A UV solar-blind nonlinear optical crystal with confined π-conjugated groups

Abstract

UV nonlinear optical (NLO) crystals producing short-wavelength lasers through the second harmonic generation (SHG) process have great significance in the advanced laser field. However, high-performance UV NLO crystals, especially in the UV solar-blind region, are still scarce. In this work, a UV solar-blind NLO compound Rb[PO₂(NH)₃(CO)₂]·0.5H₂O (RPNCO) is obtained through the ion-exchange reaction. Remarkably, the RPNCO compound exhibits an excellent balance within a wide UV transparency window (absorption edge at 220 nm), a strong SHG response (4.2 × KH₂PO₄), and suitable birefringence (Δn = 0.055@550 nm). Structural analyses and first-principles calculations reveal that the desirable optical properties of RPNCO are attributed to the confined π-conjugation effect of [PO₂(NH)₃(CO)₂] asymmetric groups, in which the non-π-conjugated PO₂(NH)₂ tetrahedral group partially decouples the π-conjugated interactions. We believe that this research work can help provide new ideas for the rational design of UV solar-blind NLO crystals.