Crystal Growth, Optical Properties Measurement, and Theoretical Calculation of BPO4

Optically perfect single crystals of BPO4 (BPO) have been grown by the top-seeding flux method. The refractive indices are measured with the prism minimum-deviation method for the first time, on the basis of which the Sellmeier equation is obtained. The measured powder nonlinear optical second-harmonic generation effect is about twice that of KH2PO4 (KDP). Electronic structure, the linear refractive indices, and second-harmonic generation (SHG) coefficients of BPO are calculated on the basis of the plane-wave pseudopotential ab initio method. The calculation values are in line with the experimental data. The crystal is nonhygroscopic, chemically stable, and has a hardness of 6.5 Mohs.