Inorganic Solid‐State Nonlinear Optical Switch with a Linearly TunableTcSpanning a Wide Temperature Range

Abstract Nonlinear optical (NLO) switch materials that turn on/off second‐harmonic generation (SHG) at a phase transition temperature ( T c ) are promising for applications in the fields of photoswitching and optical computing. However, precise control of T c remains challenging, mainly because a linearly tunable T c has not been reported to date. Herein, we report a unique selenate, tetragonal P 2 1 c [Ag(NH 3 ) 2 ] 2 SeO 4 with a = b =8.5569(2) Å and c =6.5208(2) Å that exhibits a strong SHG intensity (1.3×KDP) and a large birefringence (Δ n obv. =0.08). This compound forms a series of isostructural solid‐solution crystals [Ag(NH 3 ) 2 ] 2 S x Se 1− x O 4 ( x =0–1.00) that exhibit excellent NLO switching performance and an unprecedented linearly tunable spanning 430 to 356 K. The breaking of localized hydrogen bonds between SeO 4 2− and the cation triggers a phase transition accompanied by hydrogen bond length changes with increasing x and a linear change in the enthalpy .