Bridgman growth and characterization of birefringent crystal NaNO3

With a bigger birefringence than calcite, sodium nitrate (NaNO3) single crystal might have potential applications in fiber‐optic polarizer, opto‐isolators and polarizing prisms. However, it is difficult to grow large‐size NaNO3 crystals for their thermal conductivity anisotropy and phase transition at 275°C. In this paper, crack‐free NaNO3 crystals with size of Φ20×100 mm3 were prepared by Bridgman method with lower growth rate and lower interface temperature gradient. The dependence of the transmittance on the sample exposure time was measured and studied. The principal refractive indices of NaNO3 crystal at the wavelengths 0.4730, 0.5320, 0.6328, 1.064 and 1.338 μm were measured by auto‐collimation method. From which, we calculated and obtained the Sellmeier's equation of NaNO3 crystal. Moreover, the photoluminescence spectra were detected under the excitation at 240 nm, and NaNO3 crystal presented its fluorescence around 416 nm. High quality NaNO3 single crystals with size of Φ20×100mm3 were grown by Bridgman method. The principal refractive indices of NaNO3 crystal were measured and the corresponding Sellmeier's equation was obtained by auto‐collimation method. NaNO3 crystal demonstrates its better birefringent property. The transmittance and photoluminescence properties were also discussed in this paper.