain portions. The photohole remaining 
in the dye migrates into the plate. Notice that this mechanism applies 
regardless of the spectral region of exposure. That is, the plates can 
improve the latent image forming efficiency of emulsions that are 
sensitized to the minus blue (green and/or red) portion of the spectrum as 
well as improving imaging efficiency in the blue region of the spectrum. 
Although any conventional spectral sensitizing dye is capable of injecting 
electrons into the host tabular grain portions with which it is in 
contact, electron injection into the plates can only be achieved if the 
reduction potential of the spectral sensitizing dye is more negative than 
the conduction band of the high iodide crystal structure forming the 
plate. Thus, for the entire major faces of the grains (those portions 
provided by the host tabular grains and those portions provided by the 
plates) to be receptive to electron injection and hence for most efficient 
performance it is necessary that the spectral sensitizing dye have a 
reduction potential more positive than a threshold value of -1.30 
(preferably -1.35) volts. Spectral sensitizing dyes with reduction 
potentials increasingly more negative than the threshold value all perform 
well. Hence, the most negative reduction potentials of spectral 
sensitizing dyes contemplated are dictated solely by convenience and 
availability. Spectral sensitizing dyes with reduction potentials to -1.80 
volts are common and, for a few dyes, reduction potentials as negative as 
-2.0 volts have been identified. The advantages for selection of spectral 
sensitizing dyes with reduction potentials more negative than the 
threshold value stated above and the resulting improvements in 
photographic performance are believed to be attributable to the somewhat 
more negative conduction band of the high iodide crystal lattice structure 
forming the plates as compared to the conduction band of the FCCRS crystal 
structure forming the plates. When combinations of spectral sensitizing 
dyes are employed, exceptionally efficient performance is observed with 
each spectral sensitizing dye has a reduction potential more negative than 
the threshold value stated above. 
The emulsions of the invention can be prepared by starting with any 
conventional tabular grain emulsion in which the tabular grains exhibit an 
FCCRS crystal lattice structure. The starting tabular grains can consist 
essentially of silver bromide, silver chloride, silver chlorobromide, 
silver bromochloride, silver iodobromide, silver iodochloride, silver 
iodochlorobromide, silver iodobromochloride, silver chloroiodobromide or 
silver bromoiodochloride. 
In one preferred form starting tabular grains are high (&gt;50 mole %) 
bromide, optimally &gt;70 mole % bromide, silver halides with chloride 
preferably limited to 10 mole % or less. High bromide tabular grains are 
less soluble than high (&gt;50 mole %) chloride tabular grain emulsions and 
are therefore more resistant to halide displacement from the FCCRS crystal 
lattice structure on subsequent epitaxial deposition. Iodide inclusions in 
the starting tabular grains are preferably less than 10 mole percent, 
since the high iodide silver halide first epitaxial phase is capable of 
performing the imaging functions normally accomplished by high iodide 
inclusions. When iodide is included in the starting tabular grains, it can 
be uniformly or nonuniformly distributed in any conventional manner. 
The starting tabular grains can exhibit either {111} or {100} major faces. 
The tabular grain 100 shown in FIGS. 1 and 2 has {111} major faces. 
Tabular grains with {111} major faces, hereafter referred to as {111} 
tabular grains, usually have triangular or hexagonal major faces. 
Generally, the more uniform the tabular grain population, the higher the 
proportion of tabular grains with hexagonal major faces. In their most 
highly controlled forms {111} tabular grains with adjacent edges of 
hexagonal major faces that differ in length by less than 2:1 account for 
greater than 90 percent of the total tabular grains. Corner rounding due 
to ripening typically ranges from barely perceptible to creating almost 
circular major faces. In a specifically preferred form of the invention 
the {111} tabular grains are also high bromide tabular grains. 
Tabular grains with {100} major faces, hereafter referred to as {100} 
tabular grains, have square or rectangular major faces. In these emulsions 
a grain is normally required to have a ratio of adjacent edge lengths of 
5:1 or less to be considered tabular rather than being rod-like. In a 
specifically preferred form of the invention the {100} tabular grains are 
also high chloride tabular grains. High chloride tabular grains with {100} 
major faces show a higher level of stability against morphological 
degradation than high chloride {111} tabular grains, which rely on 
adsorbed materials to stabilize {111} grain faces. 
The starting tabular grain emulsions can have any photographically useful 
mean ECD, typically up to 10 .mu.m, but preferably the tabular grain 
emulsions have a mean ECD of 5 .mu.m or less. The starting tabular grains 
can have any thickness, ranging from the minimum reported thicknesses for 
ultrathin (&lt;0.07 .mu.m) tabular grain emulsions up to the maximum 
thickness compatible with a &gt;5 average aspect ratio. It is generally 
preferred that the starting tabular grains have a thickness of less than 
0.3 .mu.m, more preferably, less than 0.2 .mu.m, and, most preferably less 
than 0.07 .mu.m. 
The tabular grains of the starting emulsions (preferably those having a 
thickness of &lt;0.3 .mu.m, more preferably &lt;0.2 .mu.m, and most preferably 
&lt;0.07 .mu.m) account for greater than 50 percent, preferably greater than 
70 percent and most preferably greater than 90 percent of total grain 
projected area. In specifically preferred starting tabular grain emulsions 
substantially all (greater than 97 percent) of total grain projected area 
can be accounted for by tabular grains. 
The starting tabular grain emulsion can exhibit any conventional level of 
dispersity, but preferably exhibits a low level of dispersity. It is 
preferred that the starting tabular grain emulsion exhibit a coefficient 
of variation (COV) of grain diameter of less than 30 percent, most 
preferably less than 25 percent. Conventional starting tabular grain 
emulsions are known having a COV of less than 10 percent. Grain COV is 
herein defined as 100 times the standard deviation of grain ECD divided by 
mean grain ECD. 
Conventional high chloride {111} tabular grain emulsions are illustrated by 
the following: 
Wey et al U.S. Pat. No. 4,414,306; 
Maskasky U.S. Pat. No. 4,400,463; 
Maskasky U.S. Pat. No. 4,713,323; 
Takada et al U.S. Pat. No. 4,783,398; 
Nishikawa et al U.S. Pat. No. 4,952,491; 
Ishiguro et al U.S. Pat. No. 4,983,508; 
Tufano et al U.S. Pat. No. 4,804,621; 
Houle et al U.S. Pat. No. 5,035,992; 
Maskasky U.S. Pat. No. 5,061,617; 
Maskasky U.S. Pat. No. 5,178,997; 
Maskasky and Chang U.S. Pat. No. 5,178,998; 
Maskasky U.S. Pat. No. 5,183,732; 
Maskasky U.S. Pat. No. 5,185,239; 
Maskasky U.S. Pat. No. 5,217,858; 
Chang et al U.S. Pat. No. 5,252,452; 
Maskasky U.S. Pat. No. 5,298,387 and 
Maskasky U.S. Pat. No. 5,298,388. 
Conventional high bromide {111} tabular grain emulsions are illustrated by 
the following: 
Abbott et al U.S. Pat. No. 4,425,425; 
Abbott et al U.S. Pat. No. 4,425,426; 
Wilgus et al U.S. Pat. No. 4,434,226; 
Kofron et al U.S. Pat. No. 4,439,520; 
Daubendiek et al U.S. Pat. No. 4,414,310; 
Solberg et al U.S. Pat. No. 4,433,048; 
Yamada et al U.S. Pat. No. 4,647,528; 
Sugimoto et al U.S. Pat. No. 4,665,012; 
Daubendiek et al U.S. Pat. No. 4,672,027; 
Yamada et al U.S. Pat. No. 4,678,745; 
Maskasky U.S. Pat. No. 4,684,607; 
Yagi et al U.S. Pat. No. 4,686,176; 
Hayashi U.S. Pat. No. 4,783,398; 
Daubendiek et al U.S. Pat. No. 4,693,964; 
Maskasky U.S. Pat. No. 4,713,320; 
Nottorf U.S. Pat. No. 4,722,886; 
Sugimoto U.S. Pat. No. 4,755,456; 
Goda U.S. Pat. No. 4,775,617; 
Saitou et al U.S. Pat. No. 4,797,354; 
Ellis U.S. Pat. No. 4,801,522; 
Ikeda et al U.S. Pat. No. 4,806,461; 
Ohashi et al U.S. Pat. No. 4,835,095; 
Makino et al U.S. Pat. No. 4,835,322; 
Bando U.S. Pat. No. 4,839,268; 
Daubendiek et al U.S. Pat. No. 4,914,014; 
Aida et al U.S. Pat. No. 4,962,015; 
Saitou et al U.S. Pat. No. 4,977,074; 
Ikeda et al U.S. Pat. No. 4,985,350; 
Piggin et al U.S. Pat. No. 5,061,609; 
Piggin et al U.S. Pat. No. 5,061,616; 
Takehara et al U.S. Pat. No. 5,068,173; 
Nakemura et al U.S. Pat. No. 5,096,806; 
Bell et al U.S. Pat. No. 5,132,203; 
Tsaur et al U.S. Pat. No. 5,147,771; 
Tsaur et al U.S. Pat. No. 5,147,772; 
Tsaur et al U.S. Pat. No. 5,147,773; 
Tsaur et al U.S. Pat. No. 5,171,659; 
Tsaur et al U.S. Pat. No. 5,210,013; 
Antoniades et al U.S. Pat. No. 5,250,403; 
Kim et al U.S. Pat. No. 5,272,048; 
Sutton et al U.S. Pat. No. 5,334,469; 
Black et al U.S. Pat. No. 5,334,495; 
Chaffee et al U.S. Pat. No. 5,358,840; 
Delton U.S. Pat. No. 5,372,927; and 
Zola and Bryant EPO 0 362 699. 
Emulsions containing {100} major face tabular grains are illustrated by the 
following: 
Mignot U.S. Pat. No. 4,386,156; 
Maskasky U.S. Pat. No. 5,275,930; 
Maskasky U.S. Pat. No. 5,292,632; 
Brust et al U.S. Pat. No. 5,314,798; 
House et al U.S. Pat. No. 5,320,938; 
Szajewski U.S. Pat. No. 5,310,635; 
Szajewski et al U.S. Pat. No. 5,356,764; 
Saitou et al EPO 0 569 971; and 
Saito et al Jap. Patent Application 92/77261. 
The addition of epitaxial phases to the starting tabular grains has little, 
if any, impact on the mean ECD, COV, or percent of total grain projected 
area accounted for by tabular grains in the emulsions of the invention. 
Hence the values indicated above for these parameters in the starting 
tabular grain emulsions apply also to the completed emulsions according to 
the invention. 
The first epitaxial phase deposited on the starting tabular grains (the 
host tabular grain portions of the resulting composite grains) contains at 
least 90, preferably at least 95, mole percent iodide. The remaining 
halide can be bromide and/or chloride. The inclusion of minor amounts of 
halides other than iodide is typically the result of undertaking 
precipitation of the epitaxial phase by silver and iodide ion introduction 
into the starting tabular grain emulsion in the presence of bromide and/or 
chloride ions in the dispersing medium of the starting tabular grain 
emulsion that are in equilibrium with the tabular grains. Bromide and/or 
chloride ion inclusion can be limited by limiting their availability and 
is in all instances limited by the inability of the bromide and/or 
chloride ions to incorporate into the crystal lattice structure of the 
epitaxial phase, which is not an FCCRS crystal lattice structure, in 
concentrations of greater than 10 mole percent. 
Silver iodide under conditions relevant to emulsion precipitation is 
generally reported to form either a hexagonal wurtzite (.beta. phase) or 
face centered cubic zinc blende type (.gamma. phase) silver iodide phase. 
Depending upon the specific precipitation conditions selected it is 
believed that the first epitaxial phase can be any one or a combination of 
these phases. 
The first epitaxial phase preferably accounts for less than 25, more 
preferably less than 20 and, in most instances, less than 10, percent of 
the total silver forming the composite grains. The minimum amount of 
silver contained in the first epitaxial phase is determined by the 
requirement that this phase be located on at least 25 percent of the major 
faces of the host tabular grains. Fortunately, it has been discovered that 
the first epitaxial phase can be deposited on the major faces in the form 
of thin plates, preferably having thicknesses in the range of from 50 nm 
(0.05 .mu.m) to 1 nm (0.001 .mu.m). Thus, very small amounts of silver in 
the first epitaxial phase are capable of occupying a large percentage of 
the major faces of the host tabular grains. 
As the thickness of the host tabular grains decreases, it is appreciated 
that the percentage of total silver provided by the first epitaxial phase 
increases, even when the thickness of the plates and the percentage of the 
total surface they occupy remains the unchanged. Thus, with ultrathin 
(&lt;0.07 mean ECD) host tabular grains, it is contemplated that nearly 60 
percent of the total silver forming the composite grains can be provided 
by first epitaxial phase. However, even using ultrathin host tabular grain 
emulsions, it is preferred to limit the first epitaxial phase to less than 
50 percent of total silver forming the composite grains. 
Exactly how thick the plates of the first epitaxial phase should be and 
what percentage of total major face coverage should be sought for optimum 
performance depends upon the function that the first epitaxial phase is 
required to perform. If an emulsion of the invention is intended to be 
employed primarily for absorbing short blue light on exposure, short blue 
light absorption increases as the thickness of the plates is increased and 
as the percentage of the major faces of the host tabular grains occupied 
is increased. At 427 nm, the absorption maxima of silver iodide, the 
portion of a silver iodide epitaxial phase on the upper major faces of the 
host tabular grains is capable of absorbing 63 percent of the photons it 
receives when the epitaxial phase thickness is 50 nm, and 86 percent of 
the photons passing through the silver iodide epitaxial phase located on 
both major faces of the host tabular grains are absorbed. These short blue 
absorptions are so much higher than those of the silver iodobromides and 
blue spectral sensitizing dyes conventionally used for short blue 
absorption, it is apparent that the plates can be much thinner than 50 nm 
and still offer advantageous short blue light absorption. Further, it must 
be kept in mind that at conventional silver coating coverages of silver 
halide emulsions several tabular grains are positioned to intercept a 
photon received at any one point. To distribute short blue light 
absorption within the grain population and thereby use the grains to 
maximum advantage it is preferred to decrease the thickness of the plates 
to less than 25 nm, most preferably less than 10 nm, while increasing the 
percentage of the host tabular grain major surfaces they overlie. It is 
preferred that the plates occupy at least 50, most preferably at least 70, 
percent of the major faces of the host tabular grains. 
It should be specifically noted that the probability of a short blue photon 
being transmitted through an emulsion layer containing grains according to 
the invention can be reduced to such a low level that the common problem 
of blue punch through can be virtually non-existent. Stated another way, 
short blue light penetrating the emulsion layer can be reduced to such low 
levels that common protective approaches, such as yellow (blue absorbing) 
filter layers to protect underlying minus blue recording layers from blue 
light exposure can be omitted without incurring any significant imaging 
penalty. 
If, instead of short blue absorption, the emulsions of the invention are 
employed in combination with a minus blue spectral sensitizing dye with 
the function of the high iodide silver halide epitaxial phase being 
limited to providing a surface trap for photoholes, then both the 
thickness and the percentage of major face coverage of the plates can be 
reduced. Only a minimal thickness is required for a plate to function as a 
hole trap. At the same time, if the plate is not located to intercept a 
photon, it can still act as a hole trap, since lateral migration of holes 
and electrons within the FCCRS crystal lateral structure is more than 
adequate to allow this to occur. However, for maximum imaging efficiency 
it is still preferred that the plates occupy at least 25 percent of the 
major faces of the host tabular grains. 
For the composite grains to maintain high levels of imaging efficiency it 
is essential that the high iodide silver halide epitaxial phase be 
restricted to only a portion of the host tabular grain exterior surfaces. 
In the absence of further composite grain modifications to place latent 
image, described below, latent image sites are formed in the host tabular 
grains. By contrast, development of a conventional core-shell grain 
containing a high iodide silver halide shell requires that development 
begin at a high iodide surface of the grain, thereby releasing relatively 
high levels of iodide ion to solution that can slow or arrest the rate of 
subsequent development. 
In preferred forms of the invention described below modified for directing 
latent image formation to a specific grain site, as much as 99 percent of 
the exterior of the host tabular grains can be covered by the high iodide 
silver halide epitaxy. It is preferred that the high iodide silver halide 
epitaxy cover no more than 90 percent of the exterior of the host tabular 
grains. 
Since, in the absence of the high iodide silver halide epitaxy, the edges 
of the host tabular grains are the favored locations for latent image 
formation, it is preferred to leave as much of the peripheral edge of the 
host tabular grains free of the high iodide silver halide epitaxy as 
possible. For example, where only a small fraction of the total exterior 
of the host tabular grains is free of the high iodide silver halide 
epitaxy, it is preferred that the largest possible portion of this small 
fraction be located at the edges of the host tabular grains. 
It has been discovered quite unexpectedly that depositing the high iodide 
silver halide epitaxy on the host tabular grains as plates is easily 
accomplished only when the high iodide silver halide phase is precipitated 
by controlled double jet precipitation. Attempts to grow silver iodide 
plates over the major surfaces of host tabular grains by ripening out 
silver iodide Lippmann grains have not been entirely successful, often 
resulting in large plates that extend outwardly beyond the periphery of 
the host tabular grains. 
For successful high iodide plate formation on the major faces of the host 
tabular grains it has been discovered that both the iodide and bromide ion 
concentrations in the dispersing medium surrounding the grains must be 
controlled during formation of the high iodide first epitaxial phase. To 
appreciate the parameters involved it is first necessary to recognize that 
silver halide (AgX, where X represents any photographically useful halide) 
exists in a photographic emulsion in equilibrium with its component ions. 
This is illustrated as follows: 
##STR2## 
While at equilibrium almost all of the silver and halide ions are present 
in the AgX crystal structure, a low level of Ag.sup.+ and X.sup.- remain 
in solution. At any given temperature the activity product of Ag.sup.+ and 
X.sup.- is, at equilibrium, a constant and satisfies the relationship: 
EQU K.sub.sp =[Ag.sup.+ ][X.sup.- ] (II) 
where 
[Ag.sup.+ ] represents the equilibrium silver ion activity, 
[X.sup.- ] represents the equilibrium halide ion activity, and 
K.sub.sp is the solubility product constant of the silver halide. 
To avoid working with small fractions, the following relationship is also 
widely employed: 
EQU -log K.sub.sp =pAg+pX (III) 
where 
pAg represents the negative logarithm of the equilibrium silver ion 
activity and 
pX represents the negative logarithm of the equilibrium halide ion 
activity. 
The solubility product constants of the photographic silver halides are 
well known. The solubility product constants of AgCl, AgBr and AgI over 
the temperature range of from 0.degree. to 100.degree. C. are published in 
Mees and James, The Theory of the Photographic Process, 3rd Ed., 
Macmillan, 1966, at page 6. Specific values are provided in Table I. 
TABLE I 
______________________________________ 
Temperature 
AgCl AgI AgBr 
.degree.C. -logK.sub.sp -logK.sub.sp 
-logK.sub.sp 
______________________________________ 
40 9.2 15.2 11.6 
50 8.9 14.6 11.2 
60 8.6 14.1 10.8 
70 8.3 -- 10.5 
80 8.1 13.2 10.1 
90 7.6 -- 9.8 
______________________________________ 
In preparing photographic emulsions the relative amounts of Ag.sup.+ are 
maintained less than those of X.sup.- to avoid fogging the emulsion. The 
relationship in which the concentrations of Ag.sup.+ and X.sup.- in 
solution are equal is referred to as the equivalence point. The 
equivalence point is the pX of the most soluble halide present that is 
exactly half the -logK.sub.sp of the corresponding silver halide. 
To minimize the risk of halide conversion occurring in the host tabular 
grains during precipitation of the high iodide plates it is contemplated 
to limit the concentration of iodide ion in the dispersing medium during 
precipitation to a pI of greater than 4.0. Lower levels of iodide in 
solution ranging to a pI of 9.5 are contemplated. A preferred pI range of 
is from about 4.5 to 9.0. 
To maximize major face deposition of the high iodide epitaxy and minimize 
peripheral edge deposition it is preferred that the concentration of the 
remaining halide ion in solution (i.e., bromide or chloride) be maintained 
between a concentration of minimum solubility and the equivalence point. 
For example, for a high bromide host tabular grain emulsion (e.g., a 
silver bromide or iodobromide tabular grain emulsion), it is preferred to 
maintain the pBr of the dispersing medium in the range of from 3.3 and 5.4 
at 60.degree. C. The equivalence point of silver chloride at 60.degree. C. 
occurs at a pCl 4.3 and its minimum solubility occurs at a pCl of 2.4. 
Normally high bromide and high chloride tabular grain emulsions are 
precipitated with a large halide ion excess. The halide ion concentration 
in solution is well above its minimum solubility concentration. Silver 
bromide tabular grains are typically precipitated at pBr values below 3.0, 
while silver chloride tabular grains are typically precipitated at pCl 
values of less than 2.4. Thus adjustment of the remaining halide ion 
concentrations in solution, in addition to introducing concurrently iodide 
and silver ions, is contemplated for deposition of the high iodide epitaxy 
preferentially onto the major faces of the host tabular grains. 
In FIGS. 1 and 2 the high iodide epitaxy is shown as discrete triangular or 
hexagonal plates. In fact, under the conditions that most favor major face 
deposition, the high iodide epitaxy loses its linear boundaries, with 
adjacent plates often merging, as shown in FIG. 7. 
A preferred sensitization for the emulsions of the invention is to effect a 
second epitaxial deposition onto the composite tabular grains after the 
first epitaxial phase has been precipitated. The epitaxial phase can be 
formed by the epitaxial precipitation of one or more silver salts on a 
host grain of a differing composition at selected surface sites, as 
illustrated by Maskasky U.S. Pat. Nos. 4,094,684, 4,435,501, 4,463,087, 
4,471,050 and 5,275,930, Ogawa U.S. Pat. No. 4,735,894, Yamashita et al 
U.S. Pat. No. 5,011,767, Haugh et al U.K. Patent 2,038,792, Koitabashi EPO 
0 019 917, Ohya et al EPO 0 323 215, Takada EPO 0 434 012, Chen EPO 0 498 
302 and Berry and Skillman, "Surface Structures and Epitaxial Growths on 
AgBr Microcrystals", Journal of Applied Physics, Vol. 35, No. 7, July 
1964, pp. 2165-2169. 
The preferred epitaxial sensitization of emulsions according to the 
invention containing high bromide host tabular grains is to deposit 
epitaxially silver chloride at the edges or, preferably, the corners of 
the tabular grains. Minor amounts, preferably less than 10 mole percent, 
based on total silver forming the second epitaxial phase) of silver 
bromide and iodide are incorporated into the epitaxy in addition to silver 
chloride. Although the silver chloride epitaxy can to some extent overlap 
adjacent high iodide plates, the high iodide plates tend to direct epitaxy 
to the host grain exterior surfaces. Hence, epitaxial junctions are formed 
between the second epitaxial phase at the exterior surfaces of the host 
tabular grains. When the host tabular grains are high chloride tabular 
grains, the second epitaxial phase is preferably a high bromide silver 
halide composition, such as silver bromide, optionally containing minor 
amounts of chloride and/or iodide, typically limited to 10 mole percent or 
less of the second epitaxial phase. Conventional chemical sensitization, 
such as sulfur and/or gold sensitization can, if desired, by combined with 
sensitization provided by the second epitaxial phase. 
The second epitaxial phase when present preferably accounts for less than 
25 (most preferably less than 10) percent of the total silver forming the 
composite grains. The second epitaxial phase is effective, even when it 
accounts for as little as 1 mole percent of total silver. Preferably the 
second epitaxial phase accounts for at least 2, optimally at least 5, 
percent of the total silver forming the composite grains. 
When the host tabular grains have {111} major faces, a preferred technique 
for directing the second epitaxial phase to the edges and/or corners of 
the tabular grains is to employ a J aggregating spectral sensitizing dye 
as a site director, as taught by Maskasky U.S. Pat. No. 4,435,501. 
Maskasky '501 further teaches that surface iodide is capable of acting as 
a site director. Thus, the iodide in the first epitaxial phase assists in 
directing the second epitaxial phase to the edges and corners of the host 
tabular grains. When the host tabular grains have {100} major faces, 
adsorbed site directors are not required to deposit the second epitaxial 
phase at the corners of the host tabular grains, but can be employed, if 
desired. 
It is specifically contemplated to incorporate one or more dopants in the 
crystal lattice structure of either the host tabular grains or the second 
epitaxial phase, both of which exhibit an FCCRS crystal lattice structure. 
When two or more dopants are incorporated, it is specifically contemplated 
to place one dopant in the host tabular grain and another in the second 
epitaxial phase to avoid antagonistic effects that can occur when 
dissimilar dopants are present in the same grain region. Any conventional 
dopant known to be useful in an FCCRS crystal lattice can be incorporated. 
Photographically useful dopants selected from a wide range of periods and 
groups within the Periodic Table of Elements have been reported. 
Conventional dopants include ions from periods 3 to 7 (most commonly 4 to 
6) of the Periodic Table of Elements, such as Fe, Co, Ni, Ru, Rh, Pd, Re, 
Os, Ir, Pt, Mg, Al, Ca, Sc, Ti, V, Cr, Fin, Cu, Zn, Ga, Ge, As, Se, Sr, Y, 
Mo, Zr, Nb, Cd, In, Sn, Sb, Ba, La, W, Au, Hg, Tl, Pb, Bi, Ce and U. The 
dopants can be employed (a) to increase the sensitivity, (b) to reduce 
high or low intensity reciprocity failure, (c) to increase, decrease or 
reduce the variation of contrast, (d) to reduce pressure sensitivity, (e) 
to decrease dye desensitization, (f) to increase stability (including 
reducing thermal instability), (g) to reduce minimum density, and/or (h) 
to increase maximum density. For some uses any polyvalent metal ion is 
effective. The following are illustrative of conventional dopants capable 
of producing one or more of the effects noted above when incorporated in 
the silver halide epitaxy: B. H. Carroll, "Iridium Sensitization: A 
Literature Review", Photographic Science and Engineering, Vol. 24, No. 6, 
Nov./Dec. 1980, pp. 265-267; Hochstetter U.S. Pat. No. 1,951,933; De Witt 
U.S. Pat. No. 2,628,167; Spence et al U.S. Pat. No. 3,687,676 and Gilman 
et al U.S. Pat. No. 3,761,267; Ohkubo et al U.S. Pat. No. 3,890,154; 
Iwaosa et al U.S. Pat. No. 3,901,711; Yamasue et al U.S. Pat. No. 
3,901,713; Habu et al U.S. Pat. No. 4,173,483; Atwell U.S. Pat. No. 
4,269,927; Weyde U.S. Pat. No. 4,413,055; Menjo et al U.S. Pat. No. 
4,477,561; Habu et al U.S. Pat. No. 4,581,327; Kobuta et al U.S. Pat. No. 
4,643,965; Yamashita et al U.S. Pat. No. 4,806,462; Grzeskowiak et al U.S. 
Pat. No. 4,828,962; Janusonis U.S. Pat. U.S. Pat. No. 4,835,093; Leubner 
et al U.S. Pat. No. 4,902,611; Inoue et al U.S. Pat. No. 4,981,780; Kim 
U.S. Pat. No. 4,997,751; Shiba et al U.S. Pat. No. 5,057,402; Maekawa et 
al U.S. Pat. No. 5,134,060; Kawai et al U.S. Pat. No. 5,153,110; Johnson 
et al U.S. Pat. No. 5,164,292; Asami U.S. Pat. Nos. 5,166,044 and 
5,204,234; Wu U.S. Pat. No. 5,166,045; Yoshida et al U.S. Pat. No. 
5,229,263; Bell U.S. Pat. Nos. 5,252,451 and 5,252,530; Komorita et al EPO 
0 244 184; Miyoshi et al EPO 0 488 737 and 0 488 601; Ihama et al EPO 0 
368 304; Tashiro EPO 0 405 938; Murakami et al EPO 0 509 674 and 0 563 946 
and Japanese Patent Application Hei-2[1990]-249588 and Budz WO 93/02390. 
When dopant metals are present during precipitation in the form of 
coordination complexes, particularly tetra- and hexa-coordination 
complexes, both the metal ion and the coordination ligands can be occluded 
within the grains. Coordination ligands, such as halo, aquo, cyano, 
cyanate, fulminate, thiocyanate, selenocyanate, tellurocyanate, nitrosyl, 
thionitrosyl, azide, oxo, carbonyl and ethylenediamine tetraacetic acid 
(EDTA) ligands have been disclosed and, in some instances, observed to 
modify emulsion properties, as illustrated by Grzeskowiak U.S. Pat. No. 
4,847,191, McDugle et al U.S. Pat. Nos. 4,933,272, 4,981,781 and 
5,037,732, Marchetti et al U.S. Pat. No. 4,937,180, Keevert et al U.S. 
Pat. No. 4,945,035, Hayashi U.S. Pat. No. 5,112,732, Murakami et al EPO 0 
509 674, Ohya et al EPO 0 513 738, Janusonis WO 91/10166, Beavers WO 
92/16876, Pietsch et al German DD 298,320, Olm et al U.S. Pat. No. 
5,360,712, and Kuromoto et al U.S. Pat. No. 5,462,849. Olm et al and 
Kuromoto et al, cited above, disclose hexacoordination complexes 
containing organic ligands while Bigelow U.S. Pat. No. 4,092,171 discloses 
organic ligands in Pt and Pd tetra-coordination complexes. 
It is specifically contemplated to incorporate in the silver halide epitaxy 
a dopant to reduce reciprocity failure. Iridium is a preferred dopant for 
decreasing reciprocity failure. The teachings of Carroll, Iwaosa et al, 
Habu et al, Grzeskowiak et al, Kim, Maekawa et al, Johnson et al, Asami, 
Yoshida et al, Bell, Miyoshi et al, Tashiro and Murakami et al EPO 0 509 
674, each cited above, are here incorporated by reference. These teachings 
can be applied to the emulsions of the invention merely by incorporating 
the dopant in the silver halide epitaxy. 
In another specifically preferred form of the invention it is contemplated 
to incorporate in the face FCCRS crystal lattice structure of the host 
tabular grains or second epitaxial phase a dopant capable of increasing 
photographic speed by forming shallow electron traps, hereinafter also 
referred to as a SET dopant. When a photon is absorbed by a silver halide 
grain, an electron (hereinafter referred to as a photoelectron) is 
promoted from the valence band of the silver halide crystal lattice to its 
conduction band, creating a hole (hereinafter referred to as a photohole) 
in the valence band. To create a latent image site within the grain, a 
plurality of photoelectrons produced in a single imagewise exposure must 
reduce several silver ions in the crystal lattice to form a small cluster 
of Ag.sup.o atoms. To the extent that photoelectrons are dissipated by 
competing mechanisms before the latent image can form, the photographic 
sensitivity of the silver halide grains is reduced. For example, if the 
photoelectron returns to the photohole, its energy is dissipated without 
contributing to latent image formation. 
It is contemplated to dope FCCRS crystal lattice to create within it 
shallow electron traps that contribute to utilizing photoelectrons for 
latent image formation with greater efficiency. This is achieved by 
incorporating in the face centered cubic crystal lattice a dopant that 
exhibits a net valence more positive than the net valence of the ion or 
ions it displaces in the crystal lattice. For example, in the simplest 
possible form the dopant can be a polyvalent (+2 to +5) metal ion that 
displaces silver ion (Ag.sup.+) in the crystal lattice structure. The 
substitution of a divalent cation, for example, for the monovalent 
Ag.sup.+ cation leaves the crystal lattice with a local net positive 
charge. This lowers the energy of the conduction band locally. The amount 
by which the local energy of the conduction band is lowered can be 
estimated by applying the effective mass approximation as described by J. 
F. Hamilton in the journal Advances in Physics, Vol. 37 (1988) p. 395 and 
Excitonic Processes in Solids by M. Ueta, H. Kansaki, K. Kobayshi, Y. 
Toyozawa and E. Hanamura (1986), published by Springer-Verlag, Berlin, p. 
359. If a silver chloride crystal lattice structure receives a net 
positive charge of +1 by doping, the energy of its conduction band is 
lowered in the vicinity of the dopant by about 0.048 electron volts (eV). 
For a net positive charge of +2 the shift is about 0.192 eV. For a silver 
bromide crystal lattice structure a net positive charge of +1 imparted by 
doping lowers the conduction band energy locally by about 0.026 eV. For a 
net positive charge of +2 the energy is lowered by about 0.104 eV. 
When photoelectrons are generated by the absorption of light, they are 
attracted by the net positive charge at the dopant site and temporarily 
held (i.e., bound or trapped) at the dopant site with a binding energy 
that is equal to the local decrease in the conduction band energy. The 
dopant that causes the localized bending of the conduction band to a lower 
energy is referred to as a shallow electron trap because the binding 
energy holding the photoelectron at the dopant site (trap) is insufficient 
to hold the electron permanently at the dopant site. Nevertheless, shallow 
electron trapping sites are useful. For example, a large burst of 
photoelectrons generated by a high intensity exposure can be held briefly 
in shallow electron traps to protect them against immediate dissipation 
while still allowing their efficient migration over a period of time to 
latent image forming sites. 
For a dopant to be useful in forming a shallow electron trap it must 
satisfy additional criteria beyond simply providing a net valence more 
positive than the net valence of the ion or ions it displaces in the 
crystal lattice. When a dopant is incorporated into the silver halide 
crystal lattice, it creates in the vicinity of the dopant new electron 
energy levels (orbitals) in addition to those energy levels or orbitals 
which comprised the silver halide valence and conduction bands. For a 
dopant to be useful as a shallow electron trap it must satisfy these 
additional criteria: (1) its highest energy electron occupied molecular 
orbital (HOMO, also commonly referred to as the frontier orbital) must be 
filled--e.g., if the orbital will hold two electrons (the maximum possible 
number), it must contain two electrons and not one and (2) its lowest 
energy unoccupied molecular orbital (LUMO) must be at a higher energy 
level than the lowest energy level conduction band of the silver halide 
crystal lattice. If conditions (1) and/or (2) are not satisfied, there 
will be a local, dopant-derived orbital in the crystal lattice (either an 
unfilled HOMO or a LUMO) at a lower energy than the local, dopant-induced 
conduction band minimum energy, and photoelectrons will preferentially be 
held at this lower energy site and thus impede the efficient migration of 
photoelectrons to latent image forming sites. 
Metal ions satisfying criteria (1) and (2) are the following: Group 2 metal 
ions with a valence of +2, Group 3 metal ions with a valence of +3 but 
excluding the rare earth elements 58-71, which do not satisfy criterion 
(1), Group 12 metal ions with a valence of +2 (but excluding Hg, which is 
a strong desensitizer, possibly because of spontaneous reversion to 
Hg.sup.+1), Group 13 metal ions with a valence of +3, Group 14 metal ions 
with a valence of +2 or +4 and Group 15 metal ions with a valence of +3 or 
+5. Of the metal ions satisfying criteria (1) and (2) those preferred on 
the basis of practical convenience for incorporation as dopants include 
the following period 4, 5 and 6 elements: ianthanum, zinc, cadmium, 
gallium, indium, thallium, germanium, tin, lead and bismuth. Specifically 
preferred metal ion dopants satisfying criteria (1) and (2) for use in 
forming shallow electron traps are zinc, cadmium, indium, lead and 
bismuth. Specific examples of shallow electron trap dopants of these types 
are provided by DeWitt, Gilman et al, Atwell et al, Weyde et al and 
Murakima et al EPO 0 590 674 and 0 563 946, each cited above and here 
incorporated by reference. 
Metal ions in Groups 8, 9 and 10 (hereinafter collectively referred to as 
Group VIII metal ions) that have their frontier orbitals filled, thereby 
satisfying criterion (1), have also been investigated. These are Group 8 
metal ions with a valence of +2, Group 9 metal ions with a valence of +3 
and Group 10 metal ions with a valence of +4. It has been observed that 
these metal ions are incapable of forming efficient shallow electron traps 
when incorporated as bare metal ion dopants. This is attributed to the 
LUMO lying at an energy level below the lowest energy level conduction 
band of the silver halide crystal lattice. 
However, coordination complexes of these Group VIII metal ions as well as 
Ga.sup.+3 and In.sup.+3, when employed as dopants, can form efficient 
shallow electron traps. The requirement of the frontier orbital of the 
metal ion being filled satisfies criterion (1). For criterion (2) to be 
satisfied at least one of the ligands forming the coordination complex 
must be more strongly electron withdrawing than halide (i.e., more 
electron withdrawing than a fluoride ion, which is the most highly 
electron withdrawing halide ion). 
One common way of assessing electron withdrawing characteristics is by 
reference to the spectrochemical series of ligands, derived from the 
absorption spectra of metal ion complexes in solution, referenced in 
Inorganic Chemistry: Principles of Structure and Reactivity, by James E. 
Huheey, 1972, Harper and Row, New York and in Absorption Spectra and 
Chemical Bonding in Complexes by C. K. Jorgensen, 1962, Pergamon Press, 
London. From these references the following order of metal ions in the 
spectrochemical series is apparent: 
##STR3## 
The abbreviations used are as follows: ox=oxalate, dipy=dipyridine, 
phen=o-phenathroline, and phosph 
=4-methyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane. The spectrochemical 
series places the ligands in sequence in their electron withdrawing 
properties, the first (I.sup.-) ligand in the series is the least electron 
withdrawing and the last (CO) ligand being the most electron withdrawing. 
The underlining indicates the site of ligand bonding to the polyvalent 
metal ion. The efficiency of a ligand in raising the LUMO value of the 
dopant complex increases as the ligand atom bound to the metal changes 
from Cl to S to O to N to C. Thus, the ligands CN.sup.- and CO are 
especially preferred. Other preferred ligands are thiocyanate (NCS.sup.-), 
selenocyanate (NCSe.sup.-), cyanate (NCO.sup.-), tellurocyanate 
(NCTe.sup.-) and azide (N.sub.3.sup.-). 
Just as the spectrochemical series can be applied to ligands of 
coordination complexes, it can also be applied to the metal ions. The 
following spectrochemical series of metal ions is reported in Absorption 
Spectra and Chemical Bonding by C. K. Jorgensen, 1962, Pergamon Press, 
London: 
##STR4## 
The metal ions in boldface type satisfy frontier orbital requirement (1) 
above. Although this listing does not contain all the metals ions which 
are specifically contemplated for use in coordination complexes as 
dopants, the position of the remaining metals in the spectrochemical 
series can be identified by noting that an ion's position in the series 
shifts from Mn.sup.+2, the least electronegative metal, toward Pt.sup.+4, 
the most electronegative metal, as the ion's place in the Periodic Table 
of Elements increases from period 4 to period 5 to period 6. The series 
position also shifts in the same direction when the positive charge 
increases. Thus, Os.sup.+3, a period 6 ion, is more electronegative than 
Pd.sup.+4, the most electronegative period 5 ion, but less electronegative 
than Pt.sup.+4, the most electronegative period 6 ion. 
From the discussion above Rh.sup.+3, Ru.sup.+3, Pd.sup.+4, Ir.sup.+3, 
Os.sup.+3 and Pt.sup.+4 are clearly the most electro-negative metal ions 
satisfying frontier orbital requirement (1) above and are therefore 
specifically preferred. 
To satisfy the LUMO requirements of criterion (2) above the filled frontier 
orbital polyvalent metal ions of Group VIII are incorporated in a 
coordination complex containing ligands, at least one, most preferably at 
least 3, and optimally at least 4 of which are more electronegative than 
halide, with any remaining ligand or ligands being a halide ligand. When 
the metal ion is itself highly electronegative, such Os.sup.+3, only a 
single strongly electronegative ligand, such as carbonyl, for example, is 
required to satisfy LUMO requirements. If the metal ion is itself of 
relatively low electronegativity, such as Fe.sup.+2, choosing all of the 
ligands to be highly electronegative may be required to satisfy LUMO 
requirements. For example, Fe(II)(CN).sub.6 is a specifically preferred 
shallow electron trapping dopant. In fact, coordination complexes 
containing 6 cyano ligands in general represent a convenient, preferred 
class of shallow electron trapping dopants. 
Since Ga.sup.+3 and In.sup.+3 are capable of satisfying HOMO and LUMO 
requirements as bare metal ions, when they are incorporated in 
coordination complexes they can contain ligands that range in 
electronegativity from halide ions to any of the more electronegative 
ligands useful with Group VIII metal ion coordination complexes. 
For Group VIII metal ions and ligands of intermediate levels of 
electronegativity it can be readily determined whether a particular metal 
coordination complex contains the proper combination of metal and ligand 
electronegativity to satisfy LUMO requirements and hence act as a shallow 
electron trap. This can be done by employing electron paramagnetic 
resonance (EPR) spectroscopy. This analytical technique is widely used as 
an analytical method and is described in Electron Spin Resonance: A 
Comprehensive Treatise on Experimental Techniques, 2nd Ed., by Charles P. 
Poole, Jr. (1983) published by John Wiley & Sons, Inc., New York. 
Photoelectrons in shallow electron traps give rise to an EPR signal very 
similar to that observed for photoelectrons in the conduction band energy 
levels of the silver halide crystal lattice. EPR signals from either 
shallow trapped electrons or conduction band electrons are referred to as 
electron EPR signals. Electron EPR signals are commonly characterized by a 
parameter called the g factor. The method for calculating the g factor of 
an EPR signal is given by C. P. Poole, cited above. The g factor of the 
electron EPR signal in the silver halide crystal lattice depends on the 
type of halide ion(s) in the vicinity of the electron. Thus, as reported 
by R. S. Eachus, M. T. Olm, R. Janes and M. C. R. Symons in the journal 
Physica Status Solidi (b), Vol. 152 (1989), pp. 583-592, in a AgCl crystal 
the g factor of the electron EPR signal is 1.88.+-.0.001 and in AgBr it is 
1.49.+-.0.02. 
A coordination complex dopant can be identified as useful in forming 
shallow electron traps in the practice of the invention if, in the test 
emulsion set out below, it enhances the magnitude of the electron EPR 
signal by at least 20 percent compared to the corresponding undoped 
control emulsion. The undoped control emulsion is a 0.45.+-.0.05 .mu.m 
edge length AgBr octahedral emulsion precipitated, but not subsequently 
sensitized, as described for Control 1A of Marchetti et al U.S. Pat. No. 
4,937,180. The test emulsion is identically prepared, except that the 
metal coordination complex in the concentration intended to be used in the 
emulsion of the invention is substituted for Os(CN.sub.6).sup.4- in 
Example 1B of Marchetti et al. 
After precipitation, the test and control emulsions are each prepared for 
electron EPR signal measurement by first centrifuging the liquid emulsion, 
removing the supernatant, replacing the supernatant with an equivalent 
amount of warm distilled water and resuspending the emulsion. This 
procedure is repeated three times, and, after the final centrifuge step, 
the resulting powder is air dried. These procedures are performed under 
safe light conditions. 
The EPR test is run by cooling three different samples of each emulsion to 
20.degree., 40.degree. and 60.degree. K., respectively, exposing each 
sample to the filtered output of a 200 W Hg lamp at a wavelength of 365 
nm, and measuring the EPR electron signal during exposure. If, at any of 
the selected observation temperatures, the intensity of the electron EPR 
signal is significantly enhanced (i.e., measurably increased above signal 
noise) in the doped test emulsion sample relative to the undoped control 
emulsion, the dopant is a shallow electron trap. 
As a specific example of a test conducted as described above, when a 
commonly used shallow electron trapping dopant, Fe(CN).sub.6.sup.4-, was 
added during precipitation at a molar concentration of 50.times.10.sup.-6 
dopant per silver mole as described above, the electron EPR signal 
intensity was enhanced by a factor of 8 over undoped control emulsion when 
examined at 20.degree. K. 
Hexacoordination complexes are preferred coordination complexes for use in 
the practice of this invention. They contain a metal ion and six ligands 
that displace a silver ion and six adjacent halide ions in the crystal 
lattice. One or two of the coordination sites can be occupied by neutral 
ligands, such as carbonyl, aquo or ammine ligands, but the remainder of 
the ligands must be anionic to facilitate efficient incorporation of the 
coordination complex in the crystal lattice structure. Illustrations of 
specifically contemplated hexacoordination complexes for inclusion in the 
protrusions are provided by McDugle et al U.S. Pat. No. 5,037,732, 
Marchetti et al U.S. Pat. Nos. 4,937,180, 5,264,336 and 5,268,264, Keevert 
et al U.S. Pat. No. 4,945,035 and Murakami et al Japanese Patent 
Application Hei-2[1990]-249588, the disclosures of which are here 
incorporated by reference. Useful neutral and anionic organic ligands for 
hexacoordination complexes are disclosed by Olm et al U.S. Pat. No. 
5,360,712. Careful scientific investigations have revealed Group VIII 
hexahalo coordination complexes to create deep (desensitizing) electron 
traps, as illustrated R. S. Eachus, R. E. Graves and M. T. Olm J. Chem. 
Phys., Vol. 69, pp. 4580-7 (1978) and Physica Status Solidi A, vol. 57, 
429-37 (1980). 
In a specific, preferred form it is contemplated to employ as a dopant a 
hexacoordination complex satisfying the formula: 
EQU [ML.sub.6 ].sup.n (IV) 
where 
M is filled frontier orbital polyvalent metal ion, preferably Fe.sup.+2, 
Ru.sup.+2, Os.sup.+2, Co.sup.+3, Rh.sup.+3, Ir.sup.+3, Pd.sup.+4 or 
Pt.sup.+4 ; 
L.sub.6 represents six coordination complex ligands which can be 
independently selected, provided that least four of the ligands are 
anionic ligands and at least one (preferably at least 3 and optimally at 
least 4) of the ligands is more electronegative than any halide ligand; 
and 
n is -2, -3 or -4. 
The following are specific illustrations of dopants capable of providing 
shallow electron traps: 
______________________________________ 
SET-1 [Fe(CN).sub.6 ].sup.-4 
SET-2 [Ru(CN).sub.6 ].sup.-4 
SET-3 [Os(CN).sub.6 ].sup.-4 
SET-4 [Rh(CN).sub.6 ].sup.-3 
SET-5 [Ir(CN).sub.6 ].sup.-3 
SET-6 [Fe(pyrazine) (CN).sub.5 ].sup.-4 
SET-7 [RuCl(CN).sub.5 ].sup.-4 
SET-8 [OsBr(CN).sub.5 ].sup.-4 
SET-9 [RhF(CN).sub.5 ].sup.-3 
SET-10 [IrBr(CN).sub.5 ].sup.-3 
SET-11 [FeCO(CN).sub.5 ].sup.-3 
SET-12 [RuF.sub.2 (CN).sub.4 ].sup.-4 
SET-13 [OsCl.sub.2 (CN).sub.4 ].sup.-4 
SET-14 [RhI.sub.2 (CN).sub.4 ].sup.-3 
SET-15 [IrBr.sub.2 (CN).sub.4 ].sup.-3 
SET-16 [Ru(CN).sub.5 (OCN)].sup.-4 
SET-17 [Ru(CN).sub.5 (N.sub.3)].sup.-4 
SET-18 [Os(CN).sub.5 (SCN)].sup.-4 
SET-19 [Rh(CN).sub.5 (SeCN)].sup.-3 
SET-20 [Ir(CN).sub.5 (HOH)].sup.-2 
SET-21 [Fe(CN).sub.3 Cl.sub.3 ].sup.-3 
SET-22 [Ru(CO).sub.2 (CN).sub.4 ].sup.-1 
SET-23 [Os(CN)Cl.sub.5 ].sup.-4 
SET-24 [Co(CN).sub.6 ].sup.-3 
SET-25 [IrCl.sub.4 (oxalate)].sup.-4 
SET-26 [In(NCS).sub.6 ].sup.-3 
SET-27 [Ga(NCS).sub.6 ].sup.-3 
______________________________________ 
It is additionally contemplated to employ oligomeric coordination complexes 
to increase speed, as taught by Evans et al U.S. Pat. No. 5,024,931, the 
disclosure of which is here incorporated by reference. 
The SET dopants are effective in conventional concentrations, where 
concentrations are based on the total silver in both the silver in the 
tabular grains and the silver in the second epitaxial phase. Generally 
shallow electron trap forming dopants are contemplated to be incorporated 
in concentrations of at least 1.times.10.sup.-7 mole per silver mole up to 
their solubility limit, typically up to about 5.times.10.sup.-4 mole per 
silver mole. Preferred concentrations are in the range of from about 
10.sup.-5 to 10.sup.-4 mole per silver mole. 
The contrast of the photographic emulsions of the invention can be further 
increased by doping the host grains with a hexacoordination complex 
containing a nitrosyl or thionitrosyl ligand. Preferred coordination 
complexes of this type are represented by the formula: 
EQU [TE.sub.4 (NZ)E'].sup.r (V) 
where 
T is a transition metal; 
E is a bridging ligand; 
E' is E or NZ; 
r is zero, -1, -2 or -3; and 
Z is oxygen or sulfur. 
The E ligands are typically halide, but can take any of the forms found in 
the SET dopants discussed above. A listing of suitable coordination 
complexes satisfying formula V is found in McDugle et al U.S. Pat. No. 
4,933,272, the disclosure of which is here incorporated by reference. 
The contrast increasing dopants (hereinafter also referred to as NZ 
dopants) can be incorporated in the host tabular grain structure at any 
convenient location. However, if the NZ dopant is present at the surface 
of the grain, it can reduce the sensitivity of the grains. It is therefore 
preferred that the NZ dopants be located in the host grains so that they 
are separated from the grain surface by at least 1 percent (most 
preferably at least 3 percent) of the total silver precipitated in forming 
the silver iodochloride grains. Preferred contrast enhancing 
concentrations of the NZ dopants range from 1.times.10.sup.-11 to 
4.times.10.sup.-8 mole per silver mole, with specifically preferred 
concentrations being in the range from 10.sup.-10 to 10.sup.-8 mole per 
silver mole, based on silver in the host grains. It is also possible to 
locate an NZ dopant in the second epitaxial phase, but this is not a 
preferred location for this dopant. 
The chemical sensitization of the emulsions of the invention can take any 
convenient conventional form. Conventional chemical sensitizations are 
summarized in Research Disclosure, Vol. 365, September 1994, Item 36544, 
IV. Chemical sensitization. The chemical sensitizers interact with the 
exposed surfaces of the host tabular grains and the second epitaxial phase 
to increase photographic sensitivity. Reduction sensitizers, middle 
chalcogen (e.g., sulfur) sensitizers, and noble metal (e.g., gold) 
sensitizers, employed singly or in combination are specifically 
contemplated. 
The emulsions of the invention can be reduction sensitized in any 
convenient conventional manner. Conventional reduction sensitizations are 
summarized in Research Disclosure, Item 36544, cited above, IV. Chemical 
sensitization, paragraph (1). A specifically preferred class of reduction 
sensitizers are the 2-[N-(2-alkynyl)amino]-meta-chalcazoles disclosed by 
Lok et al U.S. Pat. Nos. 4,378,426 and 4,451,557, the disclosures of which 
are here incorporated by reference. 
Preferred 2-[N-(2-alkynyl)amino]-meta-chalcazoles can be represented by the 
formula: 
##STR5## 
where 
X=O, S, Se; 
R.sub.1 =(VIa) hydrogen or (VIb) alkyl or substituted alkyl or aryl or 
substituted aryl; and 
Y.sub.1 and Y.sub.2 individually represent hydrogen, alkyl groups or an 
aromatic nucleus or together represent the atoms necessary to complete an 
aromatic or alicyclic ring containing atoms selected from among carbon, 
oxygen, selenium, and nitrogen atoms. 
As disclosed by Eikenberry et al, cited above, the formula (V) compounds 
are generally effective (with the (Vb) form giving very large speed gains 
and exceptional latent image stability) when present during the heating 
step (finish) that results in chemical sensitization. 
In a preferred form of the invention, an alkynylamino substituent is 
attached to a benzoxazole, benzothiazole or benzoselenazole nucleus. In 
one specific preferred form, the compounds VIa of the present invention 
and companion non-invention compounds VIb can be represented by the 
following formula: 
##STR6## 
where VIIa--R.sub.1 =H 
VIIa1--R.sub.1 =H, R.sub.2 =H, X=O 
VIIa2--R.sub.1 =H, R.sub.2 =Me, X=O 
VIIa3--R.sub.1 =H, R.sub.2 =H, X=S 
VIIb--R.sub.1 =alkyl or aryl 
VIIb1--R.sub.1 =Me, R.sub.2 =H, X=O R.sub.3 =H 
VIIb2--R.sub.1 =Me, R.sub.2 =Me, X=O R.sub.3 =H 
VIIb3--R.sub.1 =Me, R.sub.2 =H, X=S R.sub.3 =H 
VIIb4--R.sub.1 =Ph, R.sub.2 =H, X=O R.sub.3 =H 
Other preferred VIb structures have R.sub.1 as ethyl, propyl, 
p-methoxyphenyl, p-tolyl, or p-chlorophenyl with R.sub.2 or R.sub.3 as 
halogen, methoxy, alkyl or aryl. 
Whereas previous work employing compounds with structure similar to VIa and 
VIb described speed gains of about 40% using 0.10 mmole/silver mole when 
added after sensitization and prior to forming the layer containing the 
emulsion (Lok et al U.S. Pat. No. 4,451,557), speed gains have been 
demonstrated by Eikenberry et al ranging from 66% to over 250%, depending 
on the emulsion and sensitizing dye utilized, by adding 0.02-0.03 
mmole/silver mole of VIb during the sensitization step. Significantly 
higher levels of fog are observed when the VIa compounds are employed. 
The VIb compounds of the present invention typically contains an R.sub.1 
that is an alkyl or aryl. It is preferred that the R.sub.1 be either a 
methyl or a phenyl ring for the best increase in speed and latent image 
keeping. 
The compounds of the invention are added to the silver halide emulsion at a 
point subsequent to precipitation to be present during the finish step of 
the chemical sensitization process. A preferred concentration range for 
[N-(2-alkynyl)-amino]-meta-chalcazole incorporation in the emulsion is in 
the range of from 0.002 to 0.2 (most preferably 0.005 to 0.1) mmole per 
mole of silver. In a specifically preferred form of the invention 
[N-(2-alkynyl)amino]-meta-chalcazole reduction sensitization is combined 
with conventional gold (or platinum metal) and/or middle (S, Se or Te) 
chalcogen sensitizations. These sensitizations are summarized in Research 
Disclosure Item 36544, previously cited, IV. Chemical sensitization. The 
combination of sulfur, gold and [N-(2-alkynyl)amino]-meta-chalcazole 
reduction sensitization is specifically preferred. 
A specifically preferred class of middle chalcogen sensitizers are 
tetrasubstituted middle chalcogen ureas of the type disclosed by Herz et 
al U.S. Pat. Nos. 4,749,646 and 4,810,626, the disclosures of which are 
here incorporated by reference. Preferred compounds include those 
represented by the formula: 
##STR7## 
wherein 
X is sulfur, selenium or tellurium; 
each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 can independently represent 
an alkylene, cycloalkylene, alkarylene, aralkylene or heterocyclic arylene 
group or, taken together with the nitrogen atom to which they are 
attached, R.sub.1 and R.sub.2 or R.sub.3 and R.sub.4 complete a 5 to 7 
member heterocyclic ring; and 
each of A.sub.1, A.sub.2, A.sub.3 and A.sub.4 can independently represent 
hydrogen or a radical comprising an acidic group, 
with the proviso that at least one A.sub.1 R.sub.1 to A.sub.4 R.sub.4 
contains an acidic group bonded to the urea nitrogen through a carbon 
chain containing from 1 to 6 carbon atoms. 
X is preferably sulfur and A.sub.1 R.sub.1 to A.sub.4 R.sub.4 are 
preferably methyl or carboxymethyl, where the carboxy group can be in the 
acid or salt form. 
A specifically preferred tetrasubstituted thiourea sensitizer is 
1,3-dicarboxymethyl-1,3-dimethylthiourea. 
Specifically preferred gold sensitizers are the gold (I) compounds 
disclosed by Deaton U.S. Pat. No. 5,049,485, the disclosure of which is 
here incorporated by reference. These compounds include those represented 
by the formula: 
EQU AuL.sub.2.sup.+ X.sup.- or AuL(L.sup.1).sup.+ X.sup.- (IX) 
wherein 
L is a mesoionic compound; 
X is an anion; and 
L.sup.1 is a Lewis acid donor. 
As previously disclosed, in preferred photographic applications the tabular 
grain emulsions of the invention are spectrally sensitized. One of the 
significant advantages of the invention is that the presence of a high 
iodide first epitaxial phase on the major faces of the tabular grains can 
improve the adsorption of the spectral sensitizing dye or dyes employed 
and, particularly when the oxidation potential of the dye is more negative 
than the threshold value stated above, increase the efficiency with which 
photon energy is transferred between the spectral sensitizing dye and the 
grains. 
Any conventional spectral sensitizing dye or dye combination can be 
employed with the emulsions of the invention. Suitable spectral 
sensitizing dye selections are disclosed in Research Disclosure, Item 
36544, cited above, Section V. Spectral sensitization and desensitization. 
Preferred spectral sensitizing dyes are polymethine dyes, including 
cyanine, merocyanine, complex cyanine and merocyanine (i.e., tri-, tetra- 
and polynuclear cyanine and merocyanine), oxonol, hemioxonol, styryl, 
merostyryl, streptocyanine, hemicyanine and arylidene dyes. Specifically 
preferred blue sensitizing dyes are those disclosed by Kofron et al U.S. 
Pat. No. 4,439,520. Preferred spectral sensitizing dyes also capable of 
acting as site directors for the second epitaxial phase are those 
disclosed by Maskasky U.S. Pat. No. 4,435,501 in Table I. As demonstrated 
in the Examples below spectral sensitizing dyes and, particularly, 
spectral sensitizing dye combinations having reduction potentials more 
negative than the threshold value stated above provide unexpectedly high 
levels of photographic efficiency. The supersensitizing dye combinations 
set out in Research Disclosure Item 36544, Section V, A. Sensitizing dyes, 
paragraphs (6) and (6a) are specifically contemplated. 
The following are illustrations of specific spectral sensitizing dyes 
contemplated for use with the emulsions of the invention, together with 
their oxidation (Eox) and reduction (Ered) potentials in volts: 
SS-1 
Anhydro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]thiazolothiacyanine hydroxide, 
triethylammonium salt Eox=1.300 Ered=-1.359 
SS-2 
Anhydro-3,3'-bis(3-sulfopropyl)-4'-phenylnaphtho[1,2-d]thiazolothiazolinocy 
anine hydroxide, sodium salt Eox=1.085 Ered=-1.758 
SS-3 
Anhydro-5'-chloro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]oxazolothiacyanine 
hydroxide, triethylammonium salt Eox=1.375 Ered=-1.437 
SS-4 
Anhydro-3,3'-bis(3-sulfopropyl)-4,5,4',5'-dibenzothiacyanine hydroxide, 
sodium salt Eox=1.213 Ered=-1.371 
SS-5 
Anhydro-3,3'-bis(3-sulfopropyl)-5,6-dimethoxy-4'-phenylthiacyanine 
hydroxide, sodium salt Eox=1.240 Ered=-1.401 
SS-6 
Anhydro-5-chloro-3'-ethyl-3-(4-sulfobutyl)thiacyanine, inner salt Eox=1.399 
Ered=-1.269 
SS-7 
Anhydro-5,5'-dimethoxy-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, inner 
salt Eox=1.310 Ered=-1.361 
SS-8 
Anhydro-5-chloro-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, sodium salt 
Eox=1.418 Ered=-1.309 
SS-9 
Anhydro-5,5'-bis(methylthio)-3,3'-bis(3-sulfobutyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.367 Ered=-1.249 
SS-10 
Anhydro-5,6-dimethoxy-5'-phenyl-3,3'-bis(3-sulfopropyl)thiacyanine 
hydroxide, triethylammonium salt Eox=1.240 Ered=-1.417 
SS-11 
Anhydro-3'-(2-carboxy-2-sulfoethyl)-1-ethyl-5',6'-dimethoxynaphtho[1,2-d]th 
iazolothiocyanine hydroxide, potassium salt Eox=1.153 Ered=-1.462 
SS-12 
Anhydro-3,3'-bis 
(3-sulfopropyl)-5',6'-dimethoxy-5-phenyloxathiacarbocyanine hydroxide, 
sodium salt Eox=1.259 Ered=-1.593 
SS-13 
3'-Ethyl-3-methyl-6-nitrothiathiazolinocyanined iodide Eox=1.271 
Ered=-1.774 
SS-14 
Anhydro-5'-chloro-5-phenyl-3,3'-bis(3-sulfopropyl)oxathiacyanine hydroxide, 
triethylammonium salt Eox=1.447 Ered=-1.580 
SS-15 
Anhydro-5'-fluoro-3,3'-bis(3-sulfopropyl)naphtho[1,2-d]thiazolothiacyanine 
hydroxide, triethylammonium salt Eox=1.322 Ered=-1.318 
SS-16 
Anhydro-5-chloro-3,3'-bis(sulfopropyl)naphtho[1,2-d]thiazolothiacyanine 
hydroxide, triethylammonium salt Eox=1.341 Ered=-1.273 
SS-17 
Anhydro-4',5'-benzo-3,3'-bis(3-sulfopropyl)-5-pyrrolooxathiacyanine 
hydroxide, triethylammonium salt Eox=1.334 Ered=-1.453 
SS-18 
Anhydro-4',5'-benzo-3,3'-bis(3-sulfopropyl)-5-phenyloxathiacyanine 
hydroxide, triethylammonium salt Eox =1.319 Ered=-1.484 
SS-19 
Anhydro-5,5'-dichloro-3,3'-bis(2-sulfoethyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.469 Ered=-1.206 
SS-20 
Anhydro-4',5'-benzo-5-methoxy-3,3'-bis(3-sulfopropyl)oxathiacyanine 
hydroxide, sodium salt Eox=1.283 Ered=-1.530 
SS-21 
Anhydro-5-cyano-3,3'-bis(3-sulfopropyl)-5'-phenylthiacyanine hydroxide, 
triethylammonium salt Eox=1.445 Ered=-1.234 
SS-22 
Anhydro-5'-chloro-5-pyrrolo-3,3'-bis(3-sulfopropyl)oxathiacyanine 
hydroxide, triethylammonium salt Eox=1.461 Ered=-1.380 
SS-23 
Anhydro-5,5'-dichloro-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.469 Ered=-1.215 
SS-24 
Anhydro-5,5'-diphenyl-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.387 Ered=-1.287 
SS-25 
Anhydro-5-chloro-5'-phenyl-3,3'-bis(3-sulfopropyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.428 Ered=-1.251 
SS-26 
Anhydro-5-chloro-5'-pyrrolo-3,3'-bis(3'-sulfopropyl)thiacyanine hydroxide, 
triethylammonium salt Eox=1.442 Ered=-1.212 
In addition to the features specifically described, it is recognized that 
the emulsions can contain any convenient conventional selection of 
additional features. For example, the features of the emulsions, such as 
vehicle (including peptizers and binders), hardeners, antifoggants and 
stabilizers, blended grain populations, coating physical property 
modifying addenda (coating aids, plasticizers, lubricants, antistats, 
matting agents, etc.), and dye image formers and modifiers can take any of 
the forms described in Research Disclosure, Item 36544, cited above. 
Selections of these other emulsion features are preferably undertaken as 
taught in the patents cited above to describe the starting tabular grain 
emulsions. 
EXAMPLES 
The invention can be better appreciated by reference to the following 
specific examples. The term "oxidized gelatin" is employed to indicate 
gelatin that has been treated with hydrogen peroxide to reduce its 
methionine content below detectable levels. pH was lowered by using nitric 
acid and increased by using sodium hydroxide. 
Example 1 
Host Tabular Grain Emulsion HT-1 
A silver bromide host tabular grain emulsion was prepared by charging a 
reaction vessel with 1.25 g/L of oxidized gelatin, 1.115 g/L NaBr, 0.1 g/L 
of block copolymer A, and 6 L of distilled water. 
HO-[(CH.sub.3)CHCH.sub.2 O].sub.x -(CH.sub.2 CH.sub.2 O).sub.y -[CH.sub.2 
CH(CH.sub.3)O].sub.x' -H 
x=x'=25; y=7 
block copolymer A 
The contents of the reaction vessel were adjusted to a pH of 1.78 at 
40.degree. C. Nucleation occurred during a one minute period during which 
0.8 m/L of AgNO.sub.3 and 0.84 m/L NaBr were added at the rate of 50 
mL/min. The temperature of the reaction vessel was ramped to 60.degree. C. 
after the addition of 0.0892 mole of NaBr. Ammonia was then generated in 
situ by the addition of 0.115 mole of ammonium sulfate and 0.325 mole of 
sodium hydroxide. Ammoniacal digestion was undertaken for 9 minutes, after 
which time the digestion was quenched by the addition of 0.2265 mole of 
nitric acid. Additional gelatin, 99.84 g of oxidized gelatin, and 
surfactant, block copolymer A (1.0 mL) were introduced into the reaction 
vessel. 
A first growth segment (I) then occurred over a period of 20 minutes at a 
pH of 5.85, pBr of 2.2, 60.degree. C., by introducing NaBr and AgNO.sub.3 
solutions employed for grain nucleation at the rates of 9.2 and 9.0 
mL/min, respectively. A second growth segment (II) took place over 64 
minutes by continuing precipitation as described for growth segment I, 
except that 1.6 mol/L AgNO.sub.3 was ramped from 9 to 80 mL/min and 1.679 
m/L NaBr was ramped from 9.1 to 78.5 mL/min. A final growth segment was 
conducted for 19 minutes at the terminal flow rate of growth segment II. 
The emulsion was then cooled to 40.degree. C. and adjusted to a pBr of 3.6 
during ultrafiltration. The pH of the emulsion was adjusted to 5.9. 
The resulting silver bromide tabular grain emulsion was monodispersed, 
having a COV of less than 30 percent. The average ECD of the emulsion 
grains was 1.44 .mu.m, and the average thickness of the grains was 0.10 
.mu.m. The average aspect ratio of the tabular grains 14.4. Greater than 
90 percent of total grain projected area was accounted for by tabular 
grains. 
Composite Tabular Grain Emulsion CT-1 
A reaction vessel was charged with 1 mole of Emulsion HT-1. The temperature 
of the reaction vessel was adjusted to 60.degree. C., and its pBr was 
brought to 4.0 by the slow addition of AgNO.sub.3. The silver content of 
the grains was increased by 18 percent, based on total silver, by the 
double jet precipitation of AgI over 10 minutes by adding AgNO.sub.3 and 
KI each at a flow rate of 35 mL/min. while monitoring the pI of the 
reaction vessel to control host grain metathesis. At the conclusion of 
precipitation the pI of the reaction vessel was adjusted to 7.1 with KI 
and the pH was adjusted to 5.6. 
Microscopic analysis of the resulting emulsion revealed that in excess of 
90 percent of total grain projected area was accounted for by composite 
tabular grains containing high iodide silver halide plates on their major 
faces and edges. Greater than 40 percent of the tabular grain major faces 
were covered by the high iodide plates. Scanned probe microscopy revealed 
that the plates varied from 4 to 6 nm in thickness. The plates were 
observed to contain .beta. phase silver iodide, but the presence of 
.gamma. phase silver iodide could not be excluded. Analytical electron 
microscopy observations were consistent with the plates having a high (&gt;90 
mole %) iodide content. A measured lattice constant of 6.5 .ANG. was 
observed, compared to a known lattice constant of 6.496 .ANG. for AgI. 
Some evidence of host grain metathesis was observed, and a nontabular AgI 
grain population was also present. 
Light Absorption Analysis 
The emulsion was coated at 10.76 mg/dm.sup.2 silver with an equal amount of 
gelatin on a cellulose acetate photographic support with an anithalation 
backing layer. The emulsion layer was overcoated with 21.53 mg/dm.sup.2 of 
gelatin containing 1.5 percent by weight, based on total gelatin, of 
bis(vinylsulfonyl)methane hardener. A second, identical coating was 
prepared, except that the antihalation backing was omitted. Third and 
fourth coatings identical to the first and second coatings were prepared, 
except that Emulsion HT-1 was substituted for Emulsion CT-1. 
From reflection and transmission analysis the absorptions of Emulsions HT-1 
and CT-1 as a function of wavelength were determined and are represented 
as shown in FIG. 3. Emulsion CT-1 demonstrated a significantly higher 
absorption that Emulsion HT-1 up to wavelengths approaching 500 nm. Peak 
absorption of Emulsion HT-1 was observed at 423 nm. Multiplying the 
spectral output of a 5500.degree. K. Daylight V light source by the 
absorptions of FIG. 3 over the wavelength region of 360 to 700 nm gives an 
integrated light absorption of 175.times.10.sup.10 photons/cm.sup.2 /sec 
for Emulsion HT-1 and 745.times.10.sup.10 photons/cm.sup.2 /sec for 
Emulsion CT-1. This demonstrates somewhat more than 4 times greater photon 
absorption for Emulsion CT-1 as compared to Emulsion HT-1. 
Example 2 
Host Tabular Grain Emulsion HT-2 
A silver iodobromide host tabular grain emulsion was prepared by charging a 
reaction vessel with 2 g/L of gelatin (Rousselot.TM.), 6 g/L NaBr, 0.65 mL 
of block copolymer A, and 4956 mL of distilled water. The contents of the 
reaction vessel were adjusted to a pH of 6.0 at 40.degree. C. at a pBr of 
1.35. The temperature of the reaction vessel was then raised to 70.degree. 
C. Nucleation occurred during a three minute period during which 0.393 m/L 
of AgNO.sub.3 at a rate of 87.6 mL/min and 2 m/L NaBr at a rate of 20 
mL/min were added. An ammonia digest was initiated by adding 0.27 mole of 
NH.sub.4 OH. Ammoniacal digestion was undertaken for 1.5 minutes, after 
which time the digestion was quenched by the addition of 0.37 mole of 
nitric acid. 
Distilled water in the amount of 1820 mL containing 77 g/L of gelatin with 
0.25 mL of block copolymer A was added to the reaction vessel. A first 
growth segment (I) was then conducted over 3.0 minutes by introducing 87.6 
mL/min of the 0.393 m/L AgNO.sub.3 and 13.2 mL/min of the 2 m/L NaBr while 
maintaining a pBr of 1.55. A second growth segment (II) was conducted over 
25 minutes by adding 2.75 m/L AgNO.sub.3 and 2.7085 m/L NaBr containing 
0.04125 m/L KI, each at accelerating flow rates ranging from 15 to 40 
mL/min. A third growth segment (III) was a continuation of the preceding 
growth segment, lasting 31 minutes with addition of the same solutions 
being accelerated from 40 to 102 mL/min. NaBr in the amount of 1.925 moles 
in 665 g of distilled water were then added followed by the dump addition 
of 0.36 mole of AgI Lippmann. AgNO.sub.3 at 2.75 m/L and 2 m/L NaBr were 
then each run into the reaction vessel at a constant rate of 50 mL/min 
until the pBr of the reaction vessel reached 2.4 (approximately 24 
minutes). 
The emulsion was washed at 40.degree. C. to a pBr of 3.6 by 
ultrafiltration. The pH of the emulsion was adjusted to 5.6. 
The emulsion was a run-dump silver iodobromide tabular grain emulsion. The 
grains contained 1.5 mole % I added during the run and 3 mole % I added in 
the dump following precipitation of 69 percent of total silver. 
The resulting silver iodobromide tabular grain emulsion was monodispersed, 
having a COV of less than 30 percent. The average ECD of the emulsion 
grains was 3.25 .mu.m, and the average thickness of the grains was 0.13 
.mu.m. The average aspect ratio of the tabular grains 25. Greater than 70 
percent of total grain projected area was accounted for by tabular grains. 
Composite Tabular Grain Emulsion CT-2 
Formation of this emulsion followed the description provided above for the 
preparation of Emulsion CT-1, except as noted. Emulsion HT-2 was 
substituted for Emulsion HT-1. The temperature of the reaction vessel was 
65.degree. C. AgNO.sub.3 and KI were added in two 10 minute growth 
segments. In the first segment the AgNO.sub.3 addition was accelerated 
from 3.5 to 17.5 mL/min while KI addition was accelerated from 5 to 25 
mL/min. In the second segment the AgNO.sub.3 addition was accelerated from 
17.5 to 35 mL/min while KI addition was accelerated from 25 to 50 mL/min. 
The additional AgI precipitated accounted for 20.6 percent of total silver 
forming the composite grains. 
Microscopic analysis of the resulting emulsion revealed that in excess of 
95 percent of total grain projected area was accounted for by composite 
tabular grains containing triangular and hexagonal high iodide silver 
halide plates on their major faces and edges. Greater than 55 percent of 
the tabular grain major faces were covered by the high iodide plates. 
Scanned probe microscopy revealed that the plates varied from 15 to 30 nm 
in thickness. Plates were also observed on the edges of the host tabular 
grains. A plan view of a typical grain is shown in FIG. 4, and a section 
view of typical grains is shown in FIG. 5. 
Iodide analysis revealed three distinct phases--the run iodide, the dump 
iodide and the iodide in the plates. The lattice constant of the crystal 
lattice of the plates was 6.4, indicating a high (&gt;90 mole %) iodide 
phase, probably containing a small fraction of bromide ion. 
Light Absorption Analysis 
The light absorption analysis of Example 1 was repeated using Emulsions 
HT-2 and CT-2, except additional samples of these emulsions were examined 
with the blue spectral sensitizing dye SS-23 added at concentrations of 
600 mg/Ag mole. 
From reflection and transmission analysis the absorptions of dyed and 
undyed samples Emulsions HT-2 and CT-2 as a function of wavelength were 
determined and are represented as shown in FIG. 6. Emulsion HT-2 without 
dye is shown as curve HT-2-D. It exhibits the least absorption in the blue 
region of the spectrum. Emulsion HT-2 with dye is shown as curve HT-2+D 
shows increased blue absorption, attributable to the spectral sensitizing 
dye, with peak absorption occurring in the long blue portion of the 
spectrum. Emulsion CT-2 without dye, shown as Curve CT-2-D, shows blue 
absorption superior to that of HT-2-D and shows short blue absorption 
superior to that of HT-2+D. Emulsion CT-2 with dye, shown as Curve CT-2+D, 
shows superior overall blue absorption as compared with the remaining 
emulsion samples. 
Multiplying the spectral output of a 5500.degree. K. Daylight V light 
source by the absorptions of FIG. 6 over the wavelength region of 360 to 
700 nm gives the integrated light absorptions shown in Table II. 
TABLE II 
______________________________________ 
Emulsion Integrated Light 
Sample Absorption photons/sec/cm.sup.2 
______________________________________ 
HT-2 - D 294 .times. 10.sup.10 
CT-2 - D 729 .times. 10.sup.10 
HT-2 + D 630 .times. 10.sup.10 
CT-2 + D 959 .times. 10.sup.10 
______________________________________ 
This demonstrates the superior blue light absorption that are available by 
employing the emulsions of the invention. 
Example 3 
Composite Tabular Grain Emulsion CT-3 
Starting with HT-2, but with the pBr of the emulsion adjusted to 5.06, the 
preparation procedure for CT-2 was repeated, but with these differences: 
The second growth segment in which AgNO.sub.3 and KI were added was 
reduced to 6.1 minutes. In the first growth segment KI addition was 
accelerated from 4 to 10 mL/min and in the second growth segment KI 
addition was accelerated from 10 to 16.1 mL/min. The AgNO.sub.3 flow in 
the second growth segment ended at 28.2 mL/min. The total AgI precipitated 
accounted for 9.2 percent of total silver forming the composite grains. 
A plane view of a typical grain is shown in FIG. 7, and a section view of 
typical grains is shown in FIG. 8. Compared to Emulsion CT-2, there were 
fewer high iodideplates at the edges of the host tabular grains. Also, 
instead of being discrete with triangular or hexagonal boundaries, the 
plates appeared to coalesce with adjacent plates, leaving no discernible 
boundaries between adjacent plates. 
Example 4 
Host Tabular Grain Emulsion HT-4 
A silver iodobromide host tabular grain emulsion was prepared by charging a 
reaction vessel with 0.80 g/L of oxidized gelatin, 0.851 g/L NaBr, 0.7 g/L 
of block copolymer B, and 6 L of distilled water. 
HO-(CH.sub.2 CH.sub.2 O).sub.y -[(CH.sub.3)CHCH.sub.2 O].sub.x -(CH.sub.2 
CH.sub.2 O).sub.y' -H 
x=22; y=y'=6 
block copolymer B 
The contents of the reaction vessel were adjusted to a pH of 1.78 at 
45.degree. C. Nucleation occurred during a one minute period during which 
0.5 m/L of AgNO.sub.3 and 0.54 m/L NaBr were added at the rate of 58 
mL/min. The temperature of the reaction vessel was ramped to 60.degree. C. 
after the addition of 0.098 mole of NaBr. Ammonia was then generated in 
situ by the addition of 0.077 mole of ammonium sulfate and 0.241 mole of 
sodium hydroxide. Ammoniacal digestion was undertaken for 9 minutes, after 
which time the digestion was quenched by the addition of 0.21 mole of 
nitric acid. Additional gelatin (150.0 g of oxidized gelatin), NaBr (0.123 
mole), and block copolymer B (1.4 mL) were introduced into the reaction 
vessel. 
A first growth segment (I) then occurred over a period of 20 minutes at a 
pH of 5.5, pBr of 1.6, 60.degree. C., by introducing NaBr and AgNO.sub.3 
solutions employed for grain nucleation at the rates of 15 and 16.7 
mL/min, respectively. A second growth segment (II) took place over 75 
minutes by continuing precipitation as described for growth segment I, 
except that 1.6 mol/L AgNO.sub.3 was ramped from 9 to 69 mL/min and 1.622 
m/L NaBr plus 0.0676 KI was ramped from 9.6 to 69 mL/min. A third growth 
segment (III) occurred for 8.5 minutes at the final addition rate of the 
second growth segment. A final growth segment was conducted for 20 minutes 
at the flow rate of growth segment III, except that 1.69 m/L NaBr was 
substituted for NaBr plus KI for the purpose of reducing the iodide 
concentration at the surface of the tabular grains during the 
precipitation of the final 20 percent of silver deposition. 
The emulsion was then cooled to 40.degree. C. and adjusted to a pBr of 3.5 
during ultrafiltration. The pH of the emulsion was adjusted to 5.5. 
The resulting silver iodobromide tabular grain emulsion was monodispersed, 
having a COV of less than 30 percent. The average ECD of the emulsion 
grains was 2.87 .mu.m, and the average thickness of the grains was 0.098 
.mu.m. The average aspect ratio of the tabular grains was 29.3. Greater 
than 90 percent of total grain projected area was accounted for by tabular 
grains. 
Partially Shelled Tabular Grain Control ST-4 
A one mole sample of Emulsion HT-4 was partially shelled by depositing 
silver iodobromide (36 mole % I) as a shell over the exterior of the host 
tabular grains. A total of 0.225 mole of AgBr.sub.0.64 I.sub.0.36 was 
deposited over 38.5 minutes by the double jet addition of AgNO.sub.3 as a 
silver salt solution and a mixture of NaBr and KI as a mixed halide salt 
solution. Shell precipitation was conducted at 65.degree. C. and a pBr of 
3.6. A total of 0.0918 mole of silver iodide was precipitated in the 
shell. 
Microscopic examination of the grains revealed that the shell covered all 
visible exterior edge faces of the host tabular grains and 40 percent of 
the total exterior surface. Shell growth began at the edges of the grains, 
entirely covering the edges, and then progressed inwardly as precipitation 
continued, entirely covering all areas of the major faces closer to the 
edges than the boundaries of the partial shell nearest the centers of the 
major faces. 
Composite Tabular Grain Emulsion CT-4 
The shelling procedure of Emulsion ST-4 was modified to eliminate the 
bromide added with the iodide. This resulted in the precipitation of 
0.0919 mole of silver iodide onto the host tabular grain emulsion HT-4. 
Microscopic analysis of the resulting emulsion revealed that in excess of 
90 percent of total grain projected area was accounted for by composite 
tabular grains containing high iodide silver halide plates on their major 
faces and edges. Greater than 15 percent of the tabular grain major faces 
were covered by the high iodide plates. 
Light Absorption Analysis 
The light absorption analysis of Example 2 was repeated using Emulsions 
HT-4, ST-4 and CT-4, but with 800 g of blue spectral sensitizing dye SS-23 
per silver mole adsorbed. 
The absorption performance of dyed samples is shown in FIG. 9. All of the 
dyed samples demonstrated similar absorption in the long (450 to 500 nm) 
blue region of the spectrum; but in the short (400 to 450 nm) blue region 
of the spectrum, a clear separation on absorptions was observed. Minimum 
short blue absorption was demonstrated by Emulsion HT-4 with dye (HT-4+D). 
When iodide was increased by creating a silver iodobromide shell, a clear 
increase in blue absorption was observed for Emulsion ST-4 plus dye 
(ST-4+D). However, the short blue absorption of ST-4+D was limited by the 
limited ability to incorporate iodide into the face centered cubic rock 
salt crystal lattice structure forming the shell. The superiority of 
forming a high iodide phase on the major faces of the host tabular grains 
is shown by the dyed sample of Emulsion CT-4 (CT-4+D). 
Multiplying the spectral output of a 5500.degree. K. Daylight V light 
source by the absorptions of samples of Emulsions HT-4, ST-4 and CT-4, 
with (+D) and without (-D) dye, over the wavelength region of 360 to 700 
nm gives the integrated light absorptions shown in Table III. 
TABLE III 
______________________________________ 
Emulsion Integrated Light 
Sample Absorption photons/sec/cm.sup.2 
______________________________________ 
HT-4 - D 224 .times. 10.sup.10 
ST-4 - D 369 .times. 10.sup.10 
CT-4 - D 498 .times. 10.sup.10 
HT-4 + D 807 .times. 10.sup.10 
ST-4 + D 849 .times. 10.sup.10 
CT-4 + D 995 .times. 10.sup.10 
______________________________________ 
This demonstrates the superior blue light absorption that is available by 
employing the emulsions of the invention. It further demonstrates that 
similar levels of light absorption can not be realized by adding the same 
amount of iodide as in the emulsions of the invention, but in a surface 
silver iodobromide shell. Even though CT-4 contained a high iodide phase 
covering only a minimal 15 percent of its major faces, it compared 
favorably to ST-4 that contained a silver iodobromide phase of the same 
overall iodide content distributed over 40 percent of its major faces. 
Example 5 
Host Tabular Grain Emulsion HT-5 
A silver iodobromide (3 mole % I) tabular grain emulsion was precipitated 
in the following manner: A reaction vessel was charged with 0.667 g/L 
gelatin, 1.25 g/L NaBr and 6.3 L of distilled water at 70.degree. C. The 
contents of the reaction vessel were brought to a pH of 3.5 with nitric 
acid. Nucleation occurred over a 10 sec period by the double jet addition 
of 1.4M AgNO.sub.3 at 75 mL/min and a salt at the same flow rate 
containing 1.386M NaBr and 0.014M KI. The contents of the reaction vessel 
were held for 6 minutes and then the temperature was ramped to 80.degree. 
C. over a period of 7 minutes. Then 1.5 L of a solution containing 20 g/L 
of gelatin were added, and pH was adjusted to 4.5 with NaOH. Six growth 
segments (I-VI) defining the remainder of the precipitation were conducted 
at 80.degree. C., a pH 4.5 and a pBr of 1.78 using 2.5M AgNO.sub.3 and 
2.425M NaBr containing 0.075M KI. 
Growth I took 4.5 min with silver flowing at 15.7 mL/min and the salts at 
23.6 mL/min. Growth II extended for 9 minutes during which time the silver 
flow rate was ramped from 15.7 to 27.3 mL/min, and the flow rate of the 
salts was ramped from 16.7 to 28.4 mL/min. Growth III was the same time as 
growth II, except that the respective flow rate ramps were 27.3 to 40.9 
and 28.4 to 42.5 mL/min. Growth IV extended over 13.5 minutes with the 
respective flow rate ramps of 40.9 to 66.1 and 42.5 to 68 mL/min. Growth V 
took the same time as Growth IV with the respective flow rate ramps of 
66.1 to 97.2 and 68 to 99.8 mL/min. Growth VI was 18 minutes long, and the 
respective flow rate ramps were 97.2 to 120.7 and 99.8 to 123.8 mL/min. 
The emulsion was cooled to 40.degree. C. and adjusted to a pBr of 3.6 
during ultrafiltration. The pH of the emulsion was adjusted to 5.9. The 
resulting silver iodobromide tabular grain emulsion had a COV of less than 
36 percent. The average ECD of the emulsion grains was 2.48 .mu.m, and the 
average thickness of the grains was 0.106 .mu.m. The average aspect ratio 
of the tabular grains was 23.4. Greater than 90 percent of the total grain 
projected area was accounted for by tabular grains. 
Shelled Tabular Grain Control ST-5 
Shelled tabular grain control ST-5 was precipitated similarly as ST-4 only 
using HT-5 as the substrate and at a pBr of 5.06 rather than 3.6. 
The shelled grains exhibited an average ECD of 2.81 .mu.m and an average 
grain thickness of 0.137 .mu.m. Average aspect ratio was 20.1. The iodide 
concentration of the shell was 38 mole percent, raising the overall iodide 
concentration of the shelled grains to 10.0 mole percent. 
Composite Tabular Grain Emulsion CT-5 
This emulsion was prepared similarly to composite tabular grain emulsion 
CT-4, except that host tabular grain emulsion HT-5 was employed as a 
substrate and precipitation was conducted at a pBr of 5.06 rather than 
3.6. 
The composite tabular grains exhibited an average ECD of 2.88 .mu.m and an 
average grain thickness of 0.116 .mu.m. Average aspect ratio was 24.8. The 
overall iodide concentration of the composite grains was 9.9 mole percent. 
Sensitization 
Prior to chemical sensitization, both ST-5 and CT-5 were adjusted to a pBr 
of 4.37 and epitaxially deposited with 8.0 mole % AgCl using SS-1 at 431.4 
mg/Ag mole as a dye director as taught by Maskasky, U.S. Pat. No. 
4,459,353. Subsequently chemical sensitization was effected by the 
sequential addition of 60 mg/Ag mole of NaSCN, 4 mg/Ag mole of 
N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 2 mg/Ag mole of Au(I) 
bis(trimethylthiotriazole), and 2.5 mg/Ag mole of 
3-methyl-1,3-benzothiazolium iodide to the emulsion melt followed by a 5 
min. temperature hold at 50.degree. C. At the conclusion finish of the 
heat cycle, 115 mg/Ag mole of 1-(3-acetamidophenyl)-5-mercaptotetrazole 
(APMT) were added to the melt. 
Film coatings were made on a cellulose acetate photographic film support 
with an antihalation backing layer. ST-5 and CT-5 were doctored with 1.750 
gm/Ag mole of 4-hydroxy-6-methyl-1,3,3a,7-tetra-azaindene and coated at 
the following coating coverages: silver halide 10.76 mg/dm.sup.2, gelatin 
32.28 mg/dm.sup.2, and 9.684 mg/dm.sup.2 of the yellow dye-forming coupler 
YC-1. The emulsion layer was overcoated with 8.610 mg/dm.sup.2 gelatin, to 
which 1.5 percent by weight, based on total coated gelatin, 
bis(vinylsulfonyl)methane hardener was added. 
##STR8## 
The coated emulsions were given a sensitometric exposure for 1/50" through 
a 0-3 step chart from 400 to 500 nm in 10 nm increments and then processed 
in the motion picture film process ECN-2 described in Kodak Publication 
H-24, Manual for Processing Eastman Color Films. 
The relative speeds reported in Table IV below were based on the 
reciprocals of the lux-second/cm.sup.2 required to give a density 0.2 unit 
above Dmin. 
TABLE IV 
______________________________________ 
480 nm 
430 nm (peak AgI absorption) 
(peak dye absorption) 
Relative 
Relative 
Emulsion 
Dmin Gamma Speed Speed 
______________________________________ 
ST-5 0.36 0.13 100 100 
CT-5 0.17 0.67 2230 2200 
______________________________________ 
It can be readily appreciated that the tabular grain emulsion of the 
present invention is, by reason of the high iodide epitaxial phase 
partially covering the major faces of the tabular, superior to a 
comparable tabular grain emulsion, but with an iodide saturated silver 
iodobromide shell substituted for the high iodide epitaxial phase. The 
advantage is observed in both the long and short blue regions of the 
spectrum. 
Example 6 
This example demonstrates that higher levels of photographic performance 
are realized when the spectral sensitizing dye employed has a reduction 
potential more negative than -1.30 volts. A high chloride second epitaxial 
phase was employed for chemical sensitization. 
Host Tabular Grain Emulsion HT-6 
A silver iodobromide host tabular grain emulsion was prepared by charging a 
reaction vessel with 2.083 g/L of gelatin (Rousellot.TM.), 6.25 g/L NaBr, 
0.271 g/L of the surfactant Emerest 2648.TM., a dioleate ester of 
polyethylene glycol (mol. wt. 400) (S6), and 6 L of distilled water. The 
contents of the reaction vessel were adjusted to a pH of 6.0 at 40.degree. 
0 C. after which the temperature was raised to 75.degree. C. Nucleation 
occurred during a one minute period during which 0.50 m/L of AgNO.sub.3 
and 2.0 m/L of NaBr were added at a rate of 62.0 mL/min and 22.8 mL/min, 
respectively. Ammonia was then generated in situ by the addition of 0.0282 
mole of ammonium sulfate and 0.086 mole of sodium hydroxide, which brought 
the reaction vessel to a pH of 10.2. Ammoniacal digestion was undertaken 
for 1.5 minutes after which time the digestion was quenched by the 
addition of 0.07 mole of nitric acid. An additional 176.25 g of gelatin 
(Rousellot.TM.), Surfactant S6, and 0.122 mole of NaBr were introduced 
into the reaction vessel such that the pBr was brought to 1.343 at 
75.degree. C. The pH was then adjusted to 6.0 with NaOH. 
A first growth segment (I) then occurred over a period of 3 minutes at a pH 
of 6.0, a pBr of 1.343, and a temperature of 75.degree. C. by introducing 
the silver nitrate solution employed for grain nucleation at a rate of 
85.3 mL/min and a 2.75 m/L mixed salt solution (1.5% KI, 98.5% NaBr) at a 
rate of 18.7 mL/min. A second growth segment (II) took place over 25 
minutes by continuing precipitation as described for growth segment I, 
except that 2.75 mol/L AgNO.sub.3 was ramped linearly from 18.8 to 50.0 
mL/min and the mixed halide salt was ramped linearly from 21.2 to 53.8 
mL/min. A third growth segment (III) was undertaken for 31 minutes 
employing the same reagents as in growth segment II. The flow rates were 
ramped to 127.5 and 132.2 mL/min, respectively. A fourth growth segment 
(IV) used these terminal flow rates for an additional 1.5 minutes. A final 
growth segment (V) employed a single AgNO.sub.3 jet for 3.25 minutes to 
impart a pure bromide character to the last 5% of the emulsion. 
The emulsion was then cooled to 40.degree. C. and adjusted to a pBr of 
3.378 during ultrafiltration. The pH of the emulsion was adjusted to 5.6. 
The resulting AgIBr tabular grain emulsion contained 1.5 mole % bulk 
iodide, based on total silver, and had a COV of 44 percent. The mean ECD 
of the emulsion grains was 3.29 .mu.m, and the average thickness of the 
grains was 0.103 .mu.m. The average aspect ratio of the tabular grains was 
32. Greater than 90 percent of total grain projected area was accounted 
for by tabular grains. 
Composite Tabular Grain Emulsion CT-6 
A 4 L reaction vessel was charged with one mole of HT-6 and 500 mL of 
distilled water, allowed to equilibrate at 40.degree. C. for 10 minutes 
and then brought to a temperature of 65.degree. C. In a first growth 
segment I the pBr was then raised from 3.681 to 5.261 during the first 3 
minutes of a 13.4 minute segment in which a double jet addition of 0.25N 
AgNO.sub.3 reagent was linearly ramped from 4.1 to 14.1 mL/min while a 
0.4M KI solution was linearly ramped from 4.6 to 8.1 mL/min. 
A second growth segment II followed lasting 14.3 minutes in which the 
silver nitrate was ramped from its final value in segment I to a value of 
28.1 mL/min while the KI reagent flow rate was accelerated to 26.8 mL/min. 
This and a following segment were controlled at a pBr of 5.261. A final 
growth segment III featuring constant flow rates at these terminal values 
was sufficient to confer an overall additional bulk iodide content of 9.2 
mole %, based on total silver forming the composite grains. The iodide 
present consisted essentially of a pure .beta. phase AgI composition. 
Second Epitaxial Phase 
A second epitaxial phase was grown onto the corners of the tabular grains 
contained in samples of emulsions HT-6 and CT-6. 
A 800 mL reaction vessel was charged with 0.5 mole of HT-6 or CT-6. 
Addition of 0.25N AgNO.sub.3 was used to raise the pBr from 3.394 to 4.827 
at 40.degree. C. Sufficient sodium chloride was then added to the reaction 
vessel to bring its concentration to 4 mole %. The emulsion was then dyed 
with one of the spectral sensitizing dyes identified below in an amount 
(0.981 mole) calculated to cover 75% of the emulsion surface area (383.5 
m.sup.2 /Ag mole). A double jet precipitation of 1.0M AgNO.sub.3 and 1.0M 
NaCl at 22.9 mL/min for 1.75 minutes was sufficient to generate AgCl 
epitaxial deposits almost exclusively confined to the corners of the 
tabular grains in an amount totaling 8 mole %, based on total silver. The 
analyzed composition of these deposits in HT-6 emulsion samples was 65% 
AgCl, 30% AgBr and 5% AgI. 
Sensitometric Evaluation 
To each sample receiving the second epitaxial phase as described above were 
added at 40.degree. C. in sequence the following reagents in millimoles 
per silver mole with 5 minute holds between each successive addition: 
1.2335 mmoles of NaSCN, 0.02727 mmole of 
N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0035 mmole of Au(I) 
bis(trimethylthiotriazole), and 2.5 mg of 3-methyl-1,3-benzothiazolium 
iodide. Chemical sensitization was effected by raising the emulsion melt 
containing addenda to 50.degree. C. and holding for 7.5 minutes. 
Subsequently, the melt was cooled to 40.degree. C., and 0.6453 millimole 
of 1-(3-acetamidophenyl)-5-mercaptotetrazole (APMT) was introduced. The 
melt was then prepared for coating. 
Single emulsion layer coatings were formulated containing 10.76 mg/dm.sup.2 
of silver halide, three times that amount of gelatin, and 9.684 
mg/dm.sup.2 of the yellow dye-forming coupler YC-1. The dye-forming 
coupler containing emulsion layer was overcoated with 8.608 gm/dm.sup.2 of 
gelatin and hardened with 1.5 percent by weight of 
bis(vinylsulfonyl)methane. 
Coatings were exposed through a 0-4 density step tablet for 1/50" using a 
Wratten 2B.TM. filter with a 0.6 density inconel filter and a 3000.degree. 
K. color temperature (tungsten filament balance) light source. The Wratten 
2B filter allowed transmission of light having a wavelength longer than 
410 nm. A standard 3.25 min development color negative process (Eastman 
Color Negative.TM.) was used to develop the latent image. 
In Table V the relative log speeds (derived from inertial speeds) of the 
HT-6 and CT-6 emulsions plus AgCl epitaxy host emulsions sensitized with 
varied dyes are compared. 
TABLE V 
______________________________________ 
(&gt;410 nm exposures) 
Dye/ Rel. Log Speed 
Rel. Log Speed 
Red. Potential 
HT-6 + AgCl CT-6 + AgCl 
(volts) epitaxy epitaxy 
______________________________________ 
SS-22/-1.38 106 121 
SS-4 /-1.37 125 133 
SS-1 /-1.36 114 119 
SS-21/-1.23 -- 102 
SS-23/-1.22 133 100 
______________________________________ 
From Table V it is apparent that the presence of the high iodide plates on 
the major faces of the host grains increased the speed of the emulsions 
exposed to light in the wavelength ranges which the dyes were capable of 
absorbing when spectral sensitizing dyes SS-3, SS-4 and SS-22 were 
employed. From this it was concluded that when the spectral sensitizing 
dye has a reduction potential more negative than -1.30 volts (preferably 
more negative than -1.35 volts) the spectral sensitizing dye is capable of 
injecting electrons into the high iodide plates on exposure and a higher 
photographic speed can be expected. In the absence of any spectral 
sensitizing dye the high iodide plates produce a very large speed 
advantage, as demonstrated above in Example 5. 
Example 7 
This example demonstrates that when a spectral sensitizing dye having a 
reduction potential more negative than -1.30 (preferably -1.35) volts is 
employed in combination with a compound having a reduction potential more 
negative than that of the spectral sensitizing dye (preferably having a 
reduction potential more negative than -1.40 volts) and is limited to a 
molar concentration of 35 percent or less, based on the compound and the 
spectral sensitizing dye, a further increase in photographic speed can be 
realized. 
Emulsion CT-6 with AgCl as a second epitaxial phase was prepared, coated 
and processed as in Example 6, except that a preferred spectral 
sensitizing dye SS-5 was employed alone or in combination with one of the 
other dyes shown in Table VI. 
TABLE VI 
______________________________________ 
Spectral Sensitizing 
Oxidation Potential 
Reduction Potential 
Dye (volts) (volts) 
______________________________________ 
SS-23 1.47 -1.22 
SS-22 1.46 -1.38 
SS-5 1.24 -1.4 
SS-2 1.09 -1.76 
______________________________________ 
Dye SS-23 represents a non-preferred spectral sensitizing dye lacking a 
reduction potential more negative than -1.30 volts. Dyes SS-22 and SS-5 
are representative of preferred spectral sensitizing dyes. Dye SS-2 
demonstrates a spectral sensitizing dye having a more negative reduction 
potential than any of the remaining spectral sensitizing dyes. 
Integrated light absorptions as well as minimum densities (Dmin), contrast 
(Gamma) and relative log speeds (Speed) for 365 nm Hg line exposures and 
3000.degree. K. exposures are summarized in Table VII. The integrated 
light absorptions were determined as reported in Examples 1 and 5. The 
3000.degree. K. exposures correspond to those described in Example 6. The 
365 nm Hg line exposures were conducted through a graduated density step 
tablet similarly as the 3000.degree. K. exposures, but no filters were 
employed. 
TABLE VII 
______________________________________ 
Integrated 
Light 
365 Hg Line 3000.degree. K. 
Absorption 
Dmin Gamma Dmin Gamma photons/ 
Dye Speed Speed sec/cm.sup.2 
______________________________________ 
SS-5 0.25 1.02 100 0.27 1.28 100 550.8 .times. 10.sup.10 
SS-23(15%) 
0.49 0.74 75 0.46 0.74 74 526 .times. 10.sup.10 
SS-5(85%) 
SS-22(35%) 
0.24 0.92 98 0.25 0.97 99 334.2 .times. 10.sup.10 
SS-5(65%) 
SS-2(35%) 
0.24 0.72 108 0.25 0.81 111 478.6 .times. 10.sup.10 
SS-5(65%) 
______________________________________ 
From Table VII it is apparent that when spectral sensitizing dye SS-5, 
which is a representative preferred spectral sensitizing dye having a 
reduction potential more negative than -1.30 volts, is combined with a 
minor amount of a spectral sensitizing dye that has a more positive 
reduction potential, SS-23, the result is a loss in photographic speed. 
When SS-5 is combined with a minor amount of another preferred spectral 
sensitizing dye having about the same reduction potential, SS-22, a 
minimal influence on speed is observed. However, when SS-5 is employed in 
combination with a minor amount of SS-2, a spectral sensitizing dye having 
a reduction potential more negative than that of SS-5 and more negative 
than -1.40 volts, the result is a significant increase in photographic 
speed. 
It should be specifically noted that SS-2 used in combination with SS-5 
increased speed, even though overall light absorption was less than that 
obtained with SS-5 alone. Thus, compounds having more negative reduction 
potentials than the preferred spectral sensitizing dyes can improve 
photographic speed, even when displacement of the dye by the compound 
reduces the level of dye absorption. 
Example 8 
Example 7 was repeated, except that the molar ratios of spectral 
sensitizing dyes SS-5 and SS-2 were varied. In these investigations the 
sensitizations also differed from those of Example 7 in that 17% less 
sulfur sensitizer and 12.5% less gold sensitizer were employed while an 
additional 0.250 mole of spectral sensitizing dye or dyes was added after 
the step of holding for 7.5 minutes at 50.degree. C. 
The results are summarized in Table VIII. 
TABLE VIII 
______________________________________ 
Integrated 
Light 
365 Hg Line 3000.degree. K. 
Absorption 
Dmin Gamma Dmin Gamma photons/ 
Dye Speed Speed sec/cm.sup.2 
______________________________________ 
SS-5 0.17 0.99 100 0.17 1.01 100 572.8 .times. 10.sup.10 
SS-2 0.32 0.54 88 0.30 0.57 71 414 .times. 10.sup.10 
SS-5(95%) 
0.16 1.01 102 0.16 0.98 102 562.3 .times. 10.sup.10 
SS-2(5%) 
SS-5(85%) 
0.15 0.90 109 0.16 0.89 107 535.8 .times. 10.sup.10 
SS-2(15%) 
SS-5(75%) 
0.27 0.76 97 0.26 0.80 91 523.6 .times. 10.sup.10 
SS-2(25%) 
______________________________________ 
From Table VIII it is apparent that a speed enhancement can be realized 
with a proportion of SS-2 of only 5 mole percent, based on total spectral 
sensitizing dye. A preferred proportion of dye having a more negative 
reduction potential is up to 20 mole % of the total dye, although a 
proportion of SS-2 of up to 35 mole % is shown to be advantageous in 
Example 7. 
Example 9 
This demonstrates that the addition of a SET dopant to the AgCl epitaxy can 
be relied upon to further increase photographic speed. 
An emulsion was prepared, coated, exposed and processed similar as CT-6, 
except that the sensitization was varied by adding SET-11 during 
deposition of the AgCl epitaxy in the concentrations set out in Table IX 
and the sensitization was varied as follows: Formation of the second 
epitaxial phase spectral sensitizing dye SS-1 was added in the amount of 
0.39 mmole per silver mole. Then to each sample were added at 40.degree. 
C. in sequence the following reagents in millimoles per silver mole with 5 
minute holds between each successive addition: 0.617 mmole of NaSCN, 
0.0355 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0070 mmole 
of Au(I) bis(trimethylthiotriazole), and 2.5 mg of 
3-methyl-1,3-benzothiazolium iodide. Chemical sensitization was effected 
by raising the emulsion melt containing addenda to 50.degree. C. and 
holding for 7.5 minutes. Subsequently, the melt was cooled to 40.degree. 
C., and 0.6453 millimole of 1-(3-acetamidophenyl)-5-mercaptotetrazole 
(APMT) was introduced. The melt was then prepared for coating. 
The results are summarized in Table IX. 
TABLE IX 
______________________________________ 
Dopant Level Relative 
(mppm .SIGMA.Ag) 
Speed Gamma 
______________________________________ 
0 100 0.42 
1.5* 106 0.63 
______________________________________ 
*Introduced in first 25% of AgCl epitaxy 
*Introduced in first 25% of AgCl epitaxy 
The SET-11 dopant increased speed and contrast when incorporated in a 
concentration of 1.5 molar parts per million (mppm), based on total silver 
forming the grains. The local concentration of the dopant within the AgCl 
epitaxy was 18.75 mppm. 
Example 10 
This demonstrates that the addition of a SET dopant to the host tabular 
grains can be relied upon to further increase photographic speed. 
Example 9 was repeated, except that the SET dopant, SET-2, was added only 
during precipitation of the host tabular grains. Dopant addition began 
after precipitation of X% of total silver forming the host tabular grains 
and was terminated when Y% of the total silver had been precipitated. See 
Table X below for actual X and Y values. The local concentration of the 
SET-2 dopant was 250 mppm in all instances. Additionally, the 
concentrations of the chemical sensitizers were varied as follows: 1.851 
mmole of NaSCN, 0.0178 mmole of 
N,N'-dicarboxymethyl-N,N'-dimethylthiourea, and 0.0035 mmole of Au(I) 
bis(trimethylthiotriazole). Spectral sensitization was varied by adding a 
15% SS-2 and 85% SS-5 mixture after holding at 50.degree. C. for 7.5 
minutes. 
The results with and without SET-2 dopant are summarized in Table X. 
TABLE X 
______________________________________ 
X Y Dmin Gamma Rel. Speed 
______________________________________ 
no 0.27 0.94 100 
dopant 
1 30 0.23 0.95 110 
30 60 0.19 0.94 118 
1 60 0.20 0.88 122 
60 90 0.21 0.97 108 
______________________________________ 
From Table X it is apparent that the SET dopant increased photographic 
speed and lowered minimum density. Contrast was also increased, except 
when the amount of SET dopant was doubled by extending dopant introduction 
over the range of from 1 to 60 percent of the silver addition. 
Example 11 
This demonstrates the adsorption and photographic advantages to be realized 
by employing high iodide plates on the major faces of ultrathin (t&lt;0.07 
.mu.m) host tabular grains. 
Ultrathin Host Tabular Grain Emulsion UT-11 
A silver iodobromide host tabular grain emulsion was prepared by first 
charging a reaction vessel with 1.25 g/L of oxidized gelatin, 0.625 g/L 
NaBr, 0.7 mL of a polyethylene glycol surfactant suspended with paraffin 
oil in a naphthenic distillate(NALCO 2341.TM.) and 6 L of distilled water. 
The contents of the reaction vessel were adjusted to a pH of 1.8 at 
45.degree. C. Nucleation occurred during a five second period during which 
1.67 m/L of AgNO.sub.3 and 1.645 mole/L of NaBr and 0.02505 mole/L KI were 
each added at a rate of 110 mL/min. The temperature was then adjusted to 
60.degree. C. and held for nine minutes. An additional 100 g of oxidized 
gelatin were added to the reactor, and the pH was then adjusted to 5.85 
with NaOH. Subsequently 0.098 mole of NaBr was introduced into the 
reaction vessel such that the pBr was brought to 1.84. A further pBr shift 
to 1.517 was produced by the single jet addition of 1.75 mole/L of NaBr at 
61.3 mL/min for 1.5 minutes. The remainder of the emulsion was 
precipitated over a period of 66 minutes using a triple jet. This triple 
jet consisted of 1.60 mole/L of silver nitrate accelerated from 12.5 to 96 
mL/minute, 1.75 mole/L of NaBr accelerated from 13.3 to 95.6 mL/minute, 
and 136.25 g Ag/L of a fine grain AgI Lippmann emulsion accelerated from 
12.5 to 96 mL/min. The emulsion was then cooled to 40.degree. C., 
iso-washed twice and adjusted to a pBr of 3.378 and a pH of 5.6. 
The resulting AgIBr tabular grain emulsion contained 2.5% bulk iodide and 
had a grain size COV of 52 percent. The mean ECD of the emulsion grains 
was 2.9 .mu.m, and the mean thickness of the grains was 46 nm. The average 
aspect ratio of the tabular grains was 63. Greater than 90 percent of 
total grain projected area was accounted for by tabular grains. 
Host Tabular Grain Emulsion HT-2 
This emulsion, described above, was employed to compare the absorption of 
the ultrathin tabular grain emulsion UT/HT-11 with a thicker host tabular 
grain emulsion. 
UT-11+AgI.sub.36 Br.sub.64 (9.2M % I) 
Silver iodobromide was precipitated on the major faces of a sample of the 
ultrathin tabular grains of UT/HT-11 in amount sufficient to provide an 
additional 9.2 mole % iodide. 
UT-11+AgI(9.2M % I) 
A high iodide phase was deposited on the major faces of a sample of the 
ultratin tabular grains of UT/HT-11 using the procedure used for the 
preparation of CT-2, but with the amount of additional AgI precipitated 
adjusted to 9.2M %, based on total silver. 
UT-11+AgI(40M % I) 
A high iodide phase was deposited on the major faces of a sample of the 
ultratin tabular grains of UT/HT-11 using the procedure used for the 
preparation of CT-2, but with the amount of additional AgI precipitated 
adjusted to 40M %, based on total silver. 
UT-11+AgI(55M % I) 
A high iodide phase was deposited on the major faces of a sample of the 
ultratin tabular grains of UT/HT-11 using the procedure used for the 
preparation of CT-2, but with the amount of additional AgI precipitated 
adjusted to 55M %, based on total silver. 
Light Absorption Analysis 
A sample of each of the emulsions above was coated at 10.76 mg/dm.sup.2 
silver with an equal volume of gelatin on a cellulose acetate photographic 
film support with an antihalation backing layer. The emulsion layer was 
overcoated with 21.53 mg/dm.sup.2 of gelatin containing 1.5 percent, by 
weight, based on total gelatin, of bis(vinylsulfonyl)methane hardener. 
Light absorption was determined as described above in Example 2. The 
results are shown below in Table XI. 
TABLE XI 
______________________________________ 
Emulsion Integrated Light 
Sample Absorption photons/sec/cm.sup.2 
______________________________________ 
HT-2 294 .times. 10.sup.10 
UT-11 317 .times. 10.sup.10 
UT-11 + AgI.sub.36 Br.sub.64 (9.2 M% I) 
857 .times. 10.sup.10 
UT-11 + AgI(9.2 M% I) 
966 .times. 10.sup.10 
UT-11 + AgI(40 M% I) 
1545 .times. 10.sup.10 
UT-11 + AgI(55 M% I) 
1778 .times. 10.sup.10 
______________________________________ 
Table XI demonstrates that the ultrathin tabular grains (UT-11) even 
without further iodide addition demonstrated higher absorptions than the 
host tabular grains HT-2, even though HT-2 contained a higher percentage 
of iodide than UT-11. When AgIBr containing a near-saturation level of 
iodide was deposited on the UT-11 tabular grains, absorption was increased 
markedly, but not to as great an extent as when the same amount of iodide 
was deposited as a high iodide phase. 
Table XI further demonstrates that much higher levels of iodide can be 
deposited on the major faces of the host UT-11 tabular grains and that 
absorption is further markedly increased. This demonstrates the 
feasibility increasing the proportion of total silver deposited in the 
high iodide phase to near 60 percent. 
Sensitometric Evaluation 
Sensitometric evaluation of UT-11, UT-11+AgI.sub.36 Br.sub.64 (9.2M % I) 
and UT-11+AgI(9.2M % I) was conducted as described in Example 6 for 
3000.degree. K. exposures, except that sensitization of UT-11 was varied 
to achieve optimization as follows: The addition of 1.54 mmoles of NaSCN 
then 1.336 mmoles of spectral sensitizing dye SS-23 was followed by the 
addition of 0.034 mmole of N,N'-dicarboxymethyl-N,N'-dimethylthiourea and 
then 0.00439 mmole of Ag(I)bis(trimethylthiotriazole). A heat cycle of 7.5 
minutes at 50.degree. C. was employed. The sensitizations of emulsions 
UT-11+AgI.sub.36 Br.sub.64 (9.2M % I) and UT-11+AgI(9.2M % I) were 
identical to that of UT-11, except that the concentration of 
N,N'-dicarboxymethyl-N,N'-dimethylthiourea was reduced to 0.023 mmole. The 
sensitizations of the latter two emulsions were undertaken without further 
optimization, thereby providing a comparison favoring emulsion UT-11. 
The performance of the emulsions is summarized in Table XII. 
TABLE XII 
______________________________________ 
3000.degree. K. 
Emulsion Dmin Gamma Speed 
______________________________________ 
UT-11 0.08 2.31 100 
UT-11 0.1 0.62 38 
+ AgI.sub.36 Br.sub.64 (9.2 M% I) 
UT-11 0.12 0.41 108 
+ AgI(9.2 M% I) 
______________________________________ 
From Table XII it is apparent that applying iodide to the face of the 
ultrathin tabular grains in the form of a AgIBr markedly decreased the 
speed of the emulsion. The reason for this was that the AgIBr could only 
be applied as a continuous shell over the exterior surface of the host 
tabular grains. On the other hand, the same amount of iodide deposited on 
the major faces of the host tabular grains as discrete plates left a large 
percentage of the host tabular grain surface unoccupied. This allowed the 
higher light absorption made possible by the high iodide plates to be 
translated into an increased photographic speed. 
Example 12 
This demonstrates the application of the invention to low (&lt;5) aspect ratio 
tabular grain emulsions. 
Low Aspect Ratio 
Host Tabular Grain Emulsion LHT-12 
An AgIBr low aspect ratio host tabular grain emulsion was prepared by first 
charging a reaction vessel with 1.5 g/L of oxidized gelatin, 0.6267 g/L 
NaBr, 0.15 g/L of the surfactant block copolymer A (see Example 1) and 6 L 
of distilled water. The contents of the reaction vessel were adjusted to a 
pH of 1.85 at 40.degree. C. After a temperature adjustment to 45.degree. 
C. nucleation occurred during a one minute period in which 0.8 mole/L of 
AgNO.sub.3 and 0.84 mole/L of NaBr were each added at a rate of 97.2 
mL/min. The halide excess in the reactor was increased by introducing an 
additional 0.115 mole of NaBr. The temperature was then adjusted to 
60.degree. C. over 9 minutes. A 9 minute ammoniacal digest ensued by the 
addition of 0.153 mole of ammonium sulfate activated by a pH adjustment to 
9.5 by the addition of NaOH. An additional 100 g of oxidized gelatin were 
added to the reactor along with 1 g of block copolymer A, and pH was then 
adjusted to 5.85 with HNO.sub.3. A first growth segment occurred over 5 
minutes during which the AgNO.sub.3 and KBr reagents used for nucleation 
were introduced each at 9 mL/min at a pBr of 1.776. A second growth 
segment occurred over a nine minute period at this pBr and temperature by 
introducing 1.6 mole/L AgNO.sub.3 at a linearly accelerated rate of from 9 
to 19 mL/min and 1.679 mole/L of NaBr at a linearly accelerated rate of 
from 4.7 to 16.9 mL/min. This was followed by a third growth segment of 54 
minutes at an elevated pBr of 2.633 continuing with the same reactants, 
but at linearly accelerated rates of from 20.1 to 80 mL/min for AgNO.sub.3 
and 19.4 to 76.7 mL/min for NaBr. A final growth segment using the same 
reactants lasted 18.5 minutes at a constant flow rate of 80 mL/min. The 
emulsion was then cooled to 40.degree. C., iso-washed twice and adjusted 
to a pBr of 3.378 and a pH of 5.5. 
The resulting AgBr tabular grain emulsion had a grain size COV of 11 
percent. The average ECD of the emulsion grains was 0.78 .mu.m and the 
average thickness of the grains was 0.25 .mu.m. The average aspect ratio 
of the tabular grains was 3. Greater than 90 percent of total grain 
projected area was accounted for by tabular grains. 
Composite Tabular Grain Emulsion CT-12A 
A 4 liter vessel was charged with one mole of host tabular grain emulsion 
and 1200 mL of distilled water, allowed to equilibrate at 40.degree. C. 
for 10 minutes and then brought to a temperature of 65.degree. C. The pBr 
was then raised from 3.681 to 5.261 during the first 3 minutes of a 15 
minute segment in which a double jet addition of 0.25M AgNO.sub.3 reagent 
was introduced at a linearly accelerated rate of from 2.3 to 11.6 mL/min 
while a 0.3M KI solution was introduced at a linearly accelerate rate of 
from 3.3 to 16.5 mL/min. 
A second growth segment at the same pBr followed lasting 15 minutes in 
which the AgNO.sub.3 was ramped from its final value in segment I to a 
value of 23.1 mL/min while the KI reagent flow rate was accelerated to 33 
mL/min. The emulsion was subsequently iso-washed twice. 
An overall bulk iodide content of 8.8 mole percent was found by neutron 
activation analysis. The silver iodide phase formed thin plates on the 
major faces of the host tabular grains. The plates consisted essentially 
of .beta. phase AgI. 
Composite Tabular Grain Emulsion CT-12B 
This emulsion was prepared similarly as CT-12A, except that a higher bulk 
iodide level, 21.2 mole percent, based on total silver, was found by 
neutron activation analysis. The higher iodide content resulted from a 
27.5 minute third growth segment of constant flow rates 23.1 and 33.0 
mL/min for AgNO.sub.3 and KI, respectively. 
Composite Tabular Grain Emulsion CT-12C 
This emulsion was prepared similar as CT-12B, except that a still higher 
bulk iodide level, 32.9 mole percent, based on total silver, was found by 
neutron activation analysis. The higher iodide content resulted from 
extending the third growth segment of CT-12B to 79.5 minutes. 
Light Absorption Analysis 
Two samples of each of the emulsions above, one without spectral 
sensitizing dye and one containing SS-23 at 433.2 mg/Ag mole, were coated 
at 10.76 mg/dm.sup.2 silver with an equal volume of gelatin on a cellulose 
acetate photographic film support with an antihalation backing layer. The 
emulsion layer was overcoated with 21.53 mg/dm.sup.2 of gelatin containing 
1.5 percent, by weight, based on total gelatin, of 
bis(vinylsulfonyl)methane hardener. 
Light absorption was determined as described above in Example 2. The 
results are shown below in Table XIII. 
TABLE XIII 
______________________________________ 
Undyed Integrated 
SS-23 Integrated 
Light Absorption 
Light Absorption 
Emulsion (Iodide M%) 
photons/sec/cm.sup.2 
photons/sec/cm.sup.2 
______________________________________ 
CT-12A (8.8) 671.4 .times. 10.sup.10 
1076 .times. 10.sup.10 
CT-12B (21.2) 981.8 .times. 10.sup.10 
1191.2 .times. 10.sup.10 
CT-12C (32.9) 1111.7 .times. 10.sup.10 
1270.6 .times. 10.sup.10 
______________________________________ 
By comparison with Table II, which demonstrates absorptions, with and 
without SS-23, of 20.6 mole percent iodide on a high aspect ratio tabular 
grain host, it is apparent that the low aspect ratio tabular grain host 
was also effective to produce high levels of light absorption. 
Example 13 
This demonstrates emulsions according to the invention in which the host 
tabular grains are high chloride {100} tabular grains. 
AgICl {100} Tabular Grain Host HT-13 
A silver iodochloride {100} tabular grain emulsion was prepared by charging 
a reaction vessel with 1950 g of oxidized gelatin, 30 g of NaCl, 17.8 g of 
the surfactant S6 (see Example 6) and 45.5 L of distilled water. The 
contents of the reaction vessel were brought to 35.degree. C. Nucleation 
occurred during a 1.28 minute period during which 4.0 mole/L of AgNO.sub.3 
(containing 95.5 mL/L of HgCl.sub.2), hereafter referred to as the 
AgNO.sub.3 solution, and 4.0 mole/L of NaCl, hereafter referred to as the 
salt solution, were reacted at a rate of 1100 mL/min and 1478 mL/min, 
respectively. The pCl was 2.0327. Additional water, 107 L, NaCl (22.26 g) 
and KI (6.54 g) were then introduced into the reaction vessel. 
Subsequently the pCl was brought to 2.3961. A first growth segment (I) 
then occurred over a period of 18 minutes during which the temperature was 
raised to 50.degree. C. and AgNO.sub.3 and salt solutions were double 
jetted at 129.5 and 173.9 mL/min, respectively. A second growth segment 
(II) took place over 20 minutes by continuing precipitation as described 
for growth segment I, except that the temperature was raised to 70.degree. 
C., the pCl was lowered to 1.7914; and the AgNO.sub.3 solution was ramped 
linearly to 194.3 mL/min while the salt solution was parabolically ramped 
from 260.9 to 173.9 mL/min. After a 15 minute hold, a third growth segment 
(III) was undertaken for 38 minutes during which the AgNO.sub.3 solution 
flow rate was linearly ramped from 129.5 to 388.4 mL/min and the salt 
solution flow rate was regulated to maintain the contents of the reactor 
at a pCl of 1.8208. An additional 15 minute ripening period then ensued 
followed by a pCl adjustment to 1.3496. The emulsion was then cooled to 
40.degree. C. and adjusted to a pCl of 2.2622 during ultrafiltration. The 
pH of the emulsion was adjusted to 5.67. 
The resulting AgICl {100} tabular grain emulsion contained 0.05M % iodide, 
based on total silver. The ECD of the emulsion grains was 2.59 .mu.m, and 
the average thickness of the grains was 0.143 .mu.m. The average aspect 
ratio of the tabular grains was 18. 
Composite Tabular Grain Emulsion CT-13A 
A 4 L reaction vessel was charged with one mole of the HT-13 emulsion, 
allowed to equilibrate at 40.degree. C. for 5 minutes and then brought to 
a temperature of 65.degree. C. The pCl was then raised from 1.5693 to 
4.4322 during the first few minutes of a 15 minute segment in which a 
double jet addition of 0.25N AgNO.sub.3 was introduced at a linearly 
accelerated rate of from 2.3 to 11.6 mL/min while 0.3M KI was introduced 
at a linear accelerated rate of from 3.3 to 16.5 mL/min. A second growth 
segment followed lasting 15 minutes in which the AgNO.sub.3 solution 
addition rate was linearly accelerated from its final flow rate in segment 
I to a value of 23.1 mL/min while the KI solution addition rate was 
linearly accelerated to 33 mL/min. The emulsion was iso-washed twice, 
brought to a pH of 5.6 The iodide deposited on the host tabular grains 
amounted to 7.4M %, based on the total silver forming the composite 
grains. 
Composite Tabular Grain Emulsion CT-13B 
This emulsion was prepared similarly as CT-13A, except that the pCl during 
precipitation was maintained at 1.8978. This emulsion had an analyzed 
iodide content of 9.97M %, based on the total silver forming the composite 
grains. 
Composite Tabular Grain Emulsion CT-13C 
This emulsion was precipitated similarly as CT-13B, except that AgNO.sub.3 
and KI solutions were diluted to one-tenth their concentration and 
introduced for a single growth period of 22 minutes to add only 0.58M % 
iodide, based on total silver. 
Composite Tabular Grain Emulsion CT-13D 
This emulsion was precipitated similarly as emulsion CT-13A, but with pCl 
adjusted to 1.3001 during AgI precipitation and precipitation continued 
until 23.3M % I, based on total silver, had been precipitated. The entire 
exterior surface of the tabular grains was covered with the high iodide 
second phase. 
Light Absorption Analysis 
Samples of each of the emulsions prepared as described above and sensitized 
as described below and corresponding samples sensitized without spectral 
sensitizing dye SS-23 were coated at 10.76 mg/dm.sup.2 silver with an 
equal volume of gelatin on a cellulose acetate photographic film support 
with an antihalation backing layer. The emulsion layer was overcoated with 
21.53 mg/dm.sup.2 of gelatin containing 1.5 percent, by weight, based on 
total gelatin, of bis(vinylsulfonyl)methane hardener. 
Light absorption was determined as described above in Example 2. The 
results are shown below in Table XIV. 
TABLE XIV 
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Emulsion Undyed Integrated 
SS-23 Integrated 
(2nd phase M% I) 
Light Absorption 
Light Absorption 
[2nd phase pCl] 
photons/sec/cm.sup.2 
photons/sec/cm.sup.2 
______________________________________ 
HT-13 276.1 .times. 10.sup.10 
411.0 .times. 10.sup.10 
CT-13A(7.4) 
[4.4322] 338.8 .times. 10.sup.10 
432.5 .times. 10.sup.10 
CT-13B(10) 
[1.8978] 347.5 .times. 10.sup.10 
470.0 .times. 10.sup.10 
CT-13C(0.58) 
[1.8978] 287.7 .times. 10.sup.10 
567.5 .times. 10.sup.10 
CT-13D(23.2) 
[4.4322] 533.3 .times. 10.sup.10 
510.5 .times. 10.sup.10 
______________________________________ 
Each of the composite tabular grain emulsions exhibited a higher absorption 
than the host tabular grain emulsion, with or without SS-23 present. 
Although the highest level of absorption without dye was realized by 
CT-13D, entirely covering the outer surface of the host tabular grains 
with AgI made this a poor emulsion in terms of sensitivity, as has been 
demonstrated in previous examples (see ST-5, Example 5). 
In comparing the remaining composite tabular grain emulsions CT-13A, CT-13B 
and CT-13C, the highest level of absorption with dye present was achieved 
when the second phase contained only 0.58M % I. This was attributed a 
clear preference of spectral sensitizing dye SS-23 for aggregation with a 
minimum level of iodide present. This result is believed to be a function 
of the particular dye chosen. A different result would be expected with a 
different choice of spectral sensitizing dye. From a comparison of CT-13A 
and CT-13B it is believed that forming the second phase under conditions 
that result in minimum chloride inclusions in the second phase (that is, 
at a minimum chloride ion solubility pCl of .apprxeq.1.9) is important to 
enhancing light absorption. AgI can contain up to 9M % Cl at saturation. 
It is believed that chloride inclusion in AgI reduces its light 
absorption. 
Sensitometric Evaluation 
To a sample of each composite tabular grain emulsion were added at 
40.degree. C. in sequence the following reagents in millimoles per silver 
mole with 5 minute holds between each successive addition: 1.54 mmoles of 
NaSCN, 0.65 mmole of SS-23, 0.011 mmole of 
N,N'-dicarboxymethyl-N,N'-dimethylthiourea, 0.0022 mmole of Au(I) 
bis(trimethylthiotriazole), and 2.5 mg of 3-methyl-1,3-benzothiazolium 
iodide. Chemical sensitization was effected by raising the emulsion melt 
containing addenda to 50.degree. C. and holding for 7.5 minutes. 
Subsequently, the melt was cooled to 40.degree. C., and then prepared for 
coating. 
Single emulsion layer coatings were formulated containing 10.76 mg/dm.sup.2 
of silver halide, 16.14 mg/dm.sup.2 of gelatin, and 9.684 mg/dm.sup.2 of 
the yellow dye-forming coupler YC-1. The dye-forming coupler containing 
emulsion layer also contained 1.75 g/Ag mole 
4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene and was overcoated with 8.608 
gm/dm.sup.2 of gelatin and hardened with 1.5 percent by weight of 
bis(vinylsulfonyl)methane. 
Coatings were exposed through a 0-4 density step tablet for 1/50" using a 
Wratten 2B.TM. filter with a 0.6 density inconel filter and a 3200.degree. 
K. color temperature (tungsten filament balance) light source. The Wratten 
2B filter allowed transmission of light having a wavelength longer than 
410 nm. A standard 3.25 min development color negative process (Eastman 
Color Negative.TM.) was used to develop the latent image. 
The results are summarized in Table XV. 
TABLE XV 
______________________________________ 
Emulsion (2nd phase M% I) Relative 
[2nd phase pCl] Dmin Gamma Speed 
______________________________________ 
HT-13 0.73 1.58 100 
CT-13A(7.4) 
[4.4322] 0.57 0.74 160 
CT-13B(10) 
[1.8978] 0.16 1.14 126 
CT-13C(0.58) 
[1.8978] 0.31 2.33 147 
______________________________________ 
CT-13D is not shown in Table XV, since covering the entire outer surface of 
the host tabular grains resulted in extremely low speed, attributable to 
development inhibition by iodide. Each of the composite tabular grain 
emulsions CT-13A, CT-13B and CT-13C satisfying the requirements of the 
invention showed a lower minimum density and a higher speed than the host 
tabular grain emulsion. This clearly demonstrates two of the photographic 
advantages that can be realized when the host tabular grains are high 
chloride {100} tabular grains.