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Photo- and thermo-luminescence techniques are applied to several kinds of single crystal complex oxide scintillators to reveal tunnelling-driven radiative recombination processes. The tunnelling mechanism provides the physical ground to interpret the observed luminescence and scintillation characteristics which could not be explained by classical radiative recombination schemes

A numerous set of Pr-doped YAP single crystals was prepared using Czochralski and micro-pulling down methods. Crystals codoped by bi-, tri- and tetravalent ions were prepared by the latter method as well. The scintillation performance of all the prepared materials was evaluated using radioluminescence, photoelectron yield and scintillation decay measurements at room temperature. The influence of shallow traps was studied by means of thermoluminescence in the 10-350 K temperature range. Though the intrinsic scintillation efficiency of Pr-doped YAP is higher than that of YAP:Ce, enhanced delayed radiative recombination processes are found to be responsible for lower-than-expected photoelectron yield of the former system. The possibilities of further optimization of Pr-doped YAP scintillator are discussed. © 2010 IEEE.

Thermally stimulated luminescence (TSL) glow curves and emission spectra were studied in undoped and Ce-doped Lu3 Al5 O12 single crystals by wavelength resolved TSL measurements in the 10-310 K temperature range. Isothermal phosphorescence measurements in the 10-100 K range were also performed, which point to the existence of a tunneling-driven radiative recombination process. These processes can explain the presence and time-dependence of the submicrosecond slow decay component in the scintillation decay. Electron paramagnetic resonance experiments suggest the presence of LuAl defects in the vicinity of Ce3+ ions, which are the most probable electron and hole traps participating in the tunneling-driven radiative recombination process. © 2007 The American Physical Society.

The study of impurity related defect states in pure and Sc-doped lutetium aluminum garnet Lu3Al5O12 (LuAG) has been performed by the electron spin resonance (ESR) method. A presence of both Yb3+ and Mo5+ impurity ions, incorporated into the crystals from the Lu2O3 oxide and Mo crucible during the growth process, was revealed. It was found that Yb3+ ions substitute for Lu3+ at their regular sites and Mo3+ ions substitute for Al3+ at regular octahedral sites. Concentration of Mo3+ increases by a factor of 10 in the Sc-containing crystals. (c) 2006 Elsevier B.V. All rights reserved.

Absorption, radioluminescence and thermoluminescence spectra were measured for a set of Lu3Al5O12:Ce samples consisting of a bulk single crystal and Liquid Phase Epitaxy-grown films prepared from the same raw materials. The triple peak structure within 120-200 K distinguished in thermoluminescence glow curves of the bulk crystals was ascribed to an electron trap arising due to the LuAl antisite defect. The depth of the trap associated with the dominant peak at 142 K was evaluated using the initial rise method.

Point defects acting as trap levels were investigated on undoped, Ce- and (Ce, Si)-doped Y3Al5O12 (YAG) crystals by TSL measurements performed over a wide temperature range (10-800 K). Below room temperature, a composite glow curve was observed, whose intensity strongly increased after Ce doping. Moreover, Ce doping introduced new trap levels giving rise to glow peaks in the 100-200 K range. On the other hand, Si co-doping did not influence the low T glow curve in a significant way. The spectral emission of the TSL was found to be governed by the Ce3+ 5d-4f radiative transition, while defect related higher energy emission bands were detected only in the undoped crystal. Above RT, the glow curve was found to be much more influenced by Si co-doping since a strong increase of a glow peak at about 250°C was noticed. Scintillation time decays of Ce- and Ce,Si-doped samples are also reported and compared with TSL data. The significance of the results and the potential impact of defect states on the scintillation properties are discussed.

We investigate and compare optical absorption, luminescence and scintillation properties of Pr-doped Y3Al5O12, Lu3Al5O12, Y2SiO5 and Lu2SiO5 single crystals. The processes determining the kinetics of the fast Pr3+ 5d–4f radiative transition are described. Among the studied host materials, only Lu3Al5O12 presents neither any 5d1–4f luminescence state nonradiative quenching nor Pr3+ ionization at room temperature. We evaluate the figure of merit of all materials for application as scintillators. The most promising system appears to be Lu3Al5O12 : Pr, since it combines an elevated density of 6.67 g cm−3, a fast scintillation response dominated by a 21 ns decay time and a spectrally corrected light yield about 160% with respect to that of Bi4Ge3O12 (BGO)

Participation of shallow and deep traps in the processes of energy transfer and capture is studied by means of time- resolved emission spectroscopy and thermoluminescence in several groups of Ce3+ and Pr3+-doped complex oxide single crystal scintillators. Tunnelling-driven recombination processes are distinguished in all the examined materials: closely spaced electron and hole traps give rise to the t-1 phosphorescence decays at low temperatures in the Ce-doped aluminum garnets and perovskites, while thermally assisted tunneling process is proposed to explain the temperature independent trap depth in glow curve peaks within 50-250 C in Ce-doped lutetium orthosilicates.

Luminescence and scintillation properties of single crystalline films (SCF) of Ce- and Pr-doped Y3 Al5 O12 (YAG) and Lu3 Al5 O12 (LuAG) garnets were analysed and compared with their bulk single crystal (SC) analogues. It was shown that the main peculiarities of luminescent properties of Ce- and Pr-doped YAG and LuAG SCF are due to the absence of YAl and LuAl antisite defects (AD) and to the extremely low concentration of vacancy-type defects in SCF with respect to SC. In SCF the absence of the AD-related traps results in faster energy transfer to the emission centres and accelerated scintillation response.

We investigated Czochralski-grown YAG:Pr single crystal as a potential novel scintillator. Optical characteristics including photoluminescence, radioluminescence, scintillation decay, radiation damage and thermoluminescence were measured. Their dependence on the dopant concentration was studied. The radiation damage results show that with increasing concentration of Pr the radiation damage reduces. Thermoluminescence above room temperature shows the dominant glow curve peak around 250 °C. Comparing to YAG: Ce scintillator an advantage of YAG:Pr is its much faster scintillation decay (16-17 ns at room temperature) and an absence of slow components in the decay. Therefore YAG:Pr appears as potentially interesting scintillator material.

We use various techniques to study optical and scintillation properties of Ce-doped yttrium aluminum garnet, Y3Al5O12 (YAG:Ce), in the form of a high-quality industrial single crystal. This was compared to optical ceramics prepared from YAG:Ce nanopowders. We present experimental data in the areas of optical absorption, radioluminescence, scintillation decay, photoelectron yield, thermally stimulated luminescence and radiation-induced absorption. The results point to an interesting feature-the absence of antisite (Y-A1, i.e. Y at the Al site) defects in optical ceramics. The scintillation decay of the ceramics is faster than that of the single crystal, but its photoelectron yield (measured with I lts integration time) is about 30-40% lower. Apart from the photoelectron yield value the YAG:Ce optical ceramic is fully comparable to a high quality industrial YAG:Ce single crystal and can become a competitive scintillator material. (C) 2006 Elsevier B.V. All rights reserved.