Influence of co‐dopant in the europium reduction in SrAl2O4 host

Xerogels of strontium chlorate and aluminium chlorate doped with europium (un‐co‐doped) and co‐doped with rare earth ions (Ln = Gd, Dy, Er and Y) were prepared using the proteic sol–gel route. Synchrotron radiation was used to investigate the effect of different co‐dopants on the Eu³⁺→ Eu²⁺ reduction process during the synthesis of the samples. Samples were excited at the Eu L_III‐edge and the XANES regions were analyzed. The results suggest that some of the Eu ions can be stabilized in the divalent state and that it is difficult to completely reduce Eu³⁺ to Eu²⁺ during thermal treatment. The mechanisms of the Eu reduction processes are explained by a proposed model based on the incorporation of charge‐compensation defects.     

Photoluminescence and afterglow behavior of Eu, Dy and Eu, Dy in Sr3Al2O6 matrix

This paper reports the photoluminescence and afterglow behavior of Eu²⁺ and Eu³⁺ in Sr₃Al₂O₆ matrix co-doped with Dy³⁺. The samples containing Eu²⁺ and Eu³⁺ were prepared via solid-state reaction. X-ray diffraction (XRD), photo luminescent spectroscope (PLS) and thermal luminescent spectroscope (TLS) were employed to characterize the phosphors. The comparison between the emission spectra revealed that Sr₃Al₂O₆ phosphors doped with Eu²⁺, Dy³⁺ and Eu³⁺, Dy³⁺ showed different photoluminescence. The phosphor doped with Eu³⁺, Dy³⁺ showed an intrinsic f-f transition generated from Eu³⁺, with two significant emissions at 591 and 610 nm. However, the phosphor doped with Eu²⁺, Dy³⁺ revealed a broad d-f emission centering around 512 nm. After the UV source was turned off, Eu²⁺, Dy³⁺ activated Sr₃Al₂O₆ phosphor showed excellent afterglow while Eu³⁺, Dy³⁺ activated phosphor almost showed no afterglow. Thermal simulated luminescence study indicated that the persistent afterglow of Sr₃Al₂O₆: Eu²⁺, Dy³⁺ phosphor was generated by suitable electron traps formed by the co-doped rare-earth ions (Dy³⁺) within the host.     

In situ sol-gel composition of multicomponent hybrid precursors to luminescent novel unexpected microrod of Y2SiO5:Eu employing different silicate sources

Y₂SiO₅ doped with Eu³⁺ were in situ synthesized by a hybrid precursor assembly sol-gel technology employing four different silicate sources, 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM result shows that there exist some novel unexpected morphological microrod structures owing to using the crosslinking reagents other than TEOS as silicate source. The photoluminescent properties of Y₂SiO₅:Eu³⁺ have been studied as a function of Eu³⁺ doping concentration. A cross-relaxation process between identical Eu³⁺ ions results in the quenching of the ⁵D₁ emission for high concentration sample.     

Energy transfer between Ce3+ and Eu2+ in doped KSrPO4

Powder samples of KSrPO₄ doped with Eu²⁺ and Ce³⁺ were prepared by combustion-assisted synthesis. Their structures and photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ single doped and Ce³⁺–Eu²⁺ co-doped KSrPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ co-doped KrSrPO₄ powders can possibly be applied as blue phosphors in the fields of lighting and display.     

Frequency-conversion properties of Eu doped chlorophosphate glass ceramics containing CaCl2 nanocrystals

Eu³⁺ ion doped chlorophosphate glass ceramics containing nanocrystals were successfully prepared, and their spectroscopic characterizations were done using absorption, excitation and emission spectra. For the crystallized samples, X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments evidenced the formation of CaCl₂ nanocrystals. The absorption and emission spectra investigations indicate that a considerable amount of Eu³⁺ ions was trapped in CaCl₂ nanocrystals, and therefore an efficient up- and down-frequency conversion was observed. The comparative spectroscopic studies of Eu³⁺ doped samples suggest that the investigated glass ceramics systems are potentially applicable as frequency-conversion photonics devices.     

Energy transfer from benzoic acid to lanthanide ions in benzoic acid-functionalized lanthanide-doped CaF2 nanoparticles

The preparation of benzoic acid-functionalized CaF₂:Ln³⁺ (Ln = Eu or Tb) nanoparticles and their sensitized luminescence are described in this report. First, to achieve sufficient proof for energy transfer from benzoic acid (BA) to lanthanide ions doped in nanoparticles, we employ Eu³⁺ as the microscopic probe and investigate the luminescent spectra of benzoic acid-functionalized CaF₂:Eu³⁺ (BA-CaF₂:Eu³⁺) nanoparticles. Next, to further reveal the difference between sensitized luminescence and common luminescence for Eu³⁺ doped in CaF₂ nanoparticles, we study the emission spectra of BA-CaF₂:Eu³⁺ nanoparticles excited at 286 nm and 397 nm, respectively. Finally, we analyze and compare the luminescent spectra of BA-CaF₂:Tb³⁺ and CaF₂:Ce³⁺, Tb³⁺ nanoparticles in detail. Our results indicate that both Eu³⁺ and Tb³⁺ doped in CaF₂ nanoparticles can be efficiently sensitized through benzoic acid.     

Luminescence characteristics of energy transfer between Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> in NaMgPO<Subscript>4</Subscript> phosphor

Powder samples of NaMgPO₄ doped with Eu²⁺ and Ce³⁺ were prepared and their photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ in NaMgPO₄ phosphor was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ or Ce³⁺ singly doped and Eu²⁺–Ce³⁺ codoped sodium magnesium orthophosphates, NaMgPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ codoped NaMgPO₄ phosphors in which Eu²⁺ can be efficiently excited by 390 nm are potential candidates for phosphor-converted LEDs.     

Effect of Eu contents on the structure and properties of BaLa2ZnO5:Eu phosphors

A series of Eu³⁺ doped BaLa₂ZnO₅ was prepared by a Pechini-type sol-gel method. The effect of Eu³⁺ concentration on the structure and the luminescent properties of the samples BaLa_2−xEu_xZnO₅ were investigated by powder X-ray diffraction (XRD) and photoluminescence (PL) spectra. The sample adopts the tetragonal or orthorhombic structure as the Eu³⁺ concentration reaches below 1.2 or over 1.6, respectively. The sample is a mixture of tetragonal and orthorhombic phases as the contents of dopants lie between 1.2 and 1.6. The phosphor offers the strongest red light as content of Eu³⁺ is 0.4. In addition, the crystallization processes of the complex precursors were examined by simultaneous thermogravimetry and differential thermal analysis (TG-DTA), and also the optimal heating temperature was investigated.     

Eu3+ emission in SrAl2B2O7 based phosphors

Eu³⁺ doped SrAl₂B₂O₇ phosphors were fabricated by the wet method. The structures of the phosphors were characterized by XRD. The doping content of Eu³⁺ ions in SrAl₂B₂O₇:Eu³⁺ phosphors are 1%, 4%, 6%, 8%, 10% (molar fraction), respectively. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. The luminescent properties of SrAl₂B₂O₇:Eu³⁺ phosphors are discussed. It is shown that from 4% to 6% of doping content of Eu³⁺ ions under 392 nm excitation in SrAl₂B₂O₇:Eu³⁺ phosphors is optimum.     

Eu3+离子在微晶玻璃研究中的探针作用

制备出单掺Eu³⁺离子的氟氧化物玻璃陶瓷系列样品，利用Eu³⁺离子作为荧光探针，通过热处理前后Eu³⁺离子发射光谱中电偶极子跃迁与磁偶极子跃迁强度比值的变化表征在玻璃材料中微晶是否形成，分析了Eu³⁺离子荧光发射谱中电偶极子跃迁与晶体场对称性的关系，进一步表征了稀土离子所处微晶晶格场的变化. 关键词： 微晶玻璃 探针 3+离子')" href="#">Eu³⁺离子     

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.     

Influence of nanoenvironment on luminescence of Euactivated SnO2 nanocrystals

The emission intensity of the peak at 612 nm (⁵D₀→⁷F₂) of the Eu³⁺ ions activated SnO₂ nanocrystals (doped and coated) is found to be sensitive to the nanoenvironment. We have compared the luminescence efficiencies of the nanocrystals of SnO₂ doped by Eu₂O₃ with those of SnO₂ coated by Eu₂O₃ and we found that the intensities are significantly higher in coated nanocrystals. Furthermore, it is clear from luminescence intensity measurements that Eu³⁺ ions occupy low symmetry sites in the Eu₂O₃ coated SnO₂ nanocrystal. The analysis suggests that the radiative relaxation rate is higher in Eu₂O₃ coated SnO₂ nanocrystals than Eu₂O₃ doped SnO₂ nanocrystals due to the asymmetric environment of Eu³⁺ ions in coated samples.     

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu²⁺ are resulted from the radiative energy transfer from Eu²⁺ to Eu³⁺ and consequently induces the luminescence from Eu³⁺ that is responsible for the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu²⁺ is also reported.     

White light emission from sonochemically synthesized rare earth doped ceria nanophosphors

Undoped CeO₂, and single and triple doped CeO₂:M (where M=Dy³⁺, Tb³⁺and Eu³⁺) nanophosphors were synthesized through a simple sonochemical process and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), EDS and photoluminescence (PL) spectrophotometry. The TEM micrographs show that resultant nanoparticles have flower-like shape. The doped samples showed multicolor emission on single wavelength excitation. Energy transfer was observed from host to the dopant ions. Characteristic blue emission from Dy³⁺ ions, green from Tb³⁺ ions and red from Eu³⁺ ions were observed. The CIE coordinates of the triple doped Ce_0.86Dy_0.005Tb_0.055Eu_0.08O₂ nanoflowers lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

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)     

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.     

Synthesis, structure and optical properties of Eu/TiO2 nanocrystals at room temperature

The nanocrystal samples of titanium dioxide doped with europium ion (Eu³⁺/TiO₂ nanocrystal) are synthesized by the sol-gel method with hydrothermal treatment. The Eu³⁺ contents (molar ratio) in the samples are 0, 0.5%, 1%, 2%, 3% and 4%. The X-ray diffraction, UV-Vis spectroscopy data and scanning electron microscope image show that crystallite size is reduced by the doping of Eu³⁺ into TiO₂. Comparing the Raman spectra of TiO₂ with Eu³⁺/TiO₂ (molar ratio Eu³⁺/TiO₂=1%, 2% and 4%) nanocrystals at different annealing temperatures indicates that the anatase-to-rutile phase transformation temperatures of Eu³⁺/TiO₂ nanocrystals are higher than that of TiO₂. This is due to the formation of Eu-O-Ti bonds on the surface of the TiO₂ crystallite, as characterized by the X-ray photoelectron spectroscopy. The photoluminescence spectra of TiO₂ in Eu³⁺/TiO₂ nanocrystals are interpreted by the surface self-trapped and defect-trapped exciton relaxation. The photoluminescence of Eu³⁺ in Eu³⁺/TiO₂ nanocrystals has the strongest emission intensity at 2% of Eu³⁺ concentration.     

Stability of divalent/trivalent oxidation state of europium in some Sr-based inorganic compounds

This work investigates the stability of Eu²⁺ and Eu³⁺ in some Sr-based inorganic compounds. Generally reducing condition is adopted in order to obtain Eu²⁺, however, the Eu doped SrAl₂O₄/SrLaAlO₄ case indicates that for some compounds Eu³⁺ is stabilized even in reducing atmosphere. Bond valence method is applied to explain this phenomenon and it reveals that crystal structure also determines the valence state of europium cations along with reducing/oxidizing condition. An analysis of other Eu doped Sr-based materials is performed which shows the relationship between Eu²⁺/Eu³⁺ stability and the Global Instability Index (GII). This research provides a guideline for synthesizing specific novel Eu²⁺/Eu³⁺ phosphors.     

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.     

Luminescence properties and energy transfer in Eu2+, Mn2+ codoped Na(Sr,Ba)PO4 phosphor

Eu²⁺ and Mn²⁺ singly doped and codoped Na(Sr,Ba)PO₄ phosphors were synthesized, and their luminescent properties were investigated. A broad blue emission and a broad orange emission band were observed in Na(Sr,Ba)PO₄:Eu²⁺, Mn²⁺ phosphor. The resonant-type energy transfer from Eu²⁺ to Mn²⁺ was demonstrated, and the energy transfer efficiency was also calculated according to their emission spectra. Based on the principle of energy transfer, the emission intensity ration of Eu²⁺ and Mn²⁺ could be appropriately tuned by adjusting the contents of activators. Due to the strong absorption in the 250–400 nm range, Na(Sr,Ba)PO₄:Eu²⁺, Mn²⁺ phosphor could be used as a potential candidate for near-UV white light-emitting diodes (LEDs).