AbstractThe 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 AT emission of the Ga+ centre. No such manifestations are observed for the Ax 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.