Optically-detected EPR of excitons in AgCl, AgCl:Br and AgBr

Abstract

Under irradiation with X-rays at 4K AgCl emits a broad band peaking at 2.52 eV. This luminescence shows magnetic circular polarization with a resonance in low magnetic field. EPR has been detected in the excited state giving rise to the emission. This indicates that the self-trapped exciton is the source of the emission and that self-trapping involves the 4d wavefunction of the silver ion. In AgCl crystals containing about 2 mole per cent of bromine an additional centre emits in the 2.52 eV region and excited-state EPR shows that this is due to electron-hole recombination at silver sites perturbed by bromine impurities. AgBr emits luminescence at 2.14 eV at 4K and EPR of the excited state has been measured.