SnHPO: A Layered Tin(II) Phosphate with Enhanced Birefringence.

As promising optoelectronic functional materials in the short-wavelength spectral region, such as ultraviolet (UV) and deep UV, phosphates have recently received increased attention. However, phosphate materials commonly suffer from limited birefringence owing to the highly symmetrical PO tetrahedra. We herein report a layered tin(II) phosphate with improved birefringence. By employing a polarizing microscope, the measured refractive index difference determined on a (010) wafer is 0.042@550 nm, which is very close to the calculated refractive index difference of 0.039@550 nm between and through the density functional theory (DFT) method. The largest birefringence appears on the (100) plane, which is theoretically determined to be 0.078@550 nm. Single crystals of SnHPO measuring 20 × 4 × 3 mm can be easily grown by a hydrothermal method. In addition, SnHPO is UV transparent with a short UV absorption cutoff edge of 242 nm and an optical band gap of 4.50 eV, implying that it could be a potential UV birefringent material.