Europium Activated Yttrium Oxide Research Articles

Combustion synthesis and characterisation of Eu<SUP align="right">3+</SUP>-activated Y<SUB align="right">2O<SUB align="right">3 red nanophosphors for display device applications

Europium activated yttrium oxide red phosphors have gathered more attention because of their good luminescent characteristics, acceptable atmospheric stability, reduced degradation under applied voltages, and lack of hazardous constituents. In order to achieve improved luminescent properties of Y2O3:Eu3+, the synthetic methods are playing an important role. In the present study, Eu3+ (2 mol %) doped Y2O3 nanophosphors were synthesised by the facile nitrate citrate gel combustion method at relatively low temperature and shorter duration (700°C for 2 h). Further samples were characterised by powder X-ray diffraction (XRD) technique. The morphology and particle size of the phosphors were studied by scanning electron microscope (SEM), UV reflectance spectroscopy and Raman spectroscopy. The photoluminescence measurements of the Y2O3:Eu3+ particles showed red emission peaks at 610-612 nm (5D0 → 7F2). CIE chromaticity diagram and CCT calculations confirmed that these nanophosphors can act as a red component in the fabrication of white light emitting diodes (WLEDs) for display and other optical device applications.

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.

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.

Synthesis and characterisation of europium activated yttrium oxide fine powders

In order to prepare fine powders of red emitting Y 2O 3:Eu phosphors, the reagent simultaneous addition ( SimAdd) technique was developed and the influence of some preparative conditions on morpho-structural and optical properties of phosphors was studied. There was revealed that the precipitating reagent type and the pH of the precipitation medium influence on the photoluminescence (PL) properties as well as on the microstructure and morphology of phosphor particles. The SimAdd-technique enables us to prepare fine powders (<1 μm) of Y 2O 3:Eu phosphors with relatively good PL performances to be used in modern optoelectronic devices.

Synthesis and luminescent performances of some europium activated yttrium oxide based systems

Phosphors based on solid solutions of Y2O3-La2O3-Gd2O3 and Y2O2S-La2O2S-Gd2O2S and YVO4-GdVO4 doped by Eu 3+ were synthesized by different methods. The influence of a matrix composition and an activator concentration on phosphors light-emitting performances is described in order to propose the optimized synthesis conditions. Europium-doped yttrium, lantha- num and gadolinium oxysulphides phosphors show higher CL-efficiency at low applied voltages than oxides ones. The presented results confirm that europium doped solid solutions of Y-Gd-La oxides, oxysulphides and vanadates are perspective for PL and CL application in the display manufacture. � 2004 Elsevier B.V. All rights reserved.

Properties and cathodoluminescence of Y2O2S:Eu thin films

Abstract— Europium‐activated yttrium oxysulfide thin films were fabricated by electron‐beam deposition of Y2O2S:Eu with consequent annealing in an H2S/Ar gas mixture. Transformations in film composition and surface morphology as well as corresponding changes in the optical, photoluminescent, and cathodoluminescent properties were studied and will be discussed. It is shown that 248‐nm laser irradiation of heat‐treated films improves cathodoluminescence by as much as 30%, supposedly due to annealing. The developed phosphor films have a luminance comparable to that of annealed europium‐activated yttrium oxide films and improved color properties (CIE color coordinates: x = 0.624, y = 0.329), and are suitable for display and optoelectronics applications.

Enhancement of Luminous Intensity of Spherical Y 2 O 3 : Eu Phosphors Using Flux during Aerosol Pyrolysis

Spherical phosphors of trivalent europium-activated yttrium oxide for flat panel displays were prepared from precursor solutions, which included various fluxes, by aerosol pyrolysis. The effects of the flux on the properties of prepared particles were investigated thoroughly by optical spectroscopy, X-ray spectroscopy, and scanning electron microscopy. To enhance the luminescence intensity of the spherical phosphors, the several fluxes, concentration of each flux, and synthetic temperature were examined and optimized by photoluminescence and cathodoluminescence measurements. The luminescent and physical characteristics of the prepared particles were sensitively influenced by the added flux. Particularly, the spherical phosphors produced from precursors incorporating sodium-based fluxes had relatively higher luminous efficiency. The red emission intensity of the spherical phosphor was increased by about 30% by the addition of compared with the intensity of alone. © 2003 The Electrochemical Society. All rights reserved.

Epitaxial growth of Y2O3:Eu thin films on LaAlO3

We report the epitaxial growth of europium-activated yttrium oxide (Y2O3:Eu) (001) thin films on LaAlO3 (001) using laser ablation deposition at a substrate temperature of 775 °C and 10 Hz pulse repetition rate. The orientation relationship between the films and the substrates is [110]Y2O3∥[100]LaAlO3 and [−110]Y2O3∥[010]LaAlO3 which results in a lattice mismatch of only 0.8%. Transmission electron microscopy (TEM) of the films reveals the single crystalline Y2O3:Eu thin film to contain small pores. Scanning transmission electron microscopy (STEM) imaging of the films shows the substrate always terminates with the Al sublattice. Moreover, the STEM reveals that no precipitates of Eu had formed in the films.

Relationship Between Structure and Luminescent Properties of Epitaxial Grown Y2O3:Eu Thin Films on LaAlO3 Substrates

AbstractCathodoluminescence images of individual pores have been obtained at nanometer resolution in europium-activated yttrium oxide (Y2O3:Eu) (001) thin films, epitaxially grown on LaA1O3 (001) substrates. Comparison with Z-contrast images, obtained simultaneously, directly show the “dead layer” to be about 5 nm thick. This “dead layer” is the origin of the reduced emission efficiency with increasing pore size. Pore sizes were varied by using different substrate temperatures and laser pulse repetition rates during film growth. These films are epitaxially aligned with the substrate, which is always Al terminated.

Luminescent Characteristics of Pulsed Laser Deposited Epitaxial Eu-Doped Y2O3 Films

AbstractThe growth, structural and cathodoluminescent (CL) properties of europium activated yttrium oxide (Eu:Y2O3) thin films are reported. The Eu:Y2O3 films were grown in-situ using a pulsed laser deposition technique. Our results show that Eu:Y2O3 films can grow epitaxially on (100) LaAlO3 substrates under optimized deposition parameters. The epitaxial growth of Eu:Y2O3 films on LaAlO3, which has a lattice mismatch of ∼ 60 %, is explained by matching of the atom positions in the lattices of the film and the substrate after a rotation. CL data from these films are consistent with highly crystalline Eu:Y2O3 films with an intense CL emission at 611 nm.

Modeling of Cathodoluminescence and Photoluminescence Properties of Pulsed Laser-Deposited Europium-Activated Yttrium Oxide thin Film Phosphors

ABSTRACTEuropium-activated yttrium oxide (Eu:Y2O3) thin films were deposited on (100) silicon and (0001) sapphire substrates using 248 nm KrF pulsed laser. To investigate the effect of the Eu:Y2O3 film roughness on cathodoluminescence (CL) and photoluminescence (PL) properties, the substrate surfaces with various roughnesses were used. The roughness was found to play an important role in determining CL and PL brightness of the Eu:Y2O3 films. The improvement in brightness by increasing the film roughness is due to increase in total portion of light that escapes from the surface of the phosphor film. A model has been proposed which supports strongly this explanation. Our results show that depositions with slower growth rate and lower laser energy are more important parameters than increasing the roughness to improve CL brightness of the Eu:Y2O3 thin film phosphors.

Modeling of Cathodoluminescence and Photoluminescence Properties of Pulsed Laser-Deposited Europium-Activated Yttrium Oxide Thin Film Phosphors

ABSTRACTEuropium-activated yttrium oxide (Eu:Y2O3) thin films were deposited on (100) silicon and (0001) sapphire substrates using 248 nm KrF pulsed laser. To investigate the effect of the Eu:Y2O3 film roughness on cathodoluminescence (CL) and photoluminescence (PL) properties, the substrate surfaces with various roughnesses were used. The roughness was found to play an important role in determining CL and PL brightness of the Eu:Y2O3 films. The improvement in brightness by increasing the film roughness is due to increase in total portion of light that escapes from the surface of the phosphor film. A model has been proposed which supports strongly this explanation. Our results show that depositions with slower growth rate and lower laser energy are more important parameters than increasing the roughness to improve CL brightness of the Eu:Y2O3 thin film phosphors.

Improved luminescence properties of pulsed laser deposited Eu:Y2O3thin films on diamond coated silicon substrates

Europium activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in situ on (100) bare and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared using hot filament chemical vapor deposition of diamond onto silicon. Photoluminescence brightness from Eu:Y2O3 films grown at 700 °C on diamond-coated silicon substrates was about twice that of films on bare silicon, and reached 80% of the brightness of powders. The higher brightness from Eu:Y2O3 film on diamond-coated silicon substrates is attributed to reduced internal reflections from the Eu:Y2O3 film surface, which results from the roughness of the diamond layer.

Growth and characterization of Y 2O 3:Eu 3+ phosphor films by sol-gel process

Phosphor films play an important role in high resolution display devices, remote thermometry, gas sensors, etc. These films were grown by various methods. In the present paper, europium activated yttrium oxide (Y 2O 3:Eu) phosphor films were deposited from yttrium hydroxide gels by dip and dry and spin coating methods. XRD of the films, calcinated at 700 to 1000°C showed all the prominent lines of the yttria phase. From SEM studies, it was observed that these films were uniform and defect free. Luminescence intensity was comparable with that of Y 2O 3:Eu powder samples.

Preparation and Characterization of Fine‐Grain Yttrium‐Based Phosphors by Sol‐Gel Process

The preparation, characterization, and luminescence of yttrium‐based phosphors such as europium activated yttrium oxide (red) and terbium activated yttrium aluminate (green) by sol‐gel processes is presented. The sols of yttrium hydroxide were synthesized by various routes. It was found that the sols obtained through an ion exchange column were pure and without any cross contamination. The aluminum hydroxide sols were prepared from aluminum chloride and ammonium hydroxide. A number of gel samples were synthesized by mixing stoichiometric amounts of and to obtain , and with trace amounts of rare earth, gels as activators. These gels were dried at 30 to 80°C. From the thermal analyses, all possible temperature transitions were identified. After calcination with different temperatures and durations, these phosphor powder samples were characterized for crystallization, spectral energy distribution, and morphology. The samples synthesized at lower temperatures (< 1000°C) were fully crystallized. The average particle size of these phosphors was in the range of 1 to 2 μm. From the luminescence spectral data, all possible transitions corresponding to in , and corresponding to in yttrium‐aluminum‐garnet (YAG) matrices were identified. The luminescent efficiencies of these phosphors were comparable with commercially available phosphors having larger particles (6 to 10 μm). The preparation of other yttrium‐based phosphors such as and (RE = Tm, Ce, Tb, and Eu) and the luminescence studies of these materials at low voltages for field emission display applications are in progress.

Electronic structure and optical properties of europium-activated yttrium oxide phosphor.

The electronic structure and optical properties of a red phosphor, ${\mathrm{Y}}_{2}$${\mathrm{O}}_{3}$:Eu, have been studied using the first-principles molecular-orbital and band-structure methods. Using the calculated one-electron energy levels, several properties of the host material and properties of the phosphor based on host-impurity interactions have been explained. However, it has been found that the luminescence properties of ${\mathrm{Eu}}^{3+}$ require the spin-orbit effects to be included in the computational methods.

Thermally stimulated luminescence of luminophors activated by rare-earth metals

In the last i0 years three-component mixtures of luminopors activated by rare-earth metals have found increasingly greater application in the production of luminescent lamps [1-3]. Mixtures of luminophors based on barium--magnesium--euorpium and magnesium-cerium--terbium aluminates, as well as yttrium oxide activated by europium, which were proposed in [4, 5], are the most efficient and stable during service in lamps. Their main physicochemical and service characteristics in light sources were presented in [4-10]. The work in [11-13] was devoted to the investigation of the thermally stimulated luminescence (TSL) of europium-activated yttrium oxide under the action of the cathode, x-ray, and ultraviolet emission of a high-pressure mercury quartz lamp. However, their TSL under excitation by the resonant emission of the discharging of luminescent lamp has scarcely been studied.