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Cd2+ cation doped CsPbCl3 single crystals were synthesized, and their luminescent properties were investigated under excitation with synchrotron radiation quanta with energy greater than Eg and at a sample temperature of 12 K. Pure single crystals exhibit a narrow band of exciton emission at 416.7 nm. Doping the single crystals leads to a high-energy shift of the excitonic luminescence, the appearance of new luminescent bands, the broadening of the luminescent bands, an increase in the decay time constants, and a significant enhancement of the luminescence intensity. The observed changes in luminescent parameters upon doping are discussed in terms of the crystal structure ordering, a decrease in the number of defects responsible for capturing charge carriers at the stage of electronic excitation thermalization, and a decrease in defects that quench excitonic luminescence. Doped single crystals with decay times of the order of 0.4 ns and intensities that significantly exceed the intensity of pure single crystals can be promising scintillation materials for positron emission tomography in the time-of-flight mode. [ABSTRACT FROM AUTHOR]

In this work, we compare the luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with different numbers of QWs. Structures are designed for scintillating applications, where large QW number covering particle penetration depth is necessary, and fast luminescence response is required. Special attention is devoted to increase the intensity of fast excitonic QW emission and to decrease the luminescence of the QW defect band, which has slower luminescence response and is undesired for fast scintillator applications. We found that increasing the In content in QWs suppresses the defect band luminescence and decreasing the QW growth rate increases the photoluminescence (PL) intensity of excitonic luminescence. We also show that increasing the number of InGaN further improves the PL properties of InGaN QWs. The photoluminescence and cathodoluminescence characteristics are compared and discussed. [ABSTRACT FROM AUTHOR]

Polystyrene film nanocomposites of 0.3mm thickness with embedded LaPO4-Pr nanoparticles (40 wt. %) have been synthesized. The luminescent and kinetic properties of these polystyrene composites with embedded LaPO4-Pr nanoparticles upon pulse X-ray excitation have been studied. The luminescence intensity of this polystyrene material significantly increases as it is loaded with inorganic LaPO4-Pr nanoparticles. Nanocomposite films reveal luminescence spectra typical for polystyrene activators (p-Terphenyl and POPOP) and two components of decay time kinetics of luminescence with 12 ns and 2.8 ns time constants, depending on nanoparticle sizes. The component with 12 ns decay constant arises due to the radiative transfer of the 5d-4f-emission of the Pr3+ ions in the LaPO4 nanoparticles to the polystyrene. The decay component with the time constant 2.8 ns originates from luminescence of polystyrene matrix excited by electrons emitted from nanoparticles due to the photoeffect. This nonradiative mechanism of energy transfer from nanoparticles to polystyrene matrices is determinative for nanoparticles, as their sizes are smaller than a mean free path of an electron. [ABSTRACT FROM AUTHOR]

Dy3+-, Tb3+-activated, and Tb3+/Dy3+-coactivated oxyfluoride borogermanate scintillating glasses with the density of about 6.50 g/cm³ were successfully synthesized by a melt-quenching method. The structure and optical properties including transmittance, photoluminescence (excitation and emission spectra), photoluminescence decay, and X-ray excited luminescence (XEL) behaviors were studied in detail. Our results reveal that the energy transfer efficiency from Dy3+ to Tb3+ ions increases with an increase of Tb3+ concentration. The energy transfer mechanism is determined to be electric dipole–dipole interaction. However, the XEL intensity of Tb3+ decreases with the incorporation of sensitizer Dy3+ into borogermanate scintillating glass, which may result from the different mechanisms under ultraviolet light and X-ray excitation. [ABSTRACT FROM AUTHOR]

Crack-free La3+-substituted BaCl2 single crystals without and with Eu2+ as an activator were successfully grown using the micro-pulling-down method. Luminescence bands from BaCl2 without and with the Eu2+ activator were assigned as mainly intrinsic and extrinsic, respectively. Therefore, BaCl2 as a host material is suitable for investigating the effects of the emission mechanism on the non-proportionality curves and energy resolution plots. First, the scintillation characteristics of BaCl2:La3+ (11 at. %) and BaCl2:La3+ (7.7 at. %): Eu2+ (0.5 at. %) single crystals were determined along with those of BaCl2 and BaCl2:Eu2+ (0.5 at. %) crystals. Second, the nonproportionality curves from the different emission origins in BaCl2 were confirmed to be consistent with phenomenological models. Third, the non-proportionality curves and energy resolution plots originating from intrinsic (without Eu2+) and extrinsic (with Eu2+) luminescence were compared. The results experimentally demonstrated that the emission mechanism influenced scintillator non-proportionality curves. [ABSTRACT FROM AUTHOR]

Crack-free La3+-substituted BaCl2 single crystals without and with Eu2+ as an activator were successfully grown using the micro-pulling-down method. Luminescence bands from BaCl2 without and with the Eu2+ activator were assigned as mainly intrinsic and extrinsic, respectively. Therefore, BaCl2 as a host material is suitable for investigating the effects of the emission mechanism on the non-proportionality curves and energy resolution plots. First, the scintillation characteristics of BaCl2:La3+ (11 at. %) and BaCl2:La3+ (7.7 at. %): Eu2+ (0.5 at. %) single crystals were determined along with those of BaCl2 and BaCl2:Eu2+ (0.5 at. %) crystals. Second, the nonproportionality curves from the different emission origins in BaCl2 were confirmed to be consistent with phenomenological models. Third, the non-proportionality curves and energy resolution plots originating from intrinsic (without Eu2+) and extrinsic (with Eu2+) luminescence were compared. The results experimentally demonstrated that the emission mechanism influenced scintillator non-proportionality curves. [ABSTRACT FROM AUTHOR]

The dependence of X-ray excited luminescence intensity on BaF2 nanoparticle size was studied. A sharp decrease of self-trapped exciton luminescence intensity was observed when the nanoparticle size is less than 80 nm. The main mechanism of the luminescence quenching is caused by the escape of electrons from the nanoparticles. Escape of electrons from nanoparticles is confirmed by the considerable increase of luminescence intensity of the polystyrene scintillator with embedded BaF2 nanoparticles comparing with pure polystyrene scintillator. [ABSTRACT FROM AUTHOR]

Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF2:Eu and YAlO3:Ce scintillators to single ions of H+, He+, and O3+ are measured by the corresponding pulse height over a continuous energy range using a time-of-flight-scintillator-photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) can be produced by energetic H+, He+ and O3+ ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of the scintillators to irradiation. [ABSTRACT FROM AUTHOR]

Using a phenomenological approach, the light yield is derived for inorganic scintillators as a function of the rates of linear, bimolecular, and Auger processes occurring in the electron track initiated by an x ray or a γ-ray photon. A relation between the track length and incident energy is also derived. It is found that the nonproportionality in the light yield can be eliminated if either nonlinear processes of interaction among the excited electrons, holes, and excitons can be eliminated from occurring or the high density situation can be relieved by diffusion of carriers from the track at a faster rate than the rate of activation of nonlinear processes. The influence of the track length and radius on the yield nonproportionality is discussed in view of the known experimental results. Inventing new inorganic scintillating materials with high carrier mobility can lead to a class of proportional inorganic scintillators. Results agree qualitatively with experimental results for the dependence of light yield on the incident energy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aluminate perovskites YAlO3 (YAP) and LuAlO3 (LuAP) have been identified as potential scintillator materials due to their high light output and short decay time. However, the performance of these materials is significantly reduced by point defects. In this paper, atomistic simulations provide insight into the types of point defects that are expected under various conditions in YAP and LuAP, as well as other REAlO3 compounds (where RE denotes a rare earth ion ranging from Lu to La or Y). For example, we predict that cation antisites are the dominate intrinsic defect for smaller REAlO3 compounds, with the concentration of Schottky-type defects increasing for compounds with larger RE ions. We also predict that cation vacancies will be present in association with the oxidation of the Ce activator. From these results, we show how defects affect different aspects of the scintillation process. Our aim is to provide information that can be used to aid in the intelligent optimization of this family of scintillator compounds. [ABSTRACT FROM AUTHOR]

X-ray luminescence from CdTe nanoparticles is observed when CdTe nanoparticles are encapsulated into BaFBr:Eu2+ phosphors. In contrast, negligible x-ray luminescence is observed from the unencapsulated nanoparticles, either in solution or in solid form. The origin of the x-ray luminescence is attributed to the effective energy transfer from Eu2+ ions to CdTe nanoparticles in the nanocomposite materials. The x-ray luminescence of these nanocomposites is dose dependent and the emission wavelength is size adjustable which may allow use as a type of dosimeter for both in vitro and in vivo applications. [ABSTRACT FROM AUTHOR]

Cerium doped lutetium pyro-silicate Ce3+:Lu2Si2O7 (LPS) is an inorganic scintillator that displays particularly promising performance. The spectroscopic properties of pure and Ce3+-doped Lu2Si2O7 are investigated. X-ray-excited luminescence, time-resolved excitation and emission spectroscopy, as well as decay time spectra are presented. For better understanding of the scintillation mechanism, several approaches were undertaken to locate the Ce3+ energy levels relative to levels of LPS host. To estimate the energy position of Ce3+ 4f levels with respect to the valence band, x-ray photoemission spectroscopy (XPS) was used. Scintillation properties of LPS: Ce are explained in terms of the relative positions of Ce3+-5d levels and the conduction band. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Yb[sup 3+]-doped YAlO[sub 3] single crystals have been grown by the Czochralski method with a radio-frequency heating system. Starting melt compositions of Y[sub 1-x]Yb[sub x]AlO[sub 3] were varied with x=0.02, 0.1, 0.2, 0.3, and 0.45. The best Yb[sup 3+]-doped YAlO[sub 3] single crystals were obtained for a growth rate of 1.0 mm/h. The grown crystals were transparent and almost colorless. To investigate the homogeneity, the effective segregation coefficient of the Yb ion was estimated. The absorption, photoluminescence, and luminescence decay kinetics of Yb[sup 3+]-doped YAlO[sub 3] were investigated for the temperature range 4–300 K. Very fast charge transfer luminescence of Yb[sup 3+] from the near ultraviolet to visible spectral range and the high density of the Yb-rich YAlO[sub 3] makes this material a promising candidate for fast scintillators. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]