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We report the study of the fast rise time and decay time in the ps time scale of the excitonic luminescence of a multiple quantum well (MQW) heterostructure of InGaN/GaN, including the excitation density effect. These structures were proposed as ultrafast scintillators for soft X-ray detectors and particle beam diagnostics. Measurements were carried out with a Hadland Imacon 500 streak camera following excitation of the sample by laser pulses of few tens of µJ at 266 nm and 400 nm, with pulse duration less than 200 fs. The rise time of the detected MWQ luminescence was less than 10 ps, with a possible contribution from the detection system and signal collection geometry. The calibration and the signal processing techniques employed to fully exploit the time resolution of the detection system are also described.

Ce,Mg:LuAG scintillation ceramics with Ce dopant content ranging from 0.025 at.% to 0.3 at.% and constant 0.2 at.% Mg codoping were fabricated by solid-state reaction. The effects of Ce concentration and annealing conditions on the microstructure, optical quality and scintillation properties are studied in great details. Lattice parameters as well as the absorption, photoluminescence, radioluminescence and thermoluminescence characteristics are investigated as a function of Ce content. Both the photoluminescence and scintillation decays are measured as well in order to study re-absorption and concentration quenching processes. In addition, an enhanced positive effect of air annealing on radioluminescence intensity and light yield is put in evidence. Moreover, the role of the charge transfer absorption of Ce^(4+) is investigated. Thermoluminescence measurements are performed to investigate the influence of both air annealing and Ce concentration on defects acting as traps. Finally, the correlations among steady state scintillation efficiency, light yield, thermoluminescence and Ce^(3+) concentration are found and discussed.

The In-doped LiCaAlF6 [In:LiCAF] single crystals were grown by the micro-pulling-down (μ-PD) method, and the phases, chemical compositions, transmittance and radioluminescence spectra were investigated. All the grown crystals showed high transparency and single phase of LiCAF without visible cracks and inclusions except for the end part of In2%:LiCAF crystal which included the impurity phase. In the radioluminescence spectra of the In:LiCAF crystals under X-ray irradiation, the emission peak around 750 nm was revealed.

(Gd 0.75 ,Ce 0.015 ,La 0.235 ) 2 Si 2 O 7 (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.

The ns2-type metal elements (Pb and Sn) doped LiCaAlF6 single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF6 [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF2 during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed.

Time and cost effective methods are highly desirable in research and development of new scintillators. Modern techniques like micro-pulling down (μ-PD) are suitable for material screening but are unfit for the growth of some crystals. These crystals must be grown by different methods that are usually very time demanding. Modification of halide μ-PD apparatus by custom made elements allowed us to grow cesium hafnium chloride (Cs2HfCl6) by vertical Bridgman method (VB) with significantly reduced growth time. Structural and optical properties of samples prepared from as-grown crystals were studied and compared to crystals grown by standard VB method. The X-ray diffraction confirmed the formation of cesium hafnium chloride single-phase and natural cleavage of the crystals along the (1 1 1) crystallographic plane. Photoluminescence emission, excitation, absorption, and radioluminescence spectroscopy revealed that the optical quality of the crystals grown by modified VB method was comparable to the quality of the crystals grown by standard VB method. Therefore we can use samples prepared by modified VB to estimate and optimize the performance of Cs2HfCl6 based crystals in scintillation detectors. This setup allows the time and cost-effective material screening and it is a powerful tool for the development of new halide based single crystal scintillators.

The transparent single crystals of high-melting strontium hafnate (SHO) and strontium zirconate (SZO) have been grown by the floating zone method with vertical mirror arrangement. The X-ray diffraction analysis revealed orthorhombic perovskite structures for both compounds. Evaporation of Sr-containing species during the growth was proved by micro x-ray fluorescence analysis and led to slightly Sr-poor composition in the studied materials. The overall scintillation efficiency of SHO was found to be comparable with that of Bi4Ge3O12 standard scintillator, while that of SZO was considerably lower. The emission spectrum of both compounds was red-shifted when compared to the previously intensively studied powder counterparts and the photoluminescence decay curves became accelerated with pronounced nonexponentiality. The phenomenological model applied to the temperature dependences of the luminescence data revealed that in single crystals the leading luminescence process is either strongly modified with respect to powders or is of a different origin. The scintillation light yield of both materials was determined to be only several tens of photons per MeV under alpha-ray excitation due to strong afterglow, most probably related to ionization of excited state of the luminescence center.

In this work, a group of Lu 2 SiO 5 :Tb (LSO:Tb) scintillating layers with a Tb concentration between 8% and 19% were investigated by means of synchrotron and laboratory techniques. The scintillation efficiency measurements proved that the highest light yield is obtained for a Tb concentration equal to 15%. At higher concentration, quenching processes occur which lower the light emission. The analysis of the reciprocal space maps of the (082) (280) and (040) Bragg reflections showed that LSO:Tb epilayers are well adapted on YbSO substrates for all the investigated concentrations. The spatial resolution tests demonstrated the possibility to achieve a resolution of 1 μm with a 6 μm thick scintillating layer.

Journal of luminescence 141, 137-143 (2013). doi:10.1016/j.jlumin.2013.03.036, Absorption, cathodoluminescence, excitation spectra of photoluminescence (PL) and PL decay kinetics were studied at 300 K for the double doped with Bi3+–Pr3+ and separately doped with Bi3+ and Pr3+ Lu3Al5O12 (LuAG) and Y3Al5O12 (YAG) single crystalline film (SCF) phosphors grown by the liquid phase epitaxy method. The emission bands in the UV range arising from the intrinsic radiative transitions of Bi3+ based centers, and emission bands in the visible range, related to the luminescence of excitons localized around Bi3+ based centers, were identified both in Bi–Pr and Bi-doped LuAG and YAG SCFs. The energy transfer processes from the host lattice simultaneously to Bi3+ and Pr3+ ions and from Bi3+ to Pr3+ ions were investigated. Competition between Pr3+ and Bi3+ ions in the energy transfer processes from the LuAG and YAG hosts was evidenced. The strong decrease of the intensity of Pr3+ luminescence both in LuAG:Pr and YAG:Pr SCFs phosphors, grown from Bi2O3 flux, is observed due to the quenching influence of Bi3+ flux related impurity. Due to overlap of the UV emission band of Bi3+ centers with the f–d absorption bands of Pr3+ ions in the UV range and the luminescence of excitons localized around Bi ions with the f–f absorption bands of Pr3+ ions in the visible range, an effective energy transfer from Bi3+ ions to Pr3+ ions takes place in LuAG:Bi,Pr and YAG:Bi,Pr SCFs, resulting in the appearance of slower component in the decay kinetics of the Pr3+ d–f luminescence., Published by Elsevier, New York, NY [u.a.]

We studied the processes occurring in the 5d1 excited state of Ce3+ in Gd3Ga3Al2O12 (GGAG) host. Energy transfer from Gd3+ to Ce3+ was evidenced by photoluminescence excitation spectra of Ce3+ emission. We measured temperature dependences of prompt nanosecond decays and millisecond delayed recombination decays of Ce3+ in GGAG host. The decrease of nanosecond decay times above approximately 200 K is due to thermally induced ionization of the 5d1 excited state of Ce3+. Thermal stimulated luminescence glow curve measurements after X-ray or UV (within 4f–5d1 absorption of Ce3+) irradiation at RT provide another support for the ionization effect around this temperature.

To examine scintillation response of piezoelectric crystals the 241 Am 5.5 MeV α -ray excited emission spectra of langasite family crystals, LGS (La 3 Ga 5 SiO 14 ), LNGA (La 3 Nb 0.5 Ga 5.3 Al 0.2 O 14 ) and LTGA (La 3 Ta 0.5 Ga 5.3 Al 0.2 O 14 ) were measured. Dominating emission bands were observed at 378 nm for LGS, 556 nm for LNGA and 425 nm for LTGA. X-ray excited radioluminescence intensity of these crystals was quantitatively compared with BGO standard scintillator. Photoluminescence 2D-spectra were measured as well and compared with radioluminescence ones. In LTGA also photoluminescence decays were measured for two dominant contributing emission centers. Observed emission bands within 300–360 nm and beyond 400 nm most probably belong to self-trapped or trapped excitons and lattice defects, respectively.

The optical absorption, temperature dependence of emission spectra, prompt nanosecond decays and millisecond delayed recombination decays for Pr^(3+) center in Lu_(0.8)Sc_(0.2)BO_3 host were studied. The photoluminescence decay time decreases from 16 ns (80 K) to 11 ns (300 K), but its steady-state emission intensity at 300 K is stronger than that at 80 K and towards higher temperatures is further decreasing comparatively much less with respect to the decay time shortening, which was proved to be associated with the thermal ionization processes occurring from 5d_1 relaxed state of Pr^(3+). The quantitative parameters governing the ionization processes were calculated.

Structural and optical properties of sol–gel silica based glassceramics doped with 0.1 mol% Ce and codoped with Gd at high concentrations, from 5 mol% up to 40 mol%, are investigated and compared to those of analogous samples doped only with Ce. Raman scattering, transmission electron microscopy, and x-ray diffraction reveal the formation of Gd apatite-like silicate (Gd4.67O(SiO4)3) and of Gd pyrosilicate (Gd2Si2O7) nanophases whose morphology and crystallinity depend on the Gd concentration and thermal treatments. Optical absorption measurements demonstrate the role of the densification atmosphere in modifying the charge state of Ce ions. The incorporation of Ce3+ ions in the nanophases is put in evidence by photo- and radio-luminescence results.

This work deals with luminescence and scintillation characteristics of highly efficient cerium-doped scintillators, lutetium–yttrium orthosilicate (Lu2(1−x)Y2xSiO5:Ce3+, x = 0−1). The radioluminescence, photoluminescence excitation (PLE) and emission (PL) spectra of the CeLu1, CeLu2 centers in LSO, LYSO and YSO are measured and discussed between 80 and 400 K with respect to the CeLu1 and CeLu2 features assignment and separation. The influence of yttrium concentration in Lu2(1−x)Y2xSiO5:Ce3+ on CeLu1, CeLu2 luminescence characteristics is demonstrated. Temperature dependence shows that with increasing yttrium content the onset of the CeLu1 and CeLu2 decay time decrease and CeLu1, CeLu2 delayed recombination integrals increase shift to higher temperatures. The 5d1 thermally induced excited-state ionization of both CeLu1 and CeLu2 centers is confirmed and studied by purely optical methods.

We measured temperature dependences of emission spectra, prompt nanosecond decays and millisecond delayed recombination decays for the Ce3+ center in the SrHfO3 (SHO) host. We characterized two samples with 0.1% and 5Î prepared by the acetate and citrate combustion and solid state reaction, respectively. The decrease of nanosecond decay times above approximately 220 and 260 K, respectively, is due to thermal ionization of 5d1 excited state of the Ce3+ center. Energy barrier of 300 meV, governing this process, is calculated for both the 0.1% and 5Î:SHO samples. Thermoluminescence glow curve measurement after X and UV (310 nm) irradiation at RT provides another support for the 5d1 excited-state ionization of Ce3+ in the SHO host. © 2010 Elsevier B.V. All rights reserved.

Luminescence of the Bi3+ single and dimer centers in UV and visible ranges is studied in YAG:Bi (0.13 and 0.27 at% of Bi, respectively) single crystalline films (SCFs), grown by liquid phase epitaxy from a Bi2O3 flux. The cathodoluminescence spectra, photoluminescence decays, and time-resolved spectra are measured under the excitation by accelerated electrons and synchrotron radiation with energies of 3.7 and 12 eV, respectively. The energy level structure of the Bi3+ single and dimer centers was determined. The UV luminescence of YAG:Bi SCF in the bands that peaked at 4.045 and 3.995 eV at 300 K is caused by radiative transitions of Bi3+ single and dimer centers, respectively. The excitation spectra of UV luminescence of Bi3+ single and dimer centers consist of two dominant bands, peaked at 4.7/4.315 and 5.7/6.15 eV, related to the 1S0→3P1 (A band) and 1S0→ 1P1 (C-band) transitions of Bi3+ ions, respectively. The excitation bands that peaked at 7.0 and 7.09 eV are ascribed to excitons bound with the Bi3+ single and dimer centers, respectively. The visible luminescence of YAG:Bi SCF presents superposition of several wide emission bands peaking within the 3.125–2.57 eV range and is ascribed to different types of excitons localized around the Bi3+ single and dimer centers. Apart from the above mentioned A and C bands the excitation spectra of visible luminescence contain wide bands at 5.25, 5.93, and 6.85 eV ascribed to the O2−→Bi3+ and Bi3+→Bi4+ + e charge transfer transition (CTT) in Bi3+ single and dimer centers. The observed significant differences in the decay kinetics of visible luminescence under excitation in A and C bands of Bi3+ ions, CTT bands, and in the exciton and interband transitions confirm the radiative decay of different types of excitons localized around Bi3+ ions in the single and dimer centers.

Single crystal of the Pr 3+ doped Lu 2 Si 2 O 7 was grown to test its luminescence and scintillation characteristics. Absorption, excitation and photoluminescence (PL) spectra manifest the 4f ↔ 5d transitions in the UV spectral region. Evaluation of temperature dependences of both the Pr 3+ PL decay times and intensities of the delayed radiative recombination enable to determine the ionization barrier of the 5d 1 relaxed excited state of Pr 3+ , being about 0.7–0.75 eV. Fast scintillation decay and efficient radioluminescence at room temperature indicate a good potential of this material system to become fast, high density scintillator though the mechanism of the host-Pr 3+ energy transfer are yet to be understood.