Morphology-dependent luminescence behavior of Y<Subscript>2-x</Subscript>Gd<Subscript>x</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors grown by a laser ablation

Y_2-xGd_xO₃:Eu³⁺ luminescent thin films have been grown on Al₂O₃(0001) substrates using pulsed laser deposition. Films grown under different deposition conditions have been characterized using microstructural and luminescence measurements. The crystallinity, surface morphology and photoluminescence (PL) of the films are highly dependent on the amount of Gd present. The photoluminescence (PL) brightness data obtained from Y_2-xGd_xO₃:Eu³⁺ films grown under optimized conditions have indicated that Al₂O₃(0001) is one of the most promising substrates for the growth of high-quality Y_2-xGd_xO₃:Eu³⁺ thin-film red phosphors. In particular, the incorporation of Gd into the Y₂O₃ lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y_1.35Gd_0.60Eu_0.05O₃, whose brightness was increased by a factor of 3.1 in comparison with that of Y₂O₃:Eu³⁺ films. This phosphor may be promising for application in flat-panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

Photolumiscent Properties of Nanorods and Nanoplates Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

Nanorods and nanoplates of Y₂O₃:Eu³⁺ powders were synthesized through the thermal decomposition of the Y(OH)₃ precursors using a microwave-hydrothermal method in a very short reaction time. These powders were analyzed by X-ray diffraction, field emission scanning electron microscopy, Fourrier transform Raman, as well as photoluminescence measurements. Based on these results, these materials presented nanoplates and nanorods morphologies. The broad emission band between 300 and 440 nm ascribed to the photoluminescence of Y₂O₃ matrix shifts as the procedure used in the microwave-hydrothermal assisted method changes in the Y₂O₃:Eu³⁺ samples. The presence of Eu³⁺ and the hydrothermal treatment time are responsible for the band shifts in Y₂O₃:Eu³⁺ powders, since in the pure Y₂O₃ matrix this behavior was not observed. Y₂O₃:Eu³⁺ powders also show the characteristic Eu³⁺ emission lines at 580, 591, 610, 651 and 695 nm, when excited at 393 nm. The most intense band at 610 nm is responsible for the Eu³⁺ red emission in these materials, and the Eu³⁺ lifetime for this transition presented a slight increase as the time used in the microwave-hydrothermal assisted method increases.     

Improved photoluminescence of pulsed-laser-ablated Y<Subscript>1-x</Subscript>Gd<Subscript>x</Subscript>VO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> thin film phosphors by Gd substitution

Gd-substituted Y_1-xGd_xVO₄:Eu³⁺ luminescent thin films have been grown on Al₂O₃(0001) substrates using pulsed-laser deposition. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity, surface morphology, and photoluminescence (PL) of the films are highly dependent on the amount of Gd. The photoluminescence (PL) brightness data obtained from Y_1-xGd_xVO₄:Eu³⁺ films grown under optimized conditions have indicated that the PL brightness is more dependent on the surface roughness than the crystallinity of the films. In particular, the incorporation of Gd into the YVO₄ lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y_0.57Gd_0.40Eu_0.03VO₄ thin film whose brightness was increased by a factor of 2.5 and 1.9 in comparison with that of YVO₄:Eu³⁺ and GdVO₄:Eu³⁺ films, respectively. This phosphor have application to flat panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

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.     

Luminescence thermometry using Gd<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript>

In this paper we study the possibility of using the synthesized nanopowder samples of Gd₂Zr₂O₇:Eu³⁺ for temperature measurements by analyzing the temperature effects on its photoluminescence. The nanopowder was prepared by solution combustion synthesis method. The photoluminescence spectra used for analysis of Gd₂Zr₂O₇:Eu³⁺ nano phosphor optical emission temperature dependence were acquired using continuous laser diode excitation at 405 nm. The temperature dependencies of line emission intensities of transitions from ⁵D₀ and ⁵D₁ energy levels to the ground state were analyzed. Based on this analysis we use the two lines intensity ratio method for temperature sensing. Our results show that the synthesized material can be efficiently used as thermographic phosphor up to 650 K.     

Quantum cutting in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript>: Eu<Superscript>3+</Superscript> by VUV excitation

The emission and excitation spectra of Gd₂SiO₅∶Eu³⁺ were investigated using the VUV beam line of the Beijing Synchrotron Radiation Facility (BSRF). The experimental results were discussed in the frame of visible quantum cutting process involved in Gd³⁺−Eu³⁺ system. Upon direct excitation into the⁶G _J states of Gd³⁺, two visible photon emissions from Eu³⁺ were observed. Cursory evaluation proved that Gd₂SiO₅∶Eu³⁺ is an efficient visible quantum cutter.     

Correction of the band gap of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Submicron samples of Y₂O₃:Eu³⁺ phosphor with elevated photoluminescence (PL) efficiency and activator concentration of 9 at % obtained by the sol–gel method were investigated by diffuse reflection spectroscopy and PL spectroscopy. It is found that the diffuse reflection spectrum in the vicinity of the fundamental absorption edge (<300 nm) is distorted by the superposition of the PL of Eu³⁺ ions, as a result of which the calculated value of optical band gap E _g of the Y₂O₃ matrix is overestimated. An algorithm for eliminating the PL influence on the absorption edge is proposed, and the correct E _g values are found to be 4.61 ± 0.12 and 4.50 ± 0.12 eV for annealing at 700 and 1300°C, respectively.     

Local structure of Gd<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> impurity centers in a CdF<Subscript>2</Subscript> crystal

The local crystal structure of Gd³⁺ and Eu²⁺ cubic impurity centers in cadmium fluoride is calculated within the shell model in the pair potential approximation. The local compressibility of the cationic and anionic sublattices of the host lattice is determined in the vicinity of the Gd³⁺ (Eu²⁺) impurity ion.     

Synthesis and luminescent properties of Eu<Superscript>3+</Superscript>- and Eu<Superscript>2+</Superscript>-activated sodium pyrophosphate Na<Subscript>4</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

The luminescent properties of Eu³⁺ and Eu²⁺ ions in sodium pyrophosphate, Na₄P₂O₇, have been studied. The excitation spectrum of the Eu³⁺ emission in Na₄P₂O₇ consists of several sets of bands in the range 280–535 nm due to 4f–4f transitions of Eu³⁺ ions and a broad band with a maximum at about 240 nm interpreted to be due to a charge transfer (CT) transition from oxygen 2p states to empty states of the Eu³⁺ 4f⁶-configuration. Although the CT band energy is large enough, the quantum efficiency (η) of the Eu³⁺ emission in Na₄P₂O₇ under CT excitation was estimated to be very low (η ≤ 0.01). In terms of a configurational coordinate model, this fact is interpreted as a result of the high efficiency of a radiationless relaxation from the CT state to the ⁷F₀ ground state of Eu³⁺ ions occupying sodium sites in Na₄P₂O₇. A strong reducing agent is required in order to stabilize Eu²⁺ ions in Na₄P₂O₇ during the synthesis. Several nonequivalent Eu²⁺ luminescence centers in Na₄P₂O₇ were found.     

Energy levels of rare-earth ions in Gd<Subscript>2</Subscript>O<Subscript>2</Subscript>S

The energies of the ground 4f ⁿ levels of tri- and divalent rare-earth ions with respect to the conduction and valence bands of Gd₂O₂S crystal has been determined. It is shown that the Pr³⁺, Tb³⁺, and Eu³⁺ ions can be luminescence centers in Gd₂O₂S. The levels of the Nd³⁺, Dy³⁺, Er³⁺, Tm³⁺, Sm³⁺, and Ho³⁺ ions lie in the valence band; therefore, these ions cannot play the role of activators. The ground 4f level of the Ce³⁺ ion is near the midgap, due to which Ce³⁺ effectively captures holes from the valence band and electrons from the conduction band and significantly decreases the afterglow level of the Gd₂O₂S:Pr and Gd₂O₂S:Tb phosphors.     

Spontaneous luminescence of Eu<Superscript>3+</Superscript> ions in porous Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanospheres

A study of the luminescence of Eu³⁺ ions in Y₂O₃ nanospheres indicates a significant influence of the porous structure of nanoparticles on the luminescence of dopant ions. It is shown that filling the nanopores of initially porous Y₂O₃ nanospheres shortens the decay time of the spontaneous luminescence of doping europium ions. The change in the decay time is associated with the change in the effective refractive index of the porous nanospheres.     

On the Luminescence of Ce<Superscript>3+</Superscript>, Eu<Superscript>3+</Superscript>, and Tb<Superscript>3+</Superscript> in Novel Borate LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>

This paper reports on the photoluminescence (PL) and time-resolved properties of Ce³⁺, Eu³⁺, and Tb³⁺ in novel LiSr₄(BO₃)₃ powder phosphors. Ce³⁺ shows an emission band peaking at 420 nm under 350-nm UV excitation. Energy transfer from Ce³⁺ to Mn²⁺ takes place in the co-doped samples. Eu³⁺ shows red emission under near UV excitation. LiSr₄(BO₃)₃:Eu³⁺ phosphor could be a suitable candidate for phosphor-converted solid state lighting. The luminescence lifetime is 2.13 ms for Eu³⁺ in LiSr₄(BO₃)₃:0.001Eu³⁺. As Eu³⁺ concentration increasing, the decay curves deviate from exponential behavior. Tb³⁺ shows the strongest ⁵D₄→⁷ F₅ emission line at 540 nm. Decay curves of ⁵D₄→⁷ F₅ and ⁵D₃→⁷ F₅ emission with different Tb³⁺ concentrations were also measured. Cross-relaxation process is discussed based on the decay curves.     

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.     

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.     

Spectral properties of Nd<Superscript>3+</Superscript> ions in samples of transparent Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The spectral and luminescent characteristics of samples of Y₂O₃:Nd³⁺ ceramics obtained from different precursors under different preparation conditions (the concentration of an HfO₂ compacting additive, the temperature and time of synthesis) are studied at 300 and 77 K. It is shown that the spectral positions of absorption and luminescence lines of ceramics correspond to those of a Y₂O₃:Nd³⁺ single crystal. At the same time, the absorption and luminescence spectra show an inhomogeneous broadening, characteristic of disordered crystals and glass. The energies of the ⁴ I _9/2 and ⁴ F _3/2 Stark states of the Nd³⁺ ion are calculated. The calculation results nearly coincide with the data from the literature for the Y₂O₃:Nd³⁺ single crystal and transparent ceramics. Samples containing the compacting additive show additional lines, whose intensities correlate with its concentration and the method of preparation of Y₂O₃:Nd³⁺ ultradispersed powders. It is assumed that these lines are related to the fact that either Nd³⁺ ions enter the composition of the HfO₂ compacting additive or Hf⁴⁺ ions are present in the nearest environment of Nd³⁺ ions at the boundaries of granules enriched with HfO₂.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

Optical and fluorescent properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> sol–gel planar waveguides containing Tb<Superscript>3+</Superscript> doped nanocrystals

Terbium doped Y₂O₃ planar waveguides were fabricated by sol–gel process and dip-coating using yttrium acetate as precursor. Two different doping modes were compared, i.e. introduction in the sol of dispersed Tb³⁺ions from dissolved Tb(NO₃)₃, or of nanoparticles of Tb₂O₃ or [Y₂O₃:50% Tb] from an alcoholic suspension. The chemical and nanostructural properties were analyzed by infrared spectroscopy, transmission electron microscopy and X-ray diffraction. The Tb³⁺ fluorescence properties were studied as a function of temperature and atmosphere of the thermal treatments, and of the Tb³⁺ concentration. The fluorescence properties are discussed in relation to the quenching mechanisms induced by Tb⁴⁺ transformation, residual OH groups, and crystallites size and structure. Optical propagation losses of the Tb doped Y₂O₃ planar waveguides related to the doping modes and Tb³⁺ concentration are presented. Doping sol–gel films by nanoparticles is shown to be a valuable alternative to the conventional doping from dissolved terbium salt. PACS 81.21.Fw; 84.40.Az; 78.67.Bf     

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.     

Fabrication,structure, and properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C encapsulated with YVO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> composites

The use of carbon shells offers many advantages in surface coating or surface modification due to their surface with activated carboxyl and carbonyl groups. In this study, the Fe₃O₄@C@YVO₄:Eu³⁺ composites were prepared through a simple sol–gel process. Reactive carbon interlayer was introduced as a key component, which separates lanthanide-based luminescent component from the magnetite, more importantly, it effectively prevent oxidation of the Fe₃O₄ core during the whole preparation process. The morphology, structure, magnetic, and luminescent properties of the composites were characterized by transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, X-ray photoelectron spectra, VSM, and photoluminescent spectrophotometer. As a result, the Fe₃O₄@C/YVO₄:Eu³⁺ composites with well-crystallized and core–shell structure were prepared and the YVO₄:Eu³⁺ luminescent layer decorating the Fe₃O₄@C core–shell microspheres are about 10 nm. In addition, the Fe₃O₄@C@YVO₄:Eu³⁺ composites have the excellent magnetic and luminescent properties, which allow them great potential for bioapplications such as magnetic bioseparation, magnetic resonance imaging, and drug/gene delivery.