Ultrafast and slow luminescence decays at energy transfer from impurity-bound excitons

Abstract

Different types of ultrafast radiative transitions are considered. The most interesting among them is the case when the radiative transition is accelerated by the configurational transformation of a structural unit where it occurs. Impurity-induced VUV excitation bands of doped Li2B4O7 are attributed to the creation of impurity-bound excitons. When Mn2+ is involved into exciton recombination, the radiative transition in the Mn2+3d5 configuration is accelerated and occurs on a sub-nanosecond time scale. Excitation within the UV bands is connected with energy transfer from the structural units formed by the sensitizers (Cu, Sn) and oxygen to Mn2+. In this case, Mn2+ transitions are not accelerated since its excited state appears after complete relaxation of excitation in the corresponding sensitizer’s unit. Pulsed cathodoluminescence decays are rather slow due to very slow transport of electron–hole pairs and excitons in Li2B4O7.