AlGaSe: Tuning Stability via Partial Cation Substitution and Achieving a Nonlinear Optical Property Leap.

Simultaneously achieving a large second-harmonic generation (SHG) response and high laser-induced damage threshold (LIDT) remains a critical scientific challenge in mid-infrared nonlinear optical (NLO) materials. Computational studies demonstrate that AlSe exhibits a large NLO coefficient and an ultrawide bandgap among selenides. However, its instability excludes the application potential, which attracts us to design its derivatives. Novel AlGaSe can be obtained via a chemical substitution strategy when taking AlSe as the template. AlGaSe crystallizes in the noncentrosymmetric space group , isostructural with AlSe, and its three-dimensional diamond-like structure consists of two distinct MSe (M = Al/Ga) tetrahedral units. AlGaSe exhibits an NLO effect of 1.7 × AlSe and 0.7 × AgGaS (AGS) at 2.1 μm and an LIDT of 4.3 × AGS while maintaining a relatively wide bandgap of 2.46 eV among selenides. Theoretical calculations and structural analyses reveal that the NLO performances of AlSe and AlGaSe primarily originate from the synergistic interaction between two types of tetrahedral units. The enhanced SHG effect in AlGaSe is attributed to the more distorted tetrahedra, distinct orientation differences among them, and closer packing of them. This work provides an effective strategy for designing high-performance NLO materials.