Defect states in Lu 3 Al 5 O 12 :Ce crystals

Wavelength-resolved TSL measurements after x-ray irradiation at room temperature were performed on undoped, Ce- and (Ce, Zr)-doped Lu 3 Al 5 O 12 crystals. Several glow peaks were observed in the 20-450 v C temperature region, whose intensities and emission spectra are influenced by doping. Namely, the TSL spectra are governed by defect and trace impurity-related emissions in the undoped crystal, while only the Ce 3+ emission is detected in the doped crystals. Moreover, EPR measurements performed at 12 v K revealed typical spectra of Ce 3+ (4f 1 , S =1/2) occupying Lu 3+ substitutional positions. In situ light irradiation (250-330 v nm) of the crystals results in a step-like decrease of the Ce 3+ EPR intensity. Such a behaviour can reflect a creation of Ce 4+ ions under UV irradiation or an increase of the Ce 3+ population in the excited (5d) state.     

Photoinduced oxygen-vacancy related centers in PbWO 4 : Electron spin resonance and thermally stimulated luminescence study

Using electron spin resonance (ESR) and thermally stimulated luminescence (TSL) three different electron traps based on regular W sites perturbed by oxygen vacancies have been identified in PbWO 4 . Analysis of ESR spectra parameters ( g -factor values and principal axes orientations) has shown that revealed centers are (WO 3 ) m vacancy containing complex anions associated with a defect in Pb sublattice: (WO 3 ) m m A Pb complexes. One of the centers (W 1 ) is thermally stable up to 350-370 v K, while the other two (W 2 and W 3 ) only to 270-290 v K. Above these temperatures trapped electrons become free and recombine with localized holes, giving rise to TSL glow peaks at T\approx 323\,\hbox{K} and 365\,\hbox{K} . Using the initial rise method the 323\,\hbox{K} TSL peak-shape was fitted allowing the first order recombination kinetic that gives trap parameters E = 0.88\,\hbox{eV} and s\simeq 5\ast 10^{12}1/\hbox{s} .     

Optical spectroscopy of Ce 3+ ions in BaY 2 F 8 single crystals

In the present work we report on the spectroscopic properties of the Ce 3+ ion in BaY 2 F 8 single crystals. The absorption and excitation spectra of the emission centered at 340 v nm have been measured in the temperature range 15-300 v K. The 340 v nm emission consists of two broad partially overlapping bands, peaking at 324 and 347 v nm (at 15 v K), respectively. The full width at half maximum is about 0.5 v eV at room temperature. The absorption spectrum of the lowest in energy component of the f M d transition of Ce 3+ reveals at low temperature a marked vibronic structure. High resolution (0.02 v cm m 1 ) Fourier transform infrared spectroscopy in the wave number range 500-5000 v cm m 1 and in the temperature range 9-300 v K has been exploited to monitor the f level splitting. The absorption transitions from the three Stark components of the 2 F 5/2 manifold to the four of the 2 F 7/2 one, have been monitored in the wave number range 2000-3400 v cm m 1 . The wave number separation at 9 v K between the lowest level of the ground 2 F 5/2 manifold and lowest one of the 2 F 7/2 manifold is found to be 2197.47 v cm m 1 in good agreement with the splitting detected between the two components of the d M f emission.     

Superposition-model analysis of rare-earth doped BaY 2 F 8

The energy level schemes of four rare-earth dopants (Ce 3+ , Nd 3+ , Dy 3+ , and Er 3+ ) in BaY 2 F 8 , as determined by optical absorption spectra, were fitted with a single-ion Hamiltonian and analysed within Newman's Superposition Model for the crystal field. A unified picture for the four dopants was obtained, by assuming a distortion of the F m ligand cage around the RE site; within the framework of the Superposition Model, this distortion is found to have a marked anisotropic behaviour for heavy rare earths, while it turns into an isotropic expansion of the nearest-neighbours polyhedron for light rare earths. It is also inferred that the substituting ion may occupy an off-center position with respect to the original Y 3+ site in the crystal.     

Vibronic Transitions of Trivalent Er and Ce in BaY2F8 Single Crystals

High resolution (0.02 cm^?1) Fourier transform spectroscopy was applied in the 9–300 K and 100–24,000cm^?1 ranges, respectively, to detect in Er^3? and Ce^3? doped BaY₂F₈ single crystals (1) the narrow line spectra due to the intraconfigurational 4f→4f transitions of the rare earths (RE) and (2) the possible vibronic tails accompanying the zero-phonon lines. The ²F_5/2→²F_7/2 transition was monitored for the Ce^3?-doping and the crystal field splitting of the initial and final manifold was determined. Weak vibronic spectra accompanying six among the nine investigated 4f→4f transitions of Er^3? and the ²F_5/2→²F_7/2 transition of Ce^3? were detected. The vibronic spectra amplitude was found to scale with the RE contents. On the basis of the IR- and Raman-active vibrational modes, either measured or quoted in the literature, most of the vibronic lines could be successfully assigned to the lattice modes. Violations of the selection rules were envisaged and discussed.     

Thermally stimulated luminescence and electron paramagnetic resonance studies of actinide doped calcium chloro phosphate

Electron paramagnetic resonance [EPR] and thermally stimulated luminescence [TSL] studies were conducted on self [α]-irradiated²³⁹Pu doped calcium chloro phosphate andγ-irradiated²³⁹Pu/²³⁸UO ₂ ²⁺ doped calcium chloro phosphate to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain trap parameters from both TSL and EPR data. TSL glow peaks around 135 K (# peak 1), 190 K (# peak 2), 435 K (# peak 5) and 490 K (# peak 7) were observed and their spectral characteristics have shown that Pu³⁺ and UO ₆ ⁶⁻ act as luminescent centres in calcium chloro phosphate with respective dopants. EPR studies have shown the formation of the radical ions H⁰, PO ₄ ²⁻ , O⁻, O ₂ ⁻ and [ClO]²⁻ under different conditions. Whereas the [ClO]²⁻ radical being stable up to 700 K, was not found to have any role in TSL processes, the thermal destruction of other centres was found to be primarily responsible for the TSL peaks observed. The trap depth values were determined both by using the TSL data and also the temperature variation of EPR spectra of these centres.     

Thermally stimulated luminescence of polycrystalline CdWO4 at low temperatures

CdWO₄ scintillator powders were produced via solid state reaction and investigated by thermally stimulated luminescence technique after UV irradiation. Under a heating rate of 0.1 K/s, the glow curve presented a superposition of peaks at low temperatures. Four peaks were identified below 80 K by partial heating method and their kinetic parameters were evaluated from the initial rise analysis. Measurements were also performed for heating rates of 0.05 and 0.2 K/s and allowed the kinetic study by peak position method. Surface effects due to the polycrystalline feature of the sample were investigated by comparing the results with those reported for CdWO₄ single crystals.     

Luminescent properties of Eu and Ce ions in strontium litho-silicate Li2SrSiO4

The luminescent properties of Eu²⁺ and Ce³⁺ ions in Li₂SrSiO₄ have been studied upon excitation in the 2-20 eV region. Based on the results of luminescent measurements, values of the crystal field splitting and the centroid shift of the Ce³⁺5d configuration in Li₂SrSiO₄ were found and compared with those of Ce³⁺ ions in some other inorganic compounds. The Eu²⁺ ions in Li₂SrSiO₄ exhibit a broad band emission with a maximum at 576 nm, which is due to the 4f⁶5d→4f⁷ transition. It was shown that the long-wavelength position of the Eu²⁺ emission in Li₂SrSiO₄ is caused by the large crystal-field splitting of the Eu²⁺ 4f⁶5d configuration and relatively high degree of covalency of the Eu-O bond. The stabilization of Eu²⁺ ions in Li₂SrSiO₄ during the synthesis process requires a strong reducing agent. Two phenomenological approaches to explain the low stability of Eu²⁺ in Li₂SrSiO₄ are also discussed.     

Inter- and intraconfigurational luminescence of Er 3+ ions in BaY 2 F 8 under VUV excitation

Using energy- and time-resolved spectroscopy the luminescence properties of Er 3+ doped BaY 2 F 8 crystals were investigated at 10 v K under VUV synchrotron radiation excitation. Radiative intraconfigurational f - f and interconfigurational d - f transitions in Er 3+ ions were observed under f - d excitation. Whereas the onset of 4 S 3/2 population via f - d excitation starts at 59 900 v cm m 1 , efficient excitation of emissions arising from the 2 P 3/2 state begins only above 67 000 v cm m 1 in VUV region. Such behaviour can be explained by a cross-relaxation process of the type ( 2 F(2) 5/2 , 4 I 15/2 ) M ( 2 P 3/2 , 2 P 3/2 ) taking place within f -states of Er 3+ ions finally populating the emitting 2 P 3/2 state.     

Synthesis and properties of solution-processed Eu:BaY2F8

The structural and optical properties of solution-processed Eu³⁺:BaY₂F₈ were characterized and compared to those of the sample synthesized by a solid-state reaction method. Precipitated from solution Eu³⁺:BaY₂F₈ has the fluorite (CaF₂) type of structure, which transforms completely into monoclinic form when powder is heated at 750 °C. This temperature is also sufficient for entire elimination of hydroxyl groups. The intensities of f-f emission transitions of Eu³⁺ in BaY₂F₈ were analyzed in the frame of Judd-Ofelt model and the values of 1.23×10⁻²⁰ and 1.95×10⁻²⁰ cm² were determined for Ω₂ and Ω₄ intensity parameters. The experimental lifetimes of the ⁵D₀ and ⁵D₁ levels are equal to 8.4 and 2.3 ms, respectively. The quantum efficiency of Eu³⁺ in BaY₂F₈ was evaluated to be ∼35%.     

Spectroscopic and laser properties of Er3+-doped monoclinic BaY2F8 single crystals

The luminescence and absorption properties of Ba(Y_1−x Er _x )₂F₈ (x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er³⁺-ion decay kinetics of luminescent transitions from three initial laser states, the⁴S_3/2,⁴F._9/2 and⁴I_11/2 manifolds, were measured. The crystal-field splitting schemes for allJ-manifolds which are involved in (J →J′)-luminescence transitions and stimulated emission parameters of Er³⁺ -ions in BaY₂F₈ were determined. A comparison of laser powers and efficiencies of BaY₂F₈ and Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and LiYF₄ single crystals doped with Er³⁺-ions shows the similar performance of these materials.

     

Synthesis, luminescence and crystallographic structure of Eu-doped garnet-type yafsoanite Ca3Te2(ZnO4)3

A red-emitting phosphor of Eu³⁺-doped calcium–tellurium–zinc oxide, Ca₃Te₂(ZnO₄)₃, with a garnet-type structure was synthesized by high temperature solid-state reactions. This phosphor exhibited a strong red emission. The photoluminescence excitation spectrum showed that Ca₃Te₂(ZnO₄)₃:Eu³⁺ can be effectively excited by UV–visible light. The property of long-wavelength excitation for this material has a benefit as a red phosphor in application of white light-emitting diodes. The colour coordinates were calculated. The excitation and emission spectra and luminescence decay curves were obtained using a pulsed, tunable, narrowband dye laser. Crystallographic sites and charge compensation mechanism of Eu³⁺ ions were discussed. The emission line from Eu³⁺ in intrinsic crystallographic site in the lattice was located at 579.56 nm. The emission line from Eu³⁺ in another disturbed site, which is created by the defects created by the charge-compensation, was located at 580.88 nm. The disordered crystallographic sites of Eu³⁺ are benefit for their strong red luminescence corresponding to the ⁵D₀→⁷F₂ transition.     

Lu2SiO5:Ce and Y2SiO5:Ce single crystals and single crystalline film scintillators: Comparison of the luminescent and scintillation properties

The paper is dedicated to development of scintillators based on the single crystalline films of Ce³⁺ doped Lu₂SiO₅ (LSO:Ce) and Y₂SiO₅ (YSO:Ce) orthosilicates grown by Liquid Phase Epitaxy method onto YSO substrates from melt-solutions based on the PbO–B₂O₃ flux. We also compare the luminescent and scintillation properties of Ce doped LSO:Ce and YSO:Ce single crystalline films with those of their single crystal counterparts, grown by the Czochralski method.     

Efficient fluorescence of dissolved CaF2:Tb and CaF2:Ce, Tb nanoparticles through surface coating sensitization

Oleic acid (OA)-modified CaF₂:Tb³⁺ nanoparticles with various Tb³⁺ concentrations and CaF₂:Ce³⁺, Tb³⁺ nanoparticles were synthesized. The as-prepared nanoparticles were shown to be well dissolved in some common organic solvents, such as chloroform and toluene. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The investigation of fluorescence properties of CaF₂:Tb³⁺ nanoparticles showed that the Tb³⁺ ions could be sensitized efficiently by the surface coating of OA and CaF₂:Tb³⁺ nanoparticles with 10 mol% Tb³⁺ concentrations possess the highest emission intensity. The comparison of emission for CaF₂:Ce³⁺, Tb³⁺ and CaF₂:Tb³⁺ (10 mol%) nanoparticles revealed that the emission intensity of the former is about 4.5 times as strong as that of the latter.     

Measurement of the luminescence properties of Gd2O2S:Pr,Ce,F powder scintillators under X-ray radiation

The aim of the present study was to investigate the absolute luminescence efficiency of gadolinium oxysulfide powder scintillators, doped with praseodymium, cerium and fluorine (Gd₂O₂S:Pr,Ce,F). Gd₂O₂S:Pr,Ce,F is a non-hygroscopic material, emitting green light with short decay time. For the purposes of this study, two scintillating screens with coating thicknesses 35.7 and 71.2 mg/cm², were prepared in our laboratory from Gd₂O₂S:Pr,Ce,F powder (Phosphor Technology, Ltd) by sedimentation on silica substrates. The light emitted by the phosphors under investigation was evaluated by performing measurements of the absolute efficiency under X-ray exposure conditions with tube voltages ranging from 50 to 130 kV. Results were compared with previously published data for Gd₂O₂S:Eu screens. The spectral compatibility of Gd₂O₂S:Pr,Ce,F with various existing optical detectors, was investigated after emission spectra measurements. Particle size and morphology parameters of the Gd₂O₂S:Pr,Ce,F powder phosphor were verified via scanning electron microscope (SEM) micrographs. Absolute efficiency was found to maximize at 60 kVp for the 71.2 mg/cm² and at 90 kVp for the 35.7 mg/cm² Gd₂O₂S:Pr,Ce,F screens. Absolute efficiency of the 71.2 mg/cm² Gd₂O₂S:Pr,Ce,F screen was higher in the whole X-ray tube voltage range showing potential interest for non-CT medical imaging (i.e. dental radiology) or industrial digital radiography.     

Luminescent properties of SrAl2B2O7: Ce, Tb

By using metal nitrates as starting materials, SrAl₂B₂O₇: Tb³⁺ and SrAl₂B₂O₇: Ce³⁺, Tb³⁺ powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce³⁺ to Tb³⁺ ions. The emission intensity of Tb³⁺ ions in SrAl₂B₂O₇ could be greatly intensified when Ce³⁺ ions are doped into SrAl₂B₂O₇: Tb³⁺. The decay times of SrAl₂B₂O₇: Tb³⁺ were prolonged when Ce³⁺ ions were doped. The doping of Ce³⁺ ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties.     

Influence of different annealing conditions on the luminescent properties of Li2B4O7:Mn single crystals

The influence of reducing annealing and repeated oxidizing annealing of the Li₂B₄O₇:Mn single crystals on their thermostimulated luminescence (TSL) and X-ray luminescence (XL) has been studied. Because of the oxygen vacancies formation and the dopant ions reduction, the reducing annealing results in a drastic decrease of the luminescence intensity along with the simultaneous shift of a part of the maxima and redistribution of the peak intensities. The repeated annealing in the oxidizing environment leads only to the partial reduction of the luminescent properties of the Li₂B₄O₇:Mn crystals.     

Synthesis and luminescence properties of SrAl2O4:Eu,Dy nanosheets

We report an effective method to synthesize SrAl₂O₄:Eu²⁺,Dy³⁺ nanosheets. Sheet-like precursors were firstly synthesized by the solvothermal method, and acetate was used as the raw material. Then the final products were obtained by calcinating the precursor in a weak reductive atmosphere of H₂. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD) patterns, field-emission scanning electron microscopy and transmission electron microscopy (FE-SEM and TEM) , respectively. A possible growth mechanism was proposed to reveal the formation process. Luminescence properties of the SrAl₂O₄:Eu²⁺,Dy³⁺ long-lasting phosphor were analyzed by measuring the excitation spectra, the emission spectra, the afterglow decay curve and the thermoluminescence curve. Both the photoluminescence (PL) spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties compared with the phosphors prepared by using nitrates as the raw material. Furthermore, the photoluminescence intensity was even a little higher than commercial phosphors.     

Excited-state absorption in Er: BaY2F8 and Cs3Er2Br9 and comparison with Er: LiYF4

The influence of Excited-State Absorption (ESA) on the green laser transition and the overlap of Ground-State Absorption (GSA) and ESA for 970 nm upconversion pumping in erbium is investigated in Er³⁺ : BaY₂F₈ and Cs₃Er₂Br₉. Results are compared to Er³⁺ : LiYF₄. In Er³⁺: BaY₂F₈, a good overlap between GSA and ESA is found at 969 nm in one polarization direction. The emission cross section at 550 nm is a factor of two smaller than in LiYF₄. In Cs₃Er₂Br₉, the smaller Stark splitting of the levels shifts the wavelengths of the green emission and ESA from⁴ I _{1 3/2} off resonance. It enhances, however, ground-state reabsorption. The emission cross section at 550 nm is comparable to LiYF₄. Upconversion leads to significant green fluorescence from² H _9/2. A significant population of the⁴ I _11/2 level and ESA at 970 nm are not present under 800 nm pumping.     

Lu2SiO5:Ce透明薄膜改性及其发光性能

Lu2SiO5:Ce具有高密度、高光产额、快衰减等优点,是一种性能优异的新型X射线闪烁薄膜材料.本文采用溶胶-凝胶工艺和旋涂技术,以无机盐为原料、2-甲氧基乙醇为溶剂、聚乙二醇(PEG)为改性剂,在石英基片上成功制备出Lu2SiO5:Ce透明薄膜,较为详细地研究了PEG对该薄膜发光性能的影响.结果表明当采用浓度为12....