AlGaS3: a wide band gap ternary diamond-like infrared nonlinear optical material with high laser-induced damage threshold

Nonlinear optical crystals are the critical optical devices of all-solid-state lasers. Here, we report the rational design and synthesis of a new diamond-like (DL) compound, AlGaS 3 , assembled from two strategically selected tetrahedral units: a wide HOMO-LUMO gap [AlS 4 ] and an NLO-active [GaS 4 ]. Notably, AlGaS 3 crystallises in the noncentrosymmetric monoclinic space group Cc . It features a favourable tetrahedral stacking arrangement similar to that of β -ZnS. This compound exhibits a wide band gap (3.38 eV), a high laser-induced damage threshold (LIDT) of 6.0 × AgGaS 2 , and a phase-matchable second-harmonic generation (SHG) response of 0.5 × AgGaS 2 , achieving a desirable property balance for IR NLO candidates. Theoretical calculations show that both [AlS 4 ] and [GaS 4 ] contribute to the band gap, with [GaS 4 ] underpinning the NLO activity. Additionally, AlGaS 3 exhibits congruent melting behaviour, enabling the growth of high-quality bulk crystals via the Bridgman-Stockbarger method, a crucial step for practical applications of new materials. The results confirm AlGaS 3 as a promising IR NLO material with high tolerance to laser radiation and provide new insights into developing advanced photoelectric materials with tunable properties via partial tetrahedral substitution in the DL framework.