In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.

Recent R&D Trends in Inorganic Single-Crystal Scintillator Materials for Radiation Detection

2 inch diameter single crystal growth and scintillation properties of Ce:Gd3Al2Ga3O12

Electronic structure and optical properties of the lanthanide activated RE3(Al1−xGax)5O12 (RE=Gd, Y, Lu) garnet compounds

Development of LuAG-based scintillator crystals – A review

The cover picture of the current issue refers to the Rapid Research Letter by Martin Nikl et al. [1]. It depicts the structure of a Lu3Al5O12:Ce single crystal, a possible high performance scintillator material. Its scintillation performance is, however, degraded by the occurrence of antisite defects. Such defects arise in the material structure sketched in the figure due to the occurrence of Lu3+ ions at the Al3+ octahedral sites as seen in the middle left octahedron. This defect constitutes a shallow electron trap, which delays energy delivery to the Ce3+ emission centers, and thus slows down the scintillation response of the material. Thermoluminescence measurements appear as sensitive diagnostic tool to evidence these defects in the single crystals grown.



Martin Nikl is senior scientist and head of the Laboratory of Luminescence and Scintillation Materials at the Institute of Physics of the Czech Academy of Sciences. His main research activities include the characterization of the luminescence and scintillation properties of wide band-gap materials and the influence of material defects on them.

The antisite LuAl defect‐related trap in Lu3Al5O12:Ce single crystal

Emission and excitation spectra and decay kinetics are studied for the luminescence of undoped LuAG and YAG crystals. Two emission bands are located at 4.8 eV and 3.95 eV in YAG and 4.9 eV and 3.65 eV in LuAG, excited in the Eexc>6.5 eV energy region. They are both characterized by a relatively slow (µs) decay time, and ascribed to the transitions from two different configurations of an exciton localized near an antisite defect (Y3+Al or Lu3+Al). The corresponding excitation band, peaking at 6.9 eV in YAG and 7.2 eV in LuAG, is ascribed to the exciton perturbed by the antisite defect. Besides the two slow emissions, the weak fast (ns) emission of the self-trapped exciton, strongly overlapping with the high-energy emission band, is also observed. In Ce3+-doped garnets, the presence of the antisite defects results in a considerable decrease of energy transfer efficiency from the host lattice to Ce3+ ions. The possibilities of improvement of scintillation charactristics of this material are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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Luminescence of undoped LuAG and YAG crystals

Luminescence, energy transfer and defects creation processes were studied at 4.2–300 K for Ce3+-doped Lu3Al5O12 crystals under excitation in the 2.5–11.5 eV energy range. The results obtained were compared with the characteristics of Y3Al5O12:Ce crystals. It was concluded that in both systems the efficiency of energy transfer from the host lattice to the impurity ion can be noticeably increased by the decrease of concentration of the defects responsible for their intrinsic luminescence. The origin of the optically created defects and possible mechanisms of their formation are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescence and defects creation in Ce3+-doped Lu3Al5O12 crystals

Time development of a Nphels/MeV photoelectron yield of various Ce and Pr-doped inorganic crystals (mainly garnets, perovskites and silicates) was studied in detail. Slow scintillation decay components influence time dependence, especially at those scintillators containing Lu as lattice ions where an increase of Nphels per 1 MeV in the time span 0.25–5 µs is more than 50%. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Time development of scintillating response in Ce- or Pr-doped crystals

Luminescence, energy transfer and defects creation processes were studied for the Ce3+-doped YAlO3 and LuxY1–xAlO3 (x = 0.3) crystals in the temperature range 4.2–300 K under selective photoexcitation in the energy range 3.5–11.5 eV. For the first time, defects creation spectra were measured and analyzed. Influence of the charge and ionic radii of co-doping ions on the luminescence and defects creation efficiency was considered. The origin of the defects created and possible mechanisms of their formation were discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

K. Blazek

Papers

Luminescence of undoped LuAG and YAG crystals

Luminescence and defects creation in Ce3+-doped Lu3Al5O12 crystals

Time development of scintillating response in Ce- or Pr-doped crystals

Luminescence and defects creation in Ce3+‐doped YAlO3 and Lu0.3Y0.7AlO3 crystals