Charge-transfer luminescence and spectroscopic properties of Yb3+ in aluminium and gallium garnets

Luminescence of Yb3+ from the charge-transfer state with broad emission bands and short radiative lifetimes (few to tens of nanoseconds depending on the host lattice and the temperature) is attractive for the development of fast scintillators capable of discriminating very short events. The most important currently considered application is that in solar neutrino (nu(e)) real-time spectroscopy, since the nu(e) capture by Yb-176 is followed by a specific emission signature which can accordingly excite the Yb3+ fluorescence. Studies on scintillation and luminescence in aluminium garnets containing Yb3+ have shown that these materials meet some of the required properties for such scintillators. In defining our priorities, the best compromise between host crystal, Yb3+ concentration, production method, post-growth treatment and performance is to be considered based on the studies of charge-transfer luminescence and quenching mechanisms. The experiments have been extended to a large number of compounds: YAG:Yb-YbAG, YGG:Yb-YbGG, YAP:Yb-YbAP, LaYbO3 in the form of single crystals and/or powders. In garnets, the temperature-dependent fluorescence intensity and decay time under X-ray and VUV excitations decrease at low temperatures (T < 100 K) and demonstrate the important role played by the traps. The thermoluminescence peaks show a strong dependence on the crystal history, composition and impurities introduced intentionally. The fluorescence intensity and decay time are also dependent on Yb3+ concentration and the presence of Yb2+. The results trace the major directions to optimised scintillators in terms of their efficiency and lifetime. (C) 2002 Published by Elsevier Science B.V.