Tm3+激活无水芒硝在真空紫外光激发下的发光性质

采用高温固相反应方法在空气中制备了Na2SO4:Tm2+发光材料.用X射线衍射对晶体结构进行了表征.发射光谱由Tm3+内4f12电子跃迁的窄峰组成.激发光谱分别由Tm3+离子4f12→4f115d跃迁(183nm),O2--Tm3+之间的电荷转移带(170 nm)引起的强激发谱和基质吸收(130,223,258 nm)...     

Eu,Li doped CaWO4 nanorods: Synthesis,emission-decay curves and effective-refractive index

In the present paper, CaWO₄: Eu³⁺, Li⁺ nanorods have been successfully synthesized via an oleic acid (OA)-assisted solvethermal route. The transmission electron microscope (TEM) photograph shows that the CaWO₄: Eu³⁺, Li⁺ nanorods are monodisperse and uniform nanorods with average diameter of 26 nm. The optical properties of Eu³⁺ in CaWO₄ samples, including photoluminescence (PL) excitation spectra and luminescent decay curves, are investigated in detail. Due to the form of the nanorods, the relative contribution of CTB to the nanorods sample is greater than that to the bulk counterparts. The decay time of the ⁵D₀ level (ranging from 0.94 to 0.65 ms, depending on the filling factor of the nanorods) of the nanorods is longer than that of the bulk counterpart mainly due to the reduction in the size of the nanorods, which introduces an effective-refractive index smaller than the refractive index of CaWO₄.     

掺杂浓度和烧结温度对CaWO4:Eu3+发光性能的影响

采用微乳液法合成掺杂浓度不同和烧结温度不同的CaWO₄:Eu³⁺系列荧光体, 这些荧光体都具有Eu³⁺离子的特征荧光发射. 在不同温度烧结后, 高浓度掺杂的样品(Eu³⁺掺杂30或50 mol%)可获得最大的发光强度, 低浓度掺杂的样品(掺杂0.5—2 mol%)在800 ℃烧结时也可获得优异的发光强度. 实验结果表明, Eu³⁺离子高浓度掺杂的CaWO₄:Eu³⁺在紫外光激发下可成为高效发光的荧光粉.     

Synthesis and photoluminescence properties of Sm-doped CaWO4 nanoparticles

The Sm³⁺-doped CaWO₄ nanoparticles were synthesized by hydrothermal method. The room temperature photoluminescence (PL) spectra of Sm³⁺-doped CaWO₄ nanoparticles doped with different Sm³⁺ concentrations under 405 nm excitation have been investigated. The PL spectra showed four strong emission peaks at 460, 571, 609, and 653 nm. The first emission peak at 460 nm could be due to a structural defect of the lattice, an oxygen-deficient WO₃ complex. The other three emissions at 571, 609, and 653 nm were due to the f-f forbidden transitions of the 4f electrons of Sm³⁺, corresponding to ⁴G_5/2→⁶H_5/2 (571 nm), ⁶H_7/2 (609 nm), and ⁶H_9/2 (653 nm), respectively. In addition, the optimum Sm³⁺ concentration in CaWO₄ nanoparticles for optical emission was determined to be 1.0%. The Sm³⁺⁴G_5/2→⁶H_7/2 (609 nm) emission intensity of Sm³⁺-doped CaWO₄ nanoparticles significantly increased with the increase of Sm³⁺ concentration, and showed a maximum when Sm³⁺ doping content was 1.0%. If Sm³⁺ concentration continued to increase, namely more than 1.0%, the Sm³⁺⁴G_5/2→⁶H_7/2 emission intensity would decrease. The present materials might be a promising phosphor for white-light LED applications.     

The electronic structure and photoluminescence properties of Ca2GeO4:Eu in ultraviolet and vacuum ultraviolet region

Ca₂GeO₄:Eu³⁺ phosphors were synthesized by the solid state method. The ultraviolet and vacuum ultraviolet excited photoluminescence properties were investigated in detail. It revealed that the emission of Ca₂GeO₄:Eu³⁺ comprised two parts: the red emission of Eu³⁺ and host defect emission in 330-550 nm. Ca₂GeO₄:Eu³⁺ presented intense excitation intensity at 163-200 and 466 nm, which suggested the potential applications in plasma display panels and light emitting diodes. The excitation spectra were studied to identify the photoluminescence mechanisms of Ca₂GeO₄:Eu³⁺. First principles calculation within the local density approximation of the density functional theory was applied to calculate the electronic structure and linear optical properties of Ca₂GeO₄.     

Investigation of host-to-activator energy transfer and surface losses in SrY2O4:Eu under VUV excitation

We have completed a study of the optical properties of SrY₂O₄:Eu³⁺ under vacuum ultraviolet (VUV) excitation. Reflectance measurements on the undoped material yield a calculated band gap of about 6.1 eV. Studies on the doped material indicate that Eu³⁺ occupies the Y(1) and Y(2) sites in this host. Host-to-activator energy transfer calculations indicate a preference for transfer to Eu³⁺ at the Y(2) site. Modeling of the transfer efficiency data leads us to estimate that about 35% of absorbed radiation is lost to the surface under excitation near the band edge.     

Preparation of CaWO4:Ln@SiO2 (Ln=Tb, Dy and Ho) nanoparticles by a combustion reaction and their optical properties

The CaWO₄:Ln³⁺@SiO₂ (Ln=Tb, Dy and Ho) nanoparticles were synthesized via a combustion process at 800 °C, using citric acid as chelating agent and fuel, ammonium nitrate as fuel, boric acid as flux material and silica as supports. The persistent phosphor nanoparticles were characterized by X-ray diffraction (XRD), reflectance UV-vis and fluorescence spectroscopy (PL) and transmission electron microscopy (TEM) techniques. XRD patterns indicated that crystalline calcium tungstate with scheelite structure was produced. The reflectance UV-vis spectra showed the broad absorption band of groups and the PL spectra showed the wide excitation band, broad emission band of and characteristic emissions of Ln³⁺ ions. The average particle sizes were determined by TEM, which are about 50 nm.     

Photoluminescence properties of Eu in Y(PO3)3 under VUV excitation

The photoluminescence properties of Y_1−x(PO₃)₃:xEu³⁺ (0<x≤0.2) are investigated. The excitation spectrum of Y_0.85(PO₃)₃:0.15Eu₃⁺ shows that both the (PO₃)₃³⁻ groups and the CT bands of O²⁻-Y³⁺ can efficiently absorb the excitation energy in the region of 120-250 nm. Under 147 nm excitation, the optimal emissive intensity of Y_1−x(PO₃)₃:xEu³⁺ (0<x≤0.2) is about 36% of the commercial phosphor (Y,Gd)BO₃:Eu³⁺, which hints that the absorbed energy by the host matrix could be efficiently transferred to Eu³⁺. We try to study the concentration quenching mechanism of Y_1−x(PO₃)₃:xEu³⁺ (0<x≤0.2) under 147 and 172 nm excitation.     

Photoluminescence properties of Sr(Y, Gd)2O4:Euunder VUV excitation

Vacuum ultraviolet (VUV) excitation and photoluminescence (PL) properties of Sr(Y, Gd)₂O₄ doped with Eu³⁺ were studied. The excitation spectra of SrY_1.9Eu_0.1O₄ and SrY_1.0Gd_0.9Eu_0.1O₄ had absorption in the VUV region with the absorption band edge at 149 nm, while the absorption of SrGd_1.9Eu_0.1O₄ in the VUV region was weak, which could be due to the narrow host band gap and no efficient energy transfer occurred in the VUV region. The PL spectra of all samples exhibited the characteristic emission of Eu³⁺ with the red ⁵D₀-⁷F₂ transition (611 nm) being the most prominent group.     

Energy transfers between Sm and Eu in YPO4, LaP5O14 and LaP3O9 phosphates. Potential quantum cutters for red emitting phosphors

This work concerns the studies of energy transfers between Sm³⁺ and Eu³⁺ ions in some phosphates as new luminescent materials emitting in the orange-red color. The choose of ions is based on the possibility of quantum cutting process and the matrices are selected according to the 5d bands position of Sm³⁺ ion. The Sm³⁺ and Eu³⁺ doped YPO₄, LaP₅O₁₄ and LaP₃O₉ are synthesized and spectroscopic studies in ultraviolet and vacuum ultraviolet ranges have been achieved.     

Luminescence of Ce and Pr doped Sr2Mg(BO3)2 under VUV-UV and X-ray excitation

This report presents the luminescence properties of Ce³⁺ and Pr³⁺ activated Sr₂Mg(BO₃)₂ under VUV-UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46 729, 44 643, 41 667, 38 314 and 29 762 cm⁻¹ (i.e. 214, 224, 240, 261 and 336 nm) for Ce³⁺ in the host lattice. The doublet Ce³⁺ 5d→4f emission bands were found at about 25 840 and 24 096 cm⁻¹ (387 and 415 nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce³⁺ in Sr₂Mg(BO₃)₂ were investigated. For Pr³⁺ doped samples, the lowest 5d excitation band was observed at about 42017 cm⁻¹ (238 nm), a dominant band at around 35714 cm⁻¹ (280 nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce³⁺ and Pr³⁺ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100 photons/MeV of absorbed X-ray energy for the samples Sr_1.86Ce_0.07Na_0.07Mg(BO₃)₂ and Sr_1.82Pr_0.09Na_0.09Mg(BO₃)₂ at RT, respectively.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

Enhanced photoluminescence properties of Zn2SiO4:Mn co-activated with Y/Li under VUV excitation

A series of green phosphors Zn_1.92−2xY_xLi_xSiO₄:0.08Mn²⁺ (0≤x≤0.03) were prepared by solid-state synthesis method. Phase and lattice parameters of the synthesized phosphors were characterized by powder X-ray diffractometer (XRD) and the co-doped effects of Y³⁺/Li⁺ upon emission intensity and decay time were investigated under 147 nm excitation. The results indicate that the co-doping of Y³⁺/Li⁺ has favorable influence on the photoluminescence properties of Zn₂SiO₄:Mn²⁺, and the optimal photoluminescence intensity of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 103% of that of commercial phosphor when the doping concentration of Y³⁺/Li⁺ is 0.01 mol. Additionally, the decay time of phosphor is much shortened and the decay time of Zn_1.90Y_0.01Li_0.01SiO₄:0.08Mn²⁺ is 3.39 ms, shorter by 1.83 ms than that of commercial product after Y³⁺/Li⁺ co-doping.     

Synthesis and properties of submicron range CaSO4:Eu particles

CaSO₄:Eu with particle size in submicron range was synthesized. Radiation induced Eu³⁺↔Eu²⁺ conversion as well as thermal conversion was studied. The samples showed thermal conversion above 400 °C. However, no radiation induced conversion in submicron range particles was observed. Particles heated above 400 °C coalesce and when heated at 925 °C bigger particles of 20 μm size were formed. Optical microscopy of these particles reveals red inclusion of about 5 μm inside CaSO₄ particle. It is speculated that the red inclusion is CaS:Eu²⁺.     

Luminescence of BaBr2:Eu under hydrostatic pressure

Luminescence spectra of BaBr₂:Eu²⁺ have been measured under pressures up to 27 GPa at room temperature. In the low-pressure range a red-shift of the 5d-4f transition of −225 cm⁻¹/GPa is observed. From 3 to 10 GPa a phase mixture of the original orthorhombic phase and the high-pressure monoclinic phase gives rise to two luminescence bands. Above 10 GPa the crystal is completely transformed to its high-pressure phase where two different Eu²⁺ sites exist of which, however, only one 5d-4f transition is detected. This transition exhibits a red-shift of −200 cm⁻¹/GPa. The shifts are compared with other literature data.     

Luminescence in LiCaPO4

Phase pure LiCaPO₄ was prepared by following a specific procedure involving several annealing steps, not exceeding the temperature 800 °C at any stage. Luminescence of Cu⁺ and Eu²⁺ activators is studied. A single emission band is observed for both the activators in contrast to two bands reported in earlier literature. It is argued that in the earlier work the samples were contaminated by alpha Ca₃(PO₄)₂ phase, which could be responsible for these differences. Thermoluminescence of LiCaPO₄:Eu²⁺ was found to be four times more than the commercial phosphor LiF-TLD 100. Phase pure LiCaPO₄ shows interesting luminescence properties different than those reported in the literature and hence it should prove fruitful to probe this material in future.     

Photoluminescence of Eu in SrGa2S4

A photoluminescence (PL) study of the green-emitting SrGa₂S₄:Eu²⁺ phosphor is reported. Diffuse reflectance, excitation, and emission spectra were examined with the aim to enlarge the fundamental knowledge about the emission of the Eu²⁺ ion in this lattice. The thermal dependence of the radiative properties was investigated. In particular, the Stokes shift, the crystal field splitting and the activation energy of the thermal quenching were determined. By combining these results with the information presented in literature, we discussed the location of the Eu²⁺ levels relative to the valence and conduction bands of SrGa₂S₄.     

CaWO4晶体中F型色心电子结构的研究

运用相对论的密度泛函离散变分法(DV-Xα)研究了CaWO₄晶体中F型色心的电子结构. 计算结果表明，F和F⁺心在禁带中引入了新的施主能级；分析了晶体内可能存在的光学跃迁模式，并通过过渡态的方法计算了F，F⁺心跃迁到导带底的能量分别为1.92eV和2.42eV. 因此，从理论上推断了F和F⁺心在CaWO₄晶体中可能引起650nm和515nm的吸收，由此说明CaWO₄晶体中650nm和515nm吸收带起源于晶体中的F和F⁺心. 关键词： 4晶体')" href="#">CaWO₄晶体 +心')" href="#">F和F⁺心 DV-Xα     

A white light emitting phosphor Sr1.5Ca0.5SiO4:Eu, Tb, Eu for LED-based near-UV chip: Preparation, characterization and luminescent mechanism

In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr_1.5Ca_0.5SiO₄:Eu³⁺,Tb³⁺,Eu²⁺ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu³⁺, Tb³⁺ and Eu²⁺ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange-red region (588-720 nm). These bands originated from Eu²⁺ 5d→4f, Tb³⁺⁵D₄→⁷F_J and Eu³⁺⁵D₀→⁷F_J transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb³⁺ content, both broad Eu²⁺ emission and sharp Eu³⁺ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu³⁺ to Tb³⁺, whereas the latter is attributed to the energy transfer process from Eu²⁺ to Tb³⁺. Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb³⁺ concentration varies. It was found that the nominal composition Sr_1.5Ca_0.5SiO₄:1.0%Eu³⁺, 0.07%Tb³⁺ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip.     

Luminescent properties of Tb activated GdTaO4 with M and M′ type structure under UV-VUV excitation

The photoluminescence of Tb³⁺ doped M and M′ type gadolinium orthotantalate Gd_1−xTb_xTaO₄ (0.01≤x≤0.20) was investigated under ultraviolet and vacuum ultraviolet excitation. For the samples of Gd_1−xTb_xTaO₄ with different crystallographic structures, emission spectra were the same in addition to intensity; the optimal concentration for Tb³⁺ was about 10 mol % in M type Gd_1−xTb_xTaO₄ but 5 mol % in M′ type Gd_1−xTb_xTaO₄. These differences could be corresponding with the difference in structures. In addition, compared to commercial Zn₂SiO₄: Mn²⁺, the integrated intensity of M and M′ type GdTaO₄: Tb³⁺ could reach 67% and 85%, respectively, of that at 147 nm excitation, which indicates that GdTaO₄: Tb³⁺ would be a promising vacuum ultraviolet phosphor for application in PDP and Hg-free lamp.