Characterization of an intermediate-case exciton in the 580-nm emission of Cd-doped and pure AgBr

Low-temperature photoluminescence and optically detected magnetic resonance (ODMR) techniques have been used to probe the photophysics of Cd-doped and pure AgBr. The pulsed emission data and the ODMR spectra of the 580-nm band provide evidence for an intermediate-case exciton in pure and ${\mathrm{Cd}}^{2+}$-doped AgBr. This excitonic species is intermediate between a donor-acceptor pair and a single-center exciton. Our interpretation is based on the observed g factor and the absence of a wavelength shift of the emission after pulsed excitation in pure AgBr. It is further supported by the response of the ODMR spectra as the microwave modulation frequency is changed. The two central ODMR lines observed in AgBr (g≊1.78) are assigned to transitions from the ${\mathit{m}}_{\mathit{s}}$=±1 levels to the ${\mathit{m}}_{\mathit{s}}$=0 level of an intermediate-case triplet exciton, which has an exchange coupling (singlet-triplet splitting) of -1.9±0.2 ${\mathrm{cm}}^{\mathrm{-}1}$. A weak level-anticrossing spectrum, observed at 20 mT in AgBr, is assigned to another donor-acceptor pair, which has an exchange coupling of 0.017 ${\mathrm{cm}}^{\mathrm{-}1}$. The near-gap emission in AgBr heavily doped with ${\mathrm{Cd}}^{2+}$ differs significantly from the iodide-bound exciton emission observed in AgBr. Preliminary spectroscopic studies of this sample are interpreted as a recombination of a shallow donor and either a shallow or free hole.