Synthesis,characterization and photoluminescence of Eu3+, Ce3+ co-doped CaLaAl3O7 phosphors

Powder phosphors of CaLa_{1? x} Eu _x Al₃O₇, CaLa_{1? x} Ce _x Al₃O₇ and CaLa_{0.99? x} Eu _x Ce_0.01Al₃O₇, where x = 0.01, 0.03, 0.05 and 0.07, were prepared by a combustion method. The powders were well characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence techniques. Emission spectra of Eu³⁺-doped powder phosphors showed strong red emission at 613 nm (⁵D₀ → ⁷F₂); no concentration quenching was observed. Generally, Ce³⁺ acts as an efficient sensitizer when doped with other trivalent lanthanide ions. However, interestingly, in the CaLaAl₃O₇ powder phosphors, the addition of Ce³⁺ with Eu³⁺ exhibited an adverse effect–decreased photoluminescence intensity. The reasons for this behavior are discussed.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.     

Synthesis, photoluminescence and bioconjugation of rare-earth (Eu) complexes-embedded silica nanoparticles

Eu(DBM)₃Phen-embedded silica nanoparticles were synthesized in water-in-oil (W/O) microemulsion containing aqueous phase of Eu(DBM)₃Phen, surfactant Triton X-100, cosurfactant octanol and oil-phase cyclohexane. The size and morphology of the nanoparticles were characterized by transmission electron microscopy (TEM). The low-temperature time-resolved emission spectra indicate that the Eu complex in the silica nanoparticles have longer lifetime than that of the pure complex. Under 355 nm continuous excitation, the nanoparticles show high resistance to photobleaching. The free amino groups were attached to silica surfaces by copolymerization of 3-aminopropyl(triethoxy)silane. Preliminary results demonstrated that the silica-coated Eu complex nanoparticles can be a probe in the detection of biomolecular interactions.     

The photoluminescence,afterglow and up conversion photostimulated luminescence of Eu3+ doped Mg2SnO4 phosphors

The Mg₂SnO₄:Eu³⁺ phosphor with reddish photoluminescence, green afterglow and photostimulated luminescence is obtained by the solid state method. The host related afterglow is greatly enhanced by doping of Eu³⁺ and it can last nearly 6 h when the Eu³⁺ concentration is 1 mol%. The photostimulated luminescence is found to be weakened by doping of Eu³⁺. It was revealed that all the shallow traps and a part of the deep traps are involved in afterglow. The majority of deep traps are responsible for photostimulated luminescence. The impact of doping Eu³⁺ on the afterglow and photostimulated luminescence is investigated and we propose a feasible interpretation.     

Effect of Eu3+ concentration on microstructure and photoluminescence of Sr2SiO4:Eu3+ phosphors prepared by microwave assisted sintering

In this paper, effect of Eu³⁺ doping concentrations on microstructure and photoluminescence of Sr₂SiO₄ phosphors was investigated. The Sr_2?xSiO₄:xEu³⁺ phosphors with x=0.05, 0.1, 0.2, 0.3 were synthesized by microwave assisted sintering at 1200 °C for 60 min in air. X-ray powder diffraction analysis confirmed the formation of pure Sr₂SiO₄ phase without second phase or phases of starting materials irrespective of the adding amount of Eu³⁺. From scanning electron microscopy image, it is found that with more Eu³⁺ ions introduced to Sr₂SiO₄, the shape of the particles is not much different from each other, but the particle size decreases significantly from 1 to 2 μm (when x=0.05) to less than 500 nm (when x=0.3). The emission spectrum was located obviously at 617 nm as the excitation spectrum at λ_ex=395 nm, and it had best emission intensity when x=0.1.     

Induced assembly and photoluminescence of lanthanum (Tb, Eu, Dy) complexes/ZnO/polyethylene glycol hybrid phosphors

Some novel kinds of hybrid phosphors were assembled with lanthanum (Tb, Eu, Dy) complexes (with four kinds of terbium complexes is 2,4-dihydroxybenzonic acid (DHBA), 1,10-phenanthroline (phen), acetylacetone (AA) and nicotinic acid (Nic), respectively) doped ZnO/PEG particles by co-precipitation approach derived from Zn(CH₃COO)₂ (Zn(AC)₂), NaOH, PEG as precursors at room temperature. The characteristic luminescence spectra for f-f transitions of Tb³⁺, Eu³⁺, Dy³⁺ were observed. It is worthy to point out that ZnO is the excellent host for lanthanum ions by the assembly of PEG matrices.     

AlON:Ce3+荧光粉的制备及光谱研究

采用高温固相法合成了不同浓度Ce³⁺ 掺杂的AlON荧光粉. 通过X射线和扫描电镜分析了荧光粉的物相和显微结构, 且利用荧光光谱仪测试了AlON:Ce³⁺荧光粉的发光光谱.结果表明, 荧光粉在305 nm紫外激发下发射390 nm为中心的蓝光.温度依赖荧光谱测试发现, AlON:Ce³⁺荧光粉在150 ℃ 下发射强度能保持室温发射强度的86%.因此, 该荧光粉是大功率白光发光二极管用最佳荧光粉的候选材料之一. 关键词： 光致发光 浓度猝灭 热稳定性     

Influence of Eu doping content on photoluminescence of Gd2O3:Eu phosphors prepared by liquid-phase reaction method

Europium-doped cubic Gd₂O₃:Eu³⁺ nanoparticles containing various activator content in the range of 5-15 wt% were synthesized by a liquid-phase reaction method to investigate the influence of Eu³⁺ loading on the optical properties of phosphors by using XRD, TEM, BET, spectrometer and fluorometer. The size of Gd₂O₃:Eu³⁺ powders was in the range 21-41 nm. The phosphors showed an initial increase in luminescence and then a subsequent decrease with further doping (above 10 wt%). The decay time was reduced with increasing Eu loading; however, it decreased significantly above the 10% Eu doping. From spectroscopic studies, the Eu³⁺ doping ion distribution was uniform and homogeneous up to the 10 wt% loading because no concentration quenching effect was observed. However, further Eu³⁺ doping above 10 wt% reduced the luminescence due to the concentration quenching effect, as deduced from the shortening of the decay time.     

Synthesis of CaSO4:Dy,CaSO4:Eu3+ and CaSO4:Eu2+ phosphors

${\mathrm{CaSO}}_4:\mathrm{Dy}$ is a well-known phosphor for radiation dosimetry using thermoluminescence. ${\mathrm{CaSO}}_4:\mathrm{Eu}$, phosphors also find applications in radio-photoluminescence dosimetry and PLLCD. Various syntheses of these phosphors are described and optimum procedures are suggested. Effects of various preparation methods on luminescence characteristics are discussed in terms of elimination of unwanted impurities, grain size, etc.     

Preparation and photoluminescence properties of the Eu2+, Sm3+ co-doped Li2SrSiO4 phosphors

A series of Eu²⁺ and Sm³⁺ co-doped Li₂SrSiO₄ phosphors are prepared by the high temperature solid-state reaction. The morphology, structure and spectroscopic properties of the prepared samples are characterized by scanning electron microscopy, X-ray diffraction, diffuse reflection spectra, photoluminescence spectra and electron paramagnetic resonance spectra, respectively. The effect of Sm³⁺ doping concentration on the photoluminescence intensity of the prepared samples is also investigated. The results indicate that the crystal structure of Li₂SrSiO₄ is not changed with the Eu²⁺, Sm³⁺ co-doping. The spherical-like particle size of the obtained product is about 20–30 nm in diameter. When the Sm³⁺ concentration is 0.3 mol% and the Eu²⁺ concentration is 0.7 mol%, the phosphors show the maximum emission intensity, which is 50% higher than that of Eu²⁺ doped Li₂SrSiO₄. Excited at 420 nm, the phosphor presents a single broad emission band peaking at 558 nm, which is ascribed to the 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ and ⁴G_5/2 → ⁶H_5/2 and ⁴G_5/2 → ⁶H_7/2 transitions of Sm³⁺. The Commission International de I′Eclairage chromaticity coordinates of Li₂SrSiO₄:0.7 mol% Eu²⁺, 0.3 mol% Sm³⁺ are x = 0.28, y = 0.28.     

UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO₄:Eu³⁺, Eu²⁺) and terbium doped calcium fluoride (CaF₂:Tb³⁺) phosphors have been studied. PL measurements suggest conversion of Eu³⁺ to Eu²⁺ on 254 nm irradiation corresponding to charge transfer band of Eu³⁺ ions and reduction of Eu²⁺ ions with 365 nm illumination representing a f–d transition of Eu²⁺ ions. Similar studies carried out on CaF₂:Tb³⁺ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO₄:Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF₂:Tb³⁺ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities.     

Synthesis and photoluminescence of CeO2:Eu phosphor powders

The crystalline structure and photoluminescence (PL) properties of europium-doped cerium dioxide synthesized by the solid-state reaction method were analyzed. CeO₂:Eu³⁺ phosphor powders exhibit the pure cubic fluorite phase up to 10 mol% doping concentration of Eu³⁺. With indirect excitation of CeO₂ host at 373 nm, the PL intensity quickly increases with increasing Eu³⁺ concentration, up to about 1 mol%, and then decreases indicating the concentration quenching. While with direct excitation (467 nm), much more stronger PL emissions, especially the electric dipole emission ⁵D₀-⁷F₂ at 612 nm, are observed and no concentration quenching occurs up to 10 mol% doping concentration of Eu³⁺. The nature of this behavior and the cause of the concentration quenching were discussed.     

Photophysical and photoluminescence properties of co-activated ZnS:Cu,Mn phosphors

ZnS:Cu,Mn phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux at 900 °C. The samples were characterized by X-ray powder diffraction, UV-vis absorbance spectra and photoluminescence spectra. All samples possess cubic structure. Cu has a much stronger effect on the absorption property of ZnS than Mn. Incorporation of Mn into ZnS host only slightly enhances the light absorption, while addition of Cu remarkably increases the ability of absorption due to ground state Cu⁺ absorption. The emission spectra of the ZnS:Cu,Mn phosphors consist of three bands centered at about 452, 520 and 580 nm, respectively. Introduction of Mn significantly quenches the green luminescence of ZnS:Cu. The excitation energy absorbed by Cu is efficiently transferred to Mn activators non-radiatively and the Mn luminescence can be sensitized by Cu behaving as a sensitizer (energy donor).     

Tin-doped indium oxide nanobelts grown by carbothermal reduction method

This communication discusses the formation of doped nanobelts produced by a simple route. Tin-doped indium oxide (ITO) nanobelts were obtained by a carbothermal reduction method. The nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and wavelength-dispersive X-ray spectroscopy (WDX). The results show that the nanobelts have a cubic structure, are single crystalline and doped with tin and grow in the [400] direction. PACS 81.07.-b; 61.46.+w; 68.37.Hk; 68.37.Lp     

Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca,Sr, Ba) phosphors by a simple nitrate reduction

M2Si5N8:Eu2+-based(M=Ca,Sr,Ba)red-emitting phosphors are fabricated at relatively low temperature(1200°C)and atmospheric pressure using a simple solid-state reaction process.Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance,including the amount of europium and the properties of the precursor materials.The as-prepared M2Si5N8:Eu2+-based(M=Ca,Sr,Ba)phosphors are orange in color and are intensively emitted in the red region of 580–670 nm under 465 nm excitation.     

Synthesis of α -SiC nanocrystals by carbothermal reduction of spherical nanoparticles of amorphous silicon dioxide

The method for carbothermal reduction of spherical particles of amorphous silicon dioxide is developed, and hexagonal α-SiC polytype nanocrystals are synthesized. The prepared samples are characterized by X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, and electron microscopy. The silicon carbide nanocrystals prepared have sizes in the range 5–50 nm depending on the diameter of initial silicon dioxide particles. A detailed analysis of the positions of the lines in the Raman spectra, their broadening, and shift makes it possible to reliably establish that the samples under investigation predominantly contain the 6H and 4H silicon carbide polytypes and insignificant amounts of the 2H and 3C phases. The 15R and 21R polytypes in the samples are absent. It is noted that the samples are characterized by a substantial size effect: the luminescence intensity of small silicon carbide nanocrystals is more than three times higher than that of large SiC nanocrystals.     

Synthesis, characterization, and luminescent properties of Lu2O3:Eu phosphors

Eu-doped lutetia (Lu₂O₃:Eu) nano-phosphors were synthesized by the sol-gel combustion process from a mixed aqueous solution of europium and lutetium nitrates, using organic glycine as the fuel. Powder X-ray diffraction shows that cubic Lu₂O₃:Eu crystallites are directly obtained by the sol-gel combustion process without further calcination. Electron microscopy reveals that the as-prepared phosphors are agglomerated and have a fluffy, fine, and porous morphology, consisting of primary particle size of 8-10 nm. The excitation spectrum is characterized by three dominant bands centered at 395, 466, and 534 nm, respectively. Both the photoluminescent and radioluminescent spectra are very similar and exhibit intense emission peaks centered at 612 nm due to ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The energy transfer from Lu₂O₃ host to Eu³⁺ activator is more efficient in the case of calcined phosphors than for the as-prepared phosphors due to their improved lattice perfection.