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101.
Magnesium aluminate (MgAl2O4) doped with trivalent chromium (Cr3+) was synthesized by the combustion method. The prepared sample was characterized by X-ray powder diffraction, Brunauer-Emmet-Teller (BET) adsorption isotherms and diffuse-reflectance UV-vis spectroscopy techniques. Electron paramagnetic resonance (EPR) and photoluminescence (PL) studies have been performed at room temperature and at 110 K. The EPR spectrum exhibit resonance signals at g=5.37, 4.53, 3.82, 2.26 and 1.96 characteristic of Cr3+ ions. The luminescence of Cr3+-activated MgAl2O4 exhibits a red emission peak around 686 nm from the synthesized phosphor particles upon 551 nm excitation. The luminescence is assigned to a transition from the upper 2Eg→4A2g ground state of Cr3+ ions. By correlating EPR and optical data the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) and the bonding parameters have been evaluated and discussed. The bonding parameters suggests that the ionic nature of Cr3+ ions with the ligands and the Cr3+ ions are in distorted octrahedral environment. 相似文献
102.
Eu2+ activated Ca5(PO4)3Cl blue-emitting phosphors were prepared by the conventional solid state method using CaCl2 as the chlorine source and H3BO3 as flux. The structure and luminescent properties of phosphors depend on the concentrations of Eu2+, the amount of CaCl2 and the usage of the H3BO3 flux were investigated systematically. Eu2+ and Mn2+ Co-doped Ca5(PO4)3Cl with blue and orange double-band emissions were also researched based on the optimal composition and synthesis conditions. The energy transfer between Eu2+ and Mn2+ was found in the phosphor Ca5(PO4)3Cl:Eu2+, Mn2+, and the Co-doped phosphor can be efficiently excited by near-UV light, indicating that the phoshor is a potentional candidate for n-UV LED used phosphor. 相似文献
103.
The polychromatic emission and wide-range color tuning in the luminescent nanoparticles are currently of crucial importance, due to the development of color and white light-emitting diode (LED) devices, based on such lanthanide-doped nanostructured materials. By utilization of precipitation method, Tb3+-doped and Tb3+/Eu3+-codoped NaYbF4 nanoparticles (i.e. NPs) are synthesized. For Tb3+-doped NaYbF4 NPs excited by 377 nm, green emission originating from Tb3+ is observed, where its optimum state is obtained when Tb3+ content is 25 mol% and the concentration quenching mechanism is found by electric dipole-dipole interaction. Moreover, due to the existence of energy transfer between Tb3+ and Eu3+, polychromatic emissions are realized in Tb3+/Eu3+-codoped NaYbF4 NPs as Eu3+ content increases. Through analyzing emission decay times and emission spectra, it was confirmed that the energy transfer mechanism in the synthesized NPs is governed mainly by electric dipole-dipole interaction. Furthermore, the resultant NPs also own strong resistance to temperature, which is verified by temperature-dependent emission spectra, and the activation energies of Tb3+ and Eu3+ are 0.206 and 0.207 eV, respectively. In addition, by employing designed NPs as yellow-emitting components, the fabricated white-LED emits brightness warm white light with color coordinate of (0.385, 0.380), high color rendering index of 84.3 and low correlated color temperature of 3903 K. This work does not only offer an available route to develop NPs with polychromatic emissions but also devise promising luminescent materials for improving the performance of the phosphor-converted white-LED. 相似文献
104.
采用静电纺丝技术制备了Y2O3:Eu3+纳米纤维,使用NH4HF2为氟化剂,经双坩埚法氟化和脱氨后得到YF3:Eu3+纳米纤维,再采用静电纺丝技术制备了YF3:Eu3+纳米纤维/PVP复合纳米纤维. XRD分析表明,立方相的Y2O3:Eu3+氟化后,得到了正交相的YF3:Eu3+纳米纤维,空间群为Pnma;YF3:Eu3+纳米纤维/PVP复合纳米纤维具有明显的YF3:Eu3+的衍射峰. SEM分析表明,YF3:Eu3+纳米纤维与YF3:Eu3+纳米纤维/PVP复合纳米纤维的直径分别为91±11 nm、319±43 nm,表面光滑. 用Shapiro-Wilk方法检验,纤维直径属于正态分布. 荧光光谱分析表明,YF3:Eu3+纳米纤维和YF3:Eu3+纳米纤维/PVP复合纳米纤维的最强发射峰均位于588 nm和595 nm,属于Eu3+的5D0→7F1跃迁,表明Eu3+占据YF3基质中Y3+晶格点的C2对称格位. PVP对YF3:Eu3+发光峰位没有影响,但发光强度降低;YF3:Eu3+的含量与YF3:Eu3+纳米纤维/PVP复合纳米纤维的发光强度成线性关系. 相似文献
105.
Up-conversion phosphors BaLa2ZnO5 co-doped with Ho3+/Yb3+ were synthesized by high temperature solid-state reaction method. The phase composition of the phosphors was characterized by X-ray diffraction (XRD). The structure of BaLa2ZnO5: 0.75% Ho/15% Yb phosphor was refined by the Rietveld method and results showed the decreased unit cell parameters and cell volume after doping Ho3+ and Yb3+, indicating Ho3+ and Yb3+ have successfully replaced La3+. Under the excitation of 980 nm diode laser, the strong green and weak red up-conversion emissions centered at 548 nm, 664 nm and 758 nm were observed, which originating from 5S2, 5F2→5I8, 5F4→5I8 and 5S2, 5F2→5I7 transitions of Ho3+ ions, respectively. The optimum doping concentrations of Ho3+ and Yb3+ were determined to be 0.75% and 15%, and the corresponding Commission International de L'Eclairage (CIE) coordinates are calculated to be x=0.298 and y=0.692. The related UC mechanism of Ho3+/Yb3+ co-doped BaLa2ZnO5 depending on pump power was studied in detail. The results indicate that BaLa2ZnO5: Ho3+/Yb3+ can be an effective candidate for up-conversion yellowish-green light emitter. 相似文献
106.
Barium β-alumina (Ba0.75Al11O17.25) doped with different contents of Mn2+ was prepared by conventional solid state method and analyzed by photoluminescence (PL) spectroscopy. It is found that there are multi-bands that could be attributed to Mn2+ in the PL spectra in addition to the 515 nm band ascribed to Mn2+ in Al(2). By analyzing the crystallographic structure of barium β-alumina, it is concluded that the other sites for Mn2+ can be associated with the interstitial Al(5) and Ba sites in the mirror layers. 相似文献
107.
We present a detailed investigation of the quantum efficiency of the 1S0 and 3P0,1 levels in Pr3+ doped YF3 under VUV excitation. The quantum efficiency of the 3P0,1 level was determined by the measurement and comparison of the photon fluxes of the 1S0 → 1I6 transition around 400 nm with the visible emissions occurring from the 3P0,1 levels. It was found that already at concentrations as low as 0.01% the 3P0,1 emission quantum efficiency is only about 61%. The quenching process is most probable caused by an energy transfer cross relaxation process involving the 3P0,1 levels and the 3H4 ground state. For concentrations of 0.1%, 0.5%, 1% and 10%, the quantum efficiency was determined to be about 42%, 29%, 17%, and 0.4%, respectively. The total quantum efficiency of the visible emission (380–750 nm) under excitation at 190 nm, determined by measurements of the total photon flux, has a maximum for a Pr3+ concentration of 1%. At this value, the absorption efficiency of the 4f5d absorption bands is very high and the 3P0,1 quenching is only moderate. 相似文献
108.
Li4(Sr0.96Eu0.04)(Ca1 − xMnx)(SiO4)2 phosphors were synthesized by solid-state reactions and photoluminescence (PL) properties were investigated. These phosphors have intense absorption in n-UV region, which is suitable for excitation of UV LEDs. The orange-reddish emission of Mn2+ can be adjusted by changing the Mn2+/Eu2+ ratio. Energy transfer from Eu2+ to Mn2+ is observed. Li4(Sr0.96Eu0.04)(Ca1 − xMnx)(SiO4)2 phosphors could be used in white LEDs. 相似文献
109.
ZnAl2O4:Mn green light emitting powder phosphors have been prepared by urea combustion technique involving furnace temperatures about 500 °C in a short time (<5 min). The prepared powders were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectrometry and the surface area measurements by a Brunauer-Emmet-Teller (BET) adsorption isotherms. The EPR spectrum exhibits a resonance signal at g≈2.0, which shows a six-line hyperfine structure (hfs). From the EPR spectra the spin-Hamiltonian parameters have been evaluated at room temperature as well as at 110 K. EPR and photoluminescence (PL) studies revealed that manganese ions were present in divalent state and the site symmetry around Mn2+ ions is distorted tetrahedral. The spin concentration (N), the paramagnetic susceptibility (χ) and the zero-field splitting parameter (D) have been evaluated and discussed. The green emission at 511 nm in ZnAl2O4:Mn phosphor is assigned to a transition from the upper 4T1→6A1 ground state of Mn2+ ions. 相似文献
110.
Preparation and characterization of fiber-textured SrAl2O4:Eu films grown using a homo-buffer layer 总被引:1,自引:0,他引:1
Xiaoyan Fu Hiroshi Yamada Keiko Nishikubo Hongwu Zhang Chao-Nan Xu 《Journal of Crystal Growth》2008,310(11):2885-2889
This paper describes the preparation and characterization of fiber-textured SrAl2O4:Eu films on a quartz glass substrate using a homo-buffer layer. The effect of the buffer layer on the crystallinity and adhesion was investigated by cross-section transmission electron microscopy and X-ray diffraction (XRD). The results show that the prepared film was not only well crystallized but also highly textured. The preferred orientation of this textured film was confirmed to be (0 3 1) by pole figure measurement. In addition, this film exhibits excellent optical transparency, with an average transmittance of more than 80% in the visible range. 相似文献