YZr2OZr3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er³⁺离子浓度掺杂的Y₂O₃纳米晶, 应用XRD，SEM和PL光谱对该体系材料进行了表征.在Y₂O₃:Er³⁺纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er³⁺离子摩尔浓度变化的关系, 当Er³⁺离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X 关键词： 氧化钇纳米晶 anti-Stokes PL 双光子吸收     

Y2O3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er3+离子浓度掺杂的Y2O3纳米晶,应用XRD,SEM和PL光谱对该体系材料进行了表征.在Y2O3:Er3+纳米材料体系中,观察和研究了Stokes及anti-StokesPL谱强度与Er3+离子摩尔浓度变化的关系,当Er3+离子浓度为2.0mol%时,anti-Stokes PL强度最强.粉末XRD和SEM照片分别表明:制备的Y2O3:Er3+纳米材料具有立方相结构,且粒径分布均匀.实验结果证明:anti-Stokes PL来自于这个体系中的双光子吸收过程.     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag+掺杂浓度的Y2O3:Eu纳米晶体粉末样品([Y3+]:[Eu3+]:[Ag+]=99:1:X,X=0-3.5×10-2),以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加,荧光发射强度随之增加,当X=2×10-2时达到最大值,其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加,样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱,激发光谱,X射线衍射图谱,透射电镜(TEM)照片和荧光衰减曲线的研究,分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合,从而使这一无辐射通道阻断,使发光中心Eu3+的量子效率提高;Ag+的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

Gd2O3:Eu3+纳米晶的燃烧合成及光致发光性质

采用柠檬酸作燃烧剂用燃烧合成法制备了Gd2O3:Eu3+纳米晶.用X射线衍射仪(XRD)、高分辨透射电子显微镜(HRTEM)和荧光分光光度计等对Gd2O3:Eu3+纳米晶的结构、形貌和发光性能进行了分析.结果表明:不同柠檬酸与稀土离子配比(C/M)制备的样品经800℃退火1 h后,均得到了纯立方相的Gd2O3:Eu3+纳米晶,晶粒尺寸约为30 nm,尺寸分布较窄,其中以C/M=1.0时制备的纳米晶结晶性最好,发光强度最大.Gd2O3:Eu3+纳米晶主发射峰位置均在612 nm处(5D0→7F2跃迁),激发光谱中电荷迁移态发生红移,观察到Gd3+向Eu3+的有效能量传递.对柠檬酸与稀土离子配比(C/M)对结晶度、发光性质等的影响也进行了分析和讨论.     

Solvothermal synthesis and luminescent properties of Y2Ti2O7:Eu3+ spheres

Pyrochlore‐structured yttrium titanate phosphors activated by trivalent europium ions (Y₂Ti₂O₇(YT):Eu³⁺), with spherical morphology, were synthesized at different pH values by a solvothermal process. From the structural and morphological measurements, the annealing temperature had no effect on the spherical morphology of the YT:Eu³⁺ sample. The photoluminescence excitation and emission spectra were taken by activating the Eu³⁺ ions in the YT host lattice as functions of Eu³⁺ ion concentration and annealing temperature. The optimal doping concentration was found to be 4 mol%, exhibiting an excellent orange–red emission due to the highest intensity of the ⁵D₀ → ⁷F₁ transition. When the YT:Eu³⁺ phosphor was mixed with YAG:Ce³⁺ phosphor, a brilliant white light emission was achieved. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

变温下Y2O3∶Eu3+纳米晶的荧光光谱和动力学过程

通过分析影响Y2O3: Eu3+在488nm激光激发下的5D0→7F2变温荧光发射强度的因素,建立起公式并对实验数据进行拟合,得到纳米晶的温度猝灭速率大于体材料的温度猝灭速率.测得Y2O3: Eu3+纳米晶和体材料的5D0→7F2发射峰的变温线宽,通过内应力和量子限域效应对其不同进行了解释.测量了Y2O3: Eu3+在共振激发下的5D0能级的荧光衰减时间随温度的变化,又利用公式对其进行拟合,得出了相比于体材料,纳米晶的辐射跃迁速率和无辐射跃迁速率均增大,但量子效率变小的结论.然后利用晶格畸变和表面态效应对上述结论进行了解释.     

Synthesis and electrical properties of Y2O3: Dy3+ & Eu3+ nanoparticles

Yttrium oxide (Y₂O₃) doped with Dy³⁺ & Eu³⁺ nanoparticle has been synthesized by solution combustion method. The formation of the compounds has been checked by X-ray diffraction method. The crystallite/particle size has been measured using Scherrer formula as well as by transmission electron microscopy which show that the size of the particles are in the nanorange. The frequency and temperature dependent variation of impedance Z*, dielectric constant (ε′), dielectric loss (ε″) and AC conductivity (σ) of Y₂O₃: Dy³⁺ & Eu³⁺ nanoparticles were also measured. The real and imaginary part of complex impedance makes semicircle in the complex plane. The center of semicircle arc is found to be shifted toward higher value of real part of impedance with increasing temperature. This indicates that the conductivity of the material increases with the increase in temperature. Cole–Cole plots demonstrate that the dielectric relaxation process occurs in the material. The AC conductivity (σ _AC) increases with the increase in temperature within the frequency range of 10³–10⁷ Hz confirming the hopping of the electrons in the conduction process. The value of impedance decreases sharply with increasing frequency and attains minimum value after 10⁵ Hz at all temperatures.     

Enhanced photoluminescence intensity of Y2O3: Eu3+ Sheets by codoping Pr3+ and involved energy transfer mechanisms

Y₂O₃: Eu³⁺ has been widely applied as red phosphors in the fields of displaying and illumination. Here, we report the enhanced luminescence intensity of Y₂O₃: Eu³⁺ by codoping Pr³⁺ ion. The Pr³⁺ and Eu³⁺ doped Y₂O₃ microsheets with high aspect ratio were synthesized by a simple route combining chemical precipitation and pyrolysis, which could emit intense red light centered at 610 nm under the 254 and 365 nm UV excitation. The fluorescence measurement indicated that the luminescence intensity of Y₂O₃: Eu³⁺, Pr³⁺ did not increase monotonously with increasing Pr³⁺ concentration. The highest improvement of the photoluminescence intensity of Y₂O₃:Eu³⁺ was realized in the sample doped with 2 mol% Pr³⁺, which was of 17.8% higher than the whole intensity of only Eu³⁺ doped Y₂O₃.The mechanism analysis based on SEM, XRD, fluorescence spectra, and simplified energy level diagram indicated that (1) energy transfer process between Pr³⁺ and Eu³⁺, (2) crystallinity, and (3) symmetry should respond for this nonmonotonous variation phenomenon by competition with each other. For energy transfer process between Pr³⁺ and Eu³⁺, it was suggested that the cross relaxation of ⁵D₀ + ⁷F₁(Eu³⁺)?³P₀ + ³H₆(Pr³⁺) and the efficient energy transfer from ³P₀ state of Pr³⁺ to ⁵D₁ energy level of Eu³⁺ lead to the improvement of the population of the ⁵D₀ state of Eu³⁺ so that the 610 red emission of Eu³⁺ ion was accordingly enhanced.     

Multiplesite structure and photoluminescence properties of Eu3+ doped MgO nanocrystals

MgO:Eu³⁺ nanocrystals with average diameter around 15 nm were prepared via a facile combustion method under a weak reductive atmosphere at temperature as low as 300°C. The photoluminescence spectra showed that the MgO:Eu³⁺ nanocrystals emit white light, the hypersensitive transition (⁵ D ₀→⁷ F _j of Eu³⁺) emission was prominent in the emission spectra resulting from the noinversion symmetry local site at which Eu³⁺ ions were located. Two kinds of luminescence sites of Eu³⁺ are identified by means of the fluorescence decay and site-selective spectroscopy. The excitation and absorption spectra indicated that the absorption of surface state decreased with the increase of Eu³⁺ concentration, meaning that the surface defect decreased through Eu³⁺ doping for some of them located at the disordered sites near the surface or absorbed at the surface of MgO host. Meanwhile, absorptivity and CIE chromaticity coordinates of all samples were measured; the results were in accordance with the excitation and absorption spectra and photoluminescence spectra, respectively.     

(Y0.5Lu0.5)2O3:Eu3+ nanopowders: Combustion synthesis,structure and optical properties

In this work we explored the possibility of obtaining nanocrystalline (Y_0.5Lu_0.5)₂O₃ powders, doped with europium and co-doped with praseodium, employing polymer complex solution synthesis. Polyethylene glycol, with average molecular weight 200, served both as a fuel and dispersing medium for nanocrystals formation. We investigated structure, morphology, luminescence emission and decay characteristics of obtained powders and how different concentrations of Pr co-dopant affect theirs optical characteristics.     

前驱溶液的PH值对Y2O3: Eu3＋荧光粉发光性质的影响

以甘氨酸为燃料,采用溶液燃烧法制备了Y2O3:Eu3 (3%)纳米粉末,并研究了制备过程中前驱溶液的pH值对Y2O3:Eu3 发光性质的影响.从XRD和SEM分析得到,随着溶液pH值的增大,样品颗粒逐渐变大,并且多孔粉末变得越来越致密.通过对样品发光性质的测量得到,随着pH值的增大,样品发光逐渐增强,但寿命逐渐变短.激发谱显示,基质吸收和电荷迁移带的相对强度比随着pH值的增大逐渐减小.     

Energy transfer between Eu3+ ions in a lattice with two different crystallographic sites: Y2O3:Eu3+, Gd2O3:Eu3+ and Eu2O3

The Eu³⁺ ion occupies two different crystallographic sites in (Y_1−xEu_x)₂O₃ and (Gd_1−xEu_x)₂O₃, with site symmetry S₆ and C₂. Energy transfer over more than 7 Å occurs from Eu³⁺ (S₆) ions to Eu³⁺ (C₂) ions. This is shown to be a direct one-phonon assisted process, in combination with a one-site resonant two-phonon assisted process at higher temperatures. For x = 1 there is energy migration over the Eu³⁺ (C₂) sublattice to quenching impurities. The presence of cooperative absorption points to superexchange interaction between the Eu³⁺ ions.     

纳米晶Gd2O3：Eu^3＋的制备及发光性能

采用低温燃烧合成法制备了Gd2O3：Eu^3＋纳米晶。用X射线衍射仪（XRD）、高分辨透射电子显微镜（HRTEM）和荧光光谱仪分别对样品的结构、形貌和发光性能进行了研究。结果表明，改变甘氨酸与稀土离子的比例（G／M）、退火温度可以制备出不同结构和晶粒尺寸的Gd2O3：Eu^3＋纳米晶。在退火温度为800℃，G／M等于0．83和1．0时，均得到了纯立方相的Gd2O3：Eu^3＋纳米晶，随着G／M的增加，Gd2O3：Eu^3＋从立方相逐渐向单斜相转变。粉末的晶粒尺寸随着退火温度的增高而增大，晶粒尺寸在10-30nm之间。立方相的Gd2O3：Eu^3＋纳米晶主发射峰位置在612nm（^5D^0→^7F2跃迁），激发光谱中电荷迁移态发生了红移。     

Synthesis, characterization, thermo- and photoluminescence properties of Bi3+ co-doped Gd2O3:Eu3+ nanophosphors

Gd₂O₃:Eu³⁺ (4 mol%) co-doped with Bi³⁺ (Bi = 0, 1, 3, 5, 7, 9 and 11 mol%) ions were synthesized by a low-temperature solution combustion method. The powders were calcined at 800°C and were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared and UV–Vis spectroscopy. The PXRD profiles confirm that the calcined products were in monoclinic with little cubic phases. The particle sizes were estimated using Scherrer’s method and Williamson–Hall plots and are found to be in the ranges 40–60 nm and 30–80 nm, respectively. The results are in good agreement with TEM results. The photoluminescence spectra of the synthesized phosphors excited with 230 nm show emission peaks at ～590, 612 and 625 nm, which are due to the transitions ⁵D₀→⁷F₀, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₃ of Eu³⁺, respectively. It is observed that a significant quenching of Eu³⁺ emission was observed under 230 nm excitation when Bi³⁺ was co-doped. On the other hand, upon 350 nm excitation, the luminescent intensity of Eu³⁺ ions was enhanced by incorporation of Bi³⁺ (5 mol%) ions. The introduction of Bi³⁺ ions broadened the excitation band of Eu³⁺ of which a new strong band occurred ranging from 320 to 380 nm. This has been attributed to the 6s²→6s6p transition of Bi³⁺ ions, implying a very efficient energy transfer from Bi³⁺ ions to Eu³⁺ ions. The gamma radiation response of Gd₂O₃:Eu³⁺ exhibited a dosimetrically useful glow peak at 380°C. Using thermoluminescence glow peaks, the trap parameters have been evaluated and discussed. The observed emission characteristics and energy transfer indicate that Gd₂O₃:Eu³⁺, Bi³⁺ phosphors have promising applications in solid-state lighting.     

Effects of alkali metal ions on upconversion photoluminescence intensity of Er3+-doped Y2O3 nanocrystals

We investigate upconversion emissions in alkali metal ions (Li⁺, Na⁺, and K⁺) and Er³⁺-codoped Y₂O₃ nanocrystals. By introducing Li⁺, upconversion intensity is significantly enhanced, while Na⁺ and K⁺ hardly have this influence. FT-IR data give evidence that the main mechanisms of the enhanced upconversion emission cannot be attributed to the decreased surface defects. EXAFS data and variations of enhanced upconversion intensities in different samples indicate that Li⁺ can occupy the interstitial sites in lattice and thus arouse large site asymmetry. In addition, locations in the samples and effects on the upconversion emission of Na⁺ and K⁺ are discussed.     

High-pressure optical studies of Y2O3:Eu3+ nanoparticles

Abstract

The fluorescence spectra of Y₂O₃:Eu³⁺ nanoparticles have been measured under the pressure of up to 78 kbar at room temperature. In this pressure range, a red-shift of 0.02(1) nm/kbar^?1 is noticed for the 0–2 line (⁵D₀→⁷F₂ transition). This shift is explained by the change of negative charge of the surrounding ligands. Compatibility between measured and calculated values for the 0–2 line position was obtained. The luminescence decay curves of the ⁵D₀→⁷F₂ transition were studied up to 78 kbar and were found to behave exponentially for all pressures studied. The fluorescence lifetime τ for the 0–2 line (⁵D₀→⁷F₂ transition) slowly decreased with pressure. The pressure effect on τ for the 0–2 line (⁵D₀→⁷F₂ transition) was explained by a model which considers the pressure effect on the line position, inter-ionic distance, ion volume and polarizability, molecular volume and polarizability, molecular refractive index and the refractive index medium n _med of the surrounding hydrostatic medium. The fluorescence lifetime calculated by the present model is in close correspondence with the experimental values.     

Tailoring red-green-blue emission from Er3+, Eu3+ and Tb3+ doped Y2O3 nanocrystals produced via PVA-assisted sol-gel route

Y₂O₃ luminescent nanoparticles were synthesized via PVA-assisted sol-gel method and their structural and optical properties were investigated. Effects of rare earth (Er³⁺, Eu³⁺ and Tb³⁺) doping on luminescence properties of the produced nanophosphors have been investigated under NIR (800 nm) and UV (240–300 nm) excitation. Intense infrared to red and green emissions were observed and a weak blue upconverted luminescence was also detected. Moreover, it was observed that changing the doping ions, the color emitted by the samples could be modified and different combinations of UV excitation and doping produced effective white light emissions. The obtained results demonstrate that PVA-assisted sol-gel is an effective methodology for the synthesis of rare-earth doped Y₂O₃ nanophosphors.     

纳米晶Y_2O_3:Eu~(3+)的反常拉曼散射(英文)

作者用燃烧法制备了8nm-50nm的系列纳米晶Y2O3:Eu3+,利用XRD谱确定了纳米晶的晶体结构及晶粒大小。利用两套由不同波长的激光所激发的拉曼光谱,指认了纳米晶Y2O3:Eu3+的拉曼振动模,研究其拉曼光谱。与传统的拉曼光谱学相比较,光谱呈现出明显的反常,其一,是斯托克斯与相对应的反斯托克斯谱峰波数不相等;其二,随晶粒的减小,拉曼谱有明显的变化,包括谱峰的微移、半高宽的增加,以及谱峰强度比的强烈变化;其三,随着激发波长的变化,光谱也呈现出峰位移动的明显变化。这些反常的散射光谱的变化源于纳米结构的本征缺陷。     

共掺杂效应对Y2O3:Eu3+和Gd2O3:Eu3+发光影响的理论研究

通过在Y2O3:Eu3 和Gd2O3:Eu3 发光材料中掺入Li ,Mg2 ,Al3 等离子能有效地提高材料的发光强度,根据分子动力学和密度泛函计算的结果,认为这些离子多倾向于形成C2格位附近的间隙缺陷对,导致部分Y(Gd)-O的键长增加,提高了材料的量子效率的同时使得激发峰位出现红移,是引起材料发光增强的一个原因.