Electron Trapping States in Phosphors

Abstract

It is known both theoretically and experimentally that the energy gap in polar crystals decreases with temperature, the change being about 0.0005 ev/deg. It is shown that one effect of this change is that phosphorescent decay measurements at different temperatures give indicated oscillation frequencies for trapped electrons which are too high by a factor of the order of 100. Since these apparent frequencies are already several orders of magnitude less than crystal oscillation frequencies, the indications are that the electron frequencies are not closely connected with crystal oscillation frequencies. It is shown further that the variation of energy gap with temperature may account for the few cases where thermal activation energies are larger than optical activation energies.