IMPURITY CORE-VALENCE TRANSITIONS IN RB1-XCSXCACL3 CRYSTALS

The luminescence of Rb1-xCsxCaCl3 crystals has been investigated using both pulsed X-ray excitation and pulsed synchrotron radiation. Intens e emission bands at 4.6 and 3.9 eV in the transparency region of the c rystal are ascribed to the impurity induced core-valence transitions ( CVTs) of 5pCs2+ --> 3pCl- type. The luminescence excitation spectrum e xhibits a threshold (E(t) = 14.00 +0.05 eV) corresponding to the photo n energy necessary to create holes in the 5pCs band. It is shown that two cations (Rb+ and Cs+) with partially overlapping upper core bands take part in the excitation of impurity CVTs in the crystal. It has be en found also that high energy excitation (E > 25 eV) gives a reduced decay time of the luminescence (tau = 2.45 ns) compared to the excitat ion at the core exciton peaks where tau = 2.84 ns.