Photoluminescence characteristics and energy transfer between Bi~（3＋） and Eu~（3＋） in Na_2O–CaO–GeO_2–SiO_2 glass

We report the photoluminescence（PL） of Eu^3＋-doped glass with Bi^3＋as a sensitizer. The specific glass system with the strong enhancement of the red emission of Eu3＋is obtained by adding a small number of Bi3＋ions instead of increasing the Eu^3＋ concentration. The emission band of Bi3＋overlaps with the excitation band of Eu^3＋ and the lifetime decay curves,resulting in a very efficient energy transfer from Bi^3＋ to Eu^3＋. The probability of energy transfer is strongly dependent on Bi^3＋ concentration. In addition, the intensity of 4f–4f transition is much stronger than that of a charge-transfer（CT） band in the excitation spectrum, which indicates that the Na2O–Ca O–Ge O2-Si O2 glass is a suitable red-emitting phosphor with high stability as a candidate for light-emitting diodes（LEDs）.     

VUV/UV/X-Ray Excited Luminescent Properties of Eu^3＋ and Pr^3＋ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu^3＋ and Pr^3＋ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu^3＋ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu^3＋ ions occupied Bi^3＋ sites, and there could be an energy transfer from Bi^3＋ ions to RE^3＋ ions.     

Luminescence and Energy Transfer of Eu^2＋, Mn^2＋ in SrZnP2O7

The SrZnP2OT：Eu^2＋, Mn^2＋ phosphor is synthesized by high temperature solid state reaction. The luminescence properties and the energy transfer between Eu^2＋ and Mn^2＋ are investigated. The emission bands of this phosphor peaked at 42Ohm and 67Ohm are originated from the 5d → 4f transition of Eu^2＋ and from the 4T1 （4G） --〉 6A1 （6S） transit/on of Mn^2＋, respectively. With the increasing Mn^2＋ concentration, the intensity of fixed concentra- tion Eu^2＋ decreases and the intensity of Mn^2＋ also increases. It is suggested that there is an energy transfer from Eu^2＋ to Mn^2＋ in SrZnP2O7 host. According to Dexter＇s energy transfer formula of multipolar interaction, the energy transfer between Eu^2＋ and Mn^2＋ is due to the electric dipole-quadrupole interaction of the resonance transfer.     

Luminescence Properties of Ca4GdO（BO3）3：RE （RE=Eu^3＋,Tb^3＋） under VUV Excitation

We experimentally investigated the VUV excitation luminescence properties of Ca4 GdO(B03)3 :RE (RE=Eu^3 , Tb^3 )Ca4GdO(BO3)3:Eu3 and Ca4GdO(BO3)3:Tb^3 emitted bright red and green colour light, respectively, under 172 nm excitation, resulting from the favorable position of the host absorption band (186 nm) and efficient energy transfer from Gd^3 to activators (e.g. Eu^3 or Tb^3 ) by means of secondary absorption in the Ca4GdO(BO3)3 matrix. The f-d transitions of Eu^3 and Tb^3 in the host lattice are depicted.     

Sr3Bi（PO4）3：Eu^2＋ Luminescence,Concentration Quenching and Crystallographic Sites

A blue emitting phosphor Sr3Bi（PO4）3：Eu2＋ is synthesized luminescent property is investigated. Sr3Bi（PO4 ）3 ：Eu^2＋ can by a high-temperature solid state method, and its create blue emission under the 332 radiation excitation, and the prominent luminescence in blue （423nm） due to the 4fSd^1→4f^7 transition of the Eu^2＋ ion. The crystallographic sites of the Eu^2＋ ion in Sr3Bi（PO4）3 are analyzed, and the 420 and 440 nm emission peaks of the Eu^2＋ ion are assigned to the nine-coordination and eight-coordination, respectively. The emission intensity of Sr3Bi（PO4）3：Eu^2＋ is influenced by the Eu^2＋ doping content, and the concentration quenching effect is observed. The quenching mechanism is the dipole-dipole interaction, and the critical distance of energy transfer is calculated by the concentration quenching method to be approximately 1.72nm.     

Abnormal Visible Luminescence Mechanism of Tb^3＋-Yb^3＋ Codoped SiOu-Al2O3-CaF2 Glass Studied by Time-Resolved Spectra

The upconversion energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass is investigated by time-resolved spectra. The effect of donor ion Yb^3＋ is involved in the dynamic decay behavior of acceptor ion Tb^3＋, which provides direct proof for the energy transfer from Yb^3＋ to Tb^3＋. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the 5D4 state （Tb^3＋） contain two parts： a slow decay process corresponding to its radiation, and a fast one with a decay parameter approximately twice the lifetime of the ^2F5/2 state （Yb^3＋ ）. The fast decay process is contradictory to the generally accepted cooperative sensitization upconversion rate equation model. Since the effect of the host environmental is excluded by comparative experiments, we believe that there should be another energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass in addition to the cooperative sensitization process.     

Concentration and Temperature Dependences of YBO3：Bi^3＋ Luminescence under Vacuum Ultraviolet Excitation

Bi^3＋ doped YB03 phosphors are prepared by solid state reaction and their luminescent properties are investi- gated by using synchrotron radiation instrument, Concentration and temperature dependences of YBO3：Bi3＋ luminescence under VUV/UV excitation is observed, The emission and excitation spectra are assigned, and the mechanism for these phenomena is explored, which result from the energy transfer between Bi^3＋ ions occupying different sites in YB03 crystal lattice.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3（BO3）8：Tb^3＋ Phosphor

The novel vacuum ultraviolet （VUV） excited Na3 Y9O3 （BO3）8：Tb^3＋ （NYOB：Tb^3＋） green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3＋ （20 wt%） are observed in NYOB： Tb^3＋ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3＋ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3＋ in NYOB：Tb^3＋ is first established. This newly developed NYOB：Tb^3＋ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4：Mn^2＋ and would be a potential VUV-excited green phosphor.     

Enhanced NIR emission in Ce^3＋/Er^3＋-doped YAG induced by Bi^3＋ doping

Ce^3＋/Er^3＋/Bi^3＋ triply-doped yttrium aluminum garnet （YAG） is synthesized using co-precipitation method. The Bi^3＋ concentration-dependent near-infrared （NIR） emission behavior is systemically in- vestigated. The NIR emission of Er^3＋ ions at 1531 nm is enhanced threefold by the addition of 7 mol% Bi^3＋. Bi^3＋doping results in the formation of exciton in YAG and the variation in the local environment of the doped rare-earth ions. The enhancement in NIR luminescence is ascribed to the combined effects of the sensitization of exciton→Ce^3＋ →Er^3＋ and the Bi^3＋ doping-induced adjustment of the local environment for Ce^3＋ and Er^3＋ ions.     

A novel strong green phosphor： K3Gd（PO4）2：Ce^3＋, Tb^3＋ for a UV-excited white light-emitting-diode

A series of K3Gd1-x-y（PO4）2：xCe^3＋, yTb^3＋ phosphors are synthesized by the solid-sate reaction method. X-ray diffraction and photoluminescence spectra are utilized to characterize the structures and luminescence properties of the as-synthesized phosphors. Co-doping of Ce^3＋ enhances the emission intensity of Tb^3＋ greatly through an efficient energy transfer process from Ce^3＋ to Tb^3＋. The energy transfer is confirmed by photoluminescence spectra and decay time curves analysis. The efficiency and mechanism of energy transfer are investigated carefully. Moreover, due to the non- concentration quenching property of K3Tb（PO4）2, the photoluminescence spectra of K3Tb1-x（PO4）2：xCe^3＋ are studied and the results show that when x = 0.11 the strongest Tb^3＋ green emission can be realized.     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Quantum cutting downconversion by cooperative energy transfer from Bi3+ to Yb3+ in Y2O3 phosphor

Bi~(3+) and Yb~(3+) codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method.Strong near-infrared (NIR) emission around 980 nm from Yb~(3+)(2F5/2 → 2F7/2) is observed under ultraviolet light excitation.A broad excitation band ranging from 320 to 360 nm,owing to the 6s 2 →6s6p transition of Bi~(3+) ions,is recorded when the Yb~(3+) emission is monitored,which suggests a very efficient energy transfer from Bi~(3+) ions to Yb~(3+) ions.The Yb~(3+) concentration dependences of both the Bi~(3+) and the Yb~(3+) emissions are investigated.The decay curve of Bi ~(3+) emission under the excitation of 355 nm pulse laser is used to explore the Bi~(3+) →Yb~(3+) energy transfer process.Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.     

Cooperative Quantum Cutting of Nano-Crystalline BaF2：Tb^3＋, Yb^3＋ in Oxyfluoride Glass Ceramics

We report on cooperative quantum cutting in Tb^3＋- Yb^3＋ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3＋ ions under 485 nm excitation indicates cooperative energy transfer from Tb^3＋ to Yb^3＋. The quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.     

Photoluminescence in GdVO4:Bi3+, Eu3+ red phosphor

The doubly doped (Bi³⁺ and Eu³⁺) GdVO₄ powder is synthesized by hydrolyzed colloid reaction (HCR) technique and formation of material is confirmed by XRD measurement. Surface morphology has been studied by SEM measurement and the result shows uniform surface morphology. The average particle size observed by SEM is about 1 7m. The Fritsch particle sizer is used to study the particle size distribution. It distributes from O.15 to 3.57 7m. The small particle size (less than 5 7m) and the narrow particle size distribution, are the necessary requirements of good phosphor material. Photoluminescence result shows a narrow emission line of Eu³⁺ ion (4 nm FWHM) at 618 nm. The Eu³⁺ emission intensity is enhanced by a factor of five with the addition of small amount of Bi³⁺. The emission bands of VO₄^3- and Bi³⁺ partially overlap with the excitation band of Eu³⁺. The process of energy transfer from Bi³⁺ to Eu³⁺ is discussed here. The energy transfer probability is strongly dependent upon the Bi³⁺ and Eu³⁺ concentrations, with a maximum for 0.2 mol % of Bi³⁺ and 3 mol % of Eu³⁺. It drastically decreases for higher concentrations. For photoluminescent applications, the quantum efficiency (QE) of a phosphor material is an important parameter. The QE of GdVO₄:Bi,Eu(0.2,3) is 76%. The GdVO₄:Bi,Eu(0.2,3) material is proposed as an efficient photoluminescent phosphor.     

LaOBr:Tb3+，Dy3+的发光特性及高压研究

 采用高温常压方法合成了稀土发光材料LaOBr:Tb³⁺，Dy³⁺，采用高温高压方法对材料进行了处理，研究了高温高压处理前后样品发光特性的变化，并进行了发光衰减测量。结果表明，Dy³⁺的掺杂可以将Tb³⁺的⁵D₃能级的激发能有效地驰豫到⁵D₄能级，从而使⁵D₄~⁷F_J（J＝0, 1,…,6）的发射，尤其是⁵D₄~⁷F₅的发射明显增强，使得样品的发光亮度大大提高。Dy³⁺，Tb³⁺间存在交叉驰豫共振能量传递。高压处理过程引入的杂质、材料氧化及压致晶场变化都对材料的发光特性产生影响。     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Luminescent Characteristics of LiSrBO3：Eu3＋ Phosphor for White Light Emitting Diode

LiSrBO3 ：Eu3＋ phosphor is synthesized by a high solid-state reaction method, and its luminescent characteristics are investigated. The emission and excitation spectra of LiSrBO3：Eu3＋ phosphors exhibit that the phosphors can be effectively excited by near ultraviolet （401 nm） and blue （471 nm） light, and emit 615nm red light. The effect of Eua＋ concentration on the emission spectrum of LiSrBO3：Eu3＋ phosphor is studied; the results show that the emission intensity increases with increasing Eu3＋ concentration, and then decreases because of concentration quenching. It reaches the maximum at 3mol%, and the concentration self-quenching mechanism is the dipoledipole interaction according to the Dexter theory. Under the conditions of charge compensation Li＋, Na＋ or K＋ incorporated in LiSrBO3, the luminescent intensities of LiSrBO3 ：Eua＋ phosphor are enhanced.