Tailoring ordered structures with distorted [TeO3] and aligned [ScO6] motifs for balanced nonlinear optical properties in rare-earth tellurate crystals

Abstract

Tailoring nonlinear optical (NLO) crystals with a large bandgap and wide transparency extending from ultraviolet (UV) to mid-infrared (IR) wavelengths remains a challenge due to the inherent trade-offs in these properties. Here, we report two novel scandium tellurite NLO crystals, AScTe₂O₆ (A = K, Rb), engineered through a synergistic strategy that optimizes both electron distribution and lattice vibrations. These isostructural crystals feature a unique 2D topological framework analogous to KBBF, built from distorted [TeO₃] pyramids and [ScO₆] octahedra. Notably, RbScTe₂O₆ achieves an ultrawide bandgap of 4.43 eV with a UV cutoff at 236 nm, the shortest reported among known NLO tellurates, coupled with an extended IR transparency beyond 7.0 µm. Moreover, it affords a compelling combination of a high laser-induced damage threshold of 27.8 × AgGaS₂, a strong phase-matchable second harmonic generation response of 2.3 × KDP, and a large birefringence of 0.19 at 1064 nm. The highly polarizable [TeO₃] pyramids and well-aligned [ScO₆] octahedra collectively dominate the optical anisotropy and NLO activity, as evidenced by first-principles calculations and dipole moment analyses. These outstanding attributes establish RbScTe₂O₆ as a highly promising candidate for NLO applications in wide wavelength ranges.