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.     

Synthesis and temperature-dependent optical properties of Eu3+-doped NaYSiO4 red-emitting phosphors

Abstract

Novel Eu³⁺-activated orthosilicate NaYSiO₄:xEu³⁺ (x?=?0.02, 0.05, and 0.20) red-emitting phosphors were developed for white light emitting diode applications. The X-ray diffraction (XRD), photoluminescence excitation and emission spectra, temperature-dependent curves were applied to characterize the samples. The red emission of the NaYSiO₄:Eu³⁺ phosphor corresponding to ⁵D₀→⁷F₂ (614?nm) transition was observed under the excitation of 394?nm wavelength, which is suitable for UV LED chip. The quenching temperature for NaYSiO₄:0.05Eu³⁺ was found to be over 500 K. The CIE chromaticity coordinates of NaYSiO₄:0.05Eu³⁺ are very close to the National Television System Committee (NTSC) standard red.     

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.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

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.     

Influence of calcination temperature and La3+/Bi3+/Fe3+ ratio on structure and photocatalytic activity of bismuth ferrite

Abstract

The bismuth ferrites were prepared by sol–gel method with citric acid as complexing agent. The effects of calcination temperature and ratio of Bi³⁺/Fe³⁺/La³⁺ of precursor on the phase composition, morphology and photocatalytic activity of the samples were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible spectroscopy (UV–Vis) were used to characterize resultant products. The results show that the phase composition, morphology and photocatalytic property of the products depend on the ratio of Bi³⁺/Fe³⁺/La³⁺ of precursor. Furthermore, the mechanism of photocatalytic reaction of prepared bismuth ferrite was also discussed.     

Characteristics of ZnGa2O4 phosphors synthesized by solution combustion method

ZnGa₂O₄ phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn⁺² ions. The highest PL peak was observed with Mn⁺² ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.     

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.     

Morphology and luminescence properties of BaMgAl10O17:Eu2+ blue phosphors by Aerosol Flame Deposition

BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) is widely used as a blue phosphor for fluorescent lamps and plasma display panels (PDP). The improvement of the luminescence efficiency is a significant issue for applications in plasma display panels. In this study, the Aerosol Flame Deposition (AFD) was applied to fabricate BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) particles with spherical shape and fine size in order to improve their luminescence. The sub-micrometer powder was synthesized in spherical shape in an oxy-hydrogen flame and deposited on a substrate in the form of porous film. The particle size of as-prepared powder increased with increasing the concentration of precursor solution and the heat treatment under reducing atmosphere increased particle size additionally with surface roughening due to the needle-like crystallized phases. Photoluminescence spectrum was observed at about 450nm due to the 5d–4f transition of Eu²⁺ and the intensity of phosphor was as high as 70% of that of the commercial phosphor.     

White-Light-Emitting Single Component Metal-Organic Frameworks Based on 2,3-Pyridinedicarboxylic Acid

Abstract

Two white-light-emitting MOFs, [Dy(pydc)·(H₂O)₂]·DMF_0.66 (1) and [Gd_1.9Dy_0.1(pydc)_1.5(H₂O)₃]·DMF_1.5?C460 (2), were synthesized by the reaction of a rigid ligands H₂pydc (H₂pydc = 2,3-pyridinedicarboxylic acid) and Dy(III) ions under solvothermal conditions. The emission color of compound 1 is tunable by variation of excitation light to get yellow-to-white photoluminescence. When proportion of Dy³⁺ and H₂pydc is 1:3 could obtain the single component compound 1 with CIE coordinates of (0.2935, 0.3335), which is close to (0.3333, 0.3333) of the pure white light. To investigate the matrixes effect and luminescent dye C460@MOF, Gd(III) ions and C460 were introduced to form MOFs 2 with the mixed metal centers. When concentration of C460 is 10^?3 mol/L, MOFs 2 shows CIE coordinates of (0.3255, 0.3452). This work provides a practical strategy for the development of white-light emitting phosphor based on single component MOFs, which opens a new region for WLEDs.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

R2MgSi2O7：Eu（R=Ca，Sr,Ba）荧光粉发光性能及应用

采用高温固相法制备R2MgSi2O7：Eu（R=Ca,Sr,Ba）荧光粉,并对其发光性能及封装应用进行研究。详细讨论碱土元素的种类及锶／钙的比例对激发与发射光谱的影响,同时考察激活剂Eu^2＋浓度对发光强度的影响,也考察了将Ba2MgSi2O7：Eu0.005荧光粉封装于紫光芯片中的发光特性。结果表明,荧光粉基质中碱土元素的种类及碱土元素锶钙的含量对其发射及激发光谱有较大影响,随着碱土离子Ca。’含量的增加,发射光谱逐渐红移,发光强度逐渐减弱。本文对这一变化机理进行了初步分析。当激活剂Eu^2＋摩尔浓度为0．005时,荧光粉具有较好的发光强度,并且当荧光粉的质量浓度达到19％时,LED具有较好的光效。     

Structures and luminescence properties of Eu2+- doped α-sialon phosphors for UV-LED

Eu²⁺-doped α-sialon phosphor was synthesized and structures and various luminescence properties were studied. High crystalline Ca_0.8Al_2.8Si_9.2O_1.169N_14.94 phase was successively obtained for undoped and Eu²⁺-doped samples. Eu²⁺-doped α-sialon phosphor exhibited wide absorption in ultra violet (UV) and visible range, and high broad emission band peaking at from 570 to 582 nm. The optimum compositions and process conditions was obtained from 0.75 mol% Eu²⁺–doped Ca_0.8Al_2.8Si_9.2O_1.169N_14.94 fired at 1650 °C for 2 h in 30% H₂–70% N₂ atm. In addition, fabrication of UV-light emitting diode (LED) lamp using this phosphor was conducted and the optical properties were measured. Relative quantum efficiency of the phosphor and luminous efficiency of the lamp were 83.66% and 35.28 lm/W, respectively. Those results indicated that Eu²⁺-doped α-sialon phosphor in this study was a good candidate for UV-LED light source.     

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.     

The effect of heat treatment temperature on phase formation and luminescence properties of calcium magnesium silicate glass-ceramics doped with Sm2O3

Abstract

The transparent glasses of CaO-MgO-Al₂O₃-SiO₂-ZnO system doped with Sm₂O₃ was prepared by conventional melt-quenching method. The obtained glasses were heat treated at a suitable temperature (875?°C–920?°C for 2?h) identified by differential thermal analysis (DTA). Phase formation and microstructure of glass-ceramics were characterized by X-ray diffraction and scanning electron microscopy, respectively. The optical transmission spectra were recorded by UV-Vis spectrophotometer in the wavelength range between 350 and 1000?nm. It was found that the increase in heat treatment temperature reduced the transparency of the glass-ceramics. The luminescence properties were identified by fluorescence spectroscopy. The excitation spectra of Sm₂O₃ doped CaO-MgO-Al₂O₃-SiO₂-ZnO glass-ceramic samples are in wavelength range of 550–750?nm and the emission spectra exhibited a strong orange-red luminescence composed of 562, 599 and 654?nm under excited at 402?nm. The results of XRD studies revealed the occurrence of diopside (CaMgSi₂O₆) and akermanite (Ca₂MgSi₂O₇) phases. The increasing of heat treatment temperature has no effect on the shift of emission spectra.     

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.     

The preparation of ZnGa2O4 doped with Mn‐Mg and Tm for green and blue phosphors

Phosphor powders of zinc gallate (ZnGa₂O₄) with Mg and Mn for green and Tm‐Mg for blue luminescence were prepared by solid state reaction method for their improved luminescent properties. Green‐luminescence emitting ZnMnGa₂O₄ reached maximum intensity at Mn = 0.005 mol% and further improvement was achieved by the addition of Mg²⁺. Tm‐Mg based zinc gallate phosphor exhibited a strong blue emission, centered at ∼420 nm with the maximum intensity achieved for 0.003 mol% of Mg and 0.015 mol% of Tm. This study established the possibilities of controlling the luminescent characteristics of zinc gallate by adding various elements. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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.     

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⁺.     

Morphological and Optical Characterization of Sol-Gel Synthesized Ni-Doped ZnO Nanoparticles

Abstract

In this work, Ni-doped ZnO nanoparticles (NPs) were successfully synthesized by sol-gel method. The as-synthesized nanoparticles were characterized to investigate their morphology, structure, purity and optical properties. XRD analysis confirmed the formation of nanoparticles with average particle size of approx. 30?nm. SEM observations show the agglomeration of nanoparticles. The purity of the as-prepared NPs was confirmed by EDX analysis. The defect states were revealed from the photoluminescence (PL) spectra. The overall results obtained indicate that Ni-doped ZnO nanoparticles are promising candidate to fabricate nanoscale optoelectronic devices due to their wide band gap and excellent UV emission properties.