Search

Single crystals of Ce-doped gadolinium scandium aluminum garnet (Gd3Sc2Al3O12; GSAG) with Ca2+, Mg2+ and Li+ co-dopants were grown by the Bridgman method. Regardless of melt composition, crystals tend to grow close to the congruent composition. Introduction of Ca2+ or Mg2+, as in other Ce-doped garnets, leads to an increase of absorption below 350 nm, which may indicate formation of Ce4+ states, while no effect is seen with Li+ co-doping. High Ce concentration and co-doping accelerate the scintillation rise and decay times; the codopants strongly significantly reduce the afterglow. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of two novel types of advanced composite scintillators based on single crystalline films (SCFs) of Lu3Al5O12 garnet (LuAG), doped with Ce3+ and Pr3+ ions, and substrates from single crystals (SCs) of Sc3+ doped LuAG using the liquid phase epitaxy (LPE) method. We show the possibility for simultaneous registration of α-particles and γ-quanta using separation of the decay kinetics of the SCF and crystal parts of such composite scintillators. Namely, large differences in the respective scintillation decay kinetics and decay time values tα and tγ are observed for LuAG:Ce SCF/LuAG:Sc SC and LuAG:Pr SCF/LuAG:Sc SC composite scintillators under excitation by α-particles from an 241Am (5.5 MeV) source and γ-quanta from a 137Cs (662 keV) source. Thus, both developed types of composite scintillators can be applied for simultaneous registration of α-particles and γ-quanta in mixed radiation fluxes. The rate of discrimination of the scintillation signals, coming from the SCF and SC parts of the LuAG:Ce SCF/LuAG:Sc SC composite scintillator, expressed by the tγ/tα ratio, is equal to 1.34–1.96 in the 0–1100 ns time interval. For the LuAG:Pr SCF/LuAG:Sc SC composite scintillators, more significant differences in the scintillation decay kinetics are achieved. In this case, the tγ/tα ratio for these composite scintillators reaches the values 9.6–15.6 in the wide 0–2500 ns time interval. This is the best result among all the types of composite scintillators we developed based on epitaxial structures of garnet compounds. [ABSTRACT FROM AUTHOR]

Luminescence and defect creation processes were studied by the photoluminescence, thermally stimulated luminescence, and electron paramagnetic resonance methods in the UV-irradiated single crystals of undoped YAlO3, containing small amounts of Ce, Mo, and Ti ions as accidental impurities. The luminescence of the electron antisite YAl2+-type centers of different structures was found around 2.45 eV and studied at 4.2-500 K. The luminescence of the Ti3+-related centers (2.03 and 1.73 eV) and Ti4+ centers (2.78 eV) was observed as well. Dependences of the number of the YAl2+-type and Ti3+-related centers on the UV irradiation energy, temperature, and duration, as well as on various crystal heat-treatment procedures were examined. As a result of the photostimulated electron transfer from the O2- ligand ions to Mo4+ and Ti4+ ions, the paramagnetic hole O--type centers and electron Ti3+ and Mo3+ centers are created. The antisite YAl2+-type centers are created due to the photostimulated release of electrons mainly from the Mo3+ centers to the conduction band and their subsequent trapping at the YAl3+ ions located near an oxygen vacancy or a defect at the neighboring Y3+ site. [ABSTRACT FROM AUTHOR]

The self-trapping of holes at oxygen anions was studied by electron spin resonance in UV irradiated CdWO4 crystals. Analysis of superhyperfine interaction of the holes with 183W and 111,113Cd isotopes shows that the self-trapped hole is either delocalized in the space between two energetically equivalent nearest neighbor oxygen ions or tunnels between them. When the temperature increases above 40–50 K the self-trapped holes are thermally liberated and can be retrapped by oxygen ions perturbed by impurity ions. In case of the Nb5+ or Li+ stabilizing impurities the O- centers are thermally stable up to 160–170 K. The study of kinetic characteristics of the self-trapped holes suggests that holes leave oxygen ions by thermally assisted tunneling mechanism via two slightly different channels. Corresponding ionization probabilities are defined by the Arrhenius law with an average thermal ionization energy E=90(5) meV. Calculated pre-exponential factors, about 105 s-1, are small, which is consistent with the tunneling mechanism. Thermal stability and kinetic characteristics of the trapped holes are discussed in light of the scintillation and thermoluminescence characteristics of CdWO4. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Doped Bi[sub 4]Ge[sub 3]O[sub 12] (BGO) fiber single crystals were grown by the micro-pulling-down method with the resistance heating system. Optical absorption measurements before and after x-ray irradiation (induced absorption) were performed in order to investigate the radiation damage of the crystals. The Eu[sup 3+]-doped BGO has shown higher radiation resistance with respect to the equivalently grown undoped BGO fibers. Radio- and photoluminescence characteristics were obtained to clarify the role of Eu[sup 3+] in luminescence and scintillation mechanism. Radioluminescence spectra show the intense and slow (decay time of 1.61 ms) [sup 5]D[sub 0,1]-[sup 7]F[sub x](x=0-6) radiative transitions of Eu[sup 3+], while the intrinsic BGO emission becomes weaker with respect to the undoped BGO. Photoluminescence decay of the intrinsic BGO emission becomes nonexponential and noticeably faster in Eu-doped samples, which evidences the nonradiative energy transfer from intrinsic emission centers to Eu[sup 3+] ions. Thermally stimulated luminescence (TSL) measurements above room temperature prove that Eu[sup 3+] doping strongly influences the concentration of TSL active traps. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper presents new developments in inorganic scintillators widely used for radiation detection. It addresses major emerging research topics outlining current needs for applications and material sciences issues with the overall aim to provide an up-to-date picture of the field. While the traditional forms of scintillators have been crystals and ceramics, new research on films, nanoparticles, and microstructured materials is discussed as these material forms can bring new functionality and therefore find applications in radiation detection. The last part of the contribution reports on the very recent evolutions of the most advanced theories, methods, and analyses to describe the scintillation mechanisms. [ABSTRACT FROM AUTHOR]

We study the presence of quantum tunneling between the Ce3+ activator and host traps in lutetium aluminum garnet (LuAG). We monitor the afterglow of several Ce3+ (Mg2+)-doped LuAG samples in crystal and powder forms. The experiment is performed in the extended temperature range of 77–400 K. An inverse power-law function is fit to the data. A power-law exponent close to 1 confirms that the signal observed up to temperatures around 200–250 K is due to quantum tunneling between the Ce activators and traps. [ABSTRACT FROM AUTHOR]

The scintillation characteristics of Czochralski-grown GdLu2Al2Ga3O12:Ce and GdY2Al2Ga3O12:Ce single crystals were compared for $\gamma$ -ray detection. At 662-keV $\gamma$ -rays, light yield (LY) of 30700 photons/MeV obtained for GdLu2Al2Ga3O12:Ce is higher than that of 27200 photons/MeV obtained for GdY2Al2Ga3O12:Ce, while its energy resolution is inferior (14% versus 10.6%) due to a larger nonproportionality of LY. Scintillation decays were measured using the time-correlated single photon counting technique. A fast component decay time of 48 ns with relative intensity of 71% obtained for GdLu2Al2Ga3O12:Ce is superior to that of 106 ns (57%) for GdY2Al2Ga3O12:Ce. The coincidence time spectrum was measured in reference to a fast BaF2 scintillator, and coincidence time resolution was discussed. [ABSTRACT FROM AUTHOR]

The Gd3(Al,Ga)5O12:Ce single-crystalline films were grown by a liquid phase epitaxy (LPE) technique from BaO-B2O3-BaF2 flux. The scintillation characteristics were investigated and compared to the bulk Gd3(Al2.7Ga2.3)O12:Ce single crystal (SC) grown by the Czochralski technique. The light yield (LY) and energy resolution were measured using an R6231 photomultiplier. At 5.5-MeV $\alpha$ -particles, the LY value of 7100 photons/MeV obtained for Gd3Al2.62Ga2.38O12:Ce-LPE sample is lower than that of 9310 photons/MeV for the Gd3(Al2.7Ga2.3)O12:Ce-SC sample, whereas an energy resolution of the LPE sample is better (5.9% versus 6.6%). The ratio of LY value under excitation with $\alpha$ - and $\gamma$ -rays ($\alpha /\gamma$ ratio) was also determined. Faster scintillation decay time and lower slow-component content were obtained for LPE samples with respect to Gd3(Al2.7Ga2.3)O12:Ce-SC one. [ABSTRACT FROM AUTHOR]

At 4.2-300 K, the steady-state and time-resolved emission and excitation spectra as well as the luminescence decay kinetics in the 10 μs-10 s time range are studied for the undoped and Ce3+-doped single crystals of Y2SiO5 and Lu2SiO5. At low temperatures, a broad intrinsic emission band located at 2.55 eV in Y2SiO5 and 2.58 eV in Lu2SiO5 is observed in the luminescence spectra of all the crystals studied under excitation in the charge-transfer absorption region (with Eexc > 4.2 eV). This emission reveals the slow non-exponential decay kinetics characteristic for tunneling recombination processes. In the slow decay kinetics of the low-temperature luminescence of Ce3+-doped crystals, both the multi-exponential and the non-exponential decay stages are detected. The origin of the defects, responsible for the undesirable slow low-temperature luminescence of the undoped and Ce3+-doped Y2SiO5 and Lu2SiO5 crystals is considered. A new mechanism of the processes, resulting in the appearance of different luminescence decay stages, is proposed. [ABSTRACT FROM AUTHOR]

We present the applications of time-resolved spectrometer for soft X-ray (SXR) excited luminescence measurements. We use the spectrometer to monitor the delayed recombination phenomena in the scintillation response of ZnO:Ga nanoparticles, SrHfO3 microcrystalline powder, and rare-earth doped LiCaAlF6 single crystals in an extended time and dynamic range. The nanosecond soft X-ray (E\approx 0.4\ keV) pulse plasma source is used for excitation of a scintillation process. High sensitivity of our experiment is enabled by an intense nanosecond SXR pulse with a very short absorption length (<1\ \mum) in scintillation materials and sensitive fast photomultiplier-based detection. Thus, we are able to measure decay profiles with signal-to-noise ratio as high as 10^5 and with nanosecond resolution over millisecond time range. Moreover, the presented technique allows studying powder materials, due to the aforementioned extremely short absorption length of SXR. [ABSTRACT FROM PUBLISHER]

We study the low temperature contribution to delayed recombination decay in several complex oxide scintillating crystals. We experimentally test the previously suggested hypothesis that the losses of fast scintillation light even at the lowest temperatures can be due to quantum effects. The results obtained for several material systems confirm that quantum tunneling between the luminescence center and a nearby defect is a good candidate for the origin of the observed phenomena. [ABSTRACT FROM PUBLISHER]

The Czochralski method is one of the very few melt growth techniques that are industry friendly when consid ering the combination of quality, dimensions, and cost of the produced crystals suitable for their commercialization in scintillation detectors. This method is one of the oldest and most developed crystal growth processes regard ing an adequate understanding the physical phenomena observed during solidification process and its practical expansion especially in the industrial scale production. It allows controllable formation of single-crystalline cylin drical ingots of various inorganic scintillation materials. The review summarizes recent progress on the Czochralski growth of a number of scintillation materials. The oxide crystals are mainly considered including the Ce and Pr--doped RE3AI5O12, RE = Y, Lu, aluminum garnets and newly discovered ultraefficient Ce-doped Gd3(Ga,Al)5O12 multicomponent garnet, high density PbW04 and CdW04 tungstates, Ce-doped RE2S1O5, RE = Y, Gd, Lu, oxy-orthosilicates and (Y,Lu)A103 aluminum perovskites and finally the classical Bi4Ge3O12 scintillator. Additionally, the details of the growth of other practically important non-oxide crystals, namely the Ce and Eu-doped LiCaAlF6 neutron and ultraefficient Ce-doped LaBr3 scintillators, are discussed. The potential of novel micro-pulling down growth method is briefly described in the combinatorial search for new scintillator materials. Selected luminescence and scintillation characteristics including the spectra and decay kinetics, light yield and radiation resistance are also illustrated and overviewed. [ABSTRACT FROM AUTHOR]

The research and development of new VUV scintillators includes also LuLiF4 single crystals doped by \Nd^3+. Due to their lower light yield, the \Gd^3+ codoping is studied as a tool to improve an energy transfer from the host to \Nd^3+ emission centers and increase the light yield consequently. Emission spectra and decays with respect to the different concentration of Gd and Nd ions are studied and discussed as well. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We analyze thermally stimulated luminescence (TSL) above room temperature in Ce-doped Y2SiO5 oxyorthosilicate single crystal. We perform detailed TSL glow peak analysis based on the initial rise technique to evaluate trap depths and other characteristics associated with TSL peaks. The tunneling process previously proposed to be at work in recombination mechanism of Ce-doped lutetium oxyothosilicate was not confirmed in presently studied isostructural yttrium silicate. The charge carrier transfer between traps and Ce recombination centers is rather accomplished via conduction band. [ABSTRACT FROM PUBLISHER]

Participation of shallow and deep traps in the processes of energy transfer and capture is studied by means of time- resolved emission spectroscopy and thermoluminescence in several groups of the Ce3+ and Pr3+-doped complex oxide single crystal scintillators. Tunnelling-driven recombination processes are distinguished in all the groups of examined materials: closely spaced electron and hole traps give rise to the t-1 phosphorescence decays at low temperatures in the Ce-doped aluminum garnets and perovskites, while thermally assisted tunneling process is proposed to explain temperature independent trap depth in glow curve peaks within 50-250° C in Ce-doped lutetium orthosilicates. [ABSTRACT FROM AUTHOR]

Intrinsic and Ce-related luminescence of LuAP:Ce single crystalline films (SCF) in comparison with their bulk single crystal (SC) analogs were analyzed for the first time using the time-resolved luminescence spectroscopy under synchrotron radiation excitation. Difference in luminescent properties of SCF and SC are due to the absence of the Lu-at-Al-site antisite defects (AD) and extremely low concentration of vacancy-type defects (VD) in SCF. SCF contamination by Pb ions from flux is noted, which gives rise to an additional emission band in UV range. In SCF, the absence of emission and trapping centers formed by the mentioned AD and VD can explain their favorable timing characteristics with respect to SC. The role of Pb2+ trace impurities in LuAP-based SCF scintillators is considered as well. [ABSTRACT FROM AUTHOR]

Abstract: A brief review of recent results obtained at systematic study of the luminescence and photo-thermally stimulated defect creation processes in various undoped and doped crystals is presented. Origin of the blue—B and two green—G(I) and G(II) emissions is clarified. Various localized exciton states are identified and their decay into defects is found. Origin of the defects, created at the decay of self-trapped and localized exciton states and -related states, is studied both by TSL and ESR methods. The origin of the TSL peaks and the mechanisms of defect creation and recombination processes are discussed. [Copyright &y& Elsevier]

The luminescence of excitons and antisite defects (ADs) was investigated, as well as the specific features of the excitation energy transfer from excitons and ADs to the activator (Ce3+ ion) in phosphors based on Lu3Al5O12:Ce (LuAG:Ce) single crystals and single-crystalline films, which are characterized by significantly different concentrations of ADs of the Lu3+Al type and vacancy-type defects. The luminescence band with λmax = 249 nm in LuAG:Ce single-crystal films is due to the luminescence of self-trapped excitons (STEs) at regular sites of the garnet lattice. The excited state of STEs is characterized by the presence of two radiative levels with significantly different transition probabilities, which is responsible for the presence of two excitation bands with λmax = 160 and 167 nm and two components (fast and slow) in the decay kinetics of the STE luminescence. In LuAG:Ce single crystals, in contrast to single-crystal films, the radiative relaxation of STEs in the band with λmax = 253.5 nm occurs predominantly near Lu3+Al ADs. The intrinsic luminescence of LuAG:Ce single crystals at 300 K in the band with λmax = 325 nm (τ = 540 ns), which is excited in the band with λmax = 175 nm, is due to the radiative recombination of electrons with holes localized near Lu3+Al ADs. In LuAG:Ce single crystals, the excitation of the luminescence of Ce3+ ions occurs to a large extent with the participation of ADs. As a result, slow components are present in the luminescence decay of Ce3+ ions in LuAG:Ce single crystals due to both the reabsorption of the UV AD luminescence in the 4f–5d absorption band of Ce3+ ions with λmax = 340 nm and the intermediate localization of charge carriers at ADs and vacancy-type defects. In contrast to single crystals, in phosphors based on LuAG:Ce single-crystal films, the contribution of slow components to the luminescence of Ce3+ ions is significantly smaller due to a low concentration of these types of defects. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

On-line measured radiation-induced absorption spectra and their kinetics are presented for the doped PbWO4, YAlO3:Ce and CsI crystals. In the doubly doped PbWO4:Mo,Y crystals the saturation level of the induced absorption increased with Mo concentration up to 2750 ppm. With a higher concentration it again gradually decreased. Yttrium co-doping around 100 ppm improved considerably the radiation hardness of Mo-doped PbWO4. Characteristic recovery time of these crystals was about 30 min. Positive influence of Zr+4 co-doping on characteristics of a set of YAlO3:Ce samples resulted in decrease in the induced absorption intensity. The presence of very slow recovery processes was in good agreement with thermoluminescence characteristics above room temperature reported earlier. An absorption band round 420 nm appeared in as-grown CsI crystals doped with Tl, and was related to the oxygen contamination. [Copyright &y& Elsevier]

A newly developed hybrid photo-multiplier (HPMT) was used to measure scintillation photoelectron yield Nphels(E) of well-known YAP:Ce and YAG:Ce scintillating crystals. Nphels(E) measured by the HPMT or evaluated LY(E) were compared with results obtained by the classical PMT. Generally, both crystals are characterized by roughly the same photoelectron and light yields which can reach up to 6400 phels/MeV or 24 000 ph/MeV, respectively. These yields were measured with cylindrical plates of shape ∅ 10 × 1 or 2 mm3 under 662 keV γ-ray radiation. The energy resolutions of both crystals at 662 keV are good and the best values reach ≅4.6% or ≅5.1% for YAP:Ce or YAG:Ce, respectively. [Copyright &y& Elsevier]

Single crystals of Yb-doped LiCaAlF6 were grown by the Czochralski technique under CF4 atmosphere. Photoluminescence and decay kinetics of Yb2+ center in the LiCalF6 single crystal host is described in 4–300 K. Phenomenological two excited-state-level model is introduced to obtain quantitative characteristics of the excited state dynamics of Yb2+ emission center. [Copyright &y& Elsevier]

Decay kinetics of the green emission of PbWO4:Mo crystals is measured in wide temperature range 0.4–400 K. Experimental data are satisfactorily fitted by two excited-state level model. Rapid decay-time shortening at higher temperatures is explained by thermal ionization of (MoO4)2−center. This hypothesis is confirmed by thermoluminescence measurements. The same value, 0.26 eV, of activation energy of this process is evaluated from both the thermoluminescence measurements and decay kinetics modeling. [Copyright &y& Elsevier]

Set of YAlO3:Ce single crystals co-doped with Zr4+ ions at concentrations of 0–200 ppm was characterized by photo-, radio- and thermo-luminescence, scintillation decay and light yield measurements. Positive influence of Zr co-doping was found, especially for the speed of scintillation response and lowering of TSL active traps. [Copyright &y& Elsevier]

Radiation induced absorption spectra (irradiation up to 500 Gy by 60 Co) and TSL of a set of YAP:Ce crystals co-doped by Zr 4+ were investigated. Positive effect of Zr 4+ co-doping was found, namely reduction of both the defect creation and presence of TSL active traps. Up to three absorption bands were observed in the radiation induced absorption spectra. They probably have different origin - from colour centers in the green part of the spectra to change of the Ce 3+ valency in the near UV. [ABSTRACT FROM AUTHOR]

Radio-, photo- and thermo-luminescence were measured for two sets of PbWO 4 single crystal samples doubly doped with Mo and Nb 5+ /Ta 5+ ions. Pentavalent ion codoping of PbWO 4 :Mo enhances the radioluminescence intensity to the level exceeding that of BGO scintillator. However, it introduces a new trapping level, which is reflected by the intense thermoluminescence-glow-curve peak around 100 K. This trapping center is probably responsible for the increased occurrence of slow decay components in such doubly doped PbWO 4 . [ABSTRACT FROM AUTHOR]

The experimentally observed structure in the blue emission of PbWO 4 crystals is analyzed theoretically. The full interaction Hamiltonian, including ligand field, Jahn-Teller, pseudo Jahn-Teller, and spin-orbit interactions is considered. The emission-band shape is numerically calculated using Monte-Carlo integration using both semiclassical and quantum-mechanical approaches. Theoretical results are qualitatively compared to experimentally observed spectra. [ABSTRACT FROM AUTHOR]

Pr-doped Lu3(GaxAl1-x)5O12:Pr, x=0–1, single crystals were grown by the micro-pulling-down method. We study luminescence and scintillation characteristics of the sample set focusing on their dependence on the gallium content. For x=0.4 we obtain the high figure-of-merit material with elevated density, high efficiency, and very fast scintillation response below 20 ns without any slower components. Improvement of scintillation performance is explained as due to the absence of the antisite LuAl defects that was for the first time realized in such bulk garnet single crystals grown from the high temperature melt. [ABSTRACT FROM AUTHOR]

Abstract: The radiation hardness of the set of seven samples of Mo-doped PbWO4 crystals (from 0 up to 10,000ppm) and further codoped by Y, La, Nb, is investigated. With increasing Mo concentration above 1000ppm radiation hardness increases. Codoping by Y, La can still decrease radiation-induced absorption about several tens percent at least, while influence of Nb is not clear. Induced absorption increases with the dose rate, for dose rates higher than 0.35Gy/min it achieves saturation level. As it is planned to use PbWO4 scintillating crystals at lower temperature in ALICE experiment in CERN, some measurements were performed at temperature -15°C too. Induced absorption coefficient at low temperature is 2–4 times higher with respect to room temperature and kinetic of recovery processes gets slower. [Copyright &y& Elsevier]

The influence of Ba (co)doping of PWO samples on the radioluminescence intensities has been tested. The codoping of the PWO:Mo,Nb crystals by Ba can increase markedly the intensities of the green luminescence, but only under the condition that the Ba concentrations fall into a limited concentration region. The green luminescence was also found in the PWO crystals doped only by Ba, and in the PWO crystals grown from melts with surplus of tungsten oxide. In the case of PWO:Mo,Ba crystals the increase of radioluminescence intensities with Ba concentrations is tentatively connected with inner stress caused by the difference in the size of Ba and Pb ions. [Copyright &y& Elsevier]

Scintillation, radioluminescence, photoluminescence, and thermoluminescence characteristics of Czochralski-grown Yb[sub x]Y[sub 1-x]AlO[sub 3] single crystals for x=0.02–0.45 are described. Under x-ray excitation, the intensity of Yb[sup 3+] charge-transfer luminescence is increasing with x and reaches at room temperature more than 11% of Bi[sub 4]Ge[sub 3]O[sub 12] (BGO) for x=0.45, while at 80 K it is over 170% of BGO for x>=0.3. At room temperature, scintillation decay shows a dominant decay time of 0.8–0.9 ns for x>=0.3 and no significant slow components were detected. The photoluminescence decay time is tuned by temperature and Yb concentration from tens of nanoseconds at 80 K down to about 0.8 ns at 295 K. Thermoluminescence glow curve below room temperature evidences very low concentration of shallow traps compared to the Ce-doped YAlO[sub 3] scintillator. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Assesses scintillation decays and thermoluminescence of lead tungsten tetraoxide (PWO) single crystals. Influence of lanthanum doping on decays; Correlations of emission spectra and light yield in the PWO single crystals; Mechanism of photoluminescence decay.

We report on picosecond dynamics of photoexcited carriers in CsPbCl[sub 3] nanocrystals in a CsCl host. For low carrier densities, photoexcited carriers form excitons, which decay with a characteristic time constant of 170 ps at 300 K. Under strong photoexcitation, we have observed the Auger recombination with the Auger coefficient Capprox. 10[sup -29] cm[sup 6] s[sup -1]. We have identified the onset of the Auger recombination at the carrier densities of approx. 10[sup 20] cm[sup -3] as the Mott-like transition from excitons to electron-hole plasma in nanocrystals. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Pr-doped Lu3Al5O12 (Pr:LuAG) bulk single crystals were grown by Czochralski method. The crystals were seeded-grown in the 〈111〉 direction. Dimensions up to 100mm in length and 1in in diameter were achieved without cracking. Concentrations of Pr3+ in several parts of grown crystals were measured precisely and segregation coefficients of each crystal were determined. Scintillation light yield of each part of the crystals was measured and dependence on light yield on Pr concentration was determined. Optimum concentration of Pr was clarified and compared to the standard Bi4Ge3O12(BGO) sample; Pr optimum concentration was around 0.2–0.3% and light yield of Pr:LuAG was more than two times higher than BGO. Scintillation decay of Pr:LuAG was measured and a dominant decay time of about 20ns was evaluated. [Copyright &y& Elsevier]

Radiation-induced absorption spectra were measured to study the influence of trivalent ion codoping (Y, La) on radiation hardness of PWO:Mo scintillators and to compare samples coming from two different laboratories. It follows from the experiments that trivalent ion codoping significantly reduces the induced absorption coefficient of PWO:Mo. At the same time, the shape of induced absorption spectra becomes more complicated and even bleaching of absorption after irradiation was observed in Y-codoped samples in the spectral region round 420 nm. When comparing Y and La-codoped samples, the positive effect of La is much less significant than that of Y. Also, no absorption bleaching round 420 nm after irradiation was found in the latter case. [Copyright &y& Elsevier]

Abstract: Emission and excitation spectra and luminescence decay kinetics were studied for Pr3+-doped Lu3Al5O12 and Y3Al5O12 single crystalline films (SCF) grown by the liquid phase epitaxy method from a PbO-based flux. The influence of lead-induced centers on their scintillation characteristics was clarified. It was found that the influence of single Pb2+-based centers on the characteristics of Pr3+ centers due to the Pb2+ →Pr3+ energy transfer was weak. However, an overlap of the emission spectra of single and dimer lead-induced centers with the emission spectrum of Pr3+ ions, and especially a strong overlap of the 4f–5d1 absorption band of Pr3+ ions with the slow emission of localized excitons in the 290nm band had a considerable influence on the scintillation characteristics of the Pr3+-doped SCF. [Copyright &y& Elsevier]

Shaped single crystals of (LuxGd1-x)3Ga5O12 (0.0⩽x⩽1.0) and (Yb0.05LuxGd0.95-x)3Ga5O12 (0.0⩽x⩽0.9) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)3Ga5O12 are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd3+ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd3+ or Yb3+ cations below 240 nm. A complete absence of Yb3+ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb3+ by that of Gd3+ ions. For specific composition of Lu1.5Gd1.5Ga5O12 an intense defect-host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi4Ge3O12, was found. [Copyright &y& Elsevier]

• Crystal growth of CsMgF 3 by micro-pulling-down method was investigated. • Contrary to published equilibrium phase diagram Cs 4 Mg 3 F 10 was a stable phase. • Due to evaporation, excess CsF was required to grow transparent Cs4Mg3F10 crystals. • Scintillation properties of Cs 4 Mg 3 F 10 were measured. In our search for cross-luminescence (CL) scintillators suitable for fast-timing applications, we have chosen CsMgF 3 as one of the perspective candidates. During the attempts to grow CsMgF 3 by the micro-pulling-down method, we have revealed the presence of Cs 4 Mg 3 F 10 which is in contradiction with the published equilibrium phase diagram. The Cs 4 Mg 3 F 10 has an orthorhombic structure, consisting of face-sharing MgF 6 octahedra triplets (4 triplets per unit cell), joined to 4 other triplets by corner sharing. These chain-like structures are separated by Cs+ ions. Moreover, Cs 4 Mg 3 F 10 is non-hygroscopic despite the hygroscopic nature of CsF. The best crystals were grown from CsF-rich melt to suppress off-stoichiometry due to CsF evaporation during crystal growth. Both radioluminescence spectra and scintillation decay kinetics exhibit complex character and the presence of CL in Cs 4 Mg 3 F 10 is still under question. However, due to relatively low scintillation efficiency and the presence of slow components in scintillation decay, Cs 4 Mg 3 F 10 is not suitable for fast-timing applications. [ABSTRACT FROM AUTHOR]

Abstract For the first time, an effective photostimulated creation of defects is observed under selective irradiation of the undoped Gd 3 Ga 3 Al 2 O 12 single crystal and the Ce - doped Gd 3 (Ga,Al) 5 O 12 single crystal and epitaxial film in the Gd3+ - related 8S 7/2 → 6I J and 8S 7/2 → 6P J absorption bands. Defects creation processes are investigated by the thermally stimulated luminescence (TSL) method in the 4.2–500 K temperature range. The dependences of the TSL glow curve peak intensity on the irradiation photon energy, irradiation temperature, and irradiation duration are measured and analyzed. The activation energy of the TSL glow curve peaks creation is found to be about 0.02 eV. Possible mechanisms of defects creation under irradiation in the absorption bands of Gd3+ in Gd 3 Ga 3 Al 2 O 12 and Gd 3 (Ga,Al) 5 O 12 :Ce are discussed. Highlights • Crystals and epitaxial films of undoped and Ce-doped Gd 3 (Ga,Al) 5 O 12 are studied. • Intrinsic electron centers are created under irradiation in the Gd3+ absorption bands. • The defects creation processes are investigated by the thermoluminescence method. • The activation energy of the photostimulated defects creation is about 0.02 eV. • The defects are created as a result of the {Gd3+ - > acceptor} energy transfer. [ABSTRACT FROM AUTHOR]

Particle detectors at future collider experiments will operate at high collision rates and thus will have to face high pile up and a harsh radiation environment. Precision timing capabilities can help in the reconstruction of physics events by mitigating pile up effects. In this context, radiation tolerant, scintillating crystals coupled to silicon photomultipliers (SiPMs) can provide a flexible and compact option for the implementation of a precision timing layer inside large particle detectors. In this paper, we compare the timing performance of aluminum garnet crystals (YAG: Ce, LuAG: Ce, GAGG: Ce) and the improvements of their time resolution by means of codoping with Mg 2+ ions. The crystals were read out using SiPMs from Hamamatsu glued to the rear end of the scintillator and their timing performance was evaluated by measuring the coincidence time resolution (CTR) of 150 GeV charged pions traversing a pair of crystals. The influence of crystal properties, such as density, light yield and decay kinetics on the timing performance is discussed. The best single detector time resolutions are in the range of 23–30 ps (sigma) and only achieved by codoping the garnet crystals with divalent ions, such as Mg 2 + . The much faster scintillation decay in the co-doped samples as compared to non co-doped garnets explains the higher timing performance. Samples of LSO: Ce, Ca and LYSO:Ce crystals have also been used as reference time device and showed a time resolution at the level of 17 ps, in agreement with previous results. [ABSTRACT FROM AUTHOR]

This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO 3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations in the solid solution La 1-x Ce x AlO 3 from x ​= ​0.001 up to x ​= ​1.0. From EPR measurements, Ce3+ g tensor parameters were determined as a function of Ce concentration. The g tensor has an orthorhombic symmetry even in the trigonal phase (x ​< ​0.1) suggesting that the incorporation of Ce at La site lowers the lattice symmetry near this ion. The local properties of the La 1-x Ce x AlO 3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with the Ce concentration from 0 ​ppm up to 165 ​ppm at x ​= ​0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce–O–La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain a satellite peak whose intensity linearly increases with an increase of the Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of the crystal structure modification in the vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO 3 will be determined namely by the local crystal structure near this ion. • Ce3+ incorporation in LaAlO 3 crystals is investigated by advanced EPR and NMR techniques. • Ce3+ g tensor parameters were determined as a function of Ce concentration in the range up to 100%. • Ce–O–La and Ce–O–Al chemical bonds are characterized by NMR measurements. • Crystal structure modification in the vicinity of Ce ions are determined. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric spectroscopy was performed on single crystals of pure, Ce-doped or Ce,Zr-codoped Lu3Al5O12, before and after UV- or X-irradaiation, at various frequencies within the range 100Hz–1MHz as the temperature was scanned from 110 to 353K. All samples previously subjected to ionising radiations gave spectra showing loss peaks with Arrhenius characteristics of permanent dipoles relaxation. We attribute the dipoles to defect-stabilised pairs of anion–anion vacancies (oxygen ions and oxygen vacancies) that have captured holes and photo-electrons separately, thus forming O−- and F+-like centers. The dielectric relaxation peaks disappeared in undoped or doped samples annealed at 573K, suggesting that charge carrier traps are relatively deep. UV–visible absorption spectra have also been measured, which tend to support our proposed interpretation. Further evidence for deep traps has come from thermally stimulated luminescence experiments. [Copyright &y& Elsevier]

Photo- and thermally stimulated luminescence characteristics, as well as photostimulated defects creation processes are investigated in the 85–510 K temperature range for the Li+ co-doped single crystal of Gd 3 (Ga,Al) 5 O 12 :Ce (GAGG:Ce). The results for GAGG:Ce,Li are compared with the corresponding characteristics of the GAGG:Ce and GAGG:Ce, Mg single crystals of similar host composition. The influence of Li+ and Mg2+ ions on the Ce3+ - related emission band position, temperature dependence of the photoluminescence intensity, efficiency of the Gd3+ → Ce3+ energy transfer, intensity and decay kinetics of the afterglow, and thermally stimulated luminescence characteristics is revealed. The presence of the Ce3+ → Ce4+ conversion in GAGG:Ce,Li is confirmed. The conclusion is made that, unlike GAGG:Ce,Mg, the compensation of the Li+ excess negative charge in GAGG:Ce,Li occurs due to both the Ce3+ → Ce4+ conversion and the effective formation of intrinsic crystal lattice defects. The origin of these defects as well as the origin of the electron and hole trapping centers in the GAGG:Ce,Li crystal are discussed. The defects responsible for the low-temperature TSL glow curve peak can appear in the GAGG:Ce,Li crystal for the Li+ - induced excess volume and excess negative charge compensation. Besides, the Li+ ions can stimulate the formation in the crystal of hole centers which are most probably of the O− - type centers [35]. The O− - Li+ centers will be most probably responsible for the high-temperature peaks, like the O− - Mg2+ centers. Moreover, the lack of positive charge in lattice can stimulate creation of single O− centers with low thermal stability. • Photo- and thermally stimulated luminescence of Gd3(Ga,Al)5O12:Ce single crystals co-doped with Li+ is investigated. • Co-doping with Li + leads to both the Ce3+.→ Ce4+ conversion and the formation of intrinsic defects; • Origin of the Li + -induced crystal lattice defects is considered. • Influence of the Li + co-doping on scintillation characteristics of Gd3(Ga,Al)5O12:Ce is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Using the micro-pulling-down method, Pr3+-doped Y2SiO5 single crystals have been grown and their optical and luminescence properties have been investigated. The position of the lowest 5d absorption level was found at about 246nm and an intense and fast 5d–4f luminescence peaking round 275nm with a shoulder round 315nm has been observed at room temperature. Photoluminescence decay time at room temperature was obtained to be of about 17ns in the leading decay component. [Copyright &y& Elsevier]

Abstract: Characteristics of two green emission bands, G(I) and G(II), and their origin were investigated within 0.4–300K under photoexcitation in the 3.4–6.0eV energy range for undoped and Mo6+-, Mo6+ , Y3+-, Mo6+, Nb5+-, Mo6+, Ce3+-, Cr6+-, La3+-, Ba2+- and Cd2+-doped PbWO4 crystals with different concentrations of impurity and intrinsic defects, grown by different methods and annealed at different conditions. The G(I) emission band, observed at low temperatures, located around 2.3–2.4eV and excited around 3.9eV, is usually a superposition of many closely positioned bands. The G(I) emission of undoped crystals is assumed to arise from the WO4 2− groups located in the crystal regions of lead-deficient structure. In Mo6+-doped crystals, this emission arises mainly from the MoO4 2− groups themselves. The G(II) emission band located at 2.5eV is observed only in the crystals, containing the isolated oxygen vacancies — WO3 groups. This emission appears at T>160K under excitation around 4.07eV as a result of the photo-thermally stimulated disintegration of localized exciton states and subsequent recombination of the produced electron and hole centres near WO3 groups. The G(II) emission accompanies also thermally stimulated recombination processes in PbWO4 crystals above 150K. Mainly the G(II) emission is responsible for the slow decay of the green luminescence in PbWO4 crystals. [Copyright &y& Elsevier]

Abstract: Luminescence and scintillation properties of single crystalline films (SCF) of Ce- and Pr-doped (YAG) and (LuAG) garnets were analysed and compared with their bulk single crystal (SC) analogues. It was shown that the main peculiarities of luminescent properties of Ce- and Pr-doped YAG and LuAG SCF are due to the absence of and antisite defects (AD) and to the extremely low concentration of vacancy-type defects in SCF with respect to SC. In SCF the absence of the AD-related traps results in faster energy transfer to the emission centres and accelerated scintillation response. [Copyright &y& Elsevier]

Point defects acting as trap levels were investigated on undoped, Ce- and (Ce, Si)-doped Y3Al5O12 (YAG) crystals by TSL measurements performed over a wide temperature range (10–800 K). Below room temperature, a composite glow curve was observed, whose intensity strongly increased after Ce doping. Moreover, Ce doping introduced new trap levels giving rise to glow peaks in the 100–200 K range. On the other hand, Si co-doping did not influence the low T glow curve in a significant way. The spectral emission of the TSL was found to be governed by the Ce3+ 5d–4f radiative transition, while defect related higher energy emission bands were detected only in the undoped crystal. Above RT, the glow curve was found to be much more influenced by Si co-doping since a strong increase of a glow peak at about 250°C was noticed. Scintillation time decays of Ce- and Ce,Si-doped samples are also reported and compared with TSL data. The significance of the results and the potential impact of defect states on the scintillation properties are discussed. [Copyright &y& Elsevier]