Ga- and/or In-containing AsGe sulfide glasses

Abstract: This invention is directed to the production of transparent glasses exhibiting excellent transmission far into the infrared region of the electromagnetic radiation spectrum, said glasses consisting essentially, expressed in terms of mole percent on the sulfide basis, of 55-95% GeS₂, 2-40% As₂S₃, 0.01-20% R₂S₃, wherein R is at least one trivalent network forming cation selected from the group consisting of gallium and indium, 0-10% MS x , wherein M is at least one modifying cation selected from the group consisting of aluminum, barium, cadmium, calcium, lead, lithium, mercury, potassium, silver, sodium, strontium, thallium, tin, yttrium, and a rare earth metal of the lanthanide series, 0-20% total of at least one halide selected from the group consisting of chloride and fluoride, 0-5% total selenide, and wherein the sulfur and/or selenium content can vary between 85-125% of the stoichiometric value. The difference between the temperature of the onset of crystallization and the transition temperature of the glasses is at least 150°C and commonly will be greater than 200°C.

Description: Background of the Invention U. S. Patent No. 5,240,885 (Aitken et al.) describes the preparation of rare earth metal-doped cadmium halide glasses, which glasses transmit radiation well into the infrared portion of the electromagnetic radiation spectrum due to their low phonon energy. That capability commended their utility for the fabrication of efficient lasers, amplifiers, and upconverters when doped with the appropriate rare earth metals. Because metal-sulfur bonds are generally weaker than metal-oxygen bonds, sulfide glasses exhibit much lower phonon energies than oxide glasses and, therefore, transmit radiation much further into the infrared region of the electromagnetic radiation spectrum. Accordingly, sulfide glasses were seen to have the potential of being excellent host materials of rare earth metals for applications such as those listed above requiring efficient radiative emission. Unfortunately, however, many sulfide glasses are black and, consequently, are unsuitable for some of the above applications inasmuch as such a host glass would tend to absorb the pump radiation instead of the rare earth metal dopant. One of the best known sulfide glasses, viz., arsenic sulfide, is transparent to radiation in the long wavelength range of the visible portion of the radiation spectrum as well as far into the infrared region and, hence, would appear to be a suitable host glass for rare earth metals. Nevertheless, rare earth metals have been found to be relatively insoluble in arsenic sulfide glasses, and it has proven to be difficult to dope those glasses with enough rare earth metal for sufficient pump power absorption. Rare earth metals are known to be very soluble in most oxide glasses and their apparent insolubility in arsenic sulfide glasses has be conjectured to be due to the gross structural dissimilarity existing between the latter and oxide glasses. Arsenic sulfide glasses are believed to consist of long chains and layers of covalently bonded pyramidal AsS 3 groups, whereas oxide glasses typically comprise a three-dimensional network of relatively ionically bonded MO 4 tetrahedra, where M is a so-called network-forming metal such as silicon, phosphorus, aluminum, boron etc. Rare earth metals are readily accommodated in these ionic network structures where they can compensate charge imbalances that arise from the presence of two or more network-forming metals, e.g., aluminum and silicon in aluminosilicate glasses --energetically similar sites may not exist in the two-dimensional covalent structures typical of arsenic sulfide and related glasses. JP-A-3008742 (as interpreted by the PAJ abstract) describes sulfide glasses comprising GeS 2 and As 2 S 3 , a part of the sulfur being substituted by selenium. US-A-3,214,241 describes sulfide glasses comprising germanium sulfide and sulfur and optionally other glass forming sulfides such as arsenic, gallium or indium sulfide. Also of general interest are US Patents 4,612,294 and 4,704,371. A particular problem is the difference between the temperature of the onset of crystallization (T x ) and the glass transition temperature (T g ). It is an objective of the invention to discover new transparent glass compositions exhibiting even greater thermal stability, while retaining the basic properties of gallium sulfide-containing glasses, so as to assure avoidance of devitrification when forming the glasses into fibers. That objective can be secured in glasses having compositions consisting principally of arsenic, germanium, and sulfur with small, but necessary inclusions of gallium and/or indium. Minor amounts of other glass modifiers such as Al, Sb, Li, Na, K, Ca, Sr, Ba, Ag, Hg, Tl, Cd, Sn, Pb, Y, and a rare earth metal of the lanthanide series may optionally be incorporated to adjust such properties as thermal expansion, refractive index, and thermal stability. The present invention is founded upon two fundamental features: first, the recognition that increased concentrations of As in gallium germanium sulfide glasses impart enhanced thermal stability to those glasses: and second, the recognition that the presence of some Ga and/or In is necessary to assure that the fluorescence at 1300 nm is not quenched as evaluated by measurement of the fluorescence lifetime (τ). The compositions of the subject inventive glasses consist essentially, expressed in terms of mole percent on the sulfide basis, of about 55-95% GeS 2 , 2-40% As 2 S 3 , 0.01-20% R 2 S 3 , wherein R is at least one trivalent network forming cation selected from the group consisting of gallium and indium, 0-10% MS x , wherein M is at least one modifying cation selected from the group consisting of aluminum, antimony, barium, cadmium, calcium, lead, lithium, mercury, potassium, silver, sodium, strontium, thallium, tin, yttrium, and a rare earth metal of the lanthanide series, 0-20% total chloride and/or fluoride, 0-5% total selenide, and wherein the sulfur and/or selenium content can vary between 85-125% of the stoichiometric value. When glasses having compositions encompassed within the above ranges are doped with Pr 3+ ions in an amount equivalent to at least 0.005 mole percent Pr 2 S 3 , they exhibit a τ value of at least about 300 µsec. Pr 3+ ions in much larger concentrations are operable, but an amount equivalent to about 0.5 mole percent Pr 2 S 3 has been considered to comprise a practical maximum. Brief Description of the Drawings FIGURE 1 comprises a graph illustrating the improvement in thermal stability imparted to the glass through additions of arsenic to the base composition. FIGURE 2 comprises a graph illustrating the effect on the lifetime of the fluorescence at 1300 nm (τ) exhibited by the base glass doped with Pr 3+ ions resulting from the inclusion of gallium in the glass composition. Description of Preferred Embodiments Table I reports a group of glass compositions, expressed in terms of mole percent on the sulfide basis, illustrating the subject inventive glasses. Compositions 12 and 15-18 are comparating examples. The glass compositions were doped with Pr 3+ ions to measure the level of τ. Because the glasses were prepared in the laboratory, the glasses were typically prepared by melting mixtures of the respective elements, although in some cases a given metal was batched as a sulfide. As can be appreciated, however, that practice is expensive and not necessary. The actual batch ingredients can be any materials which, upon melting together with the other batch components, are converted into the desired sulfide in the proper proportions. The batch constituents were compounded, mixed together thoroughly, and sealed into silica or VYCOR® ampoules which had been evacuated to about 1,3-0,13 mPa (10 -5 to 10 -6 Torr. The ampoules were placed into a furnace designed to impart a rocking motion to the batch during melting. After melting the batch for about 1-2 days at 850°-950°C, the melts were quenched in a blast of compressed air to form homogeneous glass rods having diameters of about 7-10 mm and lengths of about 60-70 mm, which rods were annealed at about 325°-425°C. Table I also records the transition temperature (Tg) and the temperature of the onset of crystallization (T x ), expressed in terms of °C, the difference in temperature between those measurements (T x -T g ), and the value of τ, expressed in terms of µsec, of each glass where measured. 1 2 3 4 5 6 Ga 2 S 3 7.73 6.44 6.44 5.18 3.95 3.95 GeS 2 89.27 87.69 87.69 86.18 84.72 84.72 As 2 S 3 2.97 5.84 5.84 8.62 11.31 11.31 Pr 2 S 3 0.02 0.02 0.02 0.02 0.02 0.02 Excess S -- 112.4 -- -- 103.9 -- T g 424 323 387 376 324 346 T x 566 515 558 563 545 576 T x -T g 142 192 171 186 220 231 τ 336 -- -- -- 340 340 7 8 9 10 11 12 Ga 2 S 3 2.78 3.33 0.83 1.67 -- 12.67 In 2 S 3 -- -- -- -- 0.83 -- GeS 2 83.31 66.65 83.31 83.31 83.31 87.30 As 2 S 3 13.88 29.99 15.83 15.00 15.83 -- Pr 2 S 3 0.02 0.03 0.03 0.03 0.03 0.03 Excess S -- 106.1 -- -- -- -- T g 341 273 348 340 348 422 T x 602 >517 615 630 618 544 T x -T g 261 >245 267 290 274 122 τ 366 303 351 -- 315 354 13 14 15 16 17 18 In 2 S 3 1.67 2.50 -- -- -- -- Al 2 S 3 -- -- 0.83 1.67 2.50 -- GeS 2 83.31 83.31 83.31 83.31 83.31 83.31 As 2 S 3 15.00 14.17 15.83 15.00 14.17 16.67 Pr 2 S 3 0.03 0.03 0.03 0.03 0.03 0.03 T g 345 355 349 347 312 336 T x 600 615 613 602 614 628 T x -T g 255 259 264 256 302 292 τ 312 300 0 0 0 0 Table II recites the same glass compositions, but expressed in terms of atomic percent. 1 2 3 4 5 6 Ga 4.81 3.67 3.97 3.16 2.33 2.39 Ge 27.77 24.99 27.02 6.31 24.99 25.63 As 1.85 3.33 3.60 5.26 6.67 6.84 S 65.55 68.0 65.40 65.26 66.0 65.13 Pr 0.015 0.014 0.015 .015 0.015 0.015 7 8 9 10 11 12 Ga 1.67 1.75 0.50 1.00 -- 7.79 In -- -- -- -- 0.50 -- Ge 24.99 17.49 24.99 24.99 24.99 26.83 As 8.33 15.74 9.50 9.00 9.50 -- S 65.00 65.00 65.00 65.00 65.00 65.37 Pr 0.015 0.015 0.015 0.015 0.015 0.015 13 14 15 16 17 18 In 1.00 1.50 -- -- -- -- Al -- -- 0.50 1.00 1.50 -- Ge 24.99 24.99 24.99 24.99 24.99 24.99 As 9.00 8.50 9.50 9.00 8.50 10.00 S 64.99 65.00 65.00 64.99 65.00 65.00 Pr 0.015 0.015 0.015 0.015 0.015 0.015 It will be appreciated that the above-described procedures represent laboratory practice only. That is, the batches for the inventive glasses can be melted in large commercial glass melting units and the resulting melts formed into desired glass shapes utilizing commercial glass forming techniques and equipment. It is only necessary that the batch materials be heated to a sufficiently high temperature for an adequate period of time to secure a homogeneous melt, and that melt thereafter cooled and simultaneously shaped into a body of a desired configuration at a sufficiently rapid rate to avoid the development of devitrification. The thermal stabilizing effect of As is illustrated in FIGURE 1 wherein T x -T g values are plotted as a function of the As content of several arsenic gallium germanium sulfide glasses. Laboratory experience has demonstrated that this stabilizing effect of As holds for both stoichiometric glasses and glasses containing excess sulfur. In both series of glasses, As essentially replaces Ga while maintaining the Ge content (in terms of atomic percent) at an approximately constant value. It is readily apparent from an examination of FIGURE 1 that glass compositions containing about 2 atomic percent As demonstrate T x -T g values of about 150°C and at somewhat more than about 5% As exhibit thermal stabilities in excess of 200°C, which value constitutes about the maximum limit for the barium-stabilized gallium germanium sulfide glasses disclosed in US-A-5 392 376. In contrast, As-free Example 12 offers a T x -T g value no greater than about 120°C. Example 7, containing 8.33 atomic percent As, exhibits a T x -T g value of about 260°C. Based upon extrapolated viscosity data for related arsenic sulfide and germanium-rich sulfide glasses, it has been estimated that one could reheat such a glass to a viscosity as low as 100 MPa (10 3 poise) without crystallization. Inasmuch as the preferred glass viscosities for drawing fiber via a redraw process reside in the range of 10 4 -10 6 MPa (10 5 -10 7 poise), a glass such as Example 7 ought to demonstrate more than adequate thermal stability to allow fiber fabrication via a preform redraw process. The need for incorporating some gallium and/or indium into the composition of the subject inventive glasses is illustrated through an inspection of FIGURE 2, wherein the lifetime of the fluorescence of the glass at a wavelength of 1300 nm imparted by the Pr 3+ doping (τ) is plotted as a function of the gallium content of arsenic gallium germanium sulfide glass. The glass compositions plotted in FIGURE 2 are the same as those of the stoichiometric series pictured in FIGURE 1. The data make clear that the τ for these glasses remains relatively constant at a value of about 350 µsec, provided that the glass composition contains gallium, the minimum effective concentration thereof being slightly in excess of that of the active rare earth dopant. Thus, for glasses doped with 0.02% Pr, the minimum effective gallium and/or indium concentration is about 0.03 atomic percent. For binary arsenic germanium sulfide glasses containing no gallium, τ is essentially zero and the fluorescence at 1300 nm is essentially quenched, as is illustrated in Example 18. It has been hypothesized that the presence of gallium and/or the analogous trivalent network forming cation In, creates relatively underbonded sulfur sites in these glasses. These underbonded sulfur ions, in turn, provide suitable structural sites for the incorporation of modifying cations, in this case those of the rare earth metal Pr. It has been assumed that gallium and/or indium is randomly distributed throughout the inventive glasses, thereby providing a mechanism for the uniform dispersal of the rare earth dopant and, consequently, avoiding the well recognized phenomenon of concentration quenching. Whereas aluminum is disclosed in US-A-5 392 376 to be a satisfactory network forming cation, laboratory experience has demonstrated that aluminum, unlike gallium and indium, is ineffective in avoiding fluorescence quenching in the present inventive glasses, as is illustrated in Example 15, 16, and 17. Therefore, whereas aluminum may be included as an optional modifier, where the avoidance of fluorescence quenching is desired, gallium and/or indium will be present. Based on an overall balance of properties,, the preferred inventive composition ranges consist essentially, expressed in terms of mole percent on the sulfide basis, of 60-95% GeS 2 , 5-30% As 2 S 3 , 0.1-15% R 2 S 3 , wherein R is at least one trivalent network forming cation selected from the group consisting of Ga and In, 0-10% MS x , wherein M is at least one modifying cation selected from the group consisting of aluminum, barium, cadmium, calcium, lead, lithium, mercury, potassium, silver, sodium, strontium, thallium, tin, yttrium, and a rare earth metal of the lanthanide series, 0-10% total chloride and/or fluoride, 0-3% total selenide and wherein the sulfur and/or selenium content can vary between 90-120% of the stoichiometric value. Example 9 constitutes the most preferred embodiment of the invention.

Claims: A transparent glass exhibiting excellent transmission far into the infrared region of the electromagnetic radiation spectrum consisting essentially, expressed in terms of mole percent on the sulfide basis, of 55-95% GeS 2 , 2-40% As 2 S 3 , 0.01-20% R 2 S 3 , wherein R is at least one trivalent network forming cation selected from the group consisting of gallium and indium, 0-10% MS x , wherein M is at least one modifying cation selected from the group consisting of aluminum, antimony, barium, cadmium, calcium, lead, lithium, mercury, potassium, silver, sodium, strontium, thallium, tin, yttrium, and a rare earth metal of the lanthanide series, 0-20% total of at least one halide consisting of chloride and fluoride, 0-5% total selenide, and wherein the sulfur and/or selenium content can vary between 85-125% of the stoichiometric value. A transparent glass according to claim 1 wherein the difference between the temperature of the onset of crystallization and the transition temperature is at least about 150°C. A transparent glass according to claim 1 or 2 which, when doped with praseodymium in an amount equivalent to at least 0.005% Pr 2 S 3 , exhibits a value of τ of at least about 300 µsec. A transparent glass exhibiting transmission far into the infrared region of the electromagnetic radiation spectrum consisting essentially, expressed in terms of mole percent on the sulfide basis, of 60-95% GeS 2 , 5-30% As 2 S 3 , 0.1-15% R 2 S 3 , wherein R is at least one trivalent network forming cation selected from the group consisting of gallium and indium, 0-10% MS x , wherein M is at least one modifying cation selected from the group consisting of aluminum, barium, cadmium, calcium, lead, lithium, mercury, potassium, silver, sodium, strontium, thallium, tin, yttrium, and a rare earth metal of the lanthanide series, 0-10% total of at least one halide selected from the group consisting of chloride and fluoride, 0-3% total selenide, and wherein the sulfur and/or selenium content can vary between 90-120% of the stoichiometric value. A transparent glass according to claim 4 wherein the difference between the temperature of the onset of crystallization and the transition temperature is greater than 200°C.

Inventors: AITKEN BRUCE GARDINER, NEWHOUSE MARK ANDREW, AITKEN, BRUCE GARDINER, NEWHOUSE, MARK ANDREW
Applicants: CORNING INC, CORNING INCORPORATED
Application year: 1995
Main classification: C03C3
IPC codes: C03C4, C03C3