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The alkaline earth co-doping by Mg2+ or Ca2+ ions in LYSO:Ce and LuAG:Ce stabilizes tetravalent Ce4+ ions which then participate in the scintillation process. They act as electron traps and result in reduction of afterglow and slow components in the scintillation decay [1, 2]. Excellent scintillation properties have recently been reported in epitaxial garnet films GAGG:Ce,Mg grown by liquid phase epitaxy [3].
Here we study the effect of Mg2+ co-doping on timing properties, thermal ionization effects, and shallow electron traps in (Lu0.8Gd2.2)(Al2.5Ga2.5)O12:Ce (GAGG:Ce) multicomponent epitaxial garnet films with different Mg doping from 0 to 700 ppm. The films were grown by liquid phase epitaxy from BaO-B2O3-BaF2 flux. The kinetics of emission was studied under optical excitation in the temperature range from 10 to 500 K. The results are quantitatively compared with those obtained by e-beam excitation.
The photoluminescence decay kinetics allows to detect simultaneously both the prompt electron-hole 5d-4f(Ce3+) recombination and delayed components. It was found, that the effect of Mg2+ ions on the position of 5d state in the forbidden gap is small and the activation energy related to the ionization and/or quenching processes is not notably influenced. In particular, the activation energy was between 300 and 350 meV as obtained from the temperature dependencies of integrated decays and PL spectra in samples with Mg content between 0 and 700 ppm. The signal decreased to 50 % at ~370 K independently on Mg doping. Furthermore, significant improvements of timing performance of the Mg2+ co-doped garnets have been observed, namely a substantial acceleration of the scintillation decay and considerably reduced afterglow.
[1] S. Blahuta, A. Bessiere et al., IEEE Trans. Nucl. Sci., 60, 3134 (2013)
[2] M. Nikl, K. Kamada et al., Crystal Growth & Design, 14, 4827 (2014)
[3] P. Prusa, M. Kucera Advanced Optical Materials, 5, 1600875 (2017)
