Radiative recombination at Ir 3+ sites in doped AgBr. visible luminescence

Abstract

Low-temperature ( ⪷ 25 K) photoluminescence spectra of Ir 3+-doped AgBr single crystals were obtained. These spectra are highly structured; they show a progression in a low- frequency ( ∼ 38 cm -1) resonance vibrational mode and the participation of other localized vibrations. A sharp zero-phonon (ZP) line was observed at 15622.9 cm -1. The assignment of this line as the spectral origin of the luminescence band is based upon photoluminescence excitation spectra obtained with a CW dye laser. In crystals doped with ∼ 80 molar ppm Ir 3+, the linewidth of the ZP line is ⪷ 2.0 cm -1. A Zeeman effect on the ZP line was observed. The temperature dependence of the luminescence intensity was obtained. The emission is rapidly quenched with temperature, so that no emission bands are observed above 25 K. The results of several experiments suggest that the emission originates at iridium sites in the doped crystal. Several physical models are considered as likely descriptions of the emission process. These include trapped carrier/free carrier recombination, trapped electron/trapped hole (pair) recombination, and deeply bound exciton recombination. Each is discussed in light of the experimental evidence.