1D Bi ribbon/[PO4] synergy-driven bismuth phosphates for ultraviolet nonlinear optical crystals with large SHG and birefringence

Abstract

By leveraging second-harmonic generation (SHG) capabilities, ultraviolet (UV) nonlinear optical (NLO) crystals can efficiently produce UV coherent light and are essential components for advancing UV solid-state laser systems. Herein, two new bismuth phosphates, Rb_1.32Bi_3.56P₂O₁₁ (I) and K_1.08Bi_3.64P₂O₁₁ (II), were synthesized via a high-temperature melt method. Of these, Rb_1.32Bi_3.56P₂O₁₁ exhibits a significant phase-matching SHG response (2.8× KDP) and large birefringence (0.062@532 nm, 0.053@1064 nm), along with an expanded UV transmission window. Moreover, theoretical analyses revealed that the optimized optical polarizability of Rb_1.32Bi_3.56P₂O₁₁ primarily arises from the cooperative effects of the one-dimensional (1D) polycationic ribbons and [PO₄] tetrahedra. We believe that the work will provide a valuable strategy to design UV NLO materials with good performances.