Visible luminescence properties of Er3+–Dy3+ codoped tellurite glasses

Er³⁺ and Dy³⁺ codoped tellurite glasses have been synthesized. Five emission bands in the PL spectrum under 325 nm pumping were observed. Three of them correspond to Er³⁺ and the other two correspond to Dy³⁺, respectively. The PL spectrum revealed that the intensity of Dy³⁺ characteristic emission was enhanced as Er³⁺ concentration increased while keeping Dy³⁺ concentration constant. Due to small mismatch between the energy level of Er³⁺:⁴F_7/2 and Dy³⁺:⁴F_9/2 resonant energy was possibly transferred between them. This process can give rise to an enhancement of the PL intensity of 484 and 574 nm from Dy³⁺. The PL spectra of these glasses cover the blue, green and red wavelength range and the intensities of those emission bands could be controlled by adjusting the concentration of relevant rare-earth ions. These glasses with the controllable CIE coordinates might be a potential candidate for the widely realistic application such as solid-state white lighting and multicolor display.     

Eu2+掺杂的Ca-α-SiAlON和Mg-α-SiAlON荧光粉的光学性质和电子结构

α-SiAlON是一种典型的新型硅氮氧荧光体基底材料。通过高温固相反应法合成了化学式为M0.75Eu0.05Si9.6Al2.4O0.8N15.2(M=Ca,Mg)的黄色氮氧化物荧光粉Ca-α-SiAlON:Eu2+和Mg-α-SiAlON:Eu2+。通过光致发光谱图发现,Ca0.75Eu0.05Si9.6Al2.4O0.8N15.2的发光强度比Mg0.75Eu0.05Si9.6Al2.4O0.8N15.2高得多。然后使用基于密度泛函理论的CASTEP程序,计算了两种荧光粉的能带结构和态密度。通过对态密度的分析,发现Ca的分波态密度对总态密度的贡献比Mg的大,这是因为Ca的3d能级和Eu的5d能级更接近,两者充分混合,增大了Eu的5d能带的态密度,从而解释了Ca-α-SiAlON:Eu2+的光学性能好于Mg-α-SiAlON:Eu2+的本质原因。     

Surface treatment investigation and luminescence properties of SiO2-coated Ca2BO3Cl:0.02Eu2+ phosphors via sol–gel process

SiO₂-coated Ca₂BO₃Cl:Eu²⁺ phosphors were prepared by the sol–gel method in order to enhance the chemical and thermal stabilities of Ca₂BO₃Cl:Eu²⁺ phosphor. The phase structures, microstructures and luminescence properties were studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrometer, respectively. The emission intensity of SiO₂-coated Ca₂BO₃Cl:Eu²⁺ phosphor decreased a little compared to that of the uncoated phosphor. The moisture resistances of the phosphors were comparatively examined by the aging treatment experiment in the water, and the thermal stability was studied by the temperature dependent photoluminescence spectra. The results indicated that SiO₂ coating on the surface of the phosphor particles improved the moisture-resistance and thermal stability to a large extent.     

BaMgAl10O17:Eu2+,Mn2+中Eu2+→Mn2+的能量传递

在还原气氛下采用高温固相法合成了BaMgAl10O17:Mn2 ,BaMgAl10O17:Eu2 ,BaMgAl10O17:Eu2 ,Mn2 粉末样品,测量并研究了它们的激发光谱和发射光谱性质.结果表明:BaMgAl10O17:Eu2 ,Mn2 中,Eu2 的发射光谱和Mn2 的吸收光谱之间的光谱交叠范围较大,两种离子之间发生了明显的交叉弛豫过程,即有较强的共振能量传递过程,导致在紫外光的激发下,样品BaMgAl10O17:Eu2 ,Mn2 发射光谱中以蓝光和绿光为主.     

Photoluminescence properties of Eu3+-doped Cd1−x Zn x S quantum dots

Eu³⁺-doped Cd_1−x Zn _x S (0 ≤ x ≤ 0.5) quantum dots (QDs) have been synthesized using wet chemical precipitation method. X-ray diffraction and transmission electron microscope have been used for the crystallographic and morphological characterization of synthesized nanomaterials. In order to understand the spectral characteristics of doped QDs, N₂-laser induced time resolved spectra have been recorded. Excited state lifetime values for dichromatic emission (red and violet) attributed to ⁵D₀ → ⁷F_J (J = 1, 2) transitions of Eu³⁺ and host lattice transitions have been calculated from the recorded luminescence decay curves. Decay time dependence on the dopant concentration (0.01–10 at. wt% of Cd²⁺) has been studied in detail.     

Eu2+,Mn2+在BaZnP2O7中的发光及Eu2+→Mn2+能量传递

采用高温固相法合成了BaZnP2 01:Eu2 ,Mn2 荧光粉,并对其发光性质及Eu2 对Mn2 的能量传递机理进行了研究.Eu2 和Mn2 在380 am和670 nm的发射峰分别由Eu2 的5d-14f跃迁和Mn2 的4T1(4G)-6A1(6S)跃迁产生.Eu2 对Mn2 的发光有很强的敏化作用,根据Dexter电多极相互作用的能量传递概率公式,判断出BaZnP2O7中Eu2 对Mn2 的能量传递属于电偶极-电四极相互作用引起的共振能量传递.     

Optimization of the properties of codoped single-domain Y–Ba–Cu–O bulk superconductors

The intrinsic effects of nanoscopic MnO₂ powders addition combined with Fe cation substitutions for copper sites on the microstructure and superconductive properties of YBa₂Cu₃O_7?δ (Y123) melt-solidified bulks have been investigated. On the one hand, an increase in Y₂BaCuO₅ (Y211) particle pushing, leading to an inhomogeneous bulk microstructure, is caused by increasing MnO₂ content due to increased net interfacial energy, Δσ₀; and, on the other hand, an addition of MnO₂ powders is effective in enhancing both the δT_c-type and δl-type pinning. It also shows that the Fe addition helps to optimize the high magnetic field performance and Y211 particle distribution in textured pellets. Further, this experiment suggests that a combination of the element substitution and the nanoscopic particle is a beneficial way to optimize the microstructure and superconductive properties of single-domain bulk superconductors.     

Structure dependent luminescence characterization of green–yellow emitting Sr2SiO4:Eu2+ phosphors for near UV LEDs

This paper reports on the luminescence properties of mixtures of α- and β-(Sr_0.97Eu_0.03)₂SiO₄ phosphors. These phosphors were prepared by 3 different synthesis techniques: a modified sol–gel/Pechini method, a co-precipitation method and a combustion method. The structural and optical properties of these phosphors were compared to those of solid state synthesized powders. The emission spectra consist of a weak broad blue band centered near 460 nm and a strong broad green–yellow band centered between 543 and 573 nm depending on the crystal structure. The green–yellow emission peak blue-shifts as the amount of β phase increases and the photoluminescence emission intensity and quantum efficiency of the mixed phase powders is greater than those of predominant α-phase powders when excited between 370 and 410 nm. Thus, (Sr_1?xEu_x)₂SiO₄ with larger proportion of the β phase are more promising candidates than single α-phase powders for use as a green–yellow emitting phosphor for near UV LED applications. Finally the phosphors prepared by the sol–gel/Pechini method, which have larger amount of β phase, have a higher emission intensity and quantum efficiency than those prepared by co-precipitation or combustion synthesis.     

Effects of Fe2+ content in raw materials on Mn–Zn ferrite magnetic properties

The magnetic properties of Mn–Zn ferrite such as initial permeability, saturation magnetization, Curie temperature, resistivity and power loss are affected greatly by the Fe²⁺ content in the raw materials. The experimental results show that low resistivity (ρ) and high eddy current loss (P_e) are induced by the superfluous Fe²⁺ content in the raw materials; the scant Fe²⁺ content in the raw materials will increase hysteresis loss (P_h) and decrease Curie temperature (T_c), saturation magnetization (M_s) and initial permeability (μ_i).     

Hyperfine EPR Structure of Isotopes 151Eu2+ and 153Eu2+ in Lutetium–Aluminum Garnet

Physics of the Solid State - Electron paramagnetic resonance of rhombic Eu2+ centers in single crystals of Lu3Al5O12 doped with europium ions with the natural isotope abundance was studied....     

Synthesis,structural and optical properties of Eu3+–doped Ca2V2O7 nanophosphors

Europium doped calcium pyrovanadate nanoparticles Ca₂V₂O₇:Eu³⁺, having a size of 57–63 nm, were synthesized using combustion process. Structure, morphological and optical properties of nanophosphors have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrometry (PL) and Fourier transform infra-red (FT-IR) spectroscopy. X-ray studies shows that a pure triclinic Ca₂V₂O₇ phase was obtained at 900 °C temperature. The red emission observed at 620 nm upon excitation at 305 nm is due to hypersensitive transition ⁵D₀ → ⁷F₂ of luminescent activator Eu³⁺ location at a site with no inversion symmetry in Ca₂V₂O₇ crystal lattice. High luminescent intensity and easy synthesis technique make this red phosphor a promising candidate for application as luminescent materials.     

Charge transfer transitions and location of the rare earth ion energy levels in Ca-α-SiAlON

The broad bands in the room-temperature excitation spectra of Sm³⁺-, Dy³⁺- and Tm³⁺-activated Ca-α-SiAlON phosphors are interpreted as the N³⁻-to-rare earth charge transfer transition (CTT). From the energies of the charge transfer transitions and from the optical data presented for the Eu²⁺ ion, the location of the divalent rare earth ion energy levels relative to the valence and the conduction band of Ca-α-SiAlON is derived. The salient features of the energy-level diagram are shown to be practical in explaining the temperature-dependent variations of the Eu²⁺ and Yb²⁺ luminescence efficiency in Ca-α-SiAlON. A comparative study pertaining to the nature of the Yb²⁺ and Eu²⁺ ion luminescence in Ca-α-SiAlON and in SrSi₂O₂N₂ is presented. A tentative energy-level diagram of the trivalent rare earth ions in Ca-α-SiAlON is also constructed.     

Effects of heat treatment and TiO2 content on the optical properties of Eu3+ doped TiO2–SiO2 thin films

The photoluminescence properties of Eu³⁺-doped TiO₂–SiO₂ thin films were investigated. The films were deposited on silicon substrates by the sol–gel process using the dip-coating method. The molar ratio of TiO₂ content was varied from 25% to 100%, while Europium concentration was fixed to 1%. The obtained films were calcinated at various temperatures ranging from 400 °C to 1300 °C, which allowed determining the optimal conditions for the Eu³⁺ luminescence. Meanwhile, the structure of TiO₂–SiO₂ powders, prepared in the same conditions as the films, was also studied by Raman spectroscopy. It revealed the role of Europium and SiO₂ on the stabilization of the anatase phase and the importance of the silica matrix in the control of titania particle size.     

Pressure-Induced Enhancement of the Photoluminescence in Ca 1−x Sr x F 2 :Mn 2+

The surprising disappearance of the Mn 2+ photoluminescence (PL) on passing from CaF 2 to SrF 2 through the Ca 1 m x Sr x F 2 :Mn 2+ series is investigated through pressure spectroscopy, and as a function of the temperature. The PL quenching which is observed along the series is explained on the basis of multiphonon relaxation mechanisms, which are described by a thermally activated process. In non-luminescent crystals, PL can be recovered by applying pressure. The results are accounted for through an universal equation relating the PL lifetime as a function of P (or V ) and T , using an activation energy and a transition rate that are strongly dependent on the lattice parameter (crystal volume).     

Photoluminescence properties of Er-doped β-FeSi2 grown by ion implantation

Photoluminescence (PL) properties of Er-doped β-FeSi₂ (β-FeSi₂:Er) and Er-doped Si (Si:Er) grown by ion implantation were investigated. In PL measurements at 4.2 K, the β-FeSi₂:Er showed the 1.54 μm PL due to the intra-4f shell transition of ⁴I_13/2→⁴I_15/2 in Er³⁺ ions without a defect-related PL observed in Si:Er. In the dependence of the PL intensity on excitation photon flux density, the obtained optical excitation cross-section σ in β-FeSi₂:Er (σ=7×10⁻¹⁷ cm²) is smaller than that in Si:Er (σ=1×10^-15 cm²). In the time-resolved PL and the temperature dependence of the PL intensity, the 1.54 μm PL in β-FeSi₂:Er showed a longer lifetime and larger activation energies for non-radiative recombination (NR) processes than Si:Er. These results revealed that NR centers induced by ion implantation damage were suppressed in β-FeSi₂:Er, but the energy back transfer from Er³⁺ to β-FeSi₂ was larger than Si:Er.     

Hyperfine and Quadrupole Interactions in EPR of 153Eu2+ and 151Eu2+ in Yttrium–Aluminum Garnet

Physics of the Solid State - Rhombic 153Eu2+ and 151Eu2+ centers are studied in specially grown single crystals of yttrium–aluminum garnet. The parameters of the hyperfine and quadrupole...     

The crystal structure and luminescent properties of nitrogen-rich Ca-α-sialon：Eu with saturated calcium solubility fabricated by the alloy-nitridation method

Nitrogen-rich Ca-α-sialon: Eu2+ phosphors with saturated calcium solubility are synthesized through a solid- state reaction (SSR) at 2173 K with stable alloy and nitride as the starting materials. The Ca1.83-1.5xSi8.34Al3.66OxN16-x : xEu phosphors have intensive orange emissions, whose peaks are located at approximately 585-600 nm, and the emission wavelengths tend to shift toward the red region when the Eu concentrations increase from 0.5% to 18% (mole percentage). When the Eu concentration is equal to 9%, the phosphors suffer from concentration quenching. The low-temperature photoluminescence properties indicate that Ca1.83-1.5xSi8.34Al3.66OxN16x : xEu phosphors show excellent thermal quenching. The crystal structures of Ca1.83-1.5xSi8.34Al3.66OxN16x : xEu are also investigated, and are found to have nitrogen-rich compositions with saturated calcium cations at the interstitial sites of the α-sialons. In addition, the influencing factors of α-sialons with different compositions on the crystal lattice are discussed in detail.