AgBr photophysics from optical studies of quantum confined crystals

Luminescence spectroscopy of nanocrystals (100 nm) has been used to probe the details of the low-temperature photophysics of AgBr, an indirect-gap semiconductor. Small crystallite size, moderate excitation levels, and radiative decay rates create a situation in which only one electron-hole pair exists in a given nanocrystal. These restrictions eliminate some of the decay channels and simplify the exciton emission spectrum for {}50-nm edge-length crystals. The exciton recombination in 10-nm-diam crystals dominates the emission spectrum. This emission is >10⁴ times as intense as exciton emission from a macroscopic crystal. Symmetry relaxation, carrier confinement, and impurity exclusion explain this increase in exciton emission. Doping experiments confirm the assignment of one set of exciton lines (BX₈) as recombination emission from an exciton bound to an ionized donor.