Pressure-Assisted Method for the Preparations of High-Quality AaGaS₂ and AgGaGeS₄ Crystals for Mid-Infrared Laser Applications

Abstract

Recently developed chalcogenides nonlinear optical crystals have potential application in mid-to farinfrared laser fields. However, high-quality single crystals are hard to be prepared because of high vapor pressure of sulfur component and decomposition of chalcogenides during the polycrystalline synthesis and single-crystal growth. A pressureassisted technique was performed to prepare stoichiometric AgGaS 2 and AgGaGeS 4 polycrystalline materials. On the basis of the synthesized polycrystalline materials, high-quality AgGaS 2 and AgGaGeS 4 single crystals were successfully obtained using the seed directional Bridgman method with a well-designed crucible-capsule technique. These single crystals possess high homogeneity and low absorption coefficient, making it can be applied in nonlinear optical experiments. The pressure-assisted method can also be suitable to prepare other chalcogenide and phosphide compounds. The method of polycrystalline synthesis and single crystals growth described in this work will be helpful for preparing other chalcogenides nonlinear optical crystals.

Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems

“…7,9 Considerable vaporization of AGS occurs at 1273 K, 9 where, as can be believed, marked vapor pressure is created, and unsuccessful attempts to suppress completely thermal dissociation of AGS at such temperature using a high-pressure-assisted method with Ar in specific crucible-capsule supported this foresight. 12 The experimental P S 2 – T diagram for AGS in the range of 1073–1273 K (ref. 11) allowed eliminating the AGS decomposition under a strongly fixed sulfur pressure.…”

“…30 A team from China introduced improvements in all the stages of growth that resulted in the best crystals with α from 0.01 to 0.05 cm −1 in the 0.9–10 μm range, exclusive of the range lower than 0.9 μm. 12,23,31,32 A single-temperature regime, minimizing reaction space, 1–2 mol% GeS 2 excess and a special cooling process provided high-purity stoichiometric single-phase polycrystalline material, although only at a level of XRD and EDX analysis. 31 Even with good polycrystalline material and minimizing the melt losses due to a new pressure-assisted B technology with a well-designed crucible-capsule under a high Ar pressure, as-grown crystals were really defective showing 65% transmission, optical window bounded by 8 μm, and some excess Ga and sulfur deficit.…”

“…31 Even with good polycrystalline material and minimizing the melt losses due to a new pressure-assisted B technology with a well-designed crucible-capsule under a high Ar pressure, as-grown crystals were really defective showing 65% transmission, optical window bounded by 8 μm, and some excess Ga and sulfur deficit. 12 In other experiments with high-quality polycrystalline material, crystals grown by the modified VB technology were also far from perfect. 32 This took measurement of optical, electrical and spectroscopic properties of the crystals before and after annealing under vacuum at 500 °C or with polycrystalline powder at 550 °C.…”

Homogeneity characterization in AgGaGeS4, a single crystal for nonlinear mid-IR laser applications

“…Indeed, AgGaGeS4 phase has a narrow stability whose range is comprised between 48-55 mol % GeS2 [41]. Moreover, it has been outlined that volatility of AgGaGeS4 derivatives compounds and particularly germanium sulfide (GeS2) induces stoichiometry deviations in the melt during the growth process which move crystal composition away from the stoichiometry and decreases its optical quality [42,43,44]. Consequently, this can drastically reduce the conversion efficiency of the sample [45,46,47].…”

“…Recently, several works were focused on improving polycrystalline synthesis, crystal growth and annealing conditions of the AgGaGeS4 crystal [43,44,48,49,50,51]. In the present work, a new approach is proposed in complement to these works to assess the quality of an AgGaGeS4 single crystal grown by the Bridgman-Stockbarger method.…”