Substantial reduction of trapping by Mg co-doping in LuAG:Ce, Mg epitaxial garnet films

Highlights: • LuAG:Ce, Mg epitaxial films are grown for the study of radio- and thermoluminescence. • Mg concentration increase results in lower concentration of Ce³⁺ and higher of Ce⁴⁺. • Thermoluminescence and bright burn are reduced as Mg concentration increases. • Number of trapped electrons is reduced by 4–5 orders of magnitude (3000 ppm Mg). • Hypothesis: Ce⁴⁺ ions are by far more effective in electron trapping than Ce³⁺. Six Mg²⁺ co-doped Lu₃Al₅O₁₂:Ce scintillating garnet films prepared by liquid phase epitaxy, with Mg concentration from 0 to 3000 ppm, were irradiated by X-rays and underwent a series of thermoluminescence measurements from 10 to 720 K. The thermoluminescence signal of epitaxial films originated purely from electron recombination at Ce ions. It was found that the area of all the peaks present in thermoluminescence glow curves decreased rapidly with the increase of Mg concentration; for 3000 ppm, the decrease was by 4–5 orders of magnitude. Moreover, the bright burn effect was significantly suppressed by Mg co-doping. Possible explanations, i.e., trap concentration reduction or increased competition in free electron capture between thermoluminescence traps and Ce⁴⁺ centers, were discussed.