Photostimulated luminescence of phosphors

The published data on photostimulated luminescence and some new results obtained by the authors with the KCl-Tl phosphor are analyzed. It is shown that for phosphors with associated donor-acceptor pairs photo stimulated luminescence appears as a consequence of an inter-impurity electronic transition. The kinetic aspects of the luminescence depend upon the Coulomb attraction between a quasi-free electron and a charged donor. The character of the radiative recombination is determined by the interaction energy between the two partners and by the trap depth. This enables us to consider various well-known phosphor models from a general point of view. It is emphasized that the coexistence of various mechanisms in the same phosphor must be taken into account to obtain a correct interpretation of the luminescence characteristics. It is also shown that, for the mechanism involving free holes, an exciton must be created before the recombination energy can be transferred to the luminescent center.