Monoclinic gallium selenide: an AgGaS2-type structure variant with balanced infrared nonlinear optical performance

Abstract

Nonlinear optical (NLO) materials in the middle infrared region are receiving considerable attention, and the key scientific issue for this field is to balance a large second-harmonic generation (SHG) response and high laser-induced damage threshold (LIDT). Herein, binary monoclinic Ga₂Se₃ (1) was synthesized using a facile solid-state method. Its structure can be considered as a variant of the AgGaS₂ (AGS) type, and it demonstrated excellent balanced NLO properties. The SHG intensity and LIDT of its powder sample were determined to be, respectively, about the same and 12.6-fold higher than those of AGS. Its transparency window ranges from 0.67 to 25 μm. Particle size-dependent SHG intensity measurements indicated that 1 is phase-matchable. These outstanding NLO behaviors were well verified by DFT theoretical calculations.