Effect of synthetic conditions on particle size and photo-luminescence properties of Y2O3:Eu3+ nanophosphor

In this paper, effect of synthetic conditions on the particle size, crystal structure, and the photoluminescence properties of the Y₂O₃:Eu³⁺ nanophosphor was investigated. Solvent and dispersing agent were determined as the synthetic parameters. The nanophosphor synthesized from methanol solvent showed the smaller particle size of 4 nm. The XRD analysis indicates that the crystal structure of the Y₂O₃:Eu³⁺ nanophosphor is mainly cubic crystal with orientation of (222), (440), (400), and small peak of (511) indicating monoclinic crystal. The Y₂O₃:Eu³⁺ nanophosphor synthesized by using methanol solvent and 0.1 wt.% hydroxypropyl cellulose (HPC) as a dispersing agent showed higher degree of crystallization of 10.5 of I ₍₂₂₂₎/I ₍₅₁₁₎ ratio than that without HPC. Also, the photoluminescence properties of the nanophosphor showed red color that excitation and emission wavelengths of the nanophosphor were 250 and 611 nm, respectively. Using the 250 nm UV source, the highly intensive photoluminescence peak could be achieved at 611 nm under the synthetic condition of methanol solvent adding 0.1 wt.% HPC.     

Synthesis and Luminescence Properties of Eu3+ Doped Sr2SiO4 Phosphor

Abstract

The europium doped Sr₂SiO₄ phosphors were prepared by the combustion synthesis technique. The prepared samples of europium doped Sr₂SiO₄ phosphors were characterized by the X-Ray Diffraction (XRD), Ultraviolet Visible spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectra (EDS) and Photoluminescence Technique (PL). The orthorhombic crystal structure of the prepared sample was confirmed by using XRD. The formation of fiber like nano structured nature was confirmed by the images captured using the FE-SEM technique. The band gap energies were calculated using the UV-Visible spectra of the samples and these band gap energies were observed as 4.5826?eV for Sr₂SiO₄ and 4.1748?eV for Eu (5?m%) doped Sr₂SiO₄. The two different PL emission peaks were observed for two different excitation wavelengths. One peak was observed at the 590?nm under 393?nm excitation and another peak was observed at the 615?nm under 408?nm excitation. The CIE color coordinates of the Eu³⁺ doped Sr₂SiO₄ phosphors are x?≈?0.6615, y?≈?0.3382 (red color) observed for 408?nm excitation and x?≈?0.5636, y?≈?0.4356 (orange) observed for 393?nm excitation calculated using the color calculator program radiant imaging.     

Effects of Al<Superscript>3+</Superscript> substitution on the luminescence properties of LuNbO<Subscript>4</Subscript> doped with Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> ions

The effect of Al³⁺ substitution on the enhancement of the luminescence of Lu_1–xAl_xNbO₄:Eu³⁺ and Lu_1–xAl_xNbO₄:Tb³⁺ was investigated. X-ray diffraction patterns confirmed that the Eu³⁺, Tb³⁺, and Al³⁺ ions were fully incorporated into the Lu³⁺ sites. In the case of Lu_1–xAl_xNbO₄:Eu³⁺, the predominant red emission (614 nm) was assigned to the ⁵D₀?→?⁷F₂ transition of Eu³⁺ and for x?=?0–0.05, its intensity increased up to ~125 and 108% under 395 nm (⁷F₀ → ⁵L₆) and a charge transfer band excitation, respectively. For Lu_1–xAl_xNbO₄:Tb³⁺, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the ⁵D₄?→?⁷F_J transitions of Tb³⁺. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu³⁺ and Tb³⁺, which were attributed to a large difference in the ionic radii of Al³⁺ and Lu³⁺.     

Luminescent properties of Sr2ZnSi2O7: Eu2+ phosphors prepared by combustion-assisted synthesis method

A blue-emitting phosphor Sr₂ZnSi₂O₇: Eu²⁺ was prepared by combustion-assisted synthesis method and an efficient blue emission under from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 475?nm, which corresponds to the 4f⁶5d¹??4f⁷ transitions of Eu²⁺. The excitation spectrum is a broad band extending from 250 to 450?nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The effect of doped Eu²⁺ concentration on the emission intensity of Sr₂ZnSi₂O₇: Eu²⁺ was also investigated and the corresponding concentration quenching mechanism is verified to be an electric multipole-multipole interaction.     

Optical characteristics of Bi4-xEuxTi3O12 ferroelectric thin films on fused silica substrates

Bi_4-xEu_xTi₃O₁₂ (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500?nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu³⁺ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69?eV for the samples with x?=?0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of ⁵ D ₀????⁷? F ₁ (594?nm) and ⁵ D ₀????⁷? F ₂ (617?nm) had maximum intensities when Eu³⁺ concentration was x?=?0.40. The relatively high quenching concentration of Eu³⁺ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.     

Structural and Optical Properties of Size and Morphology Controllable Nanoscale SrAl2O4: Eu2+, Dy3+

Abstract

Nanoscale SrAl₂O₄: Eu²⁺, Dy³⁺ with controllable size and morphology was synthesized by sol-gel auto-combustion method. The surface morphology and structural characterization were carried out with TEM and XRD. Optical properties were analyzed by comparing excitation spectra, emission spectra and afterglow decay of the nanoscale phosphor with that of the bulk phosphor. The results showed that citric acid acted as a soft template in the reaction system. The morphology and size changed clearly with pH value and sintering temperature. The crystallinity was affected by the quantity of citric acid. Both the nanoscale phosphors with different particle size and the bulk one have the strongest emission at 525?nm. But their strongest peaks in excitation spectra are very different from each other. The phosphorescence of nanoscale phosphor decays more rapidly than that of the bulk phosphor.     

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y₂O₃: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y₂O₃: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu^{3 +} and Bi^{3 +} concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.     

Oxynitride/nitride phosphors for white light-emitting diodes (LEDs)

Oxynitride/nitride phosphors have attracted significant attention recently because they have promising luminescence properties and superior thermal and chemical stabilities which predestinates them for use in white LEDs to generate white light. This paper reports on luminescence spectra of Eu²⁺ or Ce³⁺-activated α-SiAlON, β-SiAlON, and alkaline earth silicon nitride (M₂Si₅N₈, M = Ca, Sr, Ba). A single broad emission band is observed for all samples, and the emission color depends on the type of activators and host lattice: α-SiAlON:Ce³⁺ (blue), α-SiAlON:Eu²⁺ (yellow), β-SiAlON:Eu²⁺ (green), and M₂Si₅N₈:Eu²⁺ (red). The excitation spectrum of these oxynitride/nitride phosphors covers a wide range from ultraviolet to visible light, enabling them to be used for white LEDs when an ultraviolet or blue LED chip is combined.     

Microstructure and luminescent properties of Eu2W2O9 phosphors

A homogeneous Eu₂W₂O₉ phase with small grains (～4.0μm) was formed for the specimens fired below 1175°C. As the firing temperature was increased above 1150°C, grain growth occurred and the grain shape changed from faceted to round. The excitation spectra of the Eu₂W₂O₉ phosphor were similar to those of the Eu₂(WO₄)₃ phosphor, but the absorption band due to the O^2?→W⁶⁺ ligand to metal charge transfer was shifted to lower energies and the ⁷F_o→⁵H₃ and ⁷F_o→⁵F_2,4 transitions were not found. The intensity of the excitation and emission spectra of the Eu₂W₂O₉ phosphor considerably increased with increasing firing temperature, due to the increased grain size and changed grain shape. The intensity of the red emission band of the Eu₂W₂O₉ phosphor was higher than that of the Eu₂(WO₄)₃ phosphor. Moreover, the addition of LiCl to the Eu₂W₂O₉ phosphors considerably enhanced the intensity of their emission spectra, probably due to the increased grain size. Therefore, LiCl-added, Eu₂W₂O₉ phosphor is a promising candidate material for red color emission.     

Microwave power detection using ferroelectric thin film varactors

ABSTRACT

LaAlO₃ powders are prepared by coprecipitation of La(OH)₃ and Al(OH)₃, followed by solid state reaction method or molten salt synthesis method. The crysatlline phase evolution, micro morphology and luminescence properties of the calcined products are systematically studied by XRD, SEM/EDX and fluorescence spectroscopy. The results show that LaAlO₃ powders with high purity could be obtained at 1000°C/3h with the help of melton salt Na₂SO₄, however, impurities exist in the solid state reaction products under the same calcination condition. The as prepared sub-micrometer LaAlO₃ powders doped with Eu³⁺ ion by the molten salt method show two dominant emmision peaks of 596nm and 618nm under excitation of near ultraviolet light (314nm), both emmision peak intensity reach maximum at the Eu³⁺ doping concentration of x = 0.08. At higher Eu³⁺ doping concentration, the emmision peak intensity decreases due to the concentration quenching.     

Luminescence of YAl3 (BO3)4: Eu2+, Dy3+ phosphor and its luminescence decay characteristics

Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors are synthesized by sol-gel method. The phosphors show prominent blue luminescence due to the 4f⁷–4f⁶5d transition of Eu²⁺. The emission intensity is greatly improved when Dy³⁺ is doped into the YAl₃ (BO₃)₄:Eu²⁺ system. The 1% Dy³⁺ in Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors is the optimum doping concentration. The luminescence decay characteristics of the samples have also been investigated, exhibiting the decay times of approximately 0.1 μs, which is much shorter compare to other Eu²⁺ doped phosphors.     

Thermoelectric properties of Ca3-xEuxCo3.95Ga0.05O9+δ (0 ≤ x ≤ 0.10)

Polycrystalline samples of Ca_3–xEu_xCo_3.95Ga_0.05O_9+δ (x?=?0.00, 0.02 and 0.10) have been prepared by conventional solid-state synthesis and their thermoelectric properties measured at 25 K to 300 K. The XRD results revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were simultaneously increased with increasing Eu³⁺ content. The total thermal conductivity decreased with increasing Eu³⁺ content. A maximum dimensionless figure of merit of 0.033 at 300 K was reached for Ca_2.9Eu_0.1Co_3.95Ga_0.05O_9+δ, which is about 27 % higher than that of the undoped sample. These results suggest that the Eu is an effective doping element for improving the thermoelectric properties of Ca₃Co_3.95Ga_0.05O_9+δ.     

Photoluminescence properties of a green to red-emitting Eu3+, Tb3+ co-doped CaBi2Ta2O9 ferroelectrics

The CaBi₂Ta₂O₉ bismuth layered-structure ferroelectrics doped with rare earth ions Eu³⁺ and Tb³⁺, or co-doped with Eu³⁺/Tb³⁺ were prepared by the conventional solid-state reaction method. The microstructure and photoluminescence properties of CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ were investigated. The XRD patterns demonstrate that the rare earth ions have been effectively doped into CaBi₂Ta₂O₉ host lattices. The photoluminescence properties of CaBi₂Ta₂O₉ with different activator ions are researched in details. The novel red and green light emissions were observed under the excitation of blue and near-UV light. Notably, tunable emissions and a warm-white color have been achieved in the Eu³⁺ and Tb³⁺ co-doped CaBi₂Ta₂O₉ powders. These results suggest that CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ could be novel luminescence materials. It is also expected that rare earth doped CaBi₂Ta₂O₉ ferroelectrics can find potential applications in new multifunctional photoluminescence ferroelectric devices.     

Epitaxial recrystallization and luminescence of CaAl2O4:Eu2+ thin films prepared on sapphire substrates

Eu²⁺ doped CaAl₂O₄ thin films were prepared on c-, a-, and r-plane sapphire substrates by a sputtering method, and then post-annealed for the recrystallization. Post-annealed films have out-of-plane epitaxial orientations of (010) and (001) CaAl₂O₄ on c- and a-plane sapphire substrates, respectively, whereas the films on r-plane were composed of two epitaxial phases of (210) CaAl₂O₄ and (210) CaAl₄O₇. In-plane relationships between films and substrates were also determined by an X-ray pole figure method, demonstrating that the films were epitaxially recrystallized, but not single crystals. The emission wavelengths were independent of the orientations of epitaxial films, showing a blue emission at 448 nm under 325 nm excitation, but the emission intensity depended on the film structure.     

Luminescence and photocatalytic performance of Ca1−xTiO3:Pr3+ material

Abstract

Luminescent perovskite photocatalysts activated by Pr³⁺ were prepared by combustion. The structural phase, morphology, and chemical composition of the as-prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. The photocatalytic activities of the synthesized samples were investigated on the basis of the degradation of methylene blue (MB) under UV light irradiation. CaTiO₃:Pr³⁺ was obtained in high purity and good crystallinity with a perovskite structure. The degradation of the photocatalyst was fitted with pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Compared to CaTiO₃:Pr³⁺, Ca_1–xTiO₃:Pr³⁺ (x?=?0–0.3) multifunctional materials exhibit higher luminescence intensity and photocatalytic activity toward the degradation of MB. Ca_0.8TiO₃:0.1%Pr³⁺ exhibited the best performance.     

Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

Temperature dependence photo-luminescence of Nd<Superscript>3+</Superscript> doped PLZT ceramic

Temperature dependence of photo-luminescence for Nd³⁺ doped PLZT(9/65/35) was measured across its structural phase transition temperature. The absorption corresponding to ⁴ I _9/2 → ⁴ F _5/2, ² H _9/2 energy level near 808 nm was used for exciting the sample. The major emission bands at 0.9, 1.06, and 1.34 μm were observed. No shift in the peak position of these emission bands was observed across the diffused structural transition with increase in temperature. However, a 10% increase in FWHM was observed. The absence of any discernible peak shift is attributed to the shielding of the intra-configurational 4f-4f transitions, in trivalent Nd³⁺ ions, by external 5 s and 5d orbitals. The red shifted phonon side bands appeared with increase in temperature.     

Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion

Abstract

Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr_xTi_1-x)O₃; BZT for x?=?0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100?°C for 4?h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11?nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x?=?0.3, the Curie temperature; T_c, shifted to below room temperature. The BZT ceramics for x?=?0.1 had relatively high dielectric constant (ε), 13007, low T_c, 76?°C and comparable dielectric loss (tan δ) at T_c, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.     

Characterization of luminescent properties of Sr–Ca–Al–O multi-phases oxide phosphors

Multi-phases phosphors, which could exhibit red, green, and blue emission bands simultaneously, were synthesized by the solid-state reaction method with a flux. Starting materials of SrCO₃, CaCO₃, and Al₂O₃ were mixed and fired. H₃BO₃ and Eu₂O₃ were added as a flux and a dopant, respectively. Effects of the excitation energy and the mixing ratio of starting materials on the luminescent properties were investigated. Phase transformations and variations of luminescent properties were also observed as a function of H₃BO₃ flux amounts. Emission wavelength and intensity depended on the excitation energy as well as H₃BO₃ flux amounts. The mixture of 8SrCO₃–4CaCO₃–11Al₂O₃–0.8H₃BO₃–0.18Eu₂O₃ showed red, green, and blue emission by exciting at near UV, while 8SrCO₃–4CaCO₃–11Al₂O₃–1.2 and 1.6H₃BO₃–0.18Eu₂O₃ exhibited strong red emissions.