  The experimental evidence of an anomalous behavior in the decay times of
Tl$^+$-like impurity centers in alkali-halide crystals has generated a revival
of interest with respect to these materials. We discuss here about the
possibility that the $A_T$ emission of KCl:Tl can be considered as a double
emission, namely as a superposition of the $A_T$ and $A_X$ emission bands. The
plausibility of this hypothesis is discussed in the light of the available, old
and recent, experimental features. A quantitative test of this assumption is
performed in the framework of a model which demonstrates to be suitable for
interpreting other similar cases.
