Anomalous luminescence of impurity-bound excitons in lithium borate crystals doped with cerium ions
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The spectra and relaxation kinetics of the anomalous (τ < 10 ns) luminescence of Li6GdB3O9:Ce3+ crystals have been experimentally detected. The time-resolved vacuum ultraviolet spectroscopy study has shown that optical transitions at 6.2 eV, caused by the transfer of an electron from the 4f1 ground state of Ce3+ to autoionizing states near the conduction band bottom of a crystal, lead to the formation of an impurity-bound exciton with the hole component localized on the 4f state of Ce3+ and the electron localized on states of the conduction band bottom. It has been found that the decay of such an exciton in Li6GdB3O9:Ce3+ occurs through radiative recombination, leading to fast luminescence at 4.25 eV. The energy threshold for the formation of the impurity-bound exciton has been determined. The distribution functions of elementary relaxations over the reaction rate constants H(k), which determine the relaxation kinetics and luminescence quenching processes, have been calculated.
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