抄録
Low temperature optical spectra are studied on AgBr:Na+ and :Li+. Optical transitions corresponding to creation and decay of free indirect exciton can be understood in terms of virtual crystal model accompanied with increase of exciton gap energy in proportion to alkali concentration. In luminescence, the free exciton emission increases intensity relative to extrinsic emission with increasing alkali concentration. Emission spectra are entirely dominated by free exciton decay below 4.2°K for alkali concentration above 1×10−2 mol. Temperature dependence of free exciton emission intensity below 4.2°K revealed splitting of the free exciton energy level. Addition of 10−3 mol of Na+ or Li+ enhances relative intensity of the medium-bound exciton decay and it is concluded that alkali impurities in AgBr can bind excitons when their concentrations are relatively low.
