Effect of Mg and Ti doping on the luminescence of Y2O3:Eu

The Y₂O₃:Eu³⁺,Mg²⁺,Ti^IV materials (x_Eu: 0.02, x_Mg: 0.08, x_Ti: 0.04) were prepared by solid state reaction. The purity and crystal structure of the material was studied with the X-ray powder diffraction. Luminescence properties were studied in the UV-VUV range with the aid of synchrotron radiation. The emission of Y₂O₃:Eu³⁺,Mg²⁺,Ti^IV had a maximum at 612 nm (λ_exc: 250 nm) due to the ⁵D₀→⁷F₂ transition of Eu³⁺. The excitation spectra (λ_em: 612 nm) showed a broad band at 233 nm, due to the charge transfer transition between O²⁻ and Eu³⁺, and at 297 nm due to the Ti→Eu³⁺ energy transfer. Only very weak persistent luminescence was discovered. In the room and 10 K temperature excitation spectra, the line at 208 nm is due to the formation of a free exciton (FE) and a broad band at 199 nm was related to the valence-to-conduction band absorption of the Y₂O₃ host lattice. The absorption edge was ca. 205 nm giving 6.1 eV as the energy gap of Y₂O₃.     

Vacuum ultraviolet luminescence from a micro-pulling-down method grown Nd:(La0.9,Ba0.1)F2.9

Vacuum ultraviolet (VUV) luminescence from a Nd³⁺:(La_1−x,Ba_x)F_3−x (x=0.1) and a Nd³⁺:LaF₃ single crystal grown by the micro-pulling-down method modified for fluoride crystal growth is discussed. Emission resulting from excitation with 157 nm pulses of a F₂ laser and by 290 nm femtosecond pulses of a Ti:sapphire laser show that the luminescence spectral and temporal characteristics are similar for both excitation cases and that they have good prospects as a VUV laser material.     

Preparation and luminescent properties of BaCa2Si3O9:Eu

A blue emitting phosphor of the triclinic BaCa₂Si₃O₉:Eu²⁺ was prepared by the combustion-assisted synthesis method and an efficient blue emission ranging from the ultraviolet to visible was observed. The luminescence and crystallinity were investigated using luminescence spectrometry and X-ray diffractometry (XRD), respectively. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu²⁺ in BaCa₂Si₃O₉:Eu²⁺ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The CIE of the optimized sample Ba_0.95Ca₂Si₃O₉:Eu_0.05²⁺ was (x, y)=(0.164, 0.111). The result indicates that BaCa₂Si₃O₉:Eu²⁺ can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes (LEDs).     

Synthesis and luminescence behavior of Eu-doped CaF2 nanoparticles

Luminescent Ca_1−xF_2+x:Eu_x nanoparticles were synthesized by a chemical co-precipitation method in an ethanol solution. The Ca_1−xF_2+x:Eu_x nanoparticles exhibit a sphere-like morphology with particle diameter of about 15-20 nm. With increasing concentration of Eu³⁺ ion the intensity of XRD diffraction peaks decreased significantly and full width at half-maximum of the peaks increased gradually, which indicated that more Eu³⁺ ions resulted in the increase of structural defects. The emission spectrum of Ca_1−xF_2+x:Eu_x nanoparticles consisted of a few narrow, sharp lines corresponding to Eu³⁺ ions. The luminescence intensity of Ca_1−xF_2+x:Eu_x nanoparticles increased with increasing concentration of Eu³⁺ ion and reached a maximum at approximately 15 mol%.     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Novel red perovskite phosphor Ca2AlNbO6:Eu for white light-emitting diode application

Eu³⁺-doped perovskite phosphors of Ca₂AlNbO₆ were synthesized from a solid state reaction. A small amount of the Li₂CO₃ flux was found to greatly shorten calcination time and reduce reaction temperature. The structural and optical properties of the samples were systematically investigated. The excitation spectra of Ca₂AlNbO₆:Eu³⁺ reveal two excitation bands at 398 (⁷F₀→⁵L₆) and 466 nm (⁷F₀→⁵D₂), which match well with the two popular emissions from near-UV and blue LED chips. Under blue light excitation, the red emission of Ca₂AlNbO₆:0.05Eu³⁺ is twice more intense than that of (Y_0.95Eu_0.05)₂O₃. The chromaticity coordinates of (Ca_0.95Eu_0.05)₂AlNbO₆ (x=0.654, y=0.346) are close to the standard values (x=0.670, y=0.330) of National Television Standard Committee (NTSC). The optical properties suggest that Ca₂AlNbO₆:Eu³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

Synthesis, structure and luminescence properties of Y(V,P)O4:Eu,Bi phosphors

YVO₄:Eu³⁺-based red-emitting phosphors with the compositions of Y_0.95−xVO₄:0.05Eu³⁺,xBi³⁺ (x=0.01, 0.03, 0.05, 0.07 and 0.09) and Y_0.90(V_1−zP_z)O₄:0.05Eu³⁺,0.05Bi³⁺ (z=0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized by the high temperature solid-state method. The as-prepared phosphors have the similar tetragonal phase structure and their morphologies varied with the relative content ratio of V to P. The photoluminescence spectra for the as-synthesized phosphors show that a dominant red emission line at around 619 nm, which is due to the Eu³⁺ electric dipole transition of ⁵D₀-⁷F₂, is observed under different excitation wavelengths (254 and 365 nm). Further, the emission intensities of ⁵D₀-⁷F₂ transition upon 365 nm excitation increase sharply owing to the Bi³⁺ doping. Energy transfer process, luminescent lifetime and quantum efficiency for the selected Y_0.90(V_1−yP_y)O₄:0.05Eu³⁺,xBi³⁺phosphors were also studied in detail.     

Size-dependent microstructure and europium site preference influence fluorescent properties of Eu-doped Ca10(PO4)6(OH)2 nanocrystal

In this study, Eu³⁺-doped nanocrystalline Ca₁₀(PO₄)₆(OH)₂ (Ca_10−xEu_x(PO₄)₆(OH)₂) with different particle sizes have been prepared by the thermal decomposition of precursors. Size-dependent microstructure could be observed in nanocrystalline Ca_10−xEu_x(PO₄)₆(OH)₂. The lattices of Ca_10−xEu_x(PO₄)₆(OH)₂ nanocrystals were more distorted in comparison with the bulk, and the smaller the particle size, the more distorted the lattices. Room temperature photoluminescence showed europium site preference was also size-dependent, with the majority of Eu³⁺ ions occupying Ca(II) sites in the bulk, but more and more Eu³⁺ ions occupying Ca(I) sites in Ca_10−xEu_x(PO₄)₆(OH)₂ with decreasing particle size. Fluorescent properties of Ca_10−xEu_x(PO₄)₆(OH)₂ were considered to be influenced by both microstructure and site preference of Eu³⁺ ions. An abnormal strong intensity of ⁵D₀-⁷F₀ transition was observed in bulk and larger Ca_10−xEu_x(PO₄)₆(OH)₂ nanocrystals, but the relative intensities of ⁵D₀-⁷F₀ transition to ⁵D₀-⁷F_1,2,3,4 transition of Eu³⁺ became weaker as the particle sizes decreased. As the particle sizes became smaller, the ratios of the red emission transition (⁵D₀-⁷F₂) to the orange emission transition (⁵D₀-⁷F₁) (R/O values) first increased by comparing the bulk sample with 96 nm sample, and then decreased by comparing 96 nm sample to 57 nm sample. The quenching concentrations of Ca_10−xEu_x(PO₄)₆(OH)₂ samples increased with decreasing particle size. Possible mechanisms responsible for these phenomena were proposed. Since nanosized Ca_10−xEu_x(PO₄)₆(OH)₂ showed higher fluorescent intensities, higher R/O values and higher quenching concentrations, this material is considered to be a promising phosphor.     

Synthesis and optical properties of red emitting Eu doped CaZrO3 phosphor

Eu³⁺ activated Ca_1−xEu_xZrO₃ (x = 0.01–0.05) phosphor with perovskite structure has been synthesized by sol–gel combustion method. The structure, morphology and optical properties of materials were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometry. The XRD results indicate that crystals of CaZrO₃:Eu³⁺ belongs to orthorhombic perovskite structure. The phosphors can be effectively excited by UV light and the emission spectra results indicate that red luminescence of CaZrO₃:Eu³⁺ due to electric dipole transition ⁵D₀ → ⁷F₂ at 616 nm is dominant. Thus, these prepared phosphors show remarkable luminescent properties which find applications in display devices.     

Synthesis and photoluminescence characteristics of (Sr, Ca)3B2O6:Eu for application in white light-emitting diodes

A series of yellow-green (Sr, Ca)₃B₂O₆:Eu phosphors have been synthesized using precursors prepared via a facile sol-gel route. The solid-solution phases crystallized to materials with the formula of Sr_3−x−yCa_xEu_yB₂O₆ with varied Ca²⁺ and Eu²⁺ contents. The emission peak centered at 540 nm under near-UV excitation exhibited a broad-band distribution in the range of 450-650 nm. The dependences of the luminescence intensity on the contents of Ca²⁺ substitution and Eu²⁺ dopant were also investigated. The composition in the host lattice sensitively affected the chromaticity index. Sr_1.21Ca_1.7Eu_0.09B₂O₆ (SCB:0.09Eu) was shown to possess the highest intensity and broadest emission band. Calcining temperature was shown to greatly influence the luminescent properties of SCB:0.09Eu. It is concluded that SCB:0.09Eu can be used as an efficient yellow-green phosphor for white light-emitting diodes (white LEDs) applications.     

An example of concentration sensitive electron-phonon coupling in {(C4H9)4N}3 EuxY1−x(NCS)6 and a new hypothesis for self-quenching

The strong vibronic one-phonon side-bands of the ⁵D₀ → ⁷F₀ emission of Eu³⁺ in {(C₄H₉)₄N}₃ Eu_xY_1?x(NCS)₆ are used to compute the Huang-Rhys electron-phonon coupling factor (S₀) of Eu³⁺ with the mode at 35 cm^-1. Increasing concentration from 1 to 100 is found to lead to a doubling of the electron-phonon coupling strength. Generalization of such an effect is proposed as a new hypothesis for part of the self-quenching process of rare-earth ions.     

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.     

Synthesis and luminescence properties of red-emitting phosphors NaY0.87Eu0.13(WO4)1.2(MoO4)0.8

A series of NaY_1−yEu_y(WO₄)_2−x(MoO₄)_x (x=0−2 and y=0.06−0.15) phosphors have been prepared by a combustion route. X-ray powder diffraction, photoluminescence excitation and emission spectra were used to characterize the resulting samples. The excitation spectra of these phosphors show the strongest absorption at about 396 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. Their emission spectra show an intense red emission at 616 nm due to the ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺. As the Mo content increases, the intensity of the ⁵D₀→⁷F₂ emission of Eu³⁺ activated at wavelength of 396 nm increases and reaches a maximum when the relative ratio of Mo/W is 2:3. The intense red-emission of the tungstomolybdate phosphors at near-UV excitation suggests that the material is a potential candidate for white light emitting diode (WLEDs).     

Synthesis of Y2O3:(Li,Eu) films using phosphor powders coated with SiO2 nano particles

Y_1.9−xLi_0.1Eu_xO₃ (x=0.02, 0.05, 0.08, and 0.12) films were fabricated by spin-coating method. A colloidal silica suspension with Y_1.9−xLi_0.1Eu_xO₃ phosphor powder was exploited to obtain the highly stable and effective luminescent films onto the glass substrate. After heating as-prepared Y_1.9−xLi_0.1Eu_xO₃ films at 700 °C for 1 h, the phosphor films exhibit a high luminescent brightness as well as a strong adhesiveness on the glass substrate. The emission spectra of spin-coated and pulse-laser deposited Y_1.82Li_0.1Eu_0.08O₃ films were compared. The cathodoluminescence of the phosphor films was carried out at the anode voltage 1 kV.     

The effect of Gd3+ on the Eu3+ luminescence in RbGd3F10: Eu3+ compounds

Eu³⁺ luminescence is studied in the two polymorphic forms of RbGd₃F₁₀: Eu³⁺. In the phases where Gd³⁺ is partly replacedby Y³⁺ in order to obtain an independent variation of Eu³⁺ concentration, the quenching of Gd³⁺ luminescence by Eu³⁺ ions takes place very quickly with increasing Eu³⁺ concentration. So the transfer between Gd³⁺ and Eu³⁺ is very efficient. Besides, an important self quenching occurs as well between Gd³⁺ ions as between Eu³⁺ ions, showing strong interactions.     

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.     

在BaF2-BiF3系统中的相组成和离子电导

用固相反应法、X射线粉末衍射技术和复平面阻抗谱测量研究了BaF₂-BiF₃系统的相组成和离子电导。在此系统中发现了两种类型的Ba_1-xBi_xF_2+x固溶体:萤石型(0s≈0.5(14^1/2)a_F,c_{s< 关键词：}     

Luminescent spectral characteristics of EuxLa1 - xTa7O19 polycrystals

Eu_xLa_{1 - x}Ta₇O₁₉ geptatantalates have been synthesized (x = 0.005-10). The luminescence and excitation spectra of these geptatantalates have been investigated at 77 and 300 K. It is supposed that the Eu³⁺ luminescence spectrum for all x may be interpreted within one type optical center with D_2d symmetry. The energy level diagram of the luminescence center has been worked out. It has been found that there is concentration dependence quenching of an europium luminescence. The reasons for this are discussed.     

Photoluminescent properties of Eu 3 +(Dy 3 +)-activated YNb x Ta 1 - x O 4 and REVTa 2 O 9 (RE?=?Y, La, Gd) phosphors from the hybrid precursors

In the context, Eu³⁺ (Dy³⁺)-doped YNb_xTa_1-xO₄ and REVTa₂O₉ (RE=Y, La, Gd) phosphors have been synthesized from the hybrid precursors. Both XRD and SEM indicated the particles present good crystalline state, whose crystalline grain sizes were in the range of 0.5 to 1 μm. Besides, XRD patterns of YNb_xTa_1-xO₄ (x=0.1, 0.2, 0.3, 0.5, 0.9) have shown that the phase has been changed from M^′-type YTaO₄ to M-type YNbO₄ with increasing niobium content. Furthermore, from the luminescent spectra of Eu³⁺-doped YNb_xTa_1-xO₄, it was observed that the ⁵ D ₀–⁷ F ₂ transition of Eu³⁺ was predominated and its intensity increases with increasing niobium content, as well as the intensity ratio of ⁵ D ₀–⁷ F ₂ transition to ⁵ D ₀–⁷ F ₁ transition for Eu³⁺. The optimum concentrations of Eu³⁺ and Dy³⁺ in YNb_0.5Ta_0.5O₄ have been found to be 6 and 5 mol %, respectively. At the same time, the luminescent properties of Eu³⁺ and Dy³⁺ in REVTa₂O₉ (RE=Y, La, Gd) have also been investigated that GdVTa₂O₉:Eu³⁺ (Dy³⁺) presents high luminescence, while LaVTa₂O₉:Eu³⁺ (Dy³⁺) shows weak luminescence. PACS 78.20.-e; 78.55.-m; 61.72.Ss; 32.50.+d; 81.40 Tv     

Luminescence behavior of the Eu(TTFA)3 and TbSSA co-doped xerogel

Luminescence behavior of Eu(TTFA)₃ and TbSSA co-doped gel has been investigated. The excitation and emission spectra of the EuCl₃ and thenoyltrifluoroacetone co-doped gel appeared to exhibit intramolecular energy transfer from the coordinated thenoyltrifluoroacetonate to the europium ions, and the luminescence behavior of sulphosalicylic acid and TbCl₃ co-doped gel also indicated the synthesis of TbSSA in the gel. The luminescence behavior of x% Eu(TTFA)₃ and (1-x)% TbSSA (x=0-1) co-doped gel changed significantly with the ratio of Eu(TTFA)₃ and TbSSA. By adjusting the ratio of the Eu(TTFA)₃ and TbSSA in the gel, the luminescence of different colors which resulted from the mixture of the emission bands of Eu³⁺ ions and Tb³⁺ ions can be observed.