Growth and properties of a noncentrosymmetric polyphosphate CsLa(PO3)4 crystal with deep-ultraviolet transparency

Abstract

To explore new deep-ultraviolet (deep-UV) nonlinear optical crystals, the CsLa(PO₃)₄ crystal with noncentrosymmetric crystallographic structure was grown by spontaneous nucleation using the flux method and slow-cooling technique. A single crystal with a size of 28 mm × 14 mm × 5 mm was easily obtained. Two perfect cleavage behaviours of the CsLa(PO₃)₄ crystal were found and the reason was discussed from the point of view of bond length and symmetry. The thermal stability and specific heat capacity of CsLa(PO₃)₄ were investigated. The CsLa(PO₃)₄ crystal remarkably exhibits a deep-UV cutoff edge of 167 nm, which is one of the shortest values among phosphates to date. Polycrystalline powder of CsLa(PO₃)₄ presents a moderate second harmonic generation (SHG) response, which is about one half of that of KH₂PO₄ (KDP). Analysis of the dipole moments for the polyhedra and theoretical calculations by density functional theory (DFT) were performed for understanding the structure–function relationships in the CsLa(PO₃)₄ crystal.