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The indirect photochemical synthesis for the preparation of bandgap- or defect-engineered multicomponent garnet powders from aqueous solutions was investigated. Gd3(Ga,Al)5O12 (GGAG) doped with Ce or Ce + Eu and Lu3(Al,Sb)5O12 doped with Eu were produced by calcination of the prepared solid precursors at various conditions and their structural and luminescence properties including decay curves were thoroughly studied. In GGAG:Ce, the content of Ga was shown to have strong impact on the lattice parameter and position of the Ce3+ 5d- $4f$ emission. To induce the formation of Ce4+ ions as defects competing with electron traps, Mg2+ ions were added into the solutions and calcination in air was examined. Both factors were shown to cause the decrease of Ce3+ emission intensity and acceleration of luminescence decay in a similar way. The doping with Sb(III) required calcination of solid precursors in inert atmosphere to prevent formation of an unknown pyrochlore-type phase containing Sb(V). Low temperatures were needed to limit Sb2O3 evaporation during calcination. [ABSTRACT FROM AUTHOR]

The role and effect of stable Ce^4+ centers in Ce-doped LuAG single crystal scintillator is further studied by means of measurements of several optical, luminescence and scintillation characteristics. Two LuAG:Ce single crystal samples are compared: in one of them the dominating Ce^4 + center is stabilized by high concentration Mg^2+ codoping while the other one shows only the presence of stable Ce^3 + center. Tailored (Eu, Mg)–doped LuAG single crystal is also prepared to test the presence and thermal stability of hole traps in the host which affect the timing characteristics of Ce^4+ scintillation cycle, namely its restoration back to 4+ charge state in last step of the cycle. EPR experiment was also employed at Mg- and (Eu, Mg) doped LuAG samples and the signature of the O^ - hole center stabilized by Mg^2 + ion was clearly obtained. [ABSTRACT FROM AUTHOR]

Ce-doped lutetium aluminum garnet Lu 3 Al 5 O 12 (LuAG) nanoceramics were fabricated at 1600 °C and 1700 °C by spark-plasma sintering (SPS) method from nano-powders prepared by radiation synthesis. Both undoped and Ce-doped LuAG ceramic samples were also prepared from the nano-powders at 1700 °C with significantly increased pre-heating rate. The backscattered electron images revealed large amount of pores in all the Ce-doped samples causing their significant opacity. On the other hand, very large grains and no pores were revealed in the undoped sample, which was the only transparent one. The radioluminescence measurements revealed superior overall scintillation efficiency of the samples sintered at the temperature 1700 °C, and their defect emission in the UV region was ascribed to oxygen-vacancy-related defects such as F + centers. The photoluminescence decay of the defect emission was characterized by an extremely fast decay time of a few nanoseconds. Influence of sintering procedure and subsequent annealing on the luminescence and scintillation properties is discussed. [ABSTRACT FROM AUTHOR]