SiO2–GeO2 Soot Preform as a Core for Eu2O3 Nanocoating: Synthesis and Photophysical Study

Nowadays solid state chemists have the possibility of work with low temperature strategies to obtain solid state materials with appropriate physical and chemical properties for useful technological applications. Photonic core shell materials having a core and shell domains composed by a variety of compounds have been synthesized by different methods. In this work we used silica-germania soot prepared by vapor-phase axial deposition as a core where a nanoshell of Eu₂O₃ was deposited. A new sol-gel like method was used to obtain the Eu₂O₃ nanoshell coating the SiO₂–GeO₂ particles, which was prepared by the polymeric precursor method. The photophysical properties of Eu³⁺ were used to obtain information about the rare earth surrounding in the SiO₂–GeO₂@Eu₂O₃ material during the sintering process. The sintering process was followed by the luminescence spectra of Eu³⁺ and all the samples present the characteristic emission related to the ⁵D₀→⁷F _J (J = 0, 1, 2, 3 and 4). The ratios of the ⁵D₀→⁷F₂/⁵D₀→⁷F₁ emission intensity for the SiO₂–GeO₂@Eu₂O₃ systems were calculated and it was observed an increase in its values, indicating a low symmetry around the Eu³⁺ as the temperature increases.     

Local structure of Eu3+ ions in fluorophosphate laser glass

A fluorophosphate laser glass doped with 1.0 mol% of Eu³⁺ ions has been prepared and studied by site-selective spectroscopy to explore the local structure of Eu³⁺ ions. Site-selective ⁵ D ₀ → ⁷ F _1,2 emission spectra have been measured under resonant excitation to the ⁵ D ₀ level at different wavelengths within the ⁷ F ₀ → ⁵ D ₀ band at 16 K. Using the Stark level positions of the ⁷ F ₁ and ⁷ F ₂ levels, crystal-field analysis has been carried out. The results suggest the existence of a unique kind of site for all the environments of Eu³⁺ ions in this glass.     

The Role of the Eu<Superscript>3+</Superscript> Concentration on the SrMoO<Subscript>4</Subscript>:Eu Phosphor Properties: Synthesis,Characterization and Photophysical Studies

SrMoO₄ doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr_1−xEu_xMoO₄ powders, where x = 0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO₄:Eu³⁺ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 °C for 2 h, 2θ = 27.8° (100% peak). The excitation spectra of the SrMoO₄:Eu³⁺ (λ_Em. = 614 nm) presented the characteristic band of the Eu^3 + 5L₆ transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO₄ matrix. The emission spectra of the SrMoO₄:Eu³⁺ powders (λ_Exc. = 394 and 288 nm) show the group of sharp emission bands among 523–554 nm and 578–699 nm, assigned to the ⁵D₁→⁷F_{0,1and 2} and ⁵D₀→⁷F_{0,1,2,3 and 4}, respectively. The band related to the ⁵D₀→⁷F₀ transition indicates the presence of Eu³⁺ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the ⁵D₀→⁷F₂ transition is the most intense in the emission spectra.     

Crystal field effects on the photoluminescence properties of Y<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>VO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> phosphors

Y_1−x La _x VO₄:Eu³⁺ phosphors were synthesized using a solid-state reaction. The microstructure and surface morphology of the Y_1−x La _x VO₄:Eu³⁺ phosphors were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. PL measurements of these phosphors revealed the characteristic Eu³⁺ emissions due to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions. The Y_1−x La _x VO₄:Eu³⁺ phosphors showed strong red emission at 619 nm, which radiated from the hypersensitive transition ⁵D₀–⁷F₂ of Eu³⁺ ions. In particular, the incorporation of La into the YVO₄ lattice could induce a remarkable increase in PL. The highest emission intensity was observed in Y_0.2La_0.8VO₄:Eu³⁺, whose brightness was increased by more than 100 fold compared to that of the LaVO₄:Eu³⁺ phosphors. The Y_1−x La _x VO₄:Eu³⁺ phosphors with highly enhanced luminescence are expected to have applications in display devices.     

Temperature sensing behavior of Eu<Superscript>3+</Superscript> doped tellurite and calibo glasses

The effect of temperature on the luminescence intensity of the two bands due to ⁵ D ₁→⁷ F ₁ and ⁵ D ₀→⁷ F ₁ transitions in Eu³⁺ on excitation with the 476.5 nm line from an Ar⁺ laser has been studied in tellurite and calibo glasses. It is interesting to note that the peak intensity of the ⁵ D ₁→⁷ F ₁ transition increases with increasing temperature where as that of the ⁵ D ₀→⁷ F ₁ transition decreases. The ratio of the intensities of the two bands have been used to estimate the temperature. PACS 42.70 Ce     

Investigation of crystallographic sites of Eu in La2BaZnO5 by site-selective laser-excitation spectroscopy

La₂BaZnO₅:Eu³⁺ (0.05 mol%) was prepared by a solid-state reaction at high temperature. X-ray powder diffraction analysis confirmed the formation of single phase La₂BaZnO₅. Luminescence properties of La₂BaZnO₅:Eu³⁺ are investigated by site-selective laser-excitation and emission spectroscopy at 18 K. Two different crystallographic sites for Eu³⁺ corresponding to the La³⁺ and Ba²⁺ sites are identified from the ⁷F₀→⁵D₀ excitation spectra obtained by monitoring the ⁵D₀→⁷F_J (J=1, 2, …, 6) emissions. It is found that Eu³⁺ substituted for the Ba²⁺ ion experiences stronger crystal-field strength than Eu³⁺ substituted for the La³⁺ ion. Energy transfer between the two crystallographic Eu³⁺ centers is investigated by luminescence decay curves at 18 K.     

Europium(III) Concentration Effect on the Spectroscopic and Photoluminescent Properties of BaMoO4:Eu

BaMoO₄:Eu (BEMO) powders were synthesized by the polymeric precursor method (PPM), heat treated at 800 °C for 2 h in a heating rate of 5 °C/min and characterized by powder X-ray diffraction patterns (XRD), Fourier Transform Infra-Red (FTIR) and Raman spectroscopy, besides room temperature Photoluminescence (PL) measurements. The emission spectra of BEMO samples under excitation of 394 nm present the characteristic Eu³⁺ transitions. The relative intensities of the Eu³⁺ emissions increase as the concentration of this ion increases from 0.01 to 0.075 mol, but the luminescence is drastically quenched for the Ba_0.855Eu_0.145MoO₄ sample. The one exponential decay curves of the Eu^{3+ 5}D₀→⁷F₂ transition, λ _exc = 394 nm and λ _em = 614 nm, provided the decay times of around 0.54 ms for all samples. It was observed a broadening of the Bragg reflections and Raman bands when the Eu⁺³ concentration increases as a consequence of a more disordered material. The presence of MoO₃ and Eu₂Mo₂O₇ as additional phases in the BEMO samples where observed when the Eu³⁺ concentration was 14.5 mol%.     

Effects of electron beam current density and temperature on peak height ratios Dj/D0 for cathodoluminescence of Ln2O2S:Eu

The change in the initial and steady state (∼0 and 5 s after initiation of electron beam irradiation) peak heights from the ⁵D₂⇒⁷F₃, ⁵D₁⇒⁷F₃ and ⁵D₀⇒⁷F₂ cathodoluminescent transitions from Eu³⁺ have been studied for Ln₂O₂S:Eu³⁺ (Ln=La, Gd) phosphors. Specifically, the intensity ratio of these transitions, designated as ⁵D₁/⁵D₀, increased and then decreased for both La₂O₂S:Eu³⁺ (0.1 mole%) and Gd₂O₂S:Eu³⁺ (0.4 mole%), as the current density was changed from 10 towards a 1000 μA/cm². These effects were shown to be consistent with feeding from the higher ⁵D₂ excited state to the lower energy ⁵D₁ excited state, resulting in an increase of the ⁵D₁/⁵D₀ ratio at low current densities. At higher current densities, energy was funneled from the ⁵D₁-⁵D₀ states, resulting in a decrease of the ⁵D₁/⁵D₀ ratio. These effects of feeding versus funneling were dependent on both the Eu³⁺ concentration and current density, and changed with time (i.e., approached a steady state after ∼5 s) due to increased activator interactions from induced internal electric fields. The magnitude of thermal quenching versus interaction quenching was investigated using changes of the peak height ratios of ⁵D₂/⁵D₀ and ⁵D₁/⁵D₀.     

Sol-gel growth of Gd2MoO6:Eu nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6:Eu) and their luminescent properties

SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors. The XRD results demonstrate that the Gd₂MoO₆:Eu³⁺ layers on the SiO₂ spheres begin to crystallize after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd₂MoO₆:Eu³⁺ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu³⁺ shows a strong PL luminescence (dominated by ⁵D₀-⁷F₂ red emission at 613 nm) under the excitation of 307 nm UV light. The PL intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles.     

Luminescence properties of Y2WO6:Eu incorporated with Mo or Bi ions as red phosphors for light-emitting diode applications

In this study, the red phosphors, Y₂W_1−xMo_xO₆:Eu³⁺ and Y₂WO₆:Eu³⁺,Bi³⁺, have been investigated for light-emitting diode (LED) applications. In Y₂WO₆:Eu³⁺, the excitation band edge shifts to longer wavelength with the incorporation of Mo⁶⁺ or Bi³⁺ ions. The emission spectra exhibit ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transition of Eu³⁺ ion at 588, 593, and 610 nm, respectively. Moreover, the bluish-green luminescence of the WO₆⁶⁻ at about 460 nm is observed to decrease with the incorporation of Mo⁶⁺, which results in pure red color. Thus, this study shows that the red phosphor, Y₂WO₆:Eu³⁺, incorporated with Mo⁶⁺ or Bi³⁺ ions is advantageous for LEDs applications.     

Structure and photoluminescence of β-Ga2O3:Eu nanofibers prepared by electrospinning

Eu³⁺-doped β-Ga₂O₃ nanofibers were fabricated by electrospinning. The influence of Eu³⁺ concentration on the photoluminescence properties of the obtained nanofibers was investigated. The morphology and structure of β-Ga₂O₃:Eu³⁺ were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectra. The diameter of the Eu³⁺-doped β-Ga₂O₃ nanofibers was in the range of 180-300 nm. When the β-Ga₂O₃:Eu³⁺ nanofibers were excited by 325 nm wavelength, the main emission peak of the samples was 620 nm (⁵D₀→⁷F₂), which corresponded to a typical red emission (⁵D₀→⁷F_j (j = 1, 2, 3, 4) intra-4f transitions of Eu³⁺ ions). In addition, the concentration quench effect and energy transfer mechanism in β-Ga₂O₃:Eu³⁺ were also discussed.     

Ionic liquid-assisted hydrothermal synthesis of dendrite-like NaY(MoO4)2:Tb phosphor

Micro-sized NaY(MoO₄)₂:Tb³⁺ phosphors with dendritic morphology was synthesized by a ionic liquid-assisted hydrothermal process. X-ray diffraction (XRD) indicated that the as-prepared product is pure tetragonal phase of NaY(MoO₄)₂. Field emission scanning electron microscopy (FE-SEM) images showed that the as-prepared NaY(MoO₄)₂:Tb³⁺ phosphors have dendritic morphology. The photoluminescent (PL) spectra displayed that the as-prepared NaY(MoO₄)₂:Tb³⁺ phosphors show a stronger green emission with main emission wavelength 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺ ion, and the optimal Tb³⁺ doping concentration for obtaining maximum emission intensity was confirmed to be 10 mol%. Based on Van Uitert's and Dexter's models the electric dipole–dipole (D–D) interaction was confirmed to be responsible for the concentration quenching of ⁵D₄ fluorescence of Tb³⁺ in the NaY(MoO₄)₂:Tb³⁺ phosphors. The intrinsic radiative transition lifetime of ⁵D₄ level is found to be 0.703 ms.     

Photoluminescence properties of Eu3+-doped Gd2MoB2O9 phosphors for LED-based solid-state-lighting

Investigation was performed on luminescent properties of novel Gd_2−x Eu _x MoB₂O₉ (0.02≤x≤2.0) phosphors. The excitation spectra consist of broad band and intense narrow lines. The 4f-4f transitions are situated in a favorable position for excitation by GaN chip emission. The emission spectra consist of transitions from the ⁵D₀ level to the lower ⁷F manifold, and the emission shows no concentration quenching at higher doping level. The decay time spectra of the ⁵D₀ → ⁷F₂ emission are recorded. Under 395 nm excitation, the intensity of ⁵D₀ → ⁷F₂ transition of GdEuMoB₂O₉ is 1.2 times stronger than that of commercial Eu³⁺:Y₂O₂S phosphor. Gd₂MoB₂O₉:Eu³⁺ phosphors are promising candidates for near-UV-based solid-state-lighting (SSL).     

Ultraviolet and visible upconversion luminescence of Tm(0.1)Yb(5):FOV oxyfluoride nanophase vitroceramics

The ultraviolet upconversion luminescence of Tm³⁺ ions sensitized by Yb³⁺ ions in oxyfluoride nanophase vitroceramics when excited by a 975 nm diode laser was studied. An ultraviolet upconversion luminescence line positioned at 363.6 nm was found. It was attributed to the fluorescence transition of ¹D₂→³H₆ of Tm³⁺ ion. Several visible upconversion luminescence lines at 450.7 nm, (477.0 nm, 462.5 nm), 648.5 nm, (680.5 nm, 699.5 nm) and (777.2 nm, 800.7 nm) were also found, which result respectively from the fluorescence transitions of ¹D₂→³F₄, ¹G₄→³H₆, ¹G₄→³F₄, ³F₃→³H₆ and ³H₄→³H₆ of Tm³⁺ ion. The careful measurement and analysis of the variation of upconversion luminescence intensity F as a function of the 975 nm pumping laser power P prove that the upconversion luminescence of ¹D₂ state is partly a five-photon upconversion luminescence, and the upconversion luminescence of ¹G₄ state and ³H₄ state are respectively the three-photon and two-photon upconversion luminescence. The theoretical analysis suggested that the upconversion mechanism of the 363.6 nm ¹D₂→³H₆ upconversion luminescence is partly the cross energy transfer of {³H₄(Tm³⁺), ³F₄(Tm³⁺), ¹G₄(Tm³⁺)→¹D₂(Tm³⁺)} and {¹G₄(Tm³⁺)→³F₄(Tm³⁺), ³H₄(Tm³⁺)→¹D₂(Tm³⁺)} between Tm³⁺ ions. In addition, the upconversion luminescence of ¹G₄ and ³H₄ state results respectively from the sequential energy transfer {²F_5/2(Yb³⁺)→²F_7/2(Yb³⁺), ³H₄(Tm³⁺)→¹G₄(Tm³⁺)} and {²F_5/2(Yb³⁺) →²F_7/2(Yb³⁺), ³F₄(Tm³⁺)→³F₂(Tm³⁺)} from Yb³⁺ ions to Tm³⁺ ions. Supported by the National Natural Science Foundation of China (Grant No. 10674019)     

Synthesis and photoluminescence properties of?novel red-emitting phosphors for light emitting diodes

The novel red-emitting phosphors K₂Ba_1−x (MoO₄)₂: xEu³⁺(0.02≤x≤0.15) phosphors were prepared by solid-state reaction and their crystal structures, photo luminescent characteristics were investigated. The results show that all samples can be efficiently excited by UV (396 nm) and blue (466 nm) light, which are coupled well with the characteristic emission from UVLED and blue LED, respectively. Their emission spectra show intense red emission at 616 nm with line spectra due to the ⁵D₀–⁷F₂ transition of Eu³⁺. The XRD and photoluminescence experimental results indicate that the K₂Ba(MoO₄)₂: Eu³⁺ phosphor crystallization optimum annealing temperature occurs at about 800°C. The optimum doping concentration of Eu³⁺ is 0.10 mol, and the critical transfer distance (Rc) among Eu³⁺ ions is calculated to be about 11.126 ?. The approach to charge compensation was used: Ba²⁺→Eu³⁺+X⁻ (X=F, Cl, Br), and the charge compensation influence on the luminescent intensity of phosphors is investigated.     

Rearrangement of optical centers and stimulated radiation of Eu<Superscript>3+</Superscript> in polycrystalline huntite under optical and electron-beam excitation

Polycrystalline europium huntite EuAl₃(BO₃)₄ has been prepared by solid-phase synthesis. The spectral and kinetic characteristics of its luminescence under the excitation by a xenon lamp, single laser pulse, and electron beam have been studied. It has been established that the laser excitation of the polycrystalline samples in the ⁷ F ₀ →⁵ L ₆ transition of Eu³⁺ ions with the power density P ≥ 5 × 10⁷ W/cm² leads to the structure rearrangement of the optical centers, which is accompanied by an increase in the probability of the radiation transitions of the activator. The stimulated radiation of the main type of Eu³⁺ centers in the ⁵ D ₀→⁷ F ₁, ⁷ F ₂, and ⁷ F ₄ transitions has been obtained under the excitation by the electron beam with an energy of 200 keV and a duration of 2 ns.     

NaLa(MoO4)2∶Eu3+的水热调控合成与发光特性研究

采用水热法合成了不同粒径的NaLa(MoO₄)₂∶Eu³⁺微晶.通过调节乙二醇浓度和反应时间,研究了NaLa(MoO₄)₂∶Eu³⁺微晶的形貌演变过程,在水热条件下180 ℃反应16 h获得了均一梭子形NaLa(MoO₄)₂∶Eu³⁺微晶,其晶粒长度约为2.0 μm.荧光光谱分析表明,Eu³⁺取代了NaLa(MoO₄)₂中La³⁺的格位, Eu³⁺在613 nm处红光发射(⁵D₀–⁷F₂跃迁)的浓度猝灭机理是电偶极-电四极相互作用,并发生了Eu³⁺( ⁵D₁ ) + Eu³⁺(⁷F₀ )→ Eu³⁺( ⁵D₀ ) + Eu³⁺(⁷F₃) 交叉弛豫,由此导致浓度猝灭. 关键词： 钼酸盐 水热法 稀土离子 发光     

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.     

Temperature-dependent nepheloxetic shift of the 5 D 0→7 F 0 luminescence line of a Eu3+ ion in a superionic Na5Y(:Eu)Si4O12 single crystal

A decrease in the wavelength of the ⁵ D ₀→⁷ F ₀ luminescence line of a Eu³⁺ ion in a single crystal of the superionic conductor Na₅Y(:Eu)Si₄O₁₂ is observed as a consequence of raising the temperature. The effect is interpreted as the result of a change in the distribution of mobile Na⁺ cations in the second coordination sphere of the luminescing rare-earth ion. Fiz. Tverd. Tela (St. Petersburg) 39, 1997–2000 (November 1997)     

Correlation of photoluminescence of (La,Ln) PO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> (Ln = Gd and Y) phosphors with their crystal structures

Eu³⁺-doped (La, Ln) PO₄ (Ln = Gd and Y) phosphors were prepared by a facile co-precipitation method. Their structures and luminescent properties under UV excitation were investigated. Structural characterization of the nanostructured luminescence material was carried out with X-ray powder diffraction analysis. Scanning electron microscopy was carried out to understand the surface morphological features and grain sizes with 50–100 nm. It is found that (La, Gd) PO₄:Eu³⁺ phosphors have the same crystal structure as LaPO₄:Eu³⁺, which is monoclinic with a little different lattice parameters. In the case of (La, Y) PO₄:Eu³⁺ phosphors, however, the gradual change from monoclinic to tetragonal structure of host lattice was observed, as the amount of Y ion increased. From the photoluminescence spectra for (La, Ln) PO₄:Eu³⁺ (Ln = Gd and Y), the emission transition ⁵D₀ → ⁷F₁ has been found to be more prominent over the normal red emission transition ⁵D₀ → ⁷F₂. Furthermore, the size influence on the products was discussed. It was observed that the spectral features possess sharp and bright emission for potential applications on the monitors of the television and some other related electronic systems, in observing the images in orange–red color.