Infrared transparent selenide glasses

A selenide glass with improved mechanical and optical properties such as ended transmission in the infrared region of radiation having wavelengths beyond 15 microns; Tg in the region of 363.degree.-394.degree. C.; and thermal stability of 85.degree.-145.degree. C. based on the difference between T.sub.g and T.sub.x, comprising, on mol basis, 20-70% germanium selenide, 0.5-25% gallium selenide, indium selenide or mixtures thereof; and 5-50% of at least one alkaline earth in selenide form is described. A process for improving mechanical and optical properties of a selenide glass based on germanium selenide comprises the steps of mixing glass components, including a modifier in elemental or selenide form; melting the glass components to form a molten mixture; cooling the molten glass mixture to a solid state; annealing the solid glass; and cooling the annealed glass to about room temperature is also described. The glass components can be in elemental form or in the form of selenides, and if in elemental form, then sufficient amount of selenium is added to form selenides of the glass components.

FIELD OF THE INVENTION 
This invention relates to infrared transparent selenide glasses with 
intermediate compounds, modifiers and, optionally rare earth dopants that 
can have an infrared fluorescent, super fluorescent or lasing effect. The 
invention also relates to an improved process for forming these new 
selenide glasses. 
BACKGROUND OF THE INVENTION 
Infrared transmitting materials are known and comprise a variety of 
different materials including crystalline halides, silica and fluoride 
glasses, and chalcogenide glasses. Crystalline halides undergo plastic 
deformation and are hygroscopic, requiring cumbersome containment 
apparatus for IR systems applications. Laser glasses have been developed 
as host materials for rare earth ions but mainly for applications 
operating at wavelengths less than 3 microns. Silicate and fluoride 
glasses have been developed as optical fiber amplifiers but are limited by 
their high phonon energies relative to chalcogenide glasses. It is widely 
recognized than longer emission lifetimes and hence, efficiencies, are 
achieved with lower phonon energy host materials for rare earth ions. The 
class of chalcogenide glasses includes sulfides, selenides and tellurides 
respectively with increasing mass and weaker bonding strength. With 
increasing mass and lower bonding energy the glasses transmit to longer 
wavelengths due to the lower phonon energies. Sulfide glasses are well 
known and Harbison et al. in U.S. Pat. No. 5,599,751, herein incorporated 
by reference, describe an infrared transmitting germanium sulfide glass 
that would tolerate the addition of rare earth ions in the glass. 
Selenide glasses have been based upon As--Se and/or Ge--Se compositions. 
Glasses based upon As--Se lack the ability to dissolve rare earth ions. 
Martin in U.S. Pat. No. 4,942,144 teaches that chalcogenide, IR 
transmitting glasses can be made with the following formula: 
EQU MX+M'.sub.2 X.sub.3 +SiX.sub.2 
where M represents a metal selected from calcium, strontium, barium, zinc 
and lead. M' is the metal used to form network bridging, and represents 
aluminum or gallium and X representing S, Se or Te. A major problem with 
these glasses is that SiS.sub.2 or SiSe.sub.2 is highly hygroscopic and 
therefore the glasses are unstable in air. 
Krolla et al in U.S. Pat. No. 4,704,371 teaches using a germanium selenide 
with an alkaline earth modifier as a dopant. The patent teaches that the 
doping with the alkaline earth metals should be in the 0.05 to 1.0 atom 
percent range to remove oxide--hydroxide impurities and the doping does 
not change the properties of the glass. 
SUMMARY AND OBJECTS OF THE INVENTION 
It is an object of this invention to provide a selenide glass that has 
infrared transmission beyond 15 microns and good transmission in the 2 to 
12 micron range. 
Another object of this invention is to provide a selenide glass with 
improved solubility for rare earth ions in the selenide glass. 
Another object of the invention is a gallium and indium containing selenide 
glass with a higher T.sub.g, better stability in terms of the difference 
between T.sub.x and T.sub.g and a longer wavelength light transmitting 
range when compared with known gallium and indium containing selenide 
glasses. 
Another object of this invention is a process for improving the physical 
and optical properties of selenide glasses. 
These and other objects of the invention are attained by a germanium 
selenide glass modified with an alkaline earth modifier and an indium 
selenide, gallium selenide or mixture thereof. The selenide glasses will 
typically have at least about 5 mol % of an alkaline earth selenide 
modifier, from 20 to 70 mol % of germanium selenide, 15 to 25 mol % of a 
gallium selenide or indium selenide or mixtures thereof and, optionally or 
optically active rare earths. Sulfur can also be substituted for up to 50 
mol % of the selenium. The addition of heavy metals strontium, barium and 
indium to rare earth doped selenides glasses GeSe.sub.2 and Ga.sub.2 
Se.sub.3, have produced a new family of selenide glasses with higher glass 
transition temperatures (T.sub.g), greater thermal stability (T.sub.x 
-T.sub.g): where T.sub.x is the crystallization temperature, and longer 
wavelength infrared (IR) transmission than the glasses made from 
GeSe.sub.2 and Ga.sub.2 Se.sub.3. The new glass compositions provide an 
excellent host material for rare earth ions whose emissions can produce 
optical sources of IR light. These glasses, which can accommodate large 
quantities of rare earth ions result in increased emission efficiency and 
therefore more intense long wavelength fluorescence than other known 
infrared glasses. 
These and other objects of the invention are obtained by a process for 
improving the physical and optical properties of a selenide glass by 
batching the glass components with one or more of the modifiers and 
melting the mixture under carefully controlled conditions.

The invention having been generally described, the following example is 
given as particular embodiments of the invention to demonstrate the 
practice and advantages thereof. It is understood that the example is 
given by way of illustration and is not intended to limit in any manner 
the specification or the claims that follow. 
EXAMPLE 
A silica glass ampoule with a wall thickness of 3 mm containing a vitreous 
carbon crucible is first washed with dilute nitric acid and dried in an 
oven at about 110.degree. C. The open end of the ampoule and crucible 
assembly are then hooked up to a vacuum system consisting of a 
turbomolecular and mechanical pump. While evacuating the assembly it is 
heated using an oxygen-methane torch for about on hour or until the vacuum 
pressure no longer increases indicating the removal of moisture or any 
other physically adsorbed gasses. The evacuated ampoule assembly 
(1.times.10.sup.-6 torr) is then sealed off with a valve and brought into 
a drybox containing less than 1 parts per million (PPM) water and oxygen. 
In the drybox individual elements are weighed to provide the following 
glass composition: (BaSe).sub.32.5 (In.sub.2 Se.sub.3).sub.6.25 (Ga.sub.2 
Se.sub.3).sub.6.25 (GeSe.sub.2).sub.55.0. The purity of the elements based 
upon weight percent were Ba-99.9, In-99.99999, Ga-99.99999, Ge-99.9999, 
and Se-99.995. The selenium was further purified by distilling it to 
remove water, oxides and carbon. The total weight of the batch is 100 
grams with an additional one percent by weight selenium (1 gram) added to 
provide for volatilization losses during melting. The batch is mixed 
together and loaded into the vitreous carbon crucible within the ampoule. 
Using the vacuum valve assembly the ampoule is again sealed, removed from 
the drybox and hooked up to the vacuum system. The assembly is evacuated 
for about an hour and then the silica ampoule is sealed off with an 
oxygen-methane torch. The sealed ampoule is then placed into a furnace and 
ramped at 1.degree. C./min to 900.degree. C., held at this temperature for 
18 hours and then quenched into water. After quenching, the glass is 
annealed at 390.degree. C. for one hour and cooled at 1.degree. C./min to 
room temperature. The resulting selenide glass had T.sub.g of 390.degree. 
C. and T.sub.x of 520.degree. C. 
Samples of the selenide glass were prepared in the general manner described 
above with the compositions, T.sub.g and T.sub.x and results of optically 
active rare earth addition reported below in Table 1. Sample 14 
corresponds to the example given above. In Table 1, amounts of the glass 
components are given in mol percent and the glass components were gallium 
selenide (Ga.sub.2 Se.sub.3), germanium selenide (GeSe.sub.2), barium 
selenide (BaSe), strontium selenide (SrSe), and indium selenide (In.sub.2 
Se.sub.3). The rare earths are praseodymium (Pr), neodymium (Nd), 
dysprosium (Dy), erbium (Eb) and ytterbium (Yb). The fluorescent 
transitions, pump wavelength, output wavelength and time for the 
fluorescent lifetimes are also given in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Pump 
Meas 
Time 
Sample 
BaSe 
SrSe 
Ga.sub.2 Se.sub.3 
In.sub.2 Se.sub.3 
GeSe.sub.2 
RE T.sub.g .degree.C. 
T.sub.x .degree.C. 
Transition 
.lambda.(.mu.m) 
.lambda.(.mu.m) 
(.mu.m) 
__________________________________________________________________________ 
#1 35.5 
0 12.5 
0 55.0 
0 395 530 -- -- -- -- 
#2 35.2 
0 6.25 
6.25 
55.0 
0.1% Pr 
363 499 .sup.3 F.sub.3 /.sub.3 F.sub.4- 
-&gt;.sup.3 H.sub.5 
1.57 
2.5 106 
.sup.3 F.sub.3 /.sub.3 F.sub.4- 
&gt;.sup.3 H.sub.4 
1.57 
1.6 106 
.sup.3 H.sub.6- &gt;.sup.3 H.sub.5, 
.sup.3 H.sub.5- &gt;.sup.3 H.sub.4 
1.57 
4.5 500 
#3 32.5 
0 6.25 
6.25 
55.0 
1.0% Pr 
385 525 .sup.3 H.sub.6- &gt;.sup.3 H.sub.5, 
.sup.3 H.sub.5- &gt;.sup.3 H.sub.4 
2.00 
2.7-5.5 
60 
#4 32.5 
0 6.25 
6.25 
55.0 
0.2% Pr 
381 505 -- -- -- -- 
#5 0 32.5 
6.25 
6.25 
55.0 
0.2% Pr 
387 521 -- -- -- -- 
#6 32.5 
0 6.25 
6.25 
55.0 
0.1% Nd 
391 521 -- -- -- -- 
#7 32.5 
0 6.25 
6.25 
55.0 
0.2% Dy 
349 488 .sup.6 H.sub.11/2- &gt;.sup.3 H.sub.13/2 
1.064 
4.3 600 
#8 32.5 
0 6.25 
6.25 
55.0 
0.2% Tb 
394 499 .sup.7 F.sub.5- &gt;.sup.7 F.sub.6 
2.0 2.7-5.5 
&lt;30 
#9 325 
0 6.25 
6.25 
55.0 
0.1% Er 
391 511 .sup.6 H.sub.11/2- &gt;.sup.3 H.sub.13/2 
1.064 
4.3 520 
0.1% Dy 
#10 32.5 
0 6.25 
6.25 
55.0 
0.1% Yb 
384 488 .sup.6 H.sub.11/2- &gt;.sup.3 H.sub.13/2 
1.064 
2.7-5.5 
70 
0.1% Dy 
#11 32.5 
0 6.25 
6.25 
55.0 
10.0% Dy 
399 520 .sup.6 H.sub.11/2- &gt;.sup.3 H.sub.13/2 
1.064 
4.3 .about.5 
#12 37.5 
0 7.5 0 55.0 
0.2% Dy 
384 489 -- -- -- -- 
#13 32.5 
0 0 12.5 
55.0 
0.2% Dy 
370 488 -- -- -- -- 
#14 32.5 
0 6.25 
6.25 
55.0 
0 390 520 -- -- -- -- 
__________________________________________________________________________ 
Many modifications and variations of the present invention are possible in 
light of the above disclosed techniques. It is therefore to be understood 
that within the scope of the appended claims that the invention may be 
practiced otherwise than as specifically described.