Tailoring and Optimization of LuAG:Ce Epitaxial Film Scintillation Properties by Mg Co-Doping

Abstract

Six Mg co-doped Lu 3 Al 5 O 12 :Ce scintillating films were prepared by a liquid phase epitaxy method, having Mg concentration of 0−3000 ppm. The following luminescence and scintillation characteristics and their dependence on Mg concentration were studied: photoluminescence emission and excitation spectra, radioluminescence spectra, photoluminescence and scintillation decay curves, light yield, energy resolution, and afterglow. Light yield increases with Mg concentration until 700 ppm and becomes 15−20% higher than in the Mg-free sample. Further increase of Mg concentration leads to light yield decrease. Scintillation decay is getting faster with an increasing Mg concentration and the afterglow is significantly reduced. The results are compared to ceramics and crystals of very similar compositions.

Influence of Mg‐to‐Ce Concentration Ratio on Cathodoluminescence in LuAG and LuGAGG Single‐Crystalline Films

“…In contrast, the intensity of the broad absorption band in the UV spectrum region (below ≈300 nm) increases with an increase in the Mg 2+ concentration. Such intense UV absorption originates from the charge transfer (CT) of an electron from oxygen ligands toward tetravalent Ce 4+ ions, which arises due to the necessity of the charge compensation of the aliovalent Mg 2+ ions embedded in trivalent sites . It is worth mentioning that the LuAG:Ce,Mg film with the highest Mg content of 0.11 at% is completely transparent in the visible range without any noticeable absorption at 445 nm, which confirms that virtually all cerium ions were stabilized in the 4+ charge state.…”

“…The noticeably decreased CL intensity of the multicomponent LuGAGG:Ce,Mg films in comparison with the LuAG:Ce,Mg films can be explained as an association of two phenomena. First, the Gd 3+ sublattice, in combination with Ce 4+ centers, may create some nonradiative pathways that decrease the luminescence output . This phenomenon depends on the Mg 2+ concentration.…”

“…The slow components are caused by delayed recombination at the Ce 3+ centers of charge captured and thereafter released from the electron traps. The effect of Mg co‐doping in the films was explained by the Ce 3+ → Ce 4+ centers stabilization, which should better compete with the shallow electron traps for electron capture . This diminishes also the effect of tunneling.…”

“…This problem can be solved by co‐doping the garnet with Mg 2+ . This leads to additional afterglow reduction in LuGAGG:Ce, and especially in Lu 3 Al 5 O 12 :Ce (LuAG:Ce) systems, to both rise and decay time reduction, but also, unluckily, to LY reduction at higher Mg co‐doping. The afterglow suppression was explained by the Ce 4+ center stabilization, competing better with electronic traps for charge capture, which resulted in practical inactivation of shallow traps.…”

“…Moreover, the CL has not been studied in LuAG:Ce,Mg films; only studies of the PL, radioluminescence (RL), scintillation properties (LY, scintillation decay), and related studies were conducted . The PL is extremely weak in the Mg‐rich films because the Ce 3+ absorption bands disappear almost completely.…”