Alena Beitlerova

Temperature dependence of luminescence characteristics of Lu2(1−x)Y2xSiO5:Ce3+ scintillator grown by the Czochralski method

In this paper, we investigate the temperature dependence of luminescence characteristics of highly efficient cerium-doped scintillator, lutetium-yttrium orthosilicate Lu2(1−x)Y2xSiO5:Ce3+. The photoluminescence excitation and emission spectra have been measured in a broad temperature range. The temperature dependence of the Ce1 and Ce2 decay times shows the onset of decay time decrease at about 300 K. This observation demonstrates that unlike so far reported, the Ce2 center is not substantially quenched until room temperature. The 5d1 excited-state ionization of both Ce1 and Ce2 centers is studied by purely optical methods.

Microstructure, optical, and scintillation characteristics of Pr3+ doped Lu3Al5O12 optical ceramics

0.5, 1.0, and 5.0 at. % Pr3+ doped Lu3Al5O12 (Pr:LuAG) optical ceramics are fabricated and compared with Bi4Ge3O12 (BGO) and Pr:LuAG single crystals as for their optical, luminescence and scintillation properties. Radio-luminescence intensity of the fast UV emission based on 5d1→4f Pr3+ transition reaches up to 20 times of that of BGO single crystal reference scintillator. Photoelectron yield of the best performing 0.5 at. % Pr:LuAG ceramic sample is about 1002 phels/MeV, about 30% lower than that of BGO reference sample and about 65% lower than that of Pr:LuAG single crystal. The trapping phenomena at grain boundaries and/or structural defects are proposed as the main cause of degradation of the scintillation response of the Pr:LuAG optical ceramics.

Scintillation Properties of

We summarize the latest R&D state-of-art of Ce³⁺ and Pr³⁺-doped mixed (Lu_xY_1-x)₃Al₅O₁₂ (LuYAG) garnet scintillator crystals and compare their properties with those of Lu₃Al₅O₁₂ (LuAG) and Y₃Al₅O₁₂ (YAG) single crystal analogues. Light yield, energy resolution and proportionality were studied under radioisotope excitation within 8-1300 keV energy range. The highest light yield of about 27000 ph/MeV is obtained in the newest prepared Ce³⁺ -doped LuAG crystals while up to 17000 ph/MeV was measured in the Pr³⁺-doped ones. On the contrary, the energy resolution and proportionality are noticeably better in the Pr³⁺ -doped crystals. Mixed Ce³⁺- or Pr³⁺-doped Lu_xY_1-xAG (x=0.9-1) crystals show comparable light yield and energy resolution compared to those doped pure LuAG, but the content of slow components in scintillation pulses lower.

{\rm Ce}^{3+}

KMgF3, BaLiF3 and LiCaAlF6 (LiCAF) single crystals were grown by the Czochralski method under CF4 atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the vacuum-ultra-violet (VUV), ultra-violet and visible spectral regions. In the case of LiCAF, the X-ray induced absorption peak at 262 nm can be ascribed to F centre. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials; moreover, LiCAF shows stable VUV transmission characteristics and the most resistant surface toward what is regarded as the damage due to reaction with air atmosphere.

- and

Photoluminescence, X-ray excited radioluminescence and photoelectron yield characteristics were studied in multicomponent GdGaYAG:Ce and GdGaLuAG:Ce garnet films grown by liquid phase epitaxy. Nonradiative energy transfer from Gd3+ to activator Ce3+ ions was evidenced. At low Gd doping, , two virtually independent emission centers coexist, which compete for intensity: Ce3+ with fast 5d-4f emission and Gd3+ with slow 4f-4f emission. At higher Gd concentrations, the Ce3+ emission retrieves intensity due to the energy transferred from Gd3+ donors. At Gd concentration ~ 50% and above, the Gd3+ emission is suppressed due to energy migration and transfer to Ce3+ centers. In these samples, the host emission is also completely quenched and the best scintillator performance is achieved. Contrary to melt-grown crystals, no positive role of Ga substitution was found in epitaxial films.

{\rm Pr}^{3+}

PbWO4 single crystals with praseodymium doping in a wide concentration range (0.1–5 at % in the melt) were grown by Czochralski method. Absorption, luminescence, and scintillation characteristics were measured at room temperature. Similar to other trivalent dopants, heavy Pr3+ doping on one hand suppresses intrinsic host scintillation. On the other hand though, in the scintillation decay it introduces components with characteristic decay times within 500–2000 ns based on Pr3+ 4f-4f emission lines in the green-red part of the spectra. We discuss the suitability of such material for dual scintillation/Cherenkov light detector.

-Doped LuAG, YAG and Mixed

Highly luminescent ZnO:Ga-polystyrene composite (ZnO:Ga-PS) with ultrafast subnanosecond decay was prepared by homogeneous embedding the ZnO:Ga scintillating powder into the scintillating organic matrix. The powder was prepared by photo-induced precipitation with subsequent calcination in air and Ar/H2 atmospheres. The composite was subsequently prepared by mixing the ZnO:Ga powder into the polystyrene (10 wt% fraction of ZnO:Ga) and press compacted to the 1 mm thick pellet. Luminescent spectral and kinetic characteristics of ZnO:Ga were preserved. Radioluminescence spectra corresponded purely to the ZnO:Ga scintillating phase and emission of polystyrene at 300-350 nm was absent. These features suggest the presence of non-radiative energy transfer from polystyrene host towards the ZnO:Ga scintillating phase which is confirmed by the measurement of X-ray excited scintillation decay with picosecond time resolution. It shows an ultrafast rise time below the time resolution of the experiment (18 ps) and a single-exponential decay with the decay time around 500 ps.

{\rm Lu}_{\rm x}{\rm Y}_{1-{\rm x}}{\rm AG}

We investigate the luminescence and scintillation characteristics of highly efficient cerium-doped scintillators, lutetium-(yttrium) orthosilicate (Lu2(1-x)Y2xSiO5:Ce, x=0-1). The radioluminescence, photoluminescence excitation (PLE) and emission (PL) spectra of the Ce1, Ce2 centres as well as the decay curves and their temperature dependences are measured in the 80-500 K range. Light yield values are provided as well. The influence of yttrium concentration on the Ce1, Ce2 luminescence characteristics is demonstrated. With increasing yttrium content the onset of the Ce1 and Ce2 decay time decrease as well as the Ce1, Ce2 delayed recombination integrals increase shift to higher temperatures. The 5d1 thermally induced excited-state ionization of both Ce1 and Ce2 centres is confirmed and studied by purely optical methods.

Garnet Crystals

This paper deals with some aspects of scintillation response of Ce-doped Y-Lu aluminum garnets or perovskites in comparison with Ce-doped orthosilicates. An essential difference between the Ce-doped aluminum garnets/perovskites and orthosilicates consists in larger fluctuations of photoelectron yield of the latter scintillators where differences can reach up to 50% and measured values critically depend on the recent history of the sample (illumination by day light, thermal annealing, etc.). This behavior of Ce-doped silicates seems to be due to the vicinity of the 5d1 level of Ce3+ from the conduction band, which makes the material more sensitive to the presence of deep electron traps monitored by thermo-luminescence above room temperature. The presence of such electron trapping sites thus appears more critical than in aluminum garnets/perovskites.

Induced absorption phenomena, thermoluminescence and colour centres in KMgF3, BaLiF3 and LiCaAlF6 complex fluorides

We prepare InGaN/GaN multiple quantum well (MQW) structure by metal-organic vapour phase epitaxy and characterize it by fine XRD measurements. We demonstrate its suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft x-ray source in extended dynamical and time scales. The photoluminescence and radioluminescence were measured: we have shown that the ratio of the intensity of quantum well (QW) exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centres responsible for wide YL band, which also partially overlap with the QW peak. Further improvements of the structure are suggested, but even the presently reported decay characteristics of the excitonic emission in MQW are better compared to the currently widely used single crystal YAP:Ce or YAG:Ce scintillators. Thus, such a type of a semiconductor scintillator is highly promising for fast detection of soft x-ray and related beam diagnostics.