Oxide Phosphors Research Articles

Studies on Y 2O 3:Eu phosphor with different particle size prepared by wet chemical method

Europium activated yttrium oxide phosphors were prepared by reagent simultaneous addition technique, using oxalic acid as precipitating reagent. The aim of the paper is to establish the flux influence and thermal regime on photoluminescence and morpho-structural characteristics of phosphor powders. In this respect different mineralising agents such as sodium/lithium carbonate, sodium tetraborate ans sodium pyrophosphate were used during the thermal synthesis stage. Thermal analysis, X-ray diffraction, scanning electron microscopy, infrared spectroscopy and photoluminescence measurements were used to investigate precursor and phosphor powders. The correlation between the phosphor properties and precursor quality enabled us to select the optimal synthesis conditions.

Nanosheet Seed-Layer Assists Oriented Growth of Highly Luminescent Perovskite Films

Oxide phosphors are attractive materials for various applications in optoelectronic devices due to their high chemical stability and efficient luminescent characteristics. As yet, however, the fabrication of high-quality luminescent thin films on a glass substrate remains challenging for practical implementation. Here, we report the efficient fabrication of highly oriented luminescent perovskite oxide films on a glass substrate using a monolayer film of oxide nanosheets as the seed layer. A densely packed monolayer film of Ca2Nb3O10 nanosheets was prepared by the Langmuir−Blodgett (LB) method, where hybridization of the cationic molecules and the Ca2Nb3O10 nanosheets produced stable LB films with large-area processability. Oriented thin films with a sharp and intense emission of Pr0.002(Ca0.6Sr0.4)0.997TiO3 were successfully obtained on a glass substrate modified with a seed layer. Highly luminescent transparent films are producible on inexpensive noncrystalline substrates; this approach also enables large-area processing of high-quality thin-film phosphors.

Steady-state chemiluminescence of Eu-doped yttrium oxide crystal phosphors in the catalytic reaction of hydrogen oxidation

We report on the luminescence of Eu 3+-doped yttrium oxide phosphors brought in contact with oxyhydrogen gas mixtures at temperatures much below the gas-phase ignition point. Chemical energy released in the catalytic hydrogen oxidation is passed directly to the electron subsystem of the powder and subsequently converted into the visible luminescence radiation at 2 × 10 −6 quantum yield per H 2O molecule produced. Luminescence kinetics at various conditions are investigated to reveal the constituent stages of the catalytic energy conversion process. This observation could have far-reaching consequences including possibilities for the development of original chemiluminescent light sources, and novel electrochemical energy converters.

Synthesis and Eu 3+ concentration-dependent photoluminescence of Gd 2−xEu xO 3 nanowires

The nanowire growth behavior and photoluminescence characteristics of red-emitting oxide phosphor Gd 2− x Eu x O 3 have been investigated in the function of activator (Eu 3+) concentrations ( x=0.08, 0.12, 0.16, 0.20, and 0.24). Nanowires of Gd 2− x Eu x O 3 phosphor were prepared by the dehydration of corresponding hydroxides Gd 1− x/ 2Eu x/ 2(OH) 3 obtained by the hydrothermal reaction. Highly uniform nanowires of 20–30 nm in diameter can grow up to several tens of micrometers in length. A number of defects on the surface of Gd 1.92Eu 0.08O 3 nanowires, which are induced during structural transformation from hexagonal hydroxide to cubic oxide, strongly decrease the luminescence efficiency in comparison with that of the bulk phosphor. In contrast, the photoemission intensity of nanowires is significantly improved with increasing Eu 3+ content ( x) of Gd 2− x Eu x O 3 solid solution. The highest relative emission intensity of nanowires is observed when the x value is close to x=0.20. This content is much higher than the optimal concentration of Eu 3+ ( x=0.08–0.10) for the bulk Gd 2O 3:Eu powder.

Thermally stimulated luminescence studies in combustion synthesized polycrystalline aluminum oxide

Synthesis of materials by combustion technique results in homogeneous and fine crystalline product. Further, the technique became more popular since it not only saved time and energy but also was easy to process. Aluminum oxide phosphor was synthesized by using urea as fuel in combustion reaction. Photoluminescence (PL) and thermally stimulated luminescence (TSL) characteristics of γ-irradiated aluminum oxide samples were studied. A broad PL emission with a peak at ∼ 465 nm and a pair of strong and sharp emissions with peaks at 679 and 695 nm were observed in γ-rayed samples. The PL intensity was observed to increase with increase in γ-ray dose. Two prominent and well resolved TSL glows with peaks at 210°C and 365°C were observed in all γ-irradiated Al2O3 samples. The TSL intensity was also found to increase with increase in γ-ray dose. The TSL glow curves indicated second order kinetics.

Photoluminescence and electroluminescence from Eu-activated CaAl2O4-based multicomponent oxide thin-film phosphors

Photoluminescence (PL) and electroluminescence (EL) from newly developed Eu-activated CaAl2O4 -based multicomponent oxide phosphor thin films prepared by rf magnetron sputtering are described. Yellowish green and blue emissions in PL were obtained in as-deposited and postannealed ((CaAl2O4)1−x–(BaAl2O4)x):Eu and ((CaAl2O4)1−x–(MgAl2O4)x):Eu thin films, respectively. In addition, blue emission in EL was observed from thin-film electroluminescent (TFEL) devices fabricated by using ((CaAl2O4)1−x–(BaAl2O4)x):Eu thin films postannealed at 1000°C in an Ar+H2(5%) gas atmosphere. A luminance of 3.2cd∕m2 for blue emission was obtained in a ((CaAl2O4)0.44–(BaAl2O4)0.56):Eu TFEL device driven by a 1kHz sinusoidal wave ac voltage; the blue EL emission corresponds to the CIE color coordinates of (x=0.24, y=0.13).

Melt synthesis of oxide phosphors with K2NiF4 structures: CaLa1−xEuxGaO4

In order to synthesize compounds of various Perovskite-related structures, we have utilized a novel “melt synthesis technique” for phosphors rather than the conventional solid state reaction techniques. The solid state reactions require multi-step processes of heating/cooling with intermediate grindings to make homogeneous samples. However, for the melt synthesis, it is possible to make a homogeneous sample in a single step within a short period of time (1–60 s) due to the liquid phase reaction in the molten samples, which were melted by strong light radiation in an imaging furnace. In this study, we have prepared a red-phosphor CaLaGaO4:Eu3+ which has a perovskite—related layered K2NiF4 structure. Well-crystallized CaLa1−xEuxGaO4 samples with the K2NiF4 structure have been obtained up to x = 0.25, but there was the formation of an olivine phase when x = 0.5–1.0. The red emission at 618 nm increased with the increasing value of x up to x = 0.25.

Synthesis of Green-Emitting Phosphors by Bicontinuous Cubic Phase Process

In this study, a novel approach for preparation of terbium-doped yttrium oxide phosphors (Y2O3: Tb) by using the bicontinuous cubic phase (BCP) process was reported. EDS analysis revealed the homogeneous precipitation occurred in the BCP structure. The experimental results showed that the prepared precursor powder was yttrium hydroxide with a spherical shape, primary size 30-50nm, and amorphous structure. High crystallinity phosphors with body-centered cubic structure were obtained after heat treatment above 700oC for 4h. However, the primary size of phosphors grew to 100-200nm and the dense agglomerates with a size below 1µm were formed during the calcination. The photoluminescence analysis showed that the obtained Y2O3: Tb phosphor had a strong green emitting at 544nm. The strongest emitting intensity occurred at Tb concentration of 1mol%. This study indicated that the BCP process could be used to prepare the highly efficient yttrium oxide-based green emitting phosphors.

Studies on the synthesis of europium activated yttrium oxide by wet-chemical method

Abstract Europium activated yttrium oxide phosphor powders (Y 2 O 3 :Eu 3+ ) were prepared from yttrium–europium precursors obtained by wet-chemical method. With this purpose in view, precursors were prepared using the reagent simultaneous addition SimAdd technique from yttrium–europium nitrate and chloride as rare-earth supplier and urea, ammonium oxalate, ammonium carbonate and oxalic acid as precipitating agents. Precursors, obtained under controlled concentration, temperature and pH conditions, were fired at 1200 °C in order to generate Y 2 O 3 :Eu 3+ phosphor powders. Yttrium–europium precursors and Y 2 O 3 :Eu 3+ phosphor powders were investigated by FTIR, TGA–DTA, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and photoluminescence spectroscopy (PL) in order to put in evidence the influence of the quality of yttrium–europium precursors obtained by wet-chemical method, using the SimAdd technique on the properties of Y 2 O 3 :Eu 3+ phosphor powders.

P‐125: Small Particle Size Lanthanum Cerium Terbium Phosphate (LAP) and Yttrium Europium Oxide (YEO) Phosphors for CCFL Backlight Units in LCD Displays

AbstractSmall particle, green‐emitting lanthanum cerium terbium phosphate (LAP) and red‐emitting yttrium europium oxide (YEO) phosphors have been synthesized by a scalable continuous flow precipitation method for incorporation into white triblend phosphors for high brightness, sub‐miniature CCFLs for LCD backlight units, and the emission properties have been investigated.

Highly enhanced luminescence of ZnO green phosphors by calcining ZnS with NH 4Br as additive

Zinc oxide (ZnO) phosphors with highly efficient green emission have been prepared by calcining ZnS with NH 4Br as additive in air atmosphere. The luminescent properties of as-prepared ZnO phosphors were characterized by X-ray photoelectron spectroscopy and photoluminescence. Our results reveal that the green emission is ascribed to a transition of a photo-generated electron from the localized defect centers (V o +) to a deeply trapped hole (V Zn −) within the band gap. The addition of NH 4Br enhances the luminescent emission of ZnO by promoting the formation of vacancies of both oxygen and zinc.

Cationic disorder effects in complex oxide laser materials and phosphors

A comparative analysis of the high-resolution spectra of the Nd 3+ and Pr 3+ in strontium lanthanum hexa-aluminates, charge compensated with magnesium Sr 1− x (Nd, Pr) y La x– y Mg x Al 12− x O 19, on a large composition range is presented. The spectra are mainly dependent on the composition parameter x and show two families of centers for x < 0.5 and three for x ⩾ 0.8, with distinct spectral characteristics. Based on spectral data, composition dependence and crystal structure, tentative structural models for the these centers are proposed. It is inferred that this complex picture results from the interplay between the effects determined by the anionic coordination of the centers and the perturbative effects caused by the multiple occupation of specific sites by cations of different valence.

Polymer complex solution synthesis of (YxGd1−x)2O3:Eu3+ nanopowders

Yttrium–gadolinium–europium oxide phosphors are regarded promising for many important optical applications, for example in computed tomography medical imaging and plasma displays. In this work, we investigated procedure for (YxGd1−x)2O3:Eu3+ (x= 0, 0.25, 0.5, 0.75 and 1) nanopowder synthesis using polymer complex solution method (PCS) based on polyethylene glycol fuel (PEG). Structural and emission properties of nanopowders are investigated by X-ray diffraction, electron microscopy and photoluminescence measurements. We obtained particles of about 40nm having excellent structural ordering in cubic bixbyte type of structure – space group Ia3 for all mixed oxide compositions. Luminescence emission measurements exposed characteristic transition of the trivalent europium ion incorporated into insulating host. 5D1 and 5D0 decay time values are measured to obtain information on different kinetic processes occurring for these two emitting levels.

Comparative Study of Ga2O3 : Dy3 + Phosphors Prepared by Three Methods

Trivalent dysprosium -activated β-gallium oxide phosphors were synthesized by solid-state (SS), coprecipitation (CP), and citrate gel (CG) methods, respectively. The resulting phosphors were well characterized by X-ray diffraction, field-emission scanning electron microscopy (FESEM), and by photoluminescence and cathodoluminescence spectra. The phosphors prepared by different methods show different luminescence properties under the excitation of UV and low-voltage cathode rays. There exists an energy transfer from the host lattices to , and the energy transfer efficiency was higher in the CG-derived phosphors than those of the SS- and CP-derived phosphors. Factors influencing the intensity of luminescence and the energy transfer efficiency from host to in phosphors were investigated in detail. It is shown that the CG method is the most respected process for the preparation of phosphors.

Synthesis and Characterizations of Strontium Cerium Oxide Phosphor

A new Strontium Cerium Oxide (Sr4Ce2O7) blue phosphor with, orthorhombic structure was synthesized via standard solid state reaction method using strontium oxide and cerium oxide as a raw materials. The samples were characterized by Thermo analytical techniques (TG, DTA, and DTG), Fourier transformation infrared (FTIR) spectroscopy, Raman spectroscopy, and Photoluminescence studies at room temperature. In excitation spectra two excitation bands were located at 361 and 391 nm respectively. The emission spectrum was a broad band peaking at 474 nm, which was suitable for the doping of rare earth ions.

Fabrication of submicron-sized oxide phosphors and their spectroscopic properties

Molten salt synthesis procedure, homogeneous precipitation with urea and Li 2 SO 4 -flux aided routes are presented as interesting fabrication methods for making oxide luminescent materials. The properties of the powders made using these techniques are presented and analyzed. Emphasis is put on spectroscopic characterization of the products.

A Versatile Scheme for Preparing Single‐Phase Yttrium Oxysulfate Phosphor.

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Radiation detector based on liquid crystal light valve for large-area imaging applications

Currently most large-area radiation detectors rely on the use of a phosphor screen and an optical sensor. In such conversion process, there will be signal loss due to inefficiencies in coupling between phosphor screen and later light-detection components. This paper presents a radiation detector based on X-ray induced light transmittance of liquid crystal (LC) as a function of radiation. Our detector incorporates a europium-doped gadolinium oxide (Gd 2O 3:Eu) phosphor and an amorphous selenium (a-Se)-coupled LC light valve. The Gd 2O 3:Eu is synthesized using a low-temperature solution–combustion method, and the optical properties of the Gd 2O 3:Eu are investigated as a function of a sintering temperature. The transmission–voltage ( T– V) curve and the optical response of the detector are also investigated. Our experimental results show good T– V characteristics of the LC, switching between 12% and 86% transmission. The radiation dose is also presented in this work. The results show that our detector can operate at low X-ray dose and, therefore, a promising application is the medical-imaging detector.

Optical properties of doubly doped ZnO phosphors co-activated with lithium ions

Time-resolved laser-induced optical properties of didymium (a mixture of neodymium and praseodymium) doped zinc oxide phosphors have been studied using nitrogen laser as an excitation source at room as well as at liquid nitrogen temperatures. A comparison of optical properties (oscillator strength and dipole-moment) at room temperature and liquid nitrogen temperature has been done and is reported in this article. It is found that oscillator strength and dipole-moment values for doped ZnO are increasing with decreasing temperature. The increasing trend of the optical parameters obtained at liquid nitrogen temperature of the doped phosphors indicates increase in efficiency.

Synthesis, characterization and upconversion emission properties of the nanocrystals of Yb 3+/Er 3+-codoped YF 3–YOF–Y 2O 3 system

Nanocrystalline Yb 3+, Er 3+-codoped fluoride (YF 3), oxyfluoride (YOF), and oxide (Y 2O 3) phosphors have been synthesized by a facile pyrolysis of a yttrium trifluoroacetate precursor. YF 3, YOF and Y 2O 3 nanoparticles were demonstrated to be good host materials for lanthanides. Varied hosts led to different optical properties. Red, green, and blue up-conversion (UC) was observed upon excitation in the NIR spectral range in all synthesized compounds. The UC mechanisms were also analyzed.