Growth and spectroscopic investigations of Na2W2O7 single crystals doped with cerium and chromium ions

Abstract

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 were grown from melt by low-thermal-gradient Czochralski technique (LTG Cz) developed at NIIC SB RAS (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 excitation and emission spectra of the photoluminescence, as well as the decay curves in the temperature range 77—300 K were measured and colorimetric parameters were estimated. Comparative studies of the photoluminescence properties of undoped and doped with Ce3+ and Cr3+ ions Na2W2O7 crystals in the temperature range of 77—300 K have been carried out. It was shown that while the introduction of cerium and chromium ions in the Na2W2O7 crystal lattice didn¢t significantly effect the colorimetric parameters and optical properties, it did increase mechanical hardness of the crystals and decreased the tendency to cracking along cleavage planes. The emission color chromaticity coordinates, сorrelated color temperature and color purity for Na2W2O7:Ce and Na2W2O7:Cr crystals were calculated. The lifetimes of photoluminescence were calculated and a strong temperature dependence of the lifetimes in the range 77—300 K was shown.