Non-Centrosymmetric RbNaMgP_2O_7 with Unprecedented Thermo-Induced Enhancement of Second Harmonic Generation

摘要

It is of great difficulty to obtain deep-UV transparent materials with enhanced second harmonic generation (SHG), mainly limited by the theoretically poor transparency of these materials in the deep-UV spectral region. Here we report a new noncentrosymmetric, deep-UV transparent phosphate RbNaMgP_(2)O_(7), which undergoes a thermo-induced reversible phase transition (at a high temperature of 723 K) and correspondingly an evident SHG enhancement up to ∼1.5 times. The phase transition is aroused by the twist of [P_(2)O_(7)]~(4–) dimers with deviation from the P–O–P equilibrium positions. Theoretical analyses reveal that the enhanced SHG can be ascribed to the thermo-induced collective alignment of SHG-active [P_(2)O_(7)]~(4–) dimers along the polar axis of high-temperature phase. This work provides an unprecedented physical routine (to SHG-enhanced materials) that is distinguished from the traditional one by chemical design and synthesis.