Self-trapping of excitons is reported in AgCl nanocrystals embedded in a cr
ystalline KCI matrix. The particles, observed by atomic force microscopy, h
ave radii of several nanometers. Due to the spatial confinement only recomb
ination of the self-trapped exciton (STE) is observed. STE(Br-) and donor-a
cceptor pair recombination are absent. The time and temperature behavior of
the emission is found to be significantly different from that in bulk AgCl
. It is concluded that this is due to different self-trapped exciton config
urations: The diffuse electron is spatially confined and centered in the na
nocrystal whereas the compact hole, self-trapped at different lattice sites
, causes variations in wave-function overlap in the different STEs. Optical
ly detected magnetic resonance measurements reveal changes in g-values and
a decrease by a factor of two in the magnitude of the Zero-field splitting
of the triplet state. They also demonstrate that the AgCl nanocrystal latti
ce axes are oriented along the axes of the KCl matrix.