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

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 x 14 mm x 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.