The photoluminescent properties of Eu in MgO-Ga2O3-SiO2 nanocrystalline glass-ceramic

The MgO-Ga₂O₃-SiO₂ glass-ceramic (GC) containing MgGa₂O₄ nanocrystals and glasses doped with Eu³⁺ ions were prepared by the sol-gel method. The down-conversion and up-conversion luminescence (UCL) properties were studied. The results indicated that the relative intensity of f-f transitions of Eu³⁺ decreased in contrast with that of charge transfer (CT) absorption with the increase in heating temperature. Using a Xe lamp and 800 nm femtosecond (fs) laser excitation, strong red luminescence of Eu³⁺ in MgO-Ga₂O₃-SiO₂ glasses and GC was observed.     

The luminescence enhancement of Eu3+ ion and SnO2 nanocrystal co-doped solben gel SiO2 films

SnO₂ nanocrystal and rare-earth Eu³⁺ ion co-doped SiO₂ thin films are prepared by sol-gel and spin coating methods. The formation of tetragonal rutile structure SnO₂ nanocrystals with a uniform distribution is confirmed by X-ray diffraction and transmission electron microscopy. Fourier transform infrared spectroscopy is used to investigate the densities of the hydroxyl groups, and it is found that the emission intensity from the ⁵D₀-⁷F₂ transitions of the Eu³⁺ ions is enhanced by two orders of magnitude due to energy transfer from the oxygen-vacancy-related defects of the SnO₂ nanocrystals to nearby Eu³⁺ ions. The influences of the amounts of Sn and the post-annealing temperatures are systematically evaluated to further understand the mechanism of energy transfer. The luminescence intensity ratio of Eu³⁺ ions from electric dipole transition and magnetic dipole transition indicate the different probable locations of Eu³⁺ ions in the sol-gel thin film, which are further discussed based on temperature-dependent photoluminescence measurements.     

Combustion synthesis and photoluminescence of Eu, Dy-doped La2Zr2O7 nanocrystals

A facile and energy saving sol-gel combustion method has been used to prepare La₂Zr₂O₇ nanocrystallines. The pyrochlore La₂Zr₂O₇ nanocrystals have been obtained at a relatively low temperature with the grain size ranging from 45 to 70 nm. Eu³⁺ and Dy³⁺ have been introduced into the La₂Zr₂O₇ crystal structure, respectively, and the intense photoluminescence was observed. The relative intensity of electric dipole transition and magnetic dipole transition is considered for luminescence emission both of Eu³⁺ and Dy³⁺. The dependence of luminescence intensity on dopant concentration and the effect of Dy³⁺ co-doping on Eu³⁺ luminescence are also discussed.     

Intramolecular Energy Transfer and Co-luminescence Effect in Rare Earth Ions (La, Y, Gd and Tb) Doped with Eu3+ β-diketone Complexes

In this paper, Eu³⁺ β-diketone Complexes with the two ligands 1-(2-naphthoyl)-3, 3, 3-trifluoroacetonate (TFNB) and 2’2-bipyridine (bpy) have been synthesized. Furthermore, we reported a systematical study of the co-fluorescence effect of Eu(TFNB)₃bpy doped with inert rare earth ions (La³⁺, Gd³⁺ and Y³⁺) and luminescence ion Tb³⁺. The co-luminescence effect can be found by studying the luminescence spectra of the doped complexes, which means that the existence of the other rare earth ions (La³⁺, Y³⁺, Gd³⁺ and Tb³⁺) can enhance the luminescence intensity of the central Eu³⁺, which may be due to the intramolecular energy transfer between rare earth ions and Eu³⁺. The efficient intramolecular energy transfer in all the complexes mainly occurs between the ligand TFNB and the central Eu³⁺. Full characterization and detail studies of luminescence properties of all these synthesized materials were investigated in relation to co-fluorescence effect between the central Eu³⁺ and other inert ions. Further investigation into the luminescence properties of all the complexes show that the characteristic luminescence of the corresponding Eu³⁺ through the intramolecular energy transfers from the ligand to the central Eu³⁺. Meantime, the differences in luminescence intensity of the ⁵D₀→⁷F₂ transition, in the ⁵D₀ lifetimes and in the ⁵D₀ luminescence quantum efficiency among all the synthesized materials confirm that the doped complex Eu_0.5Tb_0.5(TFNB)₃bpy exhibits higher ⁵D₀ luminescence quantum efficiency and longer lifetime than the pure Eu(TFNB)₃bpy complex and other materials.     

Optical absorption and photoluminescence studies of Eu-doped phosphate and fluorophosphate glasses

Phosphate (P₂O₅+K₂O+BaO+Al₂O₃+Eu₂O₃) and fluorophosphate (P₂O₅+K₂O+BaO+BaF₂+Al₂O₃+Eu₂O₃) glasses with different Eu³⁺ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the ⁵D₀ emitting level of Eu³⁺ ions in these glasses. The relative luminescence intensity ratio of ⁵D₀→⁷F₂→⁵D₀→⁷F₁ transitions has been evaluated to estimate the local site symmetry around the Eu³⁺ ions. The emission spectra of these glasses show a complete removal of degeneracy for the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions. Second and fourth rank crystal-field (CF) parameters have been calculated together with the CF strength parameter by assuming the C_2v symmetry for the Eu³⁺ ions in both the phosphate and fluorophosphate glasses. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of ⁵D₀→⁷F_J (J=2, 4 and 6) to ⁵D₀→⁷F₁ transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the ⁵D₀→⁷F_J transitions. Decay curves of the ⁵D₀ level of Eu³⁺ ions in these two Eu³⁺:glass systems have been measured by monitoring the ⁵D₀→⁷F₂ transition (611 nm) at room temperature. The experimental lifetime of the ⁵D₀ level in the title glasses is found to be higher than Eu³⁺-doped niobium phosphate glasses. The analysis indicates that the lifetime of the ⁵D₀ level is found to be less sensitive to the Eu³⁺ ion concentration and addition of BaF₂ has no significant effect on the optical properties of Eu³⁺-doped phosphate glasses.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Europium doped strontium borate glasses and their optical properties

Optical absorption and luminescence spectra of europium doped strontium borate glasses prepared in different conditions are studied. It is found that the percentage of Eu³⁺ ions varies from 100 to 30% being controlled by the conditions of preparation. The mechanism, favoring reduction of europium to Eu²⁺ state in polycrystalline strontium tetraborate, is much weaker in glasses of the same composition. In samples containing mixed valence europium at densities of 8×10²⁰ cm⁻³, the efficient transfer of optical excitation from Eu³⁺ to Eu²⁺, suppressing the Eu³⁺ luminescence, has been found. The most reliable way of monitoring the percentage of europium ions in different valences for strontium borate glasses is the measuring of absorption at f-f transition ⁷F₀→⁵D₂ of Eu³⁺.     

Observation of green emission from Ce-doped gadolinium oxide nanoparticles

Green emission at around 500 nm is observed in Gd₂O₃:Ce³⁺ nanoparticles and the intensity is highly dependent on the concentration of Ce³⁺ in the nanoparticles. The luminescence of this emission displays both picosecond (ps) and millisecond (ms) lifetimes. The ms lifetime is over four orders of magnitude longer than typical luminescence lifetimes (10-40 ns) of Ce³⁺ in traditional Ce³⁺ doped phosphors and therefore likely originates from defect states. The picosecond lifetime is shorter than the typical Ce³⁺ value and is also likely due to defect or surface states. When the samples are annealed at 700 °C, this emission disappears possibly due to changes in the defect moieties or concentration. In addition, a blue emission at around 430 nm is observed in freshly prepared Gd₂O₃ undoped nanoparticles, which is attributed to the stabilizer, polyethylene glycol biscarboxymethyl ether. On aging, the undoped particles show similar emission to the doped particles with similar luminescence lifetimes. When Eu³⁺ ions are co-doped in Gd₂O₃:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu³⁺ are observed.     

The crystallinity and the photoluminescent properties of spray pyrolized ZnO phosphor containing Eu and Eu ions

A europium doped ZnO (ZnO:Eu) particle was directly synthesized by the spray pyrolysis method. The crystal structure of samples was designated by the europium ion and the synthesis temperature. We identified the coexistence of Eu²⁺ and Eu³⁺ ions in the as prepared ZnO, which was strongly influenced by the doping concentration and the synthesis temperature. With addition of a 0.5 mol% concentration of europium ions, only the Eu²⁺ ion existed in particles, while both Eu²⁺ and Eu³⁺ ions existed in sample using 1 mol% or higher concentration of europium ions. Changing the wavelength of the excitation source, we also found that both the blue and red luminescence can be obtained.     

Interaction of Sb ions with Eu ions during the room temperature synthesis of luminescent Sb2O3 nanorods: Probed through Eu luminescence

The interaction of Eu³⁺ with Sb³⁺ ions during the room temperature synthesis of luminescent Sb₂O₃ nanorods is investigated using luminescence and vibrational spectroscopic techniques. Our results demonstrate that well crystalline, oriented Sb₂O₃ nanorods having length of around 3-4 μm, a width of around 100-200 nm and luminescence at around 390 nm can be synthesized at room temperature. Incorporation of Eu³⁺ in these nanorods has been attempted and it is found that Eu³⁺ ions do not have any interaction with nanorods and their orientation. Detailed Eu³⁺ luminescence and XRD studies confirmed that a part of Sb³⁺ ions reacts with Eu³⁺ ions in the presence of hydroxyl ions (present in the medium) to form an amorphous antimony europium hydroxide compound. The amorphous compound on heating at high temperatures leads to its decomposition, giving hydrated Sb(V) oxides and Eu₂O₃ as major phases.     

Luminescence and scintillation of Eu2+‐doped high silica glass

High silica glass doped with Eu²⁺ ions was prepared as a scintillating material by impregnation of Eu ions into a porous silica glass followed by reduction sintering in CO atmosphere. A dominant emission band of the Eu²⁺ 5d–4f transition peaking around 430 nm was observed in the luminescence spectrum with the excitation peak around 280 nm and no emission from Eu³⁺ was present. Photoluminescence decay kinetics was governed by decay times of a few microseconds. The Eu²⁺‐doped high silica glass exhibited comparable energy resolution and slightly higher photoelectron yield with respect to the Bi₄Ge₃O₁₂ crystal in the pulse height spectra for X‐ray photon energies within 22–60 keV. Furthermore, a factor of 1.2 higher radioluminescence intensity was observed as well. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Unusual Ln substitutional defects: The local chemical environment of Eu and Er in nanocrystalline Nb2O5 by Ln-K edge EXAFS

The local chemical environment of the trivalent lanthanide cations in Nb₂O₅ nanopowders doped with 1 mol% of Eu³⁺ and Er³⁺, prepared via a Pechini approach, has been studied by means of EXAFS at the Ln-K edge. It can be demonstrated that the lanthanide ions enter the Nb₂O₅ structure as substitutional defects with respect to Nb, giving rise to a very large amount of disorder: both Eu³⁺ and Er³⁺ ions substitute Nb in the nine-fold coordinated site, with clustering of oxygen vacancies around the substitutional defects. Valence bond calculations have been used to validate the Ln-O distances obtained by the EXAFS fitting. The Er³⁺-doped nanocrystalline Nb₂O₅ sample shows efficient luminescence in the near infrared region around 1.5 μm. The emission and excitation spectra are affected by significant inhomogeneous broadening, in agreement with the presence of strong disorder around the dopant ions in nanosized Nb₂O₅.     

Preparation and characterization of nanosized (Y,Bi)VO4:Eu and Y(V,P)O4:Eu red phosphors

Nanosized luminescent (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ were synthesized at low temperatures either by a coprecipitation method or by a hydrothermal method from aqueous solutions. The effect of Bi³⁺ ion or P⁵⁺ ion content in the lattice, annealing temperature effects on the crystal structure and the particle size, and the luminescence property of (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ nanoparticles were examined with a field-enhanced scanning electron microscopy, XRD, and a spectrofluorometer. The pristine YVO₄:Eu³⁺, (Y,Bi)VO₄:Eu³⁺, or Y(V,P)O₄:Eu³⁺ nanoparticles are 35-50 nm in size. The luminescence spectrum of the Eu³⁺ ion was used to probe its position in the crystal lattice. The dopant ions enter the same lattice sites in the nanocrystalline as in the corresponding bulk material, resulting similar spectral features between them. Photoluminescence intensity is weak for the pristine nanoparticles. Annealing the nanoparticles at temperatures up to 1000 °C results in the increased luminescence intensity (>80% of micrometer-sized phosphors) with the minimal particle growth and the improved particle crystallinity.     

Effect of concentration on the luminescence of Eu ions in nanocrystalline La2O3

Nanocrystalline powders with various Eu³⁺ concentration (from 1 to 10 mol %) doped La₂O₃ were prepared via a combustion route. Their structure and morphology were characterized using X-ray diffraction (XRD) and High-resolution transmission electron microscopy. The emission spectra of the as-synthesized samples show that the strongest emission position is centered at 626 nm corresponding to ⁵D₀→⁷F₂ transition of Eu³⁺ ions and the intensity change of 626 nm emission is considered as a function of ultraviolet (240 nm) irradiation time. The excitation spectra at 626 nm monitoring indicate that the charge transfer state band is varies with different Eu³⁺ ion concentration. These results are attributed to the surface defects of the nanocrystals.     

SnO2:Eu nanoparticles dispersed in silica: A low-temperature synthesis and photoluminescence study

SnO₂:Eu and SnO₂:Eu nanoparticles dispersed in silica matrix were prepared at a relatively low temperature of 185 °C in ethylene glycol medium. For as-prepared SnO₂:Eu nanoparticles there exists a weak energy transfer from the SnO₂ host to the Eu³⁺ ions. However, the energy transfer can be significantly improved by dispersing the Eu³⁺-doped SnO₂ nanoparticles in silica matrix. Effective shielding of surface Eu³⁺ ions in SnO₂:Eu nanoparticles from the stabilizing ligand by silica matrix is the reason for the improved extent of energy transfer. Increase in asymmetric ratio of luminescence (ratio of the intensity of the electric dipole allowed transition, ⁵D₀→⁷F₂, to magnetic dipole allowed transition, ⁵D₀→⁷F₁) for SnO₂:Eu nanoparticles dispersed in silica compared to that of SnO₂:Eu nanoparticles, has been attributed to the distorted environment around surface Eu³⁺ ions brought about by the presence of both tin and silicon structural units. ¹¹⁹Sn and ²⁹Si MAS NMR studies on this sample confirmed that there is no interaction between the tin and silicon structural units even after heating the samples at 900 °C.     

Enhanced luminescence from spontaneously ordered Gd2O3:Eu based nanostructures

Nanostructured Gd₂O₃:Eu³⁺ and Li⁺ doped Gd₂O₃:Eu³⁺ thin films were prepared by pulsed laser ablation technique. The effects of annealing and Li⁺ doping on the structural, morphological, optical and luminescent properties are discussed. X-ray diffraction and Micro-Raman investigations indicate a phase transformation from amorphous to nanocrystalline phase and an early crystallization was observed in Li⁺ doped Gd₂O₃:Eu³⁺ thin films on annealing. AFM images of Li⁺ doped Gd₂O₃:Eu³⁺ films annealed at different temperatures especially at 973 K show a spontaneous ordering of the nanocrystals distributed uniformly all over the surface, with a hillocks (or tips) like self-assembly of nanoparticles driven by thermodynamic and kinetic considerations. Enhanced photoemission from locations corresponding to the tips suggest their use in high resolution display devices. An investigation on the photoluminescence of Gd_2−xEu_xO₃ (x=0.10) and Gd_2−x−yEu_xLi_yO₃ (x=0.10, y=0.08) thin films annealed at 973 K reveals that the enhancement in luminescence intensity of about 3.04 times on Li⁺ doping is solely due to the increase in oxygen vacancies and the flux effect of Li⁺ ions. The observed decrease in the values of asymmetric ratio from the luminescence spectra of Li⁺ doped Gd₂O₃:Eu³⁺ films at high temperature region is discussed in terms of increased EuO bond length as a result of Li⁺ doping.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

二氧化锆纳米材料中Eu3+的发光特性

研究了掺1mol%Eu³⁺的二氧化锆纳米材料随退火温度变化的发光性质，得到退火温度为600和800℃的样品中Eu³⁺的⁵D₀→⁷F₂发射在604nm处，这种现象不多见. 几种经不同退火温度处理的纳米材料样品在紫外光的照射下，稀土离子Eu³⁺的⁵D₀→⁷F₂发射的发光逐 关键词： 二氧化锆 纳米材料 3+')" href="#">Eu³⁺ 发光