Ag(Te ₂ O ₃ )(PO ₄ ): Linear and Nonlinear Optical Properties of a Noncentrosymmetric Phosphotellurite with P–O–Te Connection

By incorporating the stereochemically active lone pairs (SCALPs) Te⁴⁺ ion and <i>d</i>¹⁰-distorted transition-metal Ag⁺ ion into the phosphate system simultaneously, a new phosphotellurite, Ag(Te₂O₃)(PO₄) (ATPO), was successfully obtained. Te⁴⁺ and Ag⁺ ions exhibit highly distorted TeO₅ and AgO₅ configurations, respectively. ATPO possesses a noncentrosymmetric dense structure. It is nonlinear optical (NLO) active with a second-harmonic generation (SHG) response of ∼0.7 × KH₂PO₄. ATPO also exhibits appropriate birefringence of 0.062@546 nm, wide transparency range (cutoff edge 269 nm), and high thermal stability (stable up to 550 °C). It exhibits a relatively balanced optical performance among the reported SHG-active phosphotellurites. Theoretical calculations were performed to analyze the structure-property relationship, and the results show that highly distorted TeO₅ and AgO₅ units make the main contributions to the optical properties. This work has a positive significance for exploring SCALP-cation-based linear and nonlinear optical materials.