Luminescent properties of scintillator nanophosphors produced by flame spray pyrolysis (original) (raw)
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Phosphor powders elaborated by spray-pyrolysis: Characterizations and possible applications
Optical Materials, 2006
Several well-known phosphors compositions based on rare earth orthoborates, with the general formula LnBO 3 with Ln = [Y 0.95Ày Gd y Eu 0.05 ] or [Y 0.95Ày Gd y Tb 0.05 ], and the cubic oxide (Y 0.96 Eu 0.04 ) 2 O 3 have been synthesized by spray-pyrolysis (SP) and additional thermal treatments. Samples with the unique hexagonal YBO 3 type phase have been obtained. The particles are spherical, the average diameter is around 2 lm, with a relatively narrow spreading. The borate spheres are not dense: porosities are observed, but do not exhibit the core-shell aspect observed for Y 2 O 3 :Eu 3+ spheres. The emission spectra, the relative intensities, and the transient characteristics of phosphors under VUV excitation by a pure Xe gas discharge have been measured in a specially developed experimental set-up. The integrated Eu 3+ emission intensities are at least 50% higher for SP yttrium borates than for SP yttrium oxide; the decay times s 10 are 13 ± 1 msec and 4.6 ± 0.4 msec, respectively. Up to 80% efficiency of a commercial green phosphor (Zn 2 SiO 4 :Mn 2+ ), and s 10 = 15 ± 1 msec were easily achieved in spray pyrolysed Tb 3+ yttrium borates. The Gd/Y substitution and the annealing temperature have a very weak effect on the europium and the terbium luminescence efficiencies and decay times.
Journal of Physics D: Applied Physics, 2005
Y 2 O 3 : Eu and Zn 2 SiO 4 : Mn are the red and green phosphors actually used in plasma display panels. These phosphors have been prepared by spray pyrolysis synthesis and thermal post-treatments. Their optical properties in the vacuum ultraviolet (VUV) energy range have been investigated. The absorption coefficients have been extracted from electron energy loss spectroscopy. The luminescence properties of phosphors from spray pyrolysis have been characterized under UV or VUV excitations with different dedicated experimental set-ups: excitation spectroscopy, measurements of luminescence efficiencies under Hg lamp, pure Xe and Ne-Xe discharges, determinations of luminescence decay times under plasma excitation. The characteristics have been compared with those of corresponding commercial phosphors.
Journal of Aerosol Science, 2006
Nanoparticles of europium-doped yttrium oxide (Eu: Y 2 O 3 ) were synthesized by flame spray pyrolysis. The nanoparticles were separated by centrifugation into two size groups (5-60 nm and 50-200 nm), each characterized by laser induced fluorescence spectroscopy, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The fluorescence spectra, the electron diffraction pattern, and the XRD pattern of the large particles were typical of the stable cubic (Mn 2 O 3 type) phase of bulk Y 2 O 3 while those of small particles were quite different and indicated the possible presence of higher density metastable mixed phases-including monoclinic with some indication of a face-centered cubic phase. The size dependence of the particle properties could be attributable to the effect of surface free energy that elevated the internal particle pressure as size decreased. Doping with the lanthanide ion provided a new and useful diagnostic method for determining the crystal structure of flame-synthesized materials. ᭧
Nanoparticles of a doped oxide phosphor prepared by direct-spray pyrolysis
Journal of materials …, 2004
A gas-phase synthesis route based on spray pyrolysis with a residence/heating time of less than 0.1 s was designed to directly prepare Eu-doped Y 2 O 3 phosphor nanoparticles. The average size of the phosphor particles decreased from the submicron size to around 10 nm when the concentration of the starting solution was increased. By increasing the operating temperature, from 1500 to 1700°C, the submicron-particles were converted into a nano-particle phosphor, and their photoluminescence intensities at 611 nm (254-nm excitation) were greatly improved. This synthesis procedure has considerable potential for preparing a variety of doped luminescent nanoparticles without the need for post-treatment processing.
Thermoluminescence and photoluminescence characteristics of nanocrystalline LiNaSO 4 : Eu phosphor
Journal of Physics D: Applied Physics, 2003
Nanocrystalline K 2 Ca 2 (SO 4) 3 : Eu prepared by a co-precipitation method has been studied for its thermoluminescence (TL) and photoluminescence (PL) characteristics. The TL glow curve of the compound has a simple structure with a prominent peak at 406 K and a small peak at 462 K. TL sensitivity of the phosphor is found to be more than that of TLD-100 (LiF) but quite less compared to TLD-700H (LiF : Mg, Cu, P). The presence of two overlapping bands at around 400 and 450 nm in the PL emission spectra of the phosphor (both unexposed and exposed to gamma radiation) suggests the presence of Eu 2+ in the host compound occupying two different lattice sites. Moreover a reduction in TL sensitivity on decreasing the particle size (from 125 µm to 18.6 nm) gives a better understanding of the TL mechanism involved in the concerned phosphor. Fading and reusability of the phosphor are also studied and it is found that the phosphor is quite suitable for radiation dosimetry.
DEVELOPMENT OF NANOPHOSPHOR USING COMBUSTION TECHNIQUE
The luminescent material at nano-level is called a Nano-phosphor, these phosphors converts different types of energy into electromagnetic radiation. The phosphors at nano-level develops unique characteristic properties, which makes it a potential candidate for applications like Solar cell device, LEDs, Display devices.etc. Further the optical properties of nanophosphor are dependent on size and morphology which in turn depends on the synthesis technique employed. Combustion technique for synthesis of nanophosphors is simplest of all conventional synthesis techniques and involves simple equipment, short processing time, low energy, and is an effective method for the production of homogeneous nano-crystals and do not involve any intermediate decomposition process Present paper reports the synthesis of nanophosphors by combustion technique. INTRODUCTION Phosphors are luminescent materials that emit photons upon excitation by an gamma ray, UV radiations, electron or X-ray beam. They consists of an inert host lattice, and an activator, typically a 3d or 4f electron metal such as Eu2+/Eu3+, Ce3+, Tb3+, Gd3+, Yb3+, Dy3+, Sm3+, etc[1-5]. The phosphors are classified into broad band (d−f electronic transition) and narrow band (transition between the f levels) emitters. The process of luminescence involves multiple steps like, absorption of energy at the activator site, relaxation of excited site by subsequent emission of a photon, thereby finally return to the ground state. The absorption of energy in phosphors takes place either by the host lattice or by activator (dopant) ions, while the emission of energy originates mostly from the dopant ions. In order to develop phosphors with specific properties sometimes a second dopant is added to host lattice, often called sensitizers, it can be used to absorb the energy and transfer it to the main dopant. Phosphors are promising materials for field emission, plasma displays, light-emitting devices, imaging applications, in solar panels etc. In comparison to bulk ,nanostructured phosphors may have higher packing densities, low light-scattering effects and find wide applications ranging from biomedical applications to aircraft applications. Development of nanophosphors for specific applications requires which requires precise distribution of the dopands, in the material structure. Present paper reports combustion technique approach for development of nanophosphors.
Synthesis, characterization and thermoluminescence studies of Y2O3: Sm 3 nanophosphor
Na2SO4, LiNaSO4 and LiNaSO4: Eu 3+ nanophosphors were successfully synthesized by slow evaporation technique followed by calcination at 400° C. The resultant products were characterized by using powder Xray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis, scanning electron microscope (SEM) and transmission electron microscope (TEM). Doping with Li + ion stabilized the thenardite phase (Phase V) while, codoping with Eu 3+ promoted the phase transformation from stable thenardite to metastable mirabilite (Phase III) crystal structure. The average crystallite size was calculated by using Debye-Scherrer's formula and Williamson-Hall (W-H) plots. The optical energy band gap (Eg) of Na2SO4, LiNaSO4 and LiNaSO4: Eu 3+ were estimated from Wood and Tauc's relation which varies from 4.2-4.33 eV. Thermoluminescence (TL) studies were investigated by using γ-irradiation in the dose range 0.5-5 kGy at a heating rate of 5 °C s-1. A well resolved glow peaks at ~ 180 °C, ~ 150 °C and ~115 °C were recorded for Na2SO4, LiNaSO4 and LiNaSO4: Eu 3+ nanophosphors respectively. It was observed that isovalent doping of Li + served as quencher, while codoping of hypervalent Eu 3+ acted as activator to enhance the TL intensity of glow peak. In the present study, the extent of TL fading of LiNaSO4: Eu 3+ was 31 % compared to LiNaSO4 (52 %) and Na2SO4 (59 %). So, LiNaSO4: Eu 3+ phosphor might also have potential use in dosimetry. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) was estimated and the results were discussed.
Japanese Journal of Applied Physics, 2001
Y2O3:Eu phosphor particles were prepared by flame spray pyrolysis and compared with the particles prepared by general spray pyrolysis. The particles prepared by flame spray pyrolysis had a spherical and dense morphology and were finer than the particles prepared by general spray pyrolysis. Flame temperature was an important factor in the preparation of the phosphor particles by flame spray pyrolysis. To obtain Y2O3:Eu particles with a uniformly dense structure, a sufficiently high temperature to form monoclinic phase was required. Too low flame temperature generated nonspherical and hollow particles with cubic phase because the particles did not melt completely, and too high flame temperature of flame generated many nanoparticles due to evaporation. After stepwise post-treatment of as-prepared particles with monoclinic phase and the dense structure, Y2O3:Eu phosphor particles with high brightness and cubic phase were obtained. The Y2O3:Eu phosphor particles prepared by flame spray p...
Photoluminescence Properties of Ce1-xTbxMgAl11O19 Phosphor Particles Prepared by Spray Pyrolysis
Jpn. J. Appl. Phys, 1999
Spray pyrolysis method was applied to the preparation of submicron Ce 1−x Tb x MgAl 11 O 19 phosphor particles. The characteristics such as photoluminescence, crystallinity, and morphology were investigated under various preparation conditions. While the as-prepared particles by spray pyrolysis at temperature of 900 • C had amorphous phase, the particles calcined above 1400 • C had phase-pure magnetoplumbite structure, and its crystallinity increased with increasing the calcining temperature. The as-prepared particles had spherical morphology, submicron size, and narrow size distribution. The mean size of the particles increased from 0.5 to 1.4 µm when the spray solution concentration increased from 0.03 to 1.5 M. After calcination, the particles showed 545 nm green emission characteristic of Tb 3+ ions with optimum excitation at 280 nm. The maximum luminous intensity was obtained at x = 0.4. The optimum calcining temperature for good brightness was 1500 • C. Particles directly prepared by spray pyrolysis at 1500 • C show good green emission characteristics and maintain its sphericity and non-aggregation characteristics.
Combustion synthesis and photoluminescence properties of LaAlO3 nanophosphors doped with Yb3+ ions
Journal of Luminescence, 2014
Europium doped yttrium oxide (Y2O3:Eu) nanoparticles were synthesized by flame spray pyrolysis method and the effect of precursor solution on particle size, morphology and photoluminescence properties was studied. The particles were examined by using X-ray diffraction, s canning electron microscopy, and spectrophotometer. Compared with previous report, SEM shows fine and smooth structure for particles prepared from ethanol alcohol as precursor solution. The particle size can be controlled by varying precursor concentration, flame temperature and residence time. Upon excitation with 355 nm UV light, the particles show red emission and the PL intensity of particles using ethanol is 30% stronger than those using water as precursor solution. XRD spectra showed that the asprepared particles have a monoclinic structure, while annealing the particles at 1200°C convert monoclinic phase into cubic phase. The concentration quenching limit of the particles was found at 18% mol Eu.