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.     

Red,Yellow, Blue and Green Emission from Eu<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript> and Bi<Superscript>3+</Superscript> Doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>nano-Phosphors

Rare earth elements (RE = Eu³⁺& Dy³⁺)and Bi³⁺ doped Y₂O₃ nanoparticles were synthesized by urea hydrolysis method in ethylene glycol, which acts as reaction medium as well as a capping agent, at a low temperature of 140 °C,followed by calcination of the obtained product. Transmission electron microscope (TEM) images reveals that ovoid shaped Y₂O₃ nanoparticles of around 22–24 nm size range were obtained in this method. The respective RE and Bi³⁺ doped Y₂O₃ precursor nanoparticles when heated at 600 and 750 °C, retains the same shape as that of the as-synthesized Y₂O₃ precursor samples. From EDAX spectra, the incorporation of RE ions into the host has been studied. XRD pattern reveals the crystalline nature of the heated nanoparticles and indicate the absence of any impurity phase other than cubic Y₂O₃.However, the as-synthesized nanoparticles were highly amorphous without the presence of any sharp XRD peaks. Photoluminescence study suggests that the synthesized samples could be used as red (Eu³⁺), yellow (Dy³⁺), blue and green (Bi³⁺)emitting phosphors.     

Synthesis and Optical Characterization of Red-Emitting BaTa<Subscript>2</Subscript>O<Subscript>6</Subscript>:Eu<Superscript>3+</Superscript> Phosphors

Undoped and Eu³⁺ doped BaTa₂O₆ phosphors were synthesized via solid state reaction method and characterized by using XRD, SEM-EDS and photoluminescence (PL) analyses. The XRD results revealed that the crystal structure of BaTa₂O₆ allowed up to 10 mol% levels of Eu³⁺ ions due to the TTB characteristic network of adjacent octahedrals. SEM-EDS analyses confirmed the formation of BaTa₂O₆ structure and EuTaO₄ secondary phase. BaTa₂O_6:Eu³⁺ phosphors exhibited orange and red emissions at 592.2 nm and 615.7 nm in the visible region respectively. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of the BaTa₂O_6:Eu³⁺ phosphors that excited at λ _ex = 400 nm ranged from orangish-red to pinkish-red depending on increasing Eu³⁺ concentration.     

Synthesis and Optical Properties of Novel Red-Emitting PbNb<Subscript>2</Subscript>O<Subscript>6</Subscript>: Eu<Superscript>3+</Superscript> Phosphors

Undoped and PbNb₂O_6:Eu³⁺ (1.0 ≤ x ≤ 6.0 mol%) phosphors were synthesized at 1100 °C for 3.5 h by the conventional solid state reaction method. Synthesized PbNb₂O₆:Eu³⁺ phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed series of excitation peaks between 350 and 430 nm due to the 4f–4f transitions of Eu³⁺. For 395.0 nm excitation, emission spectra of Eu³⁺ doped samples were observed at 591 nm (orange) and 614 nm (red) due to the ⁵D₀ → ⁷F₁ transitions and ⁵D₀ → ⁷F₂ transitions, respectively. PL analysis results also showed that the emission intensity increased by increasing Eu³⁺ ion content. No concentration quenching effect was observed. The CIE chromaticity color coordinates (x,y) of the PbNb₂O₆:Eu³⁺ phosphors were found to be in the red region of the chromaticity diagram.     

The luminescent properties of lanthanide ions activated BaBPO5 in VUV-Vis range

The VUV-Vis spectroscopic properties of barium borophosphate BaBPO₅ doped with lanthanide ions are investigated. The host absorption band is found to be around 150-160 nm, the charge transfer band of Eu³⁺ is observed at about 264 nm, the f-d transitions of Ce³⁺, Eu²⁺, and Tb³⁺ in the host lattice are depicted. The partial reduction of Eu³⁺ in air atmosphere is reported.     

Luminescence spectroscopy and energy transfer in Eu2+/Mn2+-doped KCaPO4 phosphors

Eu²⁺/Mn²⁺-doped KCaPO₄ phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), SEM, photoluminescence excitation, and emission spectra, and the luminescence decay curves were measured. Mn²⁺ singly doped KCaPO₄ shows the weak origin-red luminescence band peaked at about 590 nm. The Eu²⁺/Mn²⁺ co-doped phosphors emit two distinctive luminescence bands: a blue one centered at 480 nm originating from Eu²⁺ ions and a broad red-emitting one peaked at 590 nm from Mn²⁺ ions. The luminescence intensity from Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ ions. The efficient energy transfer from Eu²⁺ to Mn²⁺ was verified by the photoluminescence spectra together with the luminescence decay curves. The resonance-type energy transfer via a dipole–quadrupole interaction mechanism was supported by the decay lifetimes. The emission colors could be tuned by changing the Mn²⁺-doping concentration.     

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.     

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT

According to the spectra of stationary X-ray excited luminescence (XEL) of BaF₂: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d?=?35?nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120?nm, does not result in effective changes of the charge state of Eu^{3 +} → Eu^{2 +} activator, in contrast to CaF₂: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF₂: Eu nanophosphors in the 590?nm emission band of Eu³⁺ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67?nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF₂: Eu nanoparticles of 58?nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu³⁺ → Eu²⁺ under the influence of long-time X-ray irradiation was revealed for the peak of 151?K. Thus, X-ray excited luminescence spectra of BaF₂: Eu nanophosphors are formed predominantly due to the emission of Eu³⁺ ions, while emission of Eu²⁺ ions is observed in the TSL spectra.     

Optical properties of Zr5Ti7O24:Eu3+ prepared by the sol–gel technique

Thermal processes can lead to the creation of photoluminescence centers in sol–gel derived Zr₅Ti₇O₂₄:Eu³⁺ (ZT:Eu³⁺) systems. Photosensitivity starts with heat treatments at 700 ^°C in air. The photoluminescence excitation occurs in the 225–550 nm range. The emission spectra covers the 550–700 nm range and consist of several sharp lines associated with transitions between the stark components of the excited states of the 4f ⁶ configuration to the ⁷ F _j states of the Eu³⁺ ion. The crystalline structure of the compound was obtained by X-ray diffraction techniques and is associated with a space group Pbcn. The thermal treatments in the 700–960 ^°C range have corresponding effects on both, the crystalline parameters and the optical properties of the europium ions. Time-resolved experiments were performed and the results are presented and discussed in order to get a better understanding of the effects of the thermal treatments on the Eu³⁺ transition lifetimes.     

The energy transfer from Eu2+ to Tb3+ in calcium chlorapatite phosphor and its potential application in LEDs

Energy transfer from Eu²⁺ to Tb³⁺ was observed by investigating the optical properties from photoluminescence spectra and decay time curves in Tb³⁺ singly doped and Eu²⁺–Tb³⁺ co-doped calcium chlorapatite, Ca₅(PO₄)₃Cl (CPCl). It is dominated by the cooperation of a phonon-assisted energy transfer process and a non-radiative resonant energy transfer process caused by the exchange interaction. Eu²⁺–Tb³⁺ co-doped calcium chlorapatite phosphors in which Tb³⁺ can be efficiently excited by 400 nm are potential candidates for phosphor-converted LED.     

PL Properties of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> With Eu<Superscript>3+</Superscript> and Dy<Superscript>3+</Superscript> for Solid State Lighting Prepared by Precipitation Method

Photoluminescence studies of pure and Dy³⁺, Eu³⁺ doped Sr₂CeO₄ compounds are presented by oxalate precipitation method for solid state lighting. The prepared samples also characterized by XRD, SEM (EDS) and FTIR spectroscopy. The pure Sr₂CeO₄ compound displays a broad band in its emission spectrum when excited with 280 nm wavelength, which peaks centered at 488 nm, which is due to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ions. Emission spectra of Sr₂CeO₄ with different concentration of Dy³⁺ ions under near UV radiation excitation, shows that intensity of luminescence spectra is found to be affected by Dy³⁺ ions, and it increases with adding some percentages of Dy³⁺ ions. The maximum doping concentration for quenching is found to be Dy³⁺?=?0.2 mol % to Sr²⁺ions. The observed broad spectrum from 400 to 560 nm is mainly due to CT transitions in Sr₂CeO₄ matrix and some fractional contribution of transitions between ⁴F_9/2 → ⁶H_15/2 of Dy³⁺ ions. Secondly the effect of Eu³⁺ doping at the Sr²⁺ site in Sr₂CeO₄, have been studied. The results obtained by doping Eu³⁺ concentrations (0.2 mol% to 1.5 mol%), the observed excitation and emission spectra reveal excellent energy transfer between Ce⁴⁺ and Eu³⁺. The phenomena of concentration quenching are explained on the basis of electron phonon coupling and multipolar interaction. This energy transfer generates white light with a color tuning from blue to red, the tuning being dependent on the Eu³⁺ concentration. The results establish that the compound Sr₂CeO₄ with Eu³⁺?=?1 mol% is an efficient “single host lattice” for the generation of white lights under near UV-LED and blue LED irradiation. The commission internationale de I’Eclairage (CIE) coordinates were calculated by Spectrophotometric method using the spectral energy distribution of prepared phosphors.     

Quantum Effect on the Energy Levels of Eu2+ Doped K2Ca2(SO4)3 Nanoparticles

Quantum confinement effect on the energy levels of Eu²⁺ doped K₂Ca₂(SO₄)₃ nanoparticles has been observed. The broad photoluminescence (PL) emission band of Eu²⁺ doped K₂Ca₂(SO₄)₃ microcrystalline sample observed at ～436 nm is found to split into two narrow well resolved bands, located at 422 and 445 nm in the nanostructure form of this material. This has been attributed to the reduction in the crystal field strength of the nanomaterials, which results in widening the energy band gap and splitting the broad 4f⁶5d energy level of Eu²⁺. Energy band gap values of the micro and nanocrystalline K₂Ca₂(SO₄)₃ samples were also determined by measuring the UV–visible absorption spectra. These values are 3.34 and 3.44 eV for the micro and nanocrystalline samples, respectively. These remarkable results suggest that activators having wide emission bands might be subjected to weak crystal strength via nanostructure materials to modify their electronic transitions. This might prove a powerful technique for producing new-advanced materials for use in the fields of solid state lasers and optoelectronic devises.     

Eu3+-site occupation in CaTiO3 perovskite material at low temperature

In order to clarify the site occupancy of rare-earth ions in rare-earth doped perovskite materials, the un-doped pure CaTiO₃ and Eu³⁺-doped CaTiO₃ samples with a series of Ca/Ti ratio were synthesized via high-temperature solid-state reaction method. X-ray diffraction (XRD) powder patterns confirm that the crystal structure keeps invariant at various Ca/Ti ratios. Measurement results of unit-cell parameters and X-ray photoelectron spectroscopy (XPS) indicate that Eu³⁺ ions enter into the Ca²⁺ site. The high-resolution photoluminescence spectra of Eu³⁺ ions at 20 K in all samples did not witness a significant change under the excitation at different wavelength, implying that Eu³⁺ ions occupy only one type of site. Considering the small spectral splitting range of ⁵D₀ → ⁷F₂ transition and the large intensity ratio of ⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁, it can be concluded that Eu³⁺ occupies Ca²⁺ site with larger coordinate numbers rather than Ti⁴⁺ site.     

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)     

Fluorinated Eu‐Doped SnO2 Nanostructures with Simultaneous Phase and Shape Control and Improved Photoluminescence

Fluorinated Eu‐doped SnO₂ nanostructures with tunable morphology (shuttle‐like and ring‐like) are prepared by a hydrothermal method, using NaF as the morphology controlling agent. X‐ray diffraction, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and energy dispersive spectroscopy are used to characterize their phase, shape, lattice structure, composition, and element distribution. The data suggest that Eu³⁺ ions are uniformly embedded into SnO₂ nanocrystallites either through substitution of Sn⁴⁺ ions or through formation of Eu‐F bonds, allowing for high‐level Eu³⁺ doping. Photoluminescence features such as transition intensity ratios and Stark splitting indicate diverse localization of Eu³⁺ ions in the SnO₂ nanoparticles, either in the crystalline lattice or in the grain boundaries. Due to formation of Eu‐F and Sn‐F bonds, the fluorinated surface of SnO₂ nanocrystallites efficiently inhibits the hydroxyl quenching effect, which accounts for their improved photoluminescence intensity.     

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.     

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     

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.     

Rare earth ions (Eu3+ and Nd3+) doped BaSnF4: transport and photoluminescence characteristics

Investigation on the X-ray diffraction results of rare earth ions such as Eu³⁺ and Nd³⁺ doped BaSnF₄ materials indicates that the doped materials show a similar pattern of BaSnF₄ with the same tetragonal structure (P₄/nmm). The transport properties of the materials have been investigated by impedance spectroscopy, and the results show that the conductivity values are closely related to both concentration and type of the dopant ion. All of these doped materials show an increase in conductivity over un-doped BaSnF₄. The highest conductivity is observed in 3 mol% Nd³⁺ ion-doped BaSnF₄ system (9.01?×?10^?4 Scm^?1), which is about one order higher in comparison to BaSnF₄ conductivity (1.1?×?10^?4 Scm^?1). The room temperature emission spectrum of BaSnF₄:Eu³⁺ and BaSnF₄:Nd³⁺ shows the characteristic bands arising from ⁵D₀?→?⁷F _j (j?=?1, 2, 3, and 4) and ⁴F_3/2 to ⁴I _j (j?=?9/2 and 11/2) transitions of Eu³⁺ and Nd³⁺ ions, respectively.     

Magnetic nanoparticles trigger cell proliferation arrest of neuro-2a cells and ROS-mediated endoplasmic reticulum stress response

The synthesis, morphological characterization, and optical properties of colloidal, Eu(III) doped Gd₂O₃ nanoparticles with different sizes and shapes are presented. Utilizing wet chemical techniques and various synthesis routes, we were able to obtain spherical, nanodisk, nanotripod, and nanotriangle-like morphology of Gd₂O₃:Eu³⁺ nanoparticles. Various concentrations of Eu³⁺ ions in the crystal matrix of the nanoparticles were tested in order to establish the levels at which the concentration quenching effect is negligible. Based on the luminescence spectra, luminescence lifetimes and optical parameters, which were calculated using the simplified Judd–Ofelt theory, correlations between the Gd₂O₃ nanoparticles morphology and Eu³⁺ ions luminescence were established, and allowed to predict the theoretical maximum quantum efficiency to reach from 61 to 98 %. We have also discussed the impact of the crystal structure of Gd₂O₃ nanoparticles, as well as coordinating environment of luminescent ions located at the surface, on the emission spectra. With the use of a tunable femtosecond laser system and the Z-scan measurement technique, the values of the effective two-photon absorption cross-section in the wavelength range from 550 to 1,200 nm were also calculated. The nonlinear optical measurements revealed maximum multi-photon absorption in the wavelength range from 600 to 750 nm.