FINE-STRUCTURE OF THE TRIPLET RELAXED EXCITED-STATE OF GA+ CENTERS IN ALKALI CHLORIDES INDUCED BY THE OFF-CENTER POSITION OF THE EXCITED GA+ ION

The luminescence of a RbCl: Ga crystal is investigated by the methods of time-resolved polarization spectroscopy in the temperature range 0.09 to 400 K. Manifestations of an off-centre displacement of an excited Ga+ ion and its tunnelling motion are found in the decay kinetics of the triplet A(T) emission of the Ga+ centre. No such manifestations are observed for the A(X) emission. A comparison of luminescence characteristics and peculiarities of the triplet relaxed excited state (RES) structure of the Ga+ centre in RbCl: Ga crystal with those of NaCl: Ga and KCl: Ga crystals is performed. The fine structure of the tetragonal Jahn-Teller minima of the triplet RES of Ga+ centres in RbCl: Ga is found to be analogous to that of KCl:Ga: the metastable state is split due to tunnelling transitions between various equivalent off-centre positions of the excited Ga+ ion, but in the emitting state the spin splitting caused by the off-centre displacement of Ga+ ion considerably dominates over the tunnel splitting of this state. Basing on the analysis of the ODMR spectra as well as of the circular polarization of Ga+ triplet luminescence and its decay kinetics, the assumption is made that the tunnel splitting energy of the triplet metastable state of Ga+ centres is less than 10(-5) eV.