M. Nikl

Scintillator-oriented combinatorial search in Ce-doped (Y,Gd)3(Ga,Al)5O12 multicomponent garnet compounds

Ce-doped (YyGd1−y)3(GaxAl1−x)5O12 (x = 0, 1, 2, 3, 4 and y = 1, 2, 3) single crystals are grown by the micro-pulling down method. X-ray diffraction and electron probe microanalysis techniques are employed to check their structure and chemical composition, respectively. Optical and photoluminescence characteristics are measured and radioluminescence spectra, light yield and scintillation decay measurements are further made to evaluate the scintillation performance. We show that balanced Gd and Ga admixture in the Y3Al5O12 structure can considerably increase the scintillation efficiency, and the spectrally corrected light yield value exceeds 44000photonMeV −1 . Scintillation decay times approach that of Ce 3+ photoluminescence decay and an additional less intense slower component is also observed. Physical aspects of energy transfer process and 5d1 excited state depopulation are discussed. The micro-pulling down technique is shown as an ideal tool for a directed combinatorial search for targeted single crystal compositions to reveal those with the highest figure-of-merit for a given application field. (Some figures may appear in colour only in the online journal)

Pr3+-doped complex oxide single crystal scintillators

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).

Optical, luminescence and scintillation characteristics of Bi-doped LuAG and YAG single crystalline films

Bi-doped Lu3Al5O12 (LuAG) single crystalline films (SCFs) of thickness within 8–31 µm were grown by the liquid-phase epitaxy method onto Y3Al5O12 (YAG) single crystal substrates using a melt solution based on a Bi2O3 flux. Their characteristics were compared with YAG : Bi SCFs grown at the same conditions. The concentration of Bi3+ ions in LuAG : Bi and YAG : Bi SCFs was varied by changing the growth temperature in the ranges 0.05–0.18 at% and 0.13–0.57 at%, respectively. The absorption, luminescence and scintillation properties of these SCFs noticeably depend on the Bi3+ concentration. Luminescence spectra of both LuAG : Bi and YAG : Bi SCF consist of two broad emission bands in the UV and visible (VIS) spectral ranges peaking at 4.155–4.085 eV and 2.45–2.66 eV, respectively. Both the UV and VIS luminescence show complex non-exponential decays. Under 241Am α-particle excitation the photoelectron yield of the best performing LuAG : Bi (0.18 at%) and YAG : Bi (0.13 at%) SCFs is about 15% and 21%, respectively, of that of the reference YAP : Ce single crystal.

Influence of Si-codoping on YAG:Ce scintillation characteristics

A set of undoped, Ce/sup 3+/-doped and Si/sup 4+/-codoped Y/sub 3/Al/sub 5/O/sub 12/ (YAG) single crystals were grown by the Czochralski method and submitted to /spl gamma/ irradiation in the dose range 1-236 Gy at RT. Their irradiation induced absorption coefficient was calculated and analyzed. Crystals also underwent light yield (LY) and scintillation decay measurements using the /sup 241/Am and /sup 22/Na radioactive sources, respectively, in 1 /spl mu/s time gate. The induced absorption at 550 nm (at the Ce/sup 3+/ luminescence peak) decreases with Ce concentration and further decrease is obtained in the Si/sup 4+/-codoped samples. LY values are independent on the Ce/sup 3+/ concentration within 0.12% - 0.3% and on the moderate Si/sup 4+/ codoping as well.

Improvement in the quality of LiCaAlF6 single crystal as window material

Abstract Three-in. size LiCaAlF 6 (LiCAF) single crystals were successfully grown by the Czochralski method. Both measurements of the transmission spectra in the VUV regions and the X-ray rocking curve analysis showed that the crystallinity of LiCAF single crystal was improved by the annealing. Optical absorption measurements in the UV/VIS spectral regions following X-ray irradiation were performed in order to compare the radiation damage with a lithography-grade CaF 2 crystal.

Comparison of the scintillation and luminescence properties of the (Lu1−xGdx)2SiO5:Ce single crystal scintillators

We provide a systematic comparison of the scintillation and luminescence properties, including emission mechanisms, of the highly efficient cerium-doped scintillators lutetium-(gadolinium) orthosilicates Lu2(SiO4)O (LSO), (Lu1−xGdx)2(SiO)4O(LGSO) and Gd2(SiO4)O (GSO). Determined characteristics manifest an advantage of LGSO:Ce with respect to both LSO:Ce and GSO:Ce for scintillator applications around room temperature. This is thanks to combined fast decay (faster than both limit compositions) high light yield, similar to that of LSO:Ce (twice higher than GSO:Ce) and low afterglow, similar to that of GSO:Ce (almost two orders of magnitude lower than LSO:Ce). High temperature applications do not, however, seem to be a suitable option for LGSO:Ce due to evidenced thermal ionization of both Ce1 and Ce2 centres above room temperature.

On the origin of cerium-related centres in lead-containing single crystalline films of Y2SiO5?:?Ce and Lu2SiO5?:?Ce

Absorption, electron spin resonance, and photo- and thermally stimulated luminescence characteristics are studied for single crystalline films (SCFs) of Y2SiO5?:?Ce and Lu2SiO5?:?Ce prepared by the liquid phase epitaxy method with the use of a PbO-containing flux. They are also compared with the characteristics of the corresponding single crystals (SCs) as well as of the undoped Y2SiO5 and Lu2SiO5 SCFs and SCs. The concentration of stable trivalent Ce3+ ions in various SCFs with different lead and cerium contents is found to be negligible. It is suggested that stable tetravalent Ce4+ ions mainly exist in the SCF due to a large concentration of Pb2+ ions whose excess volume and negative charge can be effectively compensated by relatively small tetravalent Ce4+ ions. Nevertheless, the characteristic Ce3+ emission in the SCFs of Y2SiO5?:?Ce and Lu2SiO5?:?Ce does appear under photoexcitation in the charge-transfer absorption region (Eexc?>?4.2?eV), most probably as a result of the two-photon excitation process. Ce3+ emission is observed under excitation by the ionizing radiation as well and is explained by the recombination of free electrons from the conduction band with Ce4+ ions.

Luminescence and scintillation characteristics of heavily Pr3+-doped PbWO4 single crystals

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.

Radiation damage processes in complex-oxide scintillators

Gamma radiation induced absorption processes of various scintillating materials were studied at room temperature. Single crystal of PbWO4, Ce-doped YAlO3 and Ce(Pr)-doped Y(Lu)3Al5O12 were irradiated by 60Co and doses ranging between 1-500 Gy. Broad induced absorption spectra obtained were decomposed into separate Gaussian components and tentatively ascribed to specific color centres. Supporting thermoluminescence and electron paramagnetic resonance experiments were performed to reveal the nature of charge carrier traps. The influence of codoping by aliovalent ions is also shown and discussed.

Spectroscopy and transfer processes in LuxGd1−xAlO3: Ce scintillators

Abstract Spectroscopic properties and energy transfer processes in Ce 3+ -doped RE 3+ AlO 3 orthoaluminates (for RE 3+ = Lu 3+ , Gd 3+ or Y 3+ ) or for the mixed Lu x Y 1− x and Lu x Gd 1− x are presented and summarised. Generally, spectroscopic properties of these crystals are very similar but in their Ce 3+ fluorescence and scintillation decay slow decay components appear. Temperature dependence of Ce 3+ fluorescence decays in Lu x Gd 1− x AlO 3 :Ce crystals show Ce 3+ → Gd 3+ nonradiative energy transfer followed by the opposite transfer Gd 3+ → Ce 3+ (including migration through Gd 3+ sublattice) which is responsible for slow Ce 3+ fluorescence decay component. Energy barrier between Ce 3+ and Gd 3+ interacting levels is ~ 70 meV.