The effect of bi- and threevalent cation impurities on the luminescence CsI

Abstract

The radiative relaxation of excitons in CsI single crystals is known to be connected with their localization in the neighbourhood of the lattice defects. A typical examples of the realization of an indirect luminescence are CsI(Na) single crystals and deformed CsI crystals. Therefore similar effects may be also caused by polyvalent impurities or their complexes with cation vacancies. The effect of the states of bi- (Ca, Ba) and threevalent (Sb, Bi) impurities on optical and scintillation characteristics of CsI crystals is studied. It is shown that in the crystals doped with mercury-like ions (Sn, Bi) the luminescence at 545 nm (with excitation maximum 263 nm, /spl tau/-1.6 and 4.8 /spl mu/s) connected with the intercentre transitions, and an indirect one at 420 nm (excitation 242 nm, /spl tau/-0.9 and 2.7 /spl mu/s) are observed. The variation of the state (quenching, ageing, impurity concentration, diffusional colouring) changes the correlation between different components of the luminescence: increase the output of the indirect luminescence. Similar effects are also observed in crystals, doped with alkali earth ions (Ca, Ba). The appearance of the luminescence in the blue region of the spectrum with the excitation in the same region 241 nm, (/spl tau/-1 /spl mu/s). >