G.O. Shirinyan

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

Luminescence of Yb 3 - 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 (v e ) real-time spectroscopy, since the v e capture by 1 7 6 Yb is followed by a specific emission signature which can accordingly excite the Yb 3 + fluorescence. Studies on scintillation and luminescence in aluminium garnets containing Yb 3 + have shown that these materials meet some of the required properties for such scintillators. In defining our priorities, the best compromise between host crystal, Yb 3 + 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, LaYbO 3 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 Yb 3 + concentration and the presence of Yb 2 + . The results trace the major directions to optimised scintillators in terms of their efficiency and lifetime.

Growth and light yield performance of dense Ce3+-doped (Lu,Y)AlO3 solid solution crystals

Many Ce-doped (Lu,Y)AlO 3 solid solution single crystals of various Lu/Y ratio and dopant concentration have been grown using the vertical Bridgman and Czochralski processes. Light yields of around 200% of BGO have been measured under gamma-ray excitation. The as-grown and gamma-ray-induced color centers have been compared in crystals of various composition. The absorption properties were characterized in as-grown crystals and after exposure to 1 Mrad of 60 Co. The extent of radiation-induced optical absorption was found to be dependent on the initial light transmission properties of the crystals.

Potential of existing growth methods of LuAP and related scintillators

Abstract LuAP and LuYAP are promising single-crystal scintillators for use in the next generation of positron emission tomographs. The practical crystal composition in terms of major components and Ce-doping level is however under discussion yet. Bridgman and Czochralski melt techniques are used to develop various crystal compositions for scintillation studies and final composition choice. In this paper we compare performance of 30 LuAP, LuYAP and YAP variously Ce-doped single-crystals grown by Bridgman technique, which reflect potential of existing materials and technologies. In addition to available optical properties, the chemical composition of solid solutions is described in terms of variation of Ce concentration and of Lu/Y ratio.

Formation and properties of crystalline compounds in the Lu2O3-Al2O3 system

Supercooling of the melt is a necessary condition for the formation of letetium orthoaluminate structure. Unless supercooled, a melt of Lu2O3:Al2O3 solidifies yields lutetium aluminum garnet and lutetium oxide. The growth of garnets and orthoaluminates is described briefly, and some basic physical properties of the crystals are reported.

Spectroscopic and colour centre studies of Pr-doped LuAlO3

Abstract We present the results of classical 4f2 intra-configurational absorption spectroscopy, 3 P 0 and 1 D 2 fluorescence dynamics and 4 f 2 ( 1 D 2 )→4 f5d inter-configurational excited state absorption (ESA) measurements in LuAlO3:Pr3+ crystals. As optical excitations with blue or ultraviolet (UV) photons lead to colour centre formation, these centres are studied in variously Pr-doped LuAlO3 crystals after Xe-lamp irradiation.

LuAP/LuYAP single crystals for PET scanners: effects of composition and growth history

In this paper we present results of optical and scintillation studies of three series of LuAP and LuYAP crystals differing in yttrium and cerium concentrations. Comparison of as-grown and UV-irradiated crystals has revealed two types of color centers located at 200–240 nm and 250–320 nm and giving rise to underlying absorption. The percentage of light emitted at 1 ls increases from 76% in LuYAP (Lu80%) to 85% in LuAP but is dependent on Ce concentration too. The light output for the best LuYAP and LuAP specimens of 2 � 2 � 10 mm 3 measured in the vertical geometry was 50% of LSO and 35% of LSO respectively.

Growth of LuAP/LuYAP single crystals for pet applications

The light yield and decay properties are the most crucial parameters of cerium-doped lutetium orthoaluminate (LuAlO 3 -Ce, LuAP) and yttrium containing solid solution (Lu 1 m x Y x AlO 3 -Ce, LuYAP), which will be used in Positron Emission Tomographs (PET). Both characteristics strongly depend on the optical quality and cerium concentration introduced into the crystal. Factors governing the crystal quality are commented on. A clear improvement of scintillation properties with increasing the doping concentration is demonstrated in a series of LuYAP (Lu=80 v at.%) crystals scanning the concentration range from 0.1 to 0.4 v at.%. Testing of relations is performed between the crystal doping level and low-temperature thermoluminescence spectra, as well as between the doping level and absorption spectra in UV range.