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EPR spectroscopy in X- and Q-bands was employed to trace charge carrier trapping upon exposure to X-rays of LuPO4:Eu, LuPO4:Eu,Hf and YPO4:Eu,Hf flux-grown single crystals, as well as LuPO4:Eu sintered ceramics. These data were complemented with thermoluminescence (TL) studies on the same compositions. EPR spectra proved that all the single crystals contained Pb impurity incorporated from the flux. Upon exposure to X-rays the concentration of Pb3+ changed proving that Pb participated in carrier trapping. The ionizing radiation caused also partial conversion of Eu3+ into Eu2+ and in the (Eu,Hf) doubly doped crystals also Hf4+ was transformed into Hf3+ upon exposure to X-rays. In the LuPO4:Eu sintered ceramics X-rays transformed Eu3+ into Eu2+ and the strong EPR signal of a hole trapped at O2− in the vicinity of a defect (presumably Lu3+-vacancy) was recorded. Some contribution from the PO42− molecular ion could also be observed. However, in crystals the EPR signal from the latter was much more intense compared to the former. In ceramics, the trapped hole was found to hop between the O2− ions and only below ∼70 K it localized at just one of them. Complementary measurements of TL of the samples showed meaningful differences between the glow curves of the crystals and of the ceramics. The TL glow curve of the latter contained only one band peaking around 120 °C which is related to destruction of the trapped hole being mainly the O− center. All single crystals showed multi-peak TL glow curves covering the range of 30–500 °C. They were found to result mainly from a hole released from the PO42− molecular complex and to some extent also from the O− center. The results relative to EPR and TL spectroscopy proved that in orthophosphates Eu3+ is an effective electron trapping center while holes may be trapped at impurity ions, like Pb2+, or localized at oxygen ions possibly stabilized by nearby defects, e.g. Lu-vacancies. [ABSTRACT FROM AUTHOR]

The role and effect of stable Ce^4+ centers in Ce-doped LuAG single crystal scintillator is further studied by means of measurements of several optical, luminescence and scintillation characteristics. Two LuAG:Ce single crystal samples are compared: in one of them the dominating Ce^4 + center is stabilized by high concentration Mg^2+ codoping while the other one shows only the presence of stable Ce^3 + center. Tailored (Eu, Mg)–doped LuAG single crystal is also prepared to test the presence and thermal stability of hole traps in the host which affect the timing characteristics of Ce^4+ scintillation cycle, namely its restoration back to 4+ charge state in last step of the cycle. EPR experiment was also employed at Mg- and (Eu, Mg) doped LuAG samples and the signature of the O^ - hole center stabilized by Mg^2 + ion was clearly obtained. [ABSTRACT FROM AUTHOR]

Eu-doped ternary sulfides of general formula ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay kinetics curves, were measured and evaluated in a broad temperature range (8-800 K). Calculations including quantum local crystal field potential and spin-Hamiltonian for a paramagnetic particle in D3d local symmetry and phenomenological model dealing with excited state dynamics were performed to explain the experimentally observed features. Based on the results, an energy diagram of lanthanide energy levels in KLuS2 is proposed. Color model xy-coordinates are used to compare effects of dopants on the resulting spectrum. The application potential of the mentioned compounds in the field of white LED solid state lighting or X-ray phosphors is thoroughly discussed. [ABSTRACT FROM AUTHOR]

Heat treatment is needed to increase the luminescence intensity of ZnO:Ga particles, but it comes at the cost of higher particle agglomeration. Higher agglomeration results in low transparency of scintillating powder when embedded in a matrix and constitutes one of the biggest disadvantages, besides low light yield and low stopping power, of ZnO:Ga powder. Limiting ZnO:Ga particle size is therefore a key step in order to prepare highly luminescent and transparent composites with prospects for optical applications. In this work, SiO 2 coating was successfully used to improve luminescence intensity or limitation of crystallite size growth during further annealing. Furthermore, ZnO:Ga and ZnO:Ga-SiO 2 core-shells were embedded in a polystyrene matrix., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)