GROWTH AND SPECTROSCOPIC INVESTIGATIONS OF Na2W2O7 SINGLE CRYSTALS DOPED WITH CERIUM AND CHROMIUM IONS

Alkaline tungstate crystals are promising scintillation materials for rare events search, especially for WIMP investigations. Na2W2O7 single crystals doped with 1.0 mol.% chromium and cerium ions are grown from melt by low-thermal-gradient Czochralski technique (LTG Cz) developed at Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciece (Novosibirsk, Russia) for obtaining large oxide scintillating crystals of high optical quality. Obtained doped Na2W2O7 single crystals 25 mm in length and 30 mm in diameter. The photoluminescence excitation and emission spectra, as well as the decay curves in the temperature range of 77-300 K are measured and colorimetric parameters are estimated. Comparative studies of the photoluminescence properties of Na2W2O7 crystals undoped and doped with Ce3+ and Cr3+ ions in the temperature range of 77-300 K are is carried out. It is shown that while the introduction of cerium and chromium ions in the Na2W2O7 crystal lattice does not significantly a effect the colorimetric parameters and optical properties, it does not increase mechanical hardness of the crystals and decreases the tendency to cracking along cleavage planes. The emission color chromaticity coordinates, correlated color temperature and color purity for Na2W2O7:Ce and Na2W2O7:Cr crystals are calculated. The photoluminescence lifetimes are calculated and a strong temperature dependence of the lifetimes in the range 77-300 K is shown.