Three in one: a cadmium bismuth vanadate NLO crystal exhibiting a large second-harmonic generation response and enhanced birefringence

Abstract

Inorganic nonlinear optical (NLO) crystals have attracted considerable attention due to their profound applications in laser technology. In this study, we present the synthesis of a novel cadmium bismuth vanadate crystal, Cd₂BiVO₆, through a spontaneous crystallization approach. The title compound, containing d⁰ V⁵⁺, d¹⁰ Cd²⁺, and stereo-active lone pair effect (Bi³⁺) cations, crystallizes in the non-centrosymmetric orthorhombic space group Cmc2₁ (No. 36), characterized by isolated [VO₄] tetrahedra, twisted 1D chains [Bi₂O₈]_∞ and pseudo-2D layers [Cd₆O₃₀]_∞. Remarkably, the structural characteristics endow Cd₂BiVO₆ with a strong second harmonic generation response of around 1.4 × KDP (25–53 μm), and a notably enlarged birefringence of 0.127 at 1064 nm, exceeding 6 times that of the vanadate NLO crystal Li₃VO₄ (∼0.021). Thermophysical analyses unveil its exceptional thermal stability up to 900 °C with a commendable congruent nature. Moreover, Cd₂BiVO₆ features a wide transparency range, with the UV and IR cutoff absorption edges observed at 0.395 and ∼5.8 μm, respectively. Besides, the observed optical characteristics associated with the microstructure of Cd₂BiVO₆ are explained through electronic structure calculations.