On the state of activator in CsI(Na) crystals grown under forced mixing of the melt

A.N.Panova, E.L.Vinograd, V.I.Goriletsky, S.P.Korsunova, N.N.Kosinov, A.M.Kudin, K.V.Shakhova

Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Lenin Ave., 310001 Kharkiv, Ukraine

Received March 16, 1998

Effect of NaI concentration (C) on variations of some CsI(Na) crystal characteristics has been studied. The characteristics considered include: the optical absorption coefficient in the activator band; emission intensities of excitons localized at Na+ ions (420 nm) and in the regular lattice (340 nm) in the radioluminescence (RL) at 80K; yields of stationary RL (241Am, 60keV) (L RL), g-scintillation (137 Cs, 662 keV) (Lg) and a-scintillation
(241 Am, 5.9 meV) (L a) for CsI(Na) crystals grown under the forced melt mixing. The number of activator emission centers in those crystals has been shown to increase linearly as C rises up to about 2.2*10-2mol.%. The La value attains a maximum at C 2.3 10-2 mol.% NaI while those of L RL and L g, at C 9*10-3 mol.%. The NaI solubility in CsI has been concluded to be at least 2.2*10-2 mol.% and thus to exceed substantially the literature data (from 8*10-3mol.% to 1*10-2mol.%). Therefore, the maximum Lg value is due to a sufficient number of emission centers at the specified excitation density. The fact that the C value corresponding to the maximum Lg of CsI(Na) is lower than for CsI(Tl) crystals (about 2.5*10-2mol.% of TlI) is assumed to be caused by a larger size of the distorted lattice volume in the neighborhood of the light Na+ .

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