Synthesis, Growth of Crack-Free Large-Size BaGa₄Se₇ Crystal, and Annealing Studies

The newly developed IR nonlinear optical (NLO) material BaGa4Se7(BGSe) has aroused intense research interest owing to its excellent overall properties and outstanding IR laser output performance. In this paper, the growth of high-quality large-size BGSe was investigated. To overcome the difficulty of realizing the large-scale complete reaction among the highly active metal Ba, the liquid metal Ga, and the nonmetal with high vapor pressure Se, a two temperature-zone synthetic technique was developed, and over 300 g BGSe polycrystalline raw material with high purity was synthesized at one time. To avoid the crystal cracking and increase the usage for preparing NLO device, a crystal seed with appropriate orientation was selected for vertical Bridgman technique and high-quality crystals with dimensions up to Φ40 mm × 150 mm were grown successfully. The BGSe crystals exhibit high transmittance over a wide transparent range and the absorption coefficient was estimated around 0.04 cm–1 in the range of 1–13 μm. Moreover, via the two zone thermal annealing under the atmosphere of BGSe powder vapor, the transmittance of BGSe has been significantly improved.