Synthesis, Growth of Crack-Free Large-Size BaGa ₄ Se ₇ Crystal, and Annealing Studies

The newly developed IR nonlinear optical (NLO) material BaGa ₄ Se ₇ (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 ω40 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.