Liquid-state Synthesis And Growth Of Infrared Nonlinear Optical Crystal AgGaS₂

Infrared nonlinear optical crystal has attracted much attention because of its unique physicalproperties. The chalcopyrite structure silver gallium sulfide（AgGaS₂） crystal belongs to D2d-42mpoint group which cell parameters are a=0.57580nm，c=1.03072nm. It is transparent in a regionfrom the visible to the infrared range and has a large nonlinear optical coefficient and a suitablebirefringence.AgGaS₂is an excellent infrared nonlinear optical crystal. AgGaS₂single crystalwhich is limited by the purity of materials and growth equipment is difficult to get a high-qualityand large-size.Silver compounds, gallium （III） chloride heptahydrate and sulfide have been used as reactionmaterials. AgGaS₂polycrystalline materials can be respectively prepared by solvothermal process,hydrothermal process and non-pressure process. To control experiments conditions well, after X-ray powder diffraction pattern confirmed that non-pressure process could be the best route, whichwas able to synthesize accurate stoichiometric nano AgGaS₂polycrystalline materials, in whichsilver acetate（AgAc）, gallium （III） chloride heptahydrate （GaCl₃·7H₂O） and thiourea （Tu） act asreaction material, oleylamine （OA） act as solvents oil bath heated at reflux included. The reactionmechanism was primarily discussed. The reaction has been studied among temperature, time,different feed proportioning and purity by XRD. The experiment indicates reaction temperatureand feed proportioning affecting purity, so the best synthesis temperature is170C; the appropriatetime is13h; GaCl₃·7H₂O and Tu can appropriately excess, and the AgAc excess will affect thepurity of the polycrystalline material.To eliminate the adsorption OA in the polycrystalline materials, we studied the effect ofabsolute ethanol, absolute ethanol ultrasound, distilled water, diethylamine, formic acid on thewashing OA by measuring TG-DTA. The results showed that: formic acid was the best washingreagent. In order to completely remove the oleylamine, we used tube furnace heated to hightemperatures under argon atmosphere, set different temperature range. By X-ray powderdiffraction patterns and IR, it is showed oleylamine could be completely removed at600C, at thesame time, high temperature heating was possible to increase the particle size of the polycrystallinematerial. But the polycrystalline material would be darkened in color under high temperature. Processing polycrystalline material in the tube furnace heated to1000C under argonatmosphere, quartz crucible was used to seal it. With growing of AgGaS₂single crystal by theBridgman-Stockbarger method. polycrystalline material was darkened in color result in crystal inpoor quality. Characterization of crystal: XRD showed AgGaS₂; TG-DTA curves showed meltingpoint was972C.