Luminescence Saturation Effects in Y₂O₂S: Eu Phosphor

The saturation effects of Eu³⁺ luminescence in Y₂O₂S have been investigated using a pulsed nitrogen laser at room temperature and at 80 K, and also under pulsed cathode-ray excitation at room temperature. Interaction between excited-state Eu³⁺ ions gives rise to a predominant energy-loss mechanism causing saturation. One of the two Eu³⁺ ions in the charge transfer state (CTS) is forced to relax nonradiatively to the ⁷F state by dipole-dipole interaction, and the other is promoted to a higher bound exciton state, or eventually dissociated to a free hole and a bound electron. Interaction between a Eu³⁺ ion in the ⁵D state and a CTS-Eu³⁺ ion also causes nonradiative relaxation of the ⁵D state, which causes differences in the saturation behavior of different emitting states and brings about excitation intensity dependence in the luminescence decay curves.