Small-particle semiconductors in rigid matrices

Nonlinear optical materials comprising porous glass, the pores of which contain a semiconductor material and a polymer.

FIELD OF THE INVENTION 
This invention relates to small-particle semiconductors immobilized in the 
pores of a glass matrix. 
BACKGROUND OF THE INVENTION 
The electronic and optical properties of semiconductors are known to be 
dependent on the size of the semiconductor particles. For example, there 
is a minimum size which the particles must exceed before light absorption 
occurs at the bulk bandgap (i.e., before the polymolecular cluster becomes 
a semiconductor). The onset of bulk semiconducting properties of CdS has 
been estimated to occur for particles whose diameters exceed 60 .ANG.. For 
PbS, the band gap shifts to higher energy as the semiconductor cluster 
size decreases, and eventually converges to the transition energy of the 
first excited state of the PbS molecule; bulk semiconducting properties 
appear for particles whose diameters exceed 150 .ANG.. 
The preparation of small particle semiconductors has been pursued in an 
attempt to exploit the altered electronic and optical properties of these 
materials, relative to bulk semiconductors. However, the preparation of 
extremely small particulate semiconductors is often difficult and seldom 
applicable to a wide range of semiconductor compositions. Some 
semiconductors have been prepared and studied in the gas phase, 
low-temperature matrices, reversed micelles, surfactant vesicles, bilayer 
lipid membranes, clays and as colloid suspensions in solvents containing 
various surfactants to maintain the dispersions. However, the 
small-particle semiconductors prepared by these methods may be 
intrinsically unstable towards aggregation or difficult to incorporate 
into an electronic or optical device. For a useful device, the 
small-particle semiconductor should be incorporated in a solid, preferably 
transparent, medium which can be modified by standard fabrication 
techniques and which can provide an inert or protective environment for 
the reactive semiconductor material. 
In one approach, Cd, S and Se have been added to the standard ingredients 
of normal glass to prepare CdS or CdS.sub.x Se.sub.l-x glass cutoff 
filters by standard melt procedures. Glasses of this type are commercially 
available as long-wavelength-pass optical filters, with several values for 
x. Nonlinear optical effects have been reported in these glasses, but the 
high temperatures and strongly oxidizing conditions used to prepare these 
glasses severely limit the applicability of this technique to other 
semiconductor compositions. 
Mahler, Inorganic Chem., Vol. 27, Number 3, 1988, pp. 435-436, discloses 
additional preparative methods, including metathesis in microemulsion, 
gas-solid reactions on high surface area silica, synthesis within the 
channels of perfluorocarbon sulfonic acid membranes, and generation of 
semiconductor particles within polymer films. In particular, ethylene-15% 
methacrylic acid copolymer (E-MAA) was shown to provide good mechanical 
and optical properties and confer high kinetic stability 
Rajh et al., Chemical Physics Letters, Vol 143, No. 3, 1988, pp. 305-307, 
disclose a method for incorporating quantized particles of colloidal 
semiconductors in transparent silicate glasses by mixing aqueous colloidal 
dispersions of the semiconductor with tetramethoxysilane (TMOS), 
accelerating the polymerization of the silicon alkoxide by the addition of 
NH.sub.4 OH, and drying the resulting gel over a period of months. They 
also disclose a method for producing colloidal glasses by first 
incorporating metal ions, and then, after drying to about one-half the 
original volume, adding the appropriate anions for precipitating the 
particles via gaseous H.sub.2 S or H.sub.2 Se. 
Roy et al., in "Better Ceramics Through Chemistry", Materials Res. Soc. 
Symp., Vol. 32, Ed. J. C. Brinker, D. E. Clark, D. R. Ulrich, Elsevier, 
1984, disclose the inclusion of CdS and AgX (X=Cl, Br, I) in sol-gel 
monoliths by mixing a tetraethoxysilane/ethanol solution with an aqueous 
solution of the heavy metal ion. 
Kuczynski et al., J. Phys. Chem., Vol. 89, 1985, pp. 2720-2722, disclose 
the preparation of CdS in porous Vycor.RTM. glass by soaking cleaned 
porous glass in a CdCl.sub.2 solution, drying the glass under vacuum and 
then immersing the impregnated sample in a sodium sulfide solution. 
The nonlinear optical properties of semiconductors such as degenerate 
four-wave mixing, optical bistability and phase conjugation have been 
reported (Rustagi et al., Optics Letters, Vol. 9, No. 8 (1984), pp. 
344-346, and reference cited therein). Rustagi et al., describe an 
experimental arrangement for measuring degenerate four-wave mixing of 
visible radiation in a borosilicate glass doped with the mixed 
semiconductor, CdS.sub.x Se.sub.l-x. 
The materials provided by the prior art, in which small-particle 
semiconductor particles are imbedded in porous glass or in a polymer film, 
are unsuitable for many electronic and optical applications The porous 
glass compositions are fragile and cannot be machined or polished by the 
techniques used for standard optical glass. In general, the 
polymer/semiconductor compositions lack the thermal stability or high 
optical quality necessary for most electronic and optical applications. 
For example, it is difficult to make high-quality optical fibers from the 
polymer/semiconductor composites. 
It is an object of the present invention to provide a chemically and 
mechanically stable dispersion of small semiconductor particles in an 
optically transparent and mechanically robust rigid matrix. Such materials 
are expected to have faster optical nonlinearity than bulk semiconductors. 
Wavelength tuning could be achieved conveniently by controlling the size 
and concentration of the semiconductor particles. It is a further object 
of the present invention to provide materials for generating third order 
nonlinear optical effects. 
SUMMARY OF THE INVENTION 
These objects are achieved by the present invention, which provides an 
article of manufacture consisting essentially of porous glass, the pores 
of which contain a semiconductor and a polymer. The invention also 
provides materials for generating third order nonlinear optical effects

DETAILED DESCRIPTION OF THE INVENTION 
Suitable porous glasses are amorphous matrix materials with large (10-500 
.ANG.), interconnected pores and channels, which optionally may be filled 
with readily displacable organic or inorganic compounds, e.g., organic 
solvents, water, or inorganic salts. A suitable porous glass is the glass 
sold under the trademark Vycor.RTM. (Corning Glass Works, Corning, N.Y.). 
Suitable porous glasses can also be prepared by the hydrolysis of 
precursor materials, followed by drying of the resulting gel. The pore 
size of glasses derived from sol gels can be controlled by the choice of 
solvents and by the pH of the hydrolysis conditions. Suitable simple 
glasses include SiO.sub.2, GeO.sub.2, TiO.sub.2, Y.sub.2 O.sub.3, and 
ZrO.sub.2. Suitable multicomponent glasses include SiO.sub.2 --BaO, 
SiO.sub.2 --B.sub.2 O.sub.3, SiO.sub.2 --B.sub.2 O.sub.3 --Na.sub.2 O, 
SiO.sub.2 --Na.sub.2 O, SiO.sub.2 --K.sub.2 O, SiO.sub.2 --GeO.sub.2, 
Si--Al.sub.2 O.sub.3, SiO.sub.2 --TiO.sub.2, SiO.sub.2 --Y.sub.2 O.sub.3, 
Al.sub.2 O.sub.3 --GeO.sub.2, Al.sub.2 O.sub.3 --ZrO.sub.2, TiO.sub.2 
--ZrO.sub.2, ZrO.sub.2 --SiO.sub.2, PbO--La.sub.2 O.sub.3 --ZrO.sub.2 
--TiO.sub.2. The preparations of these simple and multicomponent porous 
glasses by sol-gel routes are well known in the art. Porous glasses may 
also be prepared by the gellation of colloidal silica (e.g., Ludox.RTM., 
Du Pont Company) at high pH (pH 9), followed by drying of the resulting 
gel. The preferred glass is SiO.sub.2. 
As used herein, the expression "semiconductor material" refers to material 
that in bulk has electrical conductivity intermediate to that of an 
insulator and a metal, or a band-gap between about 0.2 and 4 volts. 
Semiconductor materials suitable for the present invention are known in 
the art. The semiconductor material may be selected from the group of 
cations consisting of Cd.sup.+2, Zn.sup.+2, Pb.sup.+2, Cu.sup.+2, 
Ga.sup.+3, In.sup.+3, and Ti.sup.+4 in combination with at least one anion 
selected from the group consisting of S.sup.-2, Se.sup.-2, O.sup.-2, 
I.sup.-, P.sup.-3, Sb.sup.-3, and As.sup.-3. Preferably, the semiconductor 
is selected from the group consisting of CdS, CdSe, ZnS, ZnSe, PbS, PbSe, 
PbI.sub.2, TiO.sub.2, In.sub.2 O.sub.3 ; sulfides of gallium, copper or 
indium; selenides of gallium, copper or indium; phosphides of cadmium, 
lead or zinc; and arsenides of cadmium, lead or zinc. The CdS, CdSe, ZnS, 
ZnSe, PbS, PbSe, PbI.sub.2, TiO.sub.2 and In.sub.2 O.sub.3 semiconductors 
listed above exist predominantly as single phase materials, resulting in 
stoichiometries which are invariant and substantially as written (i.e., 
1:1, 1:2 or 2:3). The other semiconductors can exist in more than one 
phase, resulting in stoichiometries which may vary with sample preparation 
and treatment. However, these compounds are commonly identified by the 
dominant stoichiometry: Ga.sub.2 S.sub.3, CuS, In.sub.2 S.sub.3, Ga.sub.2 
Se.sub.3, CuSe, In.sub.2 Se.sub.3, Cd.sub.3 P.sub.2, Pb.sub.3 P.sub.2, 
Zn.sub.3 P.sub.2, Cd.sub.3 As.sub.2, Pb.sub.3 As.sub.2 and Zn.sub.3 
As.sub.2. Hereinafter, these variable stoichiometry semiconductors will 
also be identified by the dominant stoichiometry, as listed above. The 
semiconductor material can contain mixtures or solid solutions derived 
from two or more of the cations listed above. The concentration of the 
semiconductor in the glass/semiconductor/polymer composite is determined 
by the amount of metal salt incorporated in the glass/semiconductor 
composite and ranges from 0.01 to 20 wt. %, based on 
semiconductor-to-glass ratios. The preferred concentration is 0.1 to 5 wt. 
%. 
It has been found that the band-gap energy of the semiconductor particles 
in the porous glass depends on the size of the particles, which can be 
controlled by the method of preparation of the particles and by the time 
and temperature of annealing. In general, the formation of small particles 
is favored by the use of the sol-gel technique (described more fully in 
"Method 1" below) and by brief, low-temperature annealing. Preferably, the 
particles of semiconductor material have a diameter less than about 500 
.ANG., and more preferably less than about 200 .ANG.. The present 
compositions exhibit minimum light-scattering and are useful as optical 
filters and for generating third order nonlinear optical effects. 
The void-filling polymer of these compositions can be derived from the 
polymerization of suitable monomers which have been adsorbed by the porous 
glass either through diffusion or capillary action. Suitable monomers are 
those which are small enough to diffuse into and fill the void spaces of 
the semiconductor-impregnated glass without cracking it or dissolving or 
reacting with the semiconductor particles. Preferable suitable monomers 
are those whose polymerization may be controlled by the use of a suitable 
initiator or by treatment of the monomer-saturated glass with heat, 
radiation, light or electron beams. Specific suitable monomers include 
methacrylate esters; acrylate esters; styrene; vinyl acetate; 
acrylonitrile; methacrylonitrile; vinylidene halides of the formula 
CH.sub.2 .dbd.C(X).sub.2, wherein X is, independently, Cl or F; 
substituted butadienes of the formula CH.sub.2 .dbd.C(R)C(R).dbd.CH.sub.2, 
wherein each R is, independently, C.sub.1 to C.sub.10 alkyl, Cl or F; 
acrylamide derivatives of the formula CH.sub.2 .dbd.CHCON(R).sub.2, 
wherein each R is, independently, H or C.sub.1 to C.sub.10 alkyl; 
methacrylamide derivatives of the formula CH.sub.2 
.dbd.C(CH.sub.3)CON(R).sub.2, wherein each R is, independently, H or 
C.sub.1 to C.sub.10 alkyl; and mixtures thereof. Methacrylate esters and 
styrene are most preferred. Methacrylates which are useful in this 
invention include branched alkyl or n-alkyl esters of C.sub.1-12 alcohols 
and methacrylic acid, for example, methyl and ethyl methacrylate. Methyl 
methacrylate is most preferred. 
Any one of the known class of azo polymerization initiators is suitable 
provided it has solubility in the monomer mixture, does not react with or 
dissolve the semiconductor, and has an appropriate half-life at the 
temperature of polymerization. "Appropriate half-life", as used herein, is 
a half-life of about 1-4 hours. Examples of such initiators include 
without limitation azocumene, 2,2'-azobis(isobutyronitrile), 
2,2'-azobis(2-methyl)butanenitrile, and 2-(t-butylazo)-2-cyanopropane. 
Other soluble non-azo initiators having an appropriate half-life can also 
be used, including, among others, benzoyl peroxide and lauroyl peroxide. 
It is also possible to fill the void-space of the glass/semiconductor 
composite with a high-melting, inert organic material of appropriate 
dimensions by partially immersing the glass/semiconductor composite in the 
melted organic material to wick it into the glass pores. This method will 
also provide a mechanically robust composite that can be machined and 
polished, but it may be less thermally stable and less resistant to 
solvent-leaching than a polymer-filled composite. 
In one embodiment, the article of manufacture of the present invention is 
prepared by adding a pH-controlled solution of silicate glass precursor to 
an aqueous solution of a metal salt, allowing the mixture to form a gel, 
drying the gel to form a metal-ion impregnated glass, exposing the dried 
gel to gaseous H.sub.2 S or H.sub.2 Se to form semiconductor particles in 
the porous glass, filling the remaining void space of the glass with 
monomer and polymerizing the monomer to form the 
glass/polymer/semiconductor composite of the invention. Alternatively, a 
piece of porous glass can be partially immersed in a solution of metal ion 
and then the solution-saturated glass dried to give the metal-ion 
impregnated glass. After the gas treatment described above, the pores are 
filled with monomer, and the monomer polymerized as before. In a third 
variant, the metal-ion impregnated glass is exposed to a solution of the 
appropriate anions to form the semiconductor particles in the porous 
glass. 
Glass/semiconductor composites can be prepared by any of the three routes 
outlined above by omitting the impregnation with monomer and initiator. 
However, these materials, which fall outside the scope of the present 
invention, are very sensitive to both atmospheric moisture and to liquids 
which can easily impregnate the still-open pores, causing clouding and 
cracking. These materials are very fragile and may be polished only by 
hand using dry techniques. They also exhibit poor optical properties. 
In contrast, the glass/semiconductor/polymer composites of the invention 
have mechanical properties similar to normal silicate glasses. They can be 
cut, machined and then polished by standard ceramic wet polishing 
techniques. The optical properties of these composites are comparable to 
those of standard optical glasses. They are unaffected by atmospheric 
moisture or most polar or nonpolar organic solvents. However, prolonged 
exposure to solvents which are known to dissolve the imbedded polymer may 
cause some leaching of the polymer. Similarly, exposure to strong bases 
may leach some of the glass from silicate glass composites. They are 
thermally stable to the decomposition point of the imbedded polymer. 
The glass/semiconductor/polymer composites of the invention can be formed 
in a variety of shapes. Disks, plates, rods, etc. can be fashioned by 
using appropriately shaped forms for the sol-gel, and subsequent cutting 
and polishing the glass/semiconductor/polymer composite. Fibers can also 
be drawn from the sol-gel solution before drying and polymer impregnation. 
Articles of manufacture in accordance with the present invention are useful 
as optical filters such as narrow band-pass, UV cut-off and long 
wavelength pass filters. In general, the glass matrix will be preformed 
into the shape desired for the filter, and the semiconductor material and 
polymer will be added as described above. The glass will then be polished 
to produce a filter with the desired optical properties. The use of such 
filters is well-known in the art. 
The present invention is further described in the following Examples, 
wherein all parts and percentages are by weight and degrees are Celsius. 
Particle sizes in the examples were determined by line-broadening of the 
X-ray diffraction pattern. In some cases, maximum particle sizes were 
estimated from measurements of the band-gap energy. A value for the 
band-gap energy greater than that observed for the bulk material indicates 
the presence of particles having a diameter of less than about 500 .ANG.. 
EXAMPLES 
General Procedures 
Preparation of glass/semiconductor/PMMA composites 
Method 1: Tetraalkylorthosilicate (0.1 mol) is diluted with methanol (0.75 
mol) and/or formamide (0.25 mol). Use of methanol/formamide mixtures leads 
to glasses with larger pores, but the drying times are also significantly 
increased. If desired, the resulting solution may be acidified with nitric 
acid to decrease the pore size of the final glass. This mixture is added 
to a stirred solution containing the desired amount of M(NO.sub.3).sub.x 
(M = Cd, Pb, Zn, Cu, In, Ga, Ti; x = 2, 3) dissolved in distilled water (1 
mol). The resulting mixture is freely fluid at this stage if pH &lt;10 and is 
poured into vials to gel. The vials can be made of any inert material 
(e.g., glass, polyethylene, polystyrene), but polymer or polymer-coated 
vials are preferred because the sol glass sticks to glass vials and may 
shatter as it shrinks. The vial is capped and heated to about 60.degree. 
C. for about 8 hours, or until a stiff clear gel results. The vial is 
uncapped and the gel is dried in the vial in flowing air at about 
60.degree. C. for about 24 hours, or until it shrinks to about 1/2 its 
original volume. The partially dried gel is removed from the vial and 
fully dried in a slow ramp heating process wherein the gel is heated to 
450.degree.-500.degree. C. over 24-48 hours in rapidly flowing (200 
cc/min) oxygen or air. 
A colorless disk of highly porous glass is obtained, except when M = Cu or 
In when the glass is pale blue-green or pale yellow, respectively. The 
glass at this stage is pure silica containing uniformly dispersed metal 
ions (M = Cd, Pb, Zn, Cu, Ga) inside a very porous and fragile framework. 
When M = Ti or In, the metal oxides, TiO.sub.2 and In.sub.2 O.sub.3, 
present in the glass at this stage are themselves semiconductors. 
Typically, the other semiconductor species are prepared from these glasses 
by evacuation of the glass on a high vacuum line followed by exposure to a 
gaseous reagent (H.sub.2 S, H.sub.2 Se, PH.sub.3, AsH.sub.3, SiMe.sub.3 I) 
while heating the glass in a tube furnace. Semiconductor cluster size, and 
hence color of the glass, can be controlled by the temperature of the 
annealing, either during or after reaction with the gaseous reagent. 
To protect the semiconductor clusters and maintain dispersion, the porosity 
of the glass is removed by filling all of the available remaining void 
volume with polymer. This can be done in an inert atmosphere by partially 
immersing the glass/semiconductor composite in methylmethacrylate (MMA) 
containing 1 wt. % VAZO-64.RTM. (Du Pont) to "wick" the monomer up to 
completely fill the pores of the glass. The impregnated glass is removed 
from the MMA/VAZO and heated in an inert atmosphere to about 60.degree. C. 
for about 8 hours, leading to polymerization of the MMA to give PMMA 
throughout the glass pores. The use of other monomers may require the use 
of different initiators or polymerization conditions as described in the 
prior art. 
The dense glass/semiconductor/PMMA composite may be cut and polished as if 
it were a normal piece of silica glass and has no residual porosity. 
Method 2: Porous sol-gel glass prepared as described in Method 1 (except 
omitting the metal nitrate salt) or commercial porous glass is partially 
immersed in a solution (preferably a highly mobile organic solvent) in 
which is dissolved the desired metal ion salt (nitrate or acetate). The 
solution is "wicked up" into the glass until the pores are completely 
filled. The solution-laden glass is then slowly dried using the protocol 
described in Method 1 for drying wet gels. The solvent and anion are 
removed by the drying process to leave metal oxide species in the pores of 
the glass. However, the dispersion of metal species is not as uniform as 
that obtained in Method 1. The dry glass is then exposed to gaseous 
reagents and the void spaces filled with polymer as described in Method 1. 
Nonlinear Optical Properties of the Composites 
A material is said to have third order nonlinearity if its index of 
refraction, n, depends on the intensity of light, I, 
EQU n=n.sub.0 +n.sub.2 I (1) 
or 
EQU .alpha.n=n.sub.2 I (2) 
where n.sub.0 represents the index of refraction at very low light 
intensity and n.sub.2 is the nonlinear refraction coefficient which 
measures the magnitude of the nonlinearity. The commonly used unit for 
n.sub.2 in MKS units is cm.sup.2 /KW. 
Another parameter that is often used to characterize third order 
nonlinearity is X.sup.(3), usually expressed in cgs units as esu. Both 
n.sub.2 and X.sup.(3) are related through the following formula (see 
"Optical Bistability: Controlling light with light", H. M. Gibbs, Academic 
Press, New York, 1987): 
##EQU1## 
The third order nonlinearity of a material can be further categorized as 
resonant and non-resonant. Resonant means the laser wavelength overlaps 
with the absorption band of the material, i.e. the material absorbs the 
light, and nonresonant means otherwise. In the case of resonant 
nonlinearity, the absorption coefficient, .alpha., of the material depends 
on the laser intensity, 
EQU .alpha.=.alpha..sub.0 +.alpha..sub.2 I (4) 
or 
EQU .DELTA..alpha.=.alpha..sub.2 I (5) 
where .alpha..sub.0 represents the absorption coefficient at very low light 
intensity and .alpha..sub.2 is the nonlinear absorption coefficient which 
also measures the magnitude of the nonlinearity. Both .DELTA..alpha. and 
.DELTA.n are related through the Kramers-Kronig relationship: 
##EQU2## 
where c is the speed of light, h is Planck's constant, E is the light 
frequency and P is the Cauchy principal value of the integral: 
##EQU3## 
Experimentally, one can measure either .DELTA..alpha. or .DELTA.n and 
obtain all the third order nonlinearity parameters, .alpha..sub.2, 
n.sub.2, and X.sup.(3) through equations (1)-(7). While for nonresonant 
nonlinearity, either n.sub.2 or X.sup.(3) alone is sufficient for 
characterizing the magnitude of the nonlinearity; an additional parameter, 
.alpha..sub.0, is needed in the case of resonant nonlinearity. This is 
because the nonlinearity depends on, and is limited by, the absorption 
coefficient of the material at the laser wavelength. Therefore in the case 
of resonant nonlinearity, .alpha..sub.2 /.alpha..sub.0, n.sub.2 
/.alpha..sub.0, and X.sup.(3) /.alpha..sub.0 are the correct parameters to 
use for measuring the nonlinearity. One can characterize the nonlinearity 
by measuring .DELTA..alpha. with the Pump-probe technique described below 
and expressing the nonlinearity either as .alpha..sub.2 /.alpha..sub.0 or 
.DELTA..alpha./.alpha..sub.0. 
If a material has significant n.sub.2 or .alpha..sub.2, many third order 
nonlinear optical phenomena such as optical bistability and phase 
conjugation (degenerate four-wave mixing) can be demonstrated. Phase 
conjugation experiments (described in the following section) have been 
performed on some of the materials of the invention. The phase conjugation 
efficiency, defined as the intensity ratio of the phase conjugated beam 
and the probe beam, is also a measure of the nonlinearity. It has 
contributions from both n.sub.2 and .alpha..sub.2 and is proportional to: 
##EQU4## 
where .lambda. is the laser wavelength and I is the intensity of the pump 
beam. The phase conjugation efficiency depends on the geometry of the 
optical set-up, the spatial quality of the laser beam, and also the 
optical quality of the sample. It is therefore not a good universal 
parameter for comparing the intrinsic nonlinearity of the material. 
Laser-induced absorption changes 
The change of sample transmission, I.sub.t, as a function of the incident 
laser power was measured by absorption changes using the pump-probe 
technique. The laser-induced transmission change measures the magnitude 
and the speed of the optical nonlinearity. The result is expressed as 
.DELTA.OD/OD.sub.0, where OD is the low-power optical density defined as 
-log(I.sub.t /I.sub.0) and .DELTA.OD is the induced change in optical 
density. 
##EQU5## 
Samples prepared for evaluation were irradiated by a dye laser, using an 
optical arrangement corresponding to that depicted in FIG. 1. As indicated 
in FIG. 1, a 10/90 beam splitter 1 (BS1) divided the dye laser pulse into 
two parts. One part, the strong pump beam, was directed sequentially to a 
mirror (M1), an attenuator and another mirror (M4). The other beam, a weak 
probe beam, was directed through a filter (F) and then to a 50/50 beam 
splitter (BS2). One part of the signal from BS2 was directed to a mirror 
(M2), which sent the signal back through BS2 and to a detector, providing 
the reference signal. The other part of the probe beam from BS2 was 
directed to a mirror (M3). The pump beam (from M4) and the probe beam 
(from M3) were directed to the sample, and overlapped at the sample 
spatially and temporally. The intensity of the probe beam transmitted 
through the sample, I.sub.t, was measured by a signal detector and divided 
by the intensity of the signal from the reference detector by a boxcar 
integrator to correct for the laser intensity fluctuations. The power 
dependence of .DELTA.OD was obtained by measuring the change in intensity 
of the transmitted beam as a function of the pump beam intensity, where 
the intensity of the pump beam is adjusted by the attenuator. 
Degenerate Four-Wave Mixing (DFWM) 
Samples prepared for evaluation were irradiated by a dye laser, using an 
optical arrangement corresponding to that depicted in FIG. 2. As indicated 
in FIG. 2, a 10/90 beam splitter 1 (BS1) divided the dye laser pulse into 
two parts. One part, the weak signal from BS1, was directed to a 50/50 
beam splitter (BS2), sending a reference beam to the reference detector 
(D.sub.R) and a probe beam (I.sub.p) to a mirror (M1). The other part of 
the signal from BS1 was directed to a 50/50 beam splitter (BS3). Part of 
this beam, the forward pump beam (I.sub.f), was directed to an attenuator 
and a mirror (M2). The other part of this beam, the backward pump beam 
(I.sub.b), was directed through a delay and then to a mirror (M3). The 
forward and backward pump beams (from M2 and M3) and the probe beam (from 
M1) are directed at the sample and overlap there spatially and temporally. 
The phase conjugated beam (I.sub. c) retraces the path followed by I.sub.p 
to BS2 and is detected by D.sub.S. The magnitude of I.sub.c measures the 
optical nonlinearity of the sample. I.sub.c was divided by the signal from 
the reference detector to correct for the laser intensity fluctuations. 
The power dependence of the nonlinearity was measured by adjusting the 
intensity of the I.sub.f with the attenuator. The time dependence of the 
nonlinearity was measured by adjusting the arrival time of the I.sub.b 
with the delay line. 
For the samples evaluated in these experiments, the dominant contribution 
to the nonlinearity is due to laser-induced absorption bleaching and the 
associated change in refractive index. The pump-probe experiment measures 
the sample absorption change, and the associated change in refractive 
index can be obtained through the Kramers-Kronig analysis. The DFWM 
experiment measures the contribution from both the absorption change and 
the refractive index change. The observation of large absorption change 
from the pump-probe experiment can be correlated to the observation of a 
strong phase-conjugated signal from the DFWM experiment. 
EXAMPLE 1 
A cadmium-loaded glass disk was prepared as described in Method 1, using 
1.00 g of cadmium nitrate dissolved in 18 mL of water, tetramethyl 
orthosilicate (15 mL), methanol (25 mL) and nitric acid (2 mL). The 
resulting solution was mixed well and poured into 25 mL polyethylene vials 
to a depth of about 1/4 inch (about 3 mL). After heating and drying, one 
of the resulting clear cadmium-loaded disks (about 0.35 g) was evacuated 
to high vacuum (10.sup.-3 torr) and then exposed to 200 torr H.sub.2 S. 
The disk was heated to 100.degree. C. for 15 min in this atmosphere and 
then for another 15 min under vacuum. After cooling to room temperature, 
the yellow disk was placed in an inert atmosphere glove box and 
impregnated with a 1% solution of Vazo-64.RTM. in methyl methacrylate 
(MMA). The MMA-saturated disk was placed in a tightly capped vial and 
heated in a vacuum oven at 60.degree. C. overnight. The MMA polymerized, 
giving a dense glass/CdS/polymethylmethacrylate PMMA) composite. An X-ray 
pattern of the composite shows the presence of crystalline CdS of particle 
size 40 .ANG.. 
The ratios of Cd:S obtained from elemental analyses of CdS-containing 
composites vary from 1.0 to 1.7, probably as a result of incomplete 
conversion of Cd.sup.+2 to CdS. 
EXAMPLES 2-21 
The procedure substantially as described in Example 1 has also been used to 
prepare other glass/semiconductor/PMMA composites, as summarized in Table 
1. In all cases, the coloration of the glass appears to be very uniform. 
The weight of metal salt given is that added to the recipe given in Example 
1 above. 
TABLE 1 
______________________________________ 
Glass/Semiconductor/PMMA Composites 
Prepared From Sol Gel Glasses 
Metal Salt.sup.a 
Semi- (Wt. Range Anion Color.sup.b 
Ex. Conductor Studied) Source 
(Range) 
______________________________________ 
1 CdS Cd(NO.sub.3).sub.2, 1.0 g 
H.sub.2 S 
Yellow (Colorless .fwdarw. 
(0.025-1.0 g) Yellow) 
2 PbS.sup.c Pb(NO.sub.3).sub.2, 
H.sub.2 S 
(Brown .fwdarw. Black) 
(0.025-1.0 g) 
3 ZnS Zn(NO.sub.3).sub.2, 0.1 g 
H.sub.2 S 
Colorless 
4 CuS Cu(NO.sub.3).sub.2, 0.1 g 
H.sub.2 S 
Green Brown 
5 Ga.sub.2 S.sub.3 
Ga(NO.sub.3).sub.3, 
H.sub.2 S 
Colorless 
(0.025-0.75 g) 
6 In.sub.2 S.sub.3 
In(NO.sub.3).sub.3, 
H.sub.2 S 
Yellow 
(0.025-1.0 g) 
7 CdSe.sup.d 
Cd(NO.sub.3).sub.2, 1.0 g 
H.sub.2 Se 
Yellow 
(0.025-1.0 g) (Yellow .fwdarw. Red) 
8 PbSe Pb(NO.sub.3).sub.2, 
H.sub.2 Se 
Black 
(0.025-0.5 g) 
9 ZnSe Zn(NO.sub.3).sub.2, 0.1 g 
H.sub.2 Se 
Yellow 
10 CuSe Cu(NO.sub.3).sub.2, 0.1 g 
H.sub.2 Se 
Brown .fwdarw. Black 
11 Ga.sub.2 Se.sub.3 
Ga(NO.sub.3).sub.3, 
H.sub.2 Se 
Yellow 
(0.025-0.75 g) 
12 In.sub.2 Se.sub.3 
In(NO.sub.3).sub.3, 
H.sub.2 Se 
(Orange .fwdarw. 
(0.025-1.0 g) Dp. Red) 
13 Cd.sub.3 P.sub.2 
Cd(NO.sub.3).sub.2, 
PH.sub.3 
(Colorless .fwdarw. Black) 
(0.025-1.0 g) 
14 Pb.sub.3 P.sub.2 
Pb(NO.sub.3).sub.2, 
PH.sub.3 
Black 
0.025 g 
15 Zn.sub.3 P.sub.2 
Zn(NO.sub.3).sub.2, 0.1 g 
PH.sub.3 
Colorless 
16 Cd.sub.3 As.sub.2 
Cd(NO.sub.3).sub.2, 0.1 g 
AsH.sub.3 
Black 
17 Pb.sub.3 As.sub.2 
Pb(NO.sub.3).sub.2, 0.1 g 
AsH.sub.3 
Black 
18 Zn.sub.3 As.sub.2 
Zn(NO.sub.3).sub.2, 0.1 g 
AsH.sub.3 
Yellow 
19 PbI.sub.2 Pb(NO.sub.3).sub.2, 0.1 g 
Me.sub.3 SiI 
Yellow 
20 TiO.sub.2 Ti(i-OC.sub.3 H.sub.7).sub.4, 
none Colorless 
0.1 g 
21 In.sub.2 O.sub.3 
In(NO.sub.3).sub.3, 1.0 g 
none Yellow 
______________________________________ 
.sup.a The amount of metal salt used for the specific example listed is 
given immediately following the salt. The numbers in parentheses indicate 
the weight range of metal salts used in preparing other, similar 
glass/semiconductor/PMMA composites. These numbers only represent the 
actual amounts used and are not meant to be limiting. 
.sup.b The colors in parentheses indicate the range of colors actually 
observed for samples of various metal loadings and annealing conditions. 
These colors are supplied only as a guide and are not meant to be 
limiting. 
.sup.c Pb:S = 1.0, as determined by elemental analysis. 
.sup.d Cd:Se = 1.3, as determined by elemental analysis. 
EXAMPLE 22 
A Vycor.RTM./CdS/PMMA composite was prepared by the procedure described in 
Method 2. A piece of Vycor.RTM. glass (1/2 inch .times. 1/2 inch .times. 
1/4 inch, Corning Glass Co. 7930 porous Vycor.RTM. glass 
70.+-.21.ANG.pores) was calcined in flowing oxygen at 500.degree. C. to 
remove water and trapped organics. The clean, cooled glass was partially 
immersed in an aqueous solution of Cd(NO.sub.3).sub.2 (1.0 g in 10 mL of 
water) until the glass pores were filled with solution. The glass was 
dried in flowing air at 60.degree. C. overnight and then at 450.degree. C. 
for 24 hours. The cooled, cadmium-loaded glass was then treated with 
H.sub.2 S and MMA as described in Example 1. The resulting composite tends 
to be unevenly colored, implying an uneven distribution of the 
semiconductor, CdS. 
EXAMPLES 23-25 
This procedure has been used to prepare other Vycor.RTM./semiconductor/PMMA 
composites, as summarized in Table 2. 
TABLE 2 
______________________________________ 
Vycor .RTM./Semiconductor/PMMA Composites 
Prepared From Vycor .RTM. Glass 
Metal Salt.sup.a 
Semi- (Wt. Range Anion Color.sup.b 
Ex. Conductor Studied) Source (Range) 
______________________________________ 
22 CdS Cd(NO.sub.3).sub.2, 1.0 
H.sub.2 S 
Yellow 
(0.025-1.0 g) 
23 PbS Pb(NO.sub.3).sub.2, 
H.sub.2 S 
Black 
(0.025-1.0 g) 
24 CdSe Cd(NO.sub.3).sub.2, 
H.sub.2 Se 
Red Orange 
(0.025-1.0 g) 
25 PbSe Pb(NO.sub.3).sub.2, 
H.sub.2 Se 
Black 
(0.025-1.0 g) 
______________________________________ 
.sup.a The amount of metal salt used for the specific example listed is 
given immediately following the salt. The numbers in parentheses indicate 
the weight range of metal salts used in preparing other, similar 
glass/semiconductor/PMMA composites. These numbers only represent the 
actual amounts used and are not meant to be limiting. 
.sup.b The colors in parentheses indicate the range of colors actually 
observed for samples of various metal loadings and annealing conditions. 
These colors are supplied only as a guide and are not meant to be 
limiting. 
EXAMPLES 26-29 
Table 3 summarizes the resonant X.sup.(3) properties of selected 
glass/semiconductor/polymer composites. In general, the nonlinearities of 
Examples 26-28 are about one order of magnitude lower than the reference 
material, CdS.sub.x Se.sub.l-x doped glass, at the wavelength studied. The 
nonlinearity of Example 29 is comparable to that of (CdS.sub.x 
Se.sub.l-x)-doped glass. CdS.sub.x Se.sub.l-x is one of the best X.sup.(3) 
materials known in the art. 
TABLE 3 
______________________________________ 
Wave- Laser Rel. Absorbance 
Ex. Sample length Power Change, .DELTA.OD/OD.sub.0 
______________________________________ 
26 PbS in 625 nm 1 MW/cm.sup.2 
-6.8% 
sol-gel 
27 In.sub.2 S.sub.3 in 
625 nm 1 MW/cm.sup.2 
-6.3% 
sol-gel 
28 In.sub.2 Se.sub.3 in 
540 nm 3.2 MW/cm.sup.2 
+5% 
sol-gel 570 nm 1.9 MW/cm.sup.2 
+2.6% 
625 nm 1.0 MW/cm.sup.2 
-5.7% 
29 CdS in 450 nm 2.8 MW/cm.sup.2 
-22% 
sol-gel 
Ref.* Corning 500 nm 3 MW/cm.sup.2 
-29% 
3-69 Filter 
______________________________________ 
*The parameters for Corning 369 (CdS.sub.x Se.sub.1-x)doped glass were 
extracted from Olbright et al., Opt. Letters, 12, 413 (1987). 
EXAMPLE 30 
Degenerate four wave mixing experiments (optical phase conjugation) were 
performed on CdS in a sol-gel glass thin film with the set-up shown in 
FIG. 2. The phase conjugation efficiency was determined to be 
1.3.times.10.sup.-3 of the probe beam, i.e., the intensity of the phase 
conjugation signal was 0.13% of the probe beam.