Tightly bound exciton in AgBr:Ir 3+

Abstract

Luminescence spectral and kinetic measurements lead to a model in which an exciton bound to a highly relaxed excited-state configuration of Ir 3+ in silver bromide undergoes radiative recombination. In addition to the previously reported infrared emission bands observed at ≈0.98 and ≈1.6 μm, a new highly structured band is seen at ≈2.5 μm. The luminescence decay lifetimes of these emissions are ≈0.3 ± 0.05, 1.8 ± 0.1, and 0.35 ± 0.05 msec, respectively, at <−10 K. The luminescence rise kinetics and decay kinetics have been studied as a function of temperature and excitation wavelength. An energy-level scheme for the Ir 3+ AgBr system is presented. It is believed that a bound-exciton state is a precursor to the trapped-electron species detected by EPR spectroscopy. A model for the low-temperature photochemistry of Ir 3+ in AgBr is given.