Inorganic Solid‐State Nonlinear Optical Switch with a Linearly Tunable Tc Spanning a Wide Temperature Range

Nonlinear optical (NLO) switch materials that turn on/off second-harmonic generation (SHG) at a phase transition temperature (Tc) are promising for applications in the fields of photoswitching and optical computing. However, precise control of Tc remains challenging, mainly because a linearly tunable Tc has not been reported to date. Herein, we report a unique selenate, tetragonal P [[EQUATION]] 21c [Ag(NH3)2]2SeO4 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 (Δnobv. = 0.08). This compound forms a series of isostructural solid-solution crystals [Ag(NH3)2]2S x Se1- x O4 (x = 0−1.00) that exhibit excellent NLO switching performance and an unprecedented linearly tunable [[EQUATION]] spanning 430 to 356 K. The breaking of localized hydrogen bonds between SeO42- and the cation triggers a phase transition accompanied by hydrogen bond length changes with increasing x and a linear change in the enthalpy [[EQUATION]] .