Exciton self-trapping in AgCl nanocrystals

Self-trapping of excitons is reported in AgCl nanocrystals embedded in a crystalline KCl matrix. The particles, observed by atomic force microscopy, have radii of several nanometers. Due to the spatial confinement only recombination of the self-trapped exciton (STE) is observed. $\mathrm{STE}({\mathrm{Br}}^{\ensuremath{-}})$ and donor-acceptor 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 configurations: The diffuse electron is spatially confined and centered in the nanocrystal whereas the compact hole, self-trapped at different lattice sites, causes variations in wave-function overlap in the different STEs. Optically 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 lattice axes are oriented along the axes of the KCl matrix.