Energy transfer phenomena in GdMgB5O10

The luminescence of Mn²⁺, Bi³⁺, Ce³⁺ and Tb³⁺ in GdMgB₅O₁₀ and some codoped materials is reported. Energy transfer rates are derived from the experiments. The Bi³⁺ → Gd³⁺ and Gd³⁺ → Bi³⁺ transfer rates are about equal at room temperature. The excitation energy is able to migrate among the Gd³⁺ sublattice. The Ce³⁺ ion is a good sensitizer for this sublattice. By diluting the Gd³⁺ sublattice with La³⁺ ions, the energy migration in Gd³⁺ zig-zag chains was blocked and interchain energy transfer occurred. Very efficient phosphors can be obtained by using Ce³⁺ as a sensitizer, the Gd³⁺ sublattice as an intermediary and Tb³⁺ as an activator.     

Energy transfer processes in Ce and Tb co-doped Ln2Si2O7 (Ln = Y, Gd)

The Ce³⁺ and Tb³⁺ co-doped Ln₂Si₂O₇ (Ln = Y, Gd) samples were prepared by sol-gel method. Structure characterization of the phosphor was carried out by X-ray diffraction. The luminescence properties of samples were analyzed by measuring the excitation and emission spectra. It was observed that excitation energy can transfer mutually between Ce³⁺ and Tb³⁺ in GPS: Ce³⁺, Tb³⁺ samples, while in Y₂Si₂O₇ :Ce³⁺, Tb³⁺ samples the energy transfer only progresses from Ce³⁺ to Tb³⁺. Based on the energy level diagrams of respective Ce³⁺, Tb³⁺ and Gd³⁺ ion, the detailed pathways for energy transfer are explained.     

White light generation in Al2O3:Ce:Tb:Mn films deposited by ultrasonic spray pyrolysis

Aluminium oxide (Al₂O₃) films doped with CeCl₃, TbCl₃ and MnCl₂ were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The films were analysed using the X-ray diffraction technique and they exhibited a very broad band without any indication of crystallinity, typical of amorphous materials. Sensitization of Tb³⁺ and Mn²⁺ ions by Ce³⁺ ions gives rise to blue, green and red simultaneous emission when the film activated by such ions is excited with UV radiation. The overall efficiency of such energy transfer results to be about 85% upon excitation at 312 nm. Energy transfer from Ce³⁺ to Tb³⁺ ions through an electric dipole-quadrupole interaction mechanism appears to be more probable than the electric dipole-dipole one. A strong white light emission for the Al₂O₃:Ce³⁺(1.3 at.%):Tb³⁺(0.2 at.%):Mn²⁺(0.3 at.%) film under UV excitation is observed. The high efficiency of energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions, resulting in cold white light emission (x = 0.30 and y = 0.32 chromaticity coordinates) makes the Ce³⁺, Tb³⁺ and Mn²⁺ triply doped Al₂O₃ film an interesting material for the design of efficient UV pumped phosphors for white light generation.     

Transfert d'energie entre les ions Ce3+ et Tb3+ dans GdAlO3

Energy transfer from the Ce³⁺ to the Tb³⁺ ion has been studied in a host GdAlO₃ structure. The maximum fluorescence intensity of Tb³⁺ is observed for the composition Gd_0.96Ce_0.02Tb_0.02AlO₃. The energy transfer from Ce³⁺ to Tb³⁺ is explained by a dipole-dipole type coulombic interaction.     

Luminescent efficiency of Eu3+ and Tb3+ in LaMgB5O10 — Type borates under excitation from 100 to 400 nm

Luminescent properties of Eu³⁺ and Tb³⁺ in doped LaMgB₅O₁₀ have been studied over the 100–400 nm excitation range. The Tb³⁺-activated borate shows an external quantum efficiency exceeding 75 % when excited in 5d levels between 180 and 205 nm. The excitation range of high efficiency is extended up to 290 nm when the terbium fluorescence is sensitized by cerium, which makes this material a good candidate for use as the green component in low-pressure mercury lamps. The vacuum UV spectra of the Ln_xLa_1?xMgB₅O₁₀ (Ln = Eu, Tb) phases show a band close to 150 nm corresponding to an excitation of the Eu³⁺ and Tb³⁺ ions transmitted through the host lattice.     

Luminescence properties and energy transfer investigations of Ce3+/Tb3+ co-doped BaY2Si3O10 phosphor

A novel phosphor BaY₂Si₃O₁₀ (BYSO): Ce³⁺, Tb³⁺ was synthesized by the conventional solid-state reaction, which displays tunable color emission from blue to blue-green under ultraviolet excitation by adjusting the radio of Ce³⁺ and Tb³⁺ appropriately. Photoluminescence characteristics were carefully investigated. We demonstrate the existence of efficient energy transfer from Ce³⁺ to Tb³⁺ in BaY₂Si₃O₁₀: Ce³⁺, Tb³⁺ phosphor. The energy transfer Ce³⁺ → Tb³⁺ was proved to be governed by dipole–quadrupole interaction.     

Studies on blue and red photoluminescence from Al2O3:Ce:Mncoatings synthesized by spray pyrolysis technique

Al₂O₃:Ce³⁺:Mn²⁺ films deposited by the spray pyrolysis technique show blue and red emissions under ultraviolet light excitation. The blue emission is due to the de-excitation of Ce³⁺ ions from their excited state 5d to the split ground state ²F. The usually weak red emission attributed to 3d→3d de-excitation of Mn²⁺ is enhanced through an efficient energy transfer from Ce³⁺ to Mn²⁺ ions. The quantum efficiency of this transfer is near to 100%. SEM and RBS have been used to analyze the surface morphology and chemical composition of Ce- and Mn-doped Al₂O₃ films. The films were also characterized by the X-ray photoelectron spectroscopy technique, and it was found that a considerable amount of Mn ions remains linked to chlorine while Ce is mostly in an oxidized state.     

Luminescence properties of LaPO4:Tb,Me (Me = Gd, Bi, Ce) under VUV excitation

The luminescence properties of LaPO₄:Tb³⁺,Me³⁺ (Me = Gd, Bi, Ce) were investigated under VUV excitation. The results indicate that only Gd³⁺ plays an intermediate role in energy transfer from the host absorption band to Tb³⁺ under 147 nm excitation, Bi³⁺ and Ce³⁺ have no contribution to improving the emission intensity of La_0.95PO₄:Tb_0.05³⁺ because the charge transfer band of Bi³⁺ is mismatching for the excitation wavelength (147 nm) and Ce³⁺ can be oxidized easily. A new band at 135 nm is observed in the excitation spectrum of La_0.92PO₄:Tb_0.05³⁺,Bi_0.03³⁺, which may correlate with the absorption of Bi²⁺.     

A novel green emitting phosphor Ca1.5Y1.5Al3.5Si1.5O12:Tb

Vacuum ultraviolet (VUV) excitation and emission properties of Tb³⁺ ion doped silico-aluminate phosphor Ca_1.5Y_1.5Al_3.5Si_1.5O₁₂:Tb³⁺ was studied. Upon excitation with vacuum ultraviolet (VUV) and near UV light excitation, the phosphor showed strong green-emission peaked at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, and the highest PL intensity at 545 nm was found at a content of about 14 mol% Tb³⁺. The 4f–5d transition absorption of Tb³⁺ is in the range from 150 nm to 260 nm, and there is an energy transfer from the host to the rare earth ions. Field emission scanning electron microscopy (FE-SEM) images showed the particle size of the phosphor was less than 3 μm.     

Thermally stable luminescence and energy transfer in Ce, Mn doped Sr2Mg(BO3)2 phosphor

Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺ and Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors have been synthesized by conventional solid state reaction technology at 900 °C for 12 h in reducing atmosphere. The phase purity, photoluminescence (PL) properties, thermal stability, energy transfer and luminescent decay curves have been investigated. Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors show blue and deep-red¹ emission bands. The deep-red emission band is attributed to the energy transfer from Ce³⁺ to Mn²⁺. The fluorescence lifetimes of Ce³⁺ in co-doped sample are shorter than that in single doped one, which confirms that the energy transfer takes place. The phosphors have weak thermal quenching. The luminescence properties of Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ make the phosphor a new bicolor emitting material.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Luminescence properties of Ce and/or Mn activated Ca10K(PO4)7 under ultraviolet and vacuum ultraviolet excitation

New Ce³⁺ and/or Mn²⁺ activated Ca₁₀K(PO₄)₇ phosphors were prepared by solid-state reaction, and their photoluminescence properties upon ultraviolet and vacuum ultraviolet excitation were investigated. Under 254 nm excitation, a series of Ca₁₀K(PO₄)₇:xMn²⁺ samples exhibit two emission bands at 463 and 650 nm, which could be attributed to oxygen defects and ⁴T₁–⁶A₁ transition of Mn²⁺, respectively. And an energy transfer from defects to Mn²⁺ has been observed. With the Mn²⁺ content increased, the emitting hues of Ca₁₀K(PO₄)₇:Mn²⁺ can range from blue to red. By co-doping Ce³⁺ to Ca₁₀K(PO₄)₇:Mn²⁺, the emission intensity of Mn²⁺ is strongly enhanced due to an efficient energy transfer by [Ce³⁺ → Mn²⁺] and [defects → Ce³⁺ → Mn²⁺]. But under 147 nm excitation, the emission intensity of Mn²⁺ in Ca₁₀K(PO₄)₇:0.25Mn²⁺ decreases slightly compared with that in Ca₁₀K(PO₄)₇:025Mn²⁺, 0.1Ce³⁺, 0.1K⁺ due to the host sensitization competition between Ce³⁺ and Mn²⁺.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

RE3+ (RE = Ce3+, Tb3+) doped BaGdF5 nanocrystals: Synthesis,optical and magnetic properties,and energy transfer

Through a citric acid assisted hydrothermal method, the RE³⁺ (RE³⁺ = Ce³⁺, Tb³⁺) doped cubic phase BaGdF₅ nanocrystals with a sphere-like morphology and an average size of 30 nm have been synthesized. The samples show paramagnetic properties at 300 K. The photoluminescence spectra of the obtained samples suggest that the existence of Ce³⁺ can dramatically enhance the emission intensity of Tb³⁺ due to an efficient energy transfer from Ce³⁺ to Tb³⁺. The energy transfer efficiency from Ce³⁺ to Tb³⁺, the critical energy transfer distance between Ce³⁺ and Tb³⁺, and the energy transfer mechanism of Ce³⁺–Tb³⁺ are discussed based on the experimental data and the theoretical analysis.     

Enhanced green emission from Tb-Bi co-doped GdAlO3 nanophosphors

Bi³⁺ and Tb³⁺ ions co-doped GdAlO₃ (GAP) nanophosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GAP phosphor confirms their orthorhombic phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of GAP:Tb³⁺, Bi³⁺ phosphors consist of a broad band in the shorter wavelength region due to the 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with the 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and some sharp peaks in the longer wavelength region due to f → f transitions of Tb³⁺ ions. The present phosphors exhibit green color due to strong ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The emission intensity was enhanced by co-doping with Bi³⁺ ions under 292 nm excitation, which indicate that the efficient energy transfer occurred from Bi³⁺ to Tb³⁺ ions.     

Efficient Bi → Nd energy transfer in Gd2O3:Bi,Nd

Bi³⁺,Nd³⁺ co-doped Gd₂O₃ were prepared by solid state reaction and the optical properties were investigated. The results show that the near-infrared emission of Nd³⁺ ions is significantly enhanced by the introducing of Bi³⁺ in co-doped samples. An efficient energy transfer from Bi³⁺ to Nd³⁺ corresponds to the near-infrared emission enhancement. The energy transfer efficiency reaches 64.1% for the sample with the strongest near-infrared emission, which has the optimized doping concentrations of 0.5% for Bi³⁺ and 2% for Nd³⁺. The interesting optical properties make Bi³⁺,Nd³⁺ co-doped Gd₂O₃ promising as the luminescent down-conversion layers in front of c-Si solar cells to enhance the performance of the solar cells.     

Growth and optical properties of (Yb3−xYx)Al5O12:Ce single crystals

To improve the infrared emission of Yb³⁺ ions doped in the garnet host Y₃Al₅O₁₂ (YAG) single crystal through the energy transfer from Ce³⁺ to Yb³⁺ ions, the 〈1 1 1〉-oriented YAG:Ce³⁺, YAG:Yb³⁺, YAG:(Ce³⁺, Yb³⁺) and Yb₃Al₅O₁₂:Ce³⁺ (YbAG:Ce³⁺) single crystals were grown using the Czochralski Method, respectively. The excitation and emission spectra of these garnet single crystals were characterized. In YAG:Ce³⁺ crystal, the yellow emission of Ce³⁺ ions present, but it was completely extinguished in YAG:(Ce³⁺, Yb³⁺) crystal and YbAG:Ce³⁺ crystal. However, the characteristic absorption bands of Ce³⁺ still existed in the excitation spectrum of Yb³⁺ ions, which showed that the energy absorbed by Ce³⁺ ions can be transferred to Yb³⁺ ions for its infrared emission.     

Ce to Tb energy transfer in alkaline earth (Ba, Sr or Ca) sulphate phosphors

Energy transfer between Ce³⁺ and Tb³⁺ dopants in alkaline earth (Ba, Sr or Ca) sulphate phosphors is investigated. Among these three phosphors, CaSO₄:Ce³⁺,Tb³⁺ showed maximum Tb³⁺ green emission on excitation with UV light. Photoluminescence measurements reveal that the emission intensity from CaSO₄:Ce³⁺,Tb³⁺ is comparable with that of the commercial green lamp phosphor Ce_0.65Tb_0.35MgAl₁₁O₁₉. Optimum concentrations of dopants in CaSO₄:Ce³⁺,Tb³⁺ are 0.2 mol% each and the optimum sintering treatment following re-crystallisation is 600 °C for 1 h duration. The effect of charge compensator in all the three phosphors is also studied.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

Luminescence and energy transfer of Mn co-doped SrSi2O2N2:Eu green-emitting phosphors

Eu²⁺ and Mn²⁺ co-doped SrSi₂O₂N₂ green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500 nm and a broad emission band centered at ca. 530 nm, attributed to 4f–5d transitions of Eu²⁺. The emission intensity of Eu²⁺ ions was greatly enhanced by introducing Mn²⁺ ions into SrSi₂O₂N₂:Eu²⁺ due to the energy transfer from Mn²⁺ to Eu²⁺. The energy transfer probability from Mn²⁺ to Eu²⁺ depends strongly on the Mn²⁺ concentration, which is maximized at a Mn²⁺ concentration of 3 mol%. It drastically decreases for higher concentrations. The results indicated that SrSi₂O₂N₂:Eu²⁺, Mn²⁺ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips.