Purification and optical properties of TlBr crystals

TlBr was synthesized by chemical precipitation, purified by the hydrothermal re-crystallization method, and grown by the vertical Bridgman method. Trace element analysis at ppb/ppm level was made using inductively coupled plasma mass spectroscopy. A significant reduction of the impurity concentration was observed as a function of the cooling rate. The concentrations of impurities of Ca, Fe, Mg, K, Zn, Cu, Na, and Si decreased obviously after hydrothermal re-crystallization. In addition, the optical properties of TlBr wafers were compared using spectra in the wavelength ranges of 400-600 and 2500-20 000 nm. Compared to the wafer grown from the re-crystallized powder, the wafer grown from the non-purified powder exhibits a large absorption coefficient and small transmission in the range of 450-600 nm, a shift of the absorption edge to a longer wavelength region, and a decrease of the average IR transmittance value.