Inorganic Solid-State Nonlinear Optical Switch with a Linearly Tunable T c Spanning a Wide Temperature Range.

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 4 ‾ ${\bar{4}}$ 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 (Δn 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 T c , x , e x p . = T 0 - k x ${{T}_{\left(c,{\rm \ }x\right),{\rm \ }\left({\rm e}{\rm x}{\rm p}.\right)}{\rm \ }={T}_{0}-kx}$ 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 Δ H x = Δ U 1 - Δ U 2 x + Δ U 2 ${{{\rm { \Delta{}}}H}_{x}=\left({\rm { \Delta{}}}{U}_{1}-{\rm { \Delta{}}}{U}_{2}\right)x+{\rm { \Delta{}}}{U}_{2}}$ .