Excited state absorption and thermoluminescence in Ce and Mg doped yttriumaluminum garnet

In this paper we report preliminary results of optical studies on Y3Al5O12 (YAG) crystals codoped with Ce and Mg. By using measurements of luminescenc e, absorption, and luminescence excitation spectra we demonstrate that alth ough the basic features introduced to the YAG host by the Ce-doping remain intact, the Mg-codoping imposes some significant changes on other propertie s of the material. These changes are potentially important for laser and/or scintillator applications of YAG:Ce and are due, most likely, to modificat ions of defect populations in the material. We characterize them by using t he techniques of thermoluminescence and excited state absorption under exci mer laser pumping. These techniques, interestingly, yield results that seem inconsistent. While the thermoluminescence signal of the Mg-doped sample i s strongly reduced, suggesting that trap concentrations in the presence of Mg are suppressed, the excited state absorption signal, which we also relat e to the traps, is higher. We offer a tentative explanation of this contrad iction between the two experiments that involves a massive transfer of elec trons from the Mg-related defects to the excited state absorption centers c aused by the excimer pump itself.