Influence of heavy magnesium codoping on emission decay in Ce-doped multicomponent garnet scintillators

Abstract

This study is aimed at the acceleration of luminescence decay in Ce-doped garnet-type scintillators by heavy aliovalent codoping. Time-resolved photoluminescence spectroscopy over a wide temperature range of LuGAGG:Ce epitaxial layers with up to 6000 ppm of codoping magnesium, and a transient absorption technique probing the population of the emitting Ce centers and energies of optical transitions at Ce³⁺ ions in the layers, enabled the interpretation of luminescence decay. Heavy Mg-codoping facilitated the luminescence decay acceleration due to the coexistence of two types of emission centers: regular ions of Ce³⁺; and Ce ions with magnesium in the immediate vicinity, i.e., Ce³⁺ + Mg²⁺ centers. In the latter centers, the activation energy for thermal quenching is 0.2 eV, instead of 0.48 eV in regular Ce³⁺ centers; and a new channel of temperature-independent nonradiative recombination occurs, pushing the low-temperature luminescence decay time from 50 ns – due to radiative recombination at regular Ce³⁺ centers – down to 10.5 ns. The magnesium content does not change the properties of the emission centers but increases the contribution of the Mg-related centers. Time-resolved cathodoluminescence spectroscopy of the layers evidences a broad applicability of the suggested model for heavy aliovalently codoped Ce-doped garnets beyond the LuGAGG:Ce thin films prospective for X-ray imaging.