The fluorescence of Cu+ in RbCl was investigated in the temperature range of 20-300 K by performing accurate lifetime measurements. By growing high purity samples, the problem has been solved concerning the behaviour of the decay process: the lifetime data were found intrinsic and not affected either by different thermal treatments or by ageing. The Cu+ de-excitation mechanism has been simply interpreted in terms of the traditional Pedrini model. Moreover, the results are in agreement with the Bosi and Nimis model, where an off-centre configuration has been foreseen. Nevertheless, preliminary decay data concerning the fluorescence of Cu+ in RbI are unusual and limit the validity of the relationship adopted in the Pedrini model for the temperature dependence of the decay lifetime. (C) 2004 Elsevier B.V. All rights reserved.