We have studied the time evolution of the photoluminescence spectra of
MnO and MnS at different temperatures. In MnO crystals, of the two em
ission bands A and B, the broad band A observed at the high-energy sid
e under steady-state measurement conditions consists of two broad band
s A' and A'' differing in their transient properties. A' is the fastes
t-decaying band. Each band A' and A'' is accompanied at low temperatur
e by a set of narrow sidebands. The emitting levels of the A' and A''
band are thermally depopulated via a level lying about 130 cm-1 higher
. The A' and A'' emissions are assigned to Mn ions unperturbed and per
turbed by impurities, respectively. The broad band B observed on the l
ow-energy side grows to the detriment of emission A' and A'' with incr
easing temperature. It is tentatively assigned to Mn2+ perturbed by Mn
ions with higher valence. The results on MnS powder show similarities
with those of MnO, but they are affected by some surface effects.