Synthesis, characterization and theoretical studies of nonlinear optical crystal Sr2B5O9(OH)·H2O

Abstract

Strontium borate Sr₂B₅O₉(OH)·H₂O (space group C2, No. 5) has been synthesized in high yields using a facile hydrothermal method. The UV-Vis-NIR diffuse reflectance spectrum shows that it has a wide transparency range extending from UV to NIR with the short-wavelength cut off edge below 190 nm. Second-harmonic generation (SHG) has been measured with a 1064 nm laser using the Kurtz and Perry technique, which shows that Sr₂B₅O₉(OH)·H₂O is phase matchable and the powder SHG effect is approximately 3 times that of KDP. It also has a high thermal stability up to 500 °C which has been identified by TG, DSC and variable-temperature PXRD. These properties make it possible for application as a UV nonlinear optical (NLO) material. Based on the electronic band structure, the optical refractive indices, birefringence, and SHG coefficients of Sr₂B₅O₉(OH)·H₂O are calculated, which are consistent with experiments. In addition, the electronic structure, SHG-weighted electron density and real-space atom-cutting analyses are performed to elucidate the origin of its NLO properties.