Influence of γ-radiation on photoluminescence properties of YPO4:Eu3+,Ce3+ and YPO4:Dy3+,Ce3+ phosphors

Hexagonal YPO₄ phosphors doped with Eu³⁺/Dy³⁺ and co-doped with Ce³⁺ were synthesized by a hydrothermal route assisted using lauric acid as a capping agent. The prepared phosphors were characterized by transmission electron microscopy, infrared spectroscopy, powder X-ray diffraction and photoluminescence spectra. YPO₄: Eu³⁺ gives two red emission peaks at 587 and 610?nm corresponding to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions, respectively. YPO₄: Dy³⁺ exhibits two emission peaks at 485?nm (blue) and 575?nm (yellow) corresponding to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions, respectively. Ce³⁺ ions enhanced the emission intensity as a co-dopant in both phosphors. Moreover, the effect of γ-radiation in the dose range 5–300?kGy on the photoluminescence behaviour of YPO₄:Eu³⁺,Ce³⁺ and YPO₄:Dy³⁺,Ce³⁺ was also investigated. Quenching of emission intensity, after irradiation at 5 and 300?kGy, was observed in both the phosphors due to loss of excess energy through a non-radiative relaxation process.     

Structural and superconducting properties of Eu1−xPrxBaSrCu3O7−δ

We have investigated the structural and superconducting properties of Eu_1−xPr_xBaSrCu₃O_7−δ by X-ray diffraction analysis, AC and DC magnetization and DC resistivity measurements. The parent compound crystallizes in the orthorhombic symmetry which transforms to tetragonal symmetry at x=0.2. Superconducting transition temperature T_c decreases monotonically with increasing x which approaches zero at x=0.6. The enhancement in critical concentration x_cr observed in Eu_1−xPr_xBa₂Cu₃O_7−δ on replacing 50 at.% Ba by Sr is attributed to the resulting local structural changes.     

基于YAG:Ce3+荧光粉复合Eu3+ 掺杂荧光玻璃的激光照明器件

采用结晶法和低温共烧结法制备了Eu~(3+)掺杂的Y_3Al_5O_(12)∶Ce~(3+)荧光玻璃,对制备出的样品进行能量色散X射线谱和光致发光光谱测试,表明稀土离子Eu~(3+)与YAG∶Ce~(3+)荧光粉已掺入荧光玻璃。掺杂不同含量Eu_2O_3的YAG∶Ce~(3+)荧光玻璃封装成的激光照明器件在驱动电流100 mA下,经过STC-4000快速光谱仪和PMS-80可见光谱分析系统测试,掺杂质量分数1%YAG∶Ce~(3+)复合质量分数9%的Eu~(3+)的荧光玻璃封装的激光照明器件发光效率为267.1 lm/W。激光照明器件随着电流的增加,其显色指数逐渐增大,但增加幅度较小。     

The luminescence and energy transfer in Pr3+–Ce3+ co-doped Lu0.8Sc0.2BO3 crystals

Lu_0.8Sc_0.2BO₃ crystals doped with 1 at%Ce³⁺ and co-doped 0.1 at% and 0.5 at%Pr³⁺ were grown by the Czochralski method. The concentrations of Pr³⁺ and Ce³⁺ in crystals were measured by the ICP-AES method. Absorption spectra, VUV–UV spectra, fluorescence decay time and X-ray excitation luminescence spectra were investigated at room temperature. The excitation luminescence spectra of Ce³⁺ emission and decay curves from the lower excited state levels of the 4f¹5d¹ and 5d¹ electronic configurations of the Pr³⁺ and Ce³⁺ conspicuously indicated the non-radiative energy transfer from Pr³⁺ to Ce³⁺. The detailed pathways were shown in the energy level diagram of the respective Ce³⁺ and Pr³⁺ in Lu_0.8Sc_0.2BO₃ host. In addition, the scintillation efficiency data indicated that the energy transfer effect is directly associated with the Pr³⁺ concentration.     

Synthesis,structure and magnetic entropy change of polycrystalline La1−xKxMnO3+δ

The use of a sol–gel synthetic method allows the preparation, at temperatures as low as 873 K, of single-phase perovskites in the potassium-doped lanthanide manganites La_1−xK_xMnO_3+δ. Samples prepared at 1273 K remain single phase and are constituted by submicrometer homogeneous particles, without deviation from nominal stoichiometries upon heating. These materials exhibit paramagnetic-to-ferromagnetic phase transitions at 230, 283, 338, and 344 K for x=0.075, 0.10, 0.165, and 0.20, respectively. By measuring the sample magnetization as a function of field and temperature we have determined the magnetic entropy change associated with these transitions. It is suggested by the results that these materials can be utilized as suitable magnetic refrigerants with very large temperature span.     

Magnetic behavior of the alloys CeCuyGa4−y and Ce1−xLaxCuGa3

The results of magnetic susceptibility (x), electrical resistivity (ρ) and heat-capacity (C) measurements of the alloys CeCu_yGa_4−y (y = 0.5, 1.0, 1.25 and 1.5) and Ce_1−xLa_xCuGa₃ (x = 0.2 and 0.9), crystallizing in the BaAl₄-type tetragonal structure, are reported. The Kondo effect tends to dominate with increasing y. All the data for the y = 0.5 alloy are consistent with the onset of ferromagnetic ordering at 6 K. For y = 1.0 and 1.25, though ρ gradually drops below 6 K, the C data do not show the existence of magnetic ordering above 2 K; presumably, for y = 1.0, 1.25 and 1.5, long-range magnetic ordering sets in below 2 K. Above all, C tends to increase with decreasing temperature before the onset of long range magnetic ordering and the values of C/T per Ce mol are considerably diminished for x = 0.9. It is proposed that this C/T enhancement lies in the magnetic precursor effects and not on the heavy-fermion behaviour.     

Photoconductivity and photodielectric effect in LiY1 − x Lu x F4 crystals doped with Ce3+ and Yb3+ ions

Time and spectral dependences of the dielectric permittivity of the LiY_{1 ? x} Lu _x F₄ (x = 0, 0.5, and 1) crystals doped with Ce³⁺ and co-doped with Yb³⁺ ions under UV laser excitation were studied by the 8-mm microwave resonant technique at room temperature. The obtained photoconductivity spectrum in 240–310 nm spectral range was interpreted as a stepwise photoionization spectrum of the Ce³⁺ ions due to sequential 4f–5d and 5d–6s transitions. Average lifetimes of free and defect trapped (color centers) charge carriers were estimated.     

Rovibrational states of H+ 3. Part 2: The energy region between 9000 cm−1 and 13000 cm−1 including empirical corrections for the non-adiabatic effects

The first part of this series focused on the calculation of the rovibrational states of H⁺ ₃ in the energy region below 9000 cm^?1, where most of the experimentally determined and assigned term values are located. The theoretically justified empirical correction for the non-adiabatic coupling corrections, which was obtained and tested in that study is extended and applied here in the calculation of the rovibrational states of H⁺ ₃ to term values up to 13000 cm^?1, which is above the barrier to linearity. In particular, predictions are made for the 5v ₂ bands, which are the subject of current experimental investigations, hopefully aiding with our results in the assignment of the spectral lines observed.     

Luminescence of Eu2+–vc− dipoles and their associates in CsI:Eu crystals

Spectral-kinetics properties of photo-scintillation excited with single light pulses of a nitrogen laser (λ=337.1 nm, t_1/2=5 ns, Q=1 mJ) have been studied in CsI:Eu crystals at temperature within 80–300 K. It is found that the exponential decay of 463 nm emission band has a time constant which grows from 0.85 μs at 78 K to 1.6 μs at 380 K. Such an anomalous temperature behavior of 463 nm emission decay kinetics is discussed in terms of the crystal thermal expansion. It has been proposed that 463 nm emission is caused by a cluster center consisting of three dipoles Eu²⁺v_c^? bounded with each other in a hexagon. Owing to the exchange resonance in the cluster, the energy passes from an excited dipole to a non-excited one and the distance between them gets longer due to thermal expansion of the crystal.     

Effect of PbCl2 addition on structure, OH− content, and upconversion luminescence in Yb3+/Er3+-codoped germanate glasses

Yb³⁺/Er³⁺-codoped oxychloride germanate glasses have been synthesized by a conventional melting and quenching method. Structural properties were obtained based on Raman-spectra investigation, indicating that PbCl₂ plays an important role in the formation of the glass network and has an important influence on the phonon density and the maximum phonon energy. The Judd–Ofelt intensity parameters and quantum efficiencies were calculated based on the Judd–Ofelt theory and lifetime measurements. The enhanced upconversion luminescence intensity of Er³⁺ with increasing PbCl₂ content could not be explained only by the maximum phonon-energy change of the host glasses. For the first time, the effect of PbCl₂ addition on phonon density, OH^– content, and upconversion luminescence in oxychloride glasses has been discussed and evaluated. The results show that the effect of phonon density and OH^– content on upconversion luminescence in oxychloride glasses is much stronger than that of the decrease of the maximum phonon energy. The possible upconversion luminescence mechanisms have also been estimated and are discussed.     

Intracenter luminescence of Mn2+ in Cd1−x MnxTe and Cd1−x−y MnxMgyTe under intense optical pumping

A comparative analysis of the kinetic properties of intracenter 3d luminescence of Mn²⁺ ions in the dilute magnetic superconductors Cd_1?x Mn_xTe and Cd_1?x?y Mn_xMg_yTe is carried out. The influence of relative concentrations of the cation components on the position of the intracenter luminescence peak indicates that the introduction of magnesium enhances crystal field fluctuations. As a result, the processes facilitating nonlinear quenching of luminescence are suppressed. The kinetics of 3d-luminescence quenching in Cd_1?x Mn_xTe are accelerated considerably upon elevation of optical excitation level due to the evolution of cooperative processes in the system of excited manganese ions.     

Crystal structure and luminescence properties of Lu3+ and Mg2+ incorporated silicate garnet [Ca3−(x+0.06)LuxCe0.06](Sc2−yMgy)Si3O12

The yellow-emitting phosphor [Ca_3?(x+0.06)Lu_xCe_0.06](Sc_2?yMg_y)Si₃O₁₂ obtained from Lu³⁺ and Mg²⁺ co-modified green-emitting silicate garnet Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce³⁺) exhibits promising applications for white LEDs. In this paper, we discuss the effect of charge balance on the garnet structure formation. The changes of bond length and covalence caused by the replacement of Lu³⁺ and Mg²⁺ for Ca²⁺ and Sc³⁺ are analyzed. The shift of the Ce³⁺ emission and excitation can be attributed to the combined results from crystal field splitting effect and centroid shift of Ce³⁺ 5d levels. Thermal stability is analyzed according to configurational coordinate diagram.     

Synthesis and scintillation properties of GdCl3:Ce3+ (Gd1−xCexCl3, x = 0.005–0.08)

Single crystals of GdCl₃ doped with different concentrations of Ce³⁺ have been grown using the Bridgman–Stockbarger technique and their luminescence and scintillation properties were investigated. The luminescence spectrum of GdCl₃:Ce³⁺ is complex and consists of two bands with maxima at 350 nm and 370 nm. The maximal light yield in GdCl₃:Ce³⁺ was observed at ～1 mol% of Ce³⁺ (more than 38 000 ph/MeV).     

Crystal structure and electrical transport properties of polycrystalline TbMn1−xFexO3

Polycrystalline TbMn_1−xFe_xO₃ (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) were synthesized by solid sintering method. The Rietveld refinement results based on the X-ray powder diffraction (XRD) data showed that all samples were identified as orthorhombic perovskite structure with space group Pbnm (62). The lattice parameters a and c increased, while the b decreased with increasing of Fe content, indicating the crystal unit cell shrinks in the ab-plane and extends along c-axis with increasing concentration of Fe. Temperature dependent resistance (R–T) was also measured. The transition temperature of TbMn_1−xFe_xO₃ samples increased monotonically with increase of x. The activation energy of TbMn_1−xFe_xO₃ decreased with increasing Fe content (x≤0.5) and increased with increasing Fe content when x>0.5, meaning that the TbMn_0.5Fe_0.5O₃ has the lowest activation energy. These results implied that the transition temperature and conductivity could be controlled by impuring different elements, especially to obtained better performance as for the semiconductor materials working at broad temperature.     

A new red-emitting phosphor of Eu3+-doped Sr2MgMoxW1−xO6 for solid state lighting

The white light-emitting diode has recently attracted great attention as a promising candidate for next generation lighting. The solid solution of Sr_1.80Eu_0.10Li_0.10MgMo_xW_1?xO₆ was synthesized via high-temperature solid-state reaction and this solid solution is treated as a promising red emitting phosphor for white light-emitting diodes. In our cases, the X-ray diffraction, excitation spectra, emission spectra and decay curves of these solid solutions were measured as a function of the Mo/W ratio to characterize the structural and luminescent properties. The excitation bands of the series of phosphors are consistent well with the region of near ultraviolet light, and the phosphors present better color purity than the commercial phosphor Y₂O₂S:Eu³⁺ in current use. Taking these properties into consideration, this kind of material may find a great potential application as a red phosphor for near-ultraviolet excited white light-emitting diodes.     

Fourier spectrum of CH3OH between 950 and 1100 cm−1

The infrared spectrum ofCH₃OH between 950 and HOOcm⁻¹ has been measured by a high resolution Fourier transform spectrometer. This spectral region is of particular interest because of its overlapping with the CO₂ laser emissions used for exciting the CH₃OH laser. A catalog of 3410 assigned lines is presented, as well as the Taylor development tables for evaluating the energies of the upper levels of the corresponding transitions.     

Thermally stimulated luminescence and persistent luminescence of β-irradiated YAG:Pr3+ nanophosphors produced by combustion synthesis

In this work, the thermally stimulated luminescence (TSL) and persistent luminescence (PLUM) properties of praseodymium doped yttrium aluminum garnet (YAG:Pr³⁺) exposed to β-irradiation are reported. X-ray diffraction (XRD) confirms a single phase of YAG obtained by the combustion method. Transmission electron microscopy (TEM) shows that powder particles appear to be irregular crystals with an average size of 67 nm. TSL glow-curve deconvolution of YAG:Pr³⁺ after β-irradiation consist in six peaks centered at 394, 450, 467, 543, 637 and 705 K. The TSL fading and PLUM signals were found to be associated with at least with two different kinds of traps, corresponding to the peaks located at 394, 450 and 467 K. YAG:Pr³⁺ nanophosphors analyzed in this work showed interesting features about the dosimetric sensitivity as well as the reproducibility for both TSL/PLUM techniques, with good linearity dose response. These results indicate that nanocrystalline YAG:Pr3⁺ is a good candidate for dosimetric applications in the range of 80 mGy-20 Gy.     

Synthesis and ionic conduction of C3A-type nasicon Na3+3x−yY1−xSi3−yPyO9

In the solid solutions of Na_3+3x−yY_1−xSi_3−yP_yO₉, new fast Na⁺ -conductors were obtained. The ionic conductivity, σ, and the activation energy, E, of the most conductive material, Na_4.425Y_0.375Si_2.55P_0.45O₉ were 5 × 10⁻³ S/cm at 300°C and 10 kcal/mol, respectively. Those values were strongly dependent upon the composition. With an increase of Na concentration, [Na], σ increased and E decreased. Accommodation of higher [Na] in the structure was madefeasible by decreasing [Y] and increasing [P]. Based on the crystal structure assumed for Na_3+3x−yY_1−xSi_3−yP_yO₉ and on the above results, a conduction model was presented. The structural consideration revealed that a conduction path is formed along the 〈1 1 1 〉 direction, where Y³⁺ ions locate in the way of Na⁺ ions.     

Ionic conductivity and crystal structure for the Li3−2xCr2−xTax(PO4)3 system

The monoclinic phase (P2₁/n) was formed for 0≤x≤0.6 and the NASICON-type rhombohedral phase (R3̄c) was obtained for the region 0.8≤x≤1.2 in the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The activation energy for Li⁺ migration was ca. 0.45 eV for the monoclinic structure and ca. 0.36 eV for the rhombohedral structure. The maximum conductivity of 8.4×10⁻⁶ S cm⁻¹ at 298 K was obtained for x=0.8 of the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The conductivity of LiCrTa(PO₄)₃ was enhanced about three to five times by the addition of the lithium salt due to the improvement of the sinterablity. The maximum conductivity was 2.4×10⁻⁵ S cm⁻¹ at 298 K for LiCrTa(PO₄)₃–0.2Li₃BO₃.