Eu Phosphor Particles Research Articles

Micronization of KSrPO4:Eu and KBaPO4:Eu phosphor particles for white light-emitting diodes by pulsed laser ablation in liquid

Eu2+-doped KSrPO4 and KBaPO4 phosphors have attracted much attention for white light-emitting diode (W-LED) applications. In this study, pulsed laser ablation in liquid (PLAL) was carried out in order to micronize fatally aggregated particles of KSrPO4:Eu2+ and KBaPO4:Eu2+ by H2 reduction under a high temperature to a suitable size for the W-LED applications. The diameter of aggregated particles after H2 reduction (approximately 2.0 μm) was successfully decreased to about half by PLAL, which is suitable for the W-LED applications. Furthermore, PLAL was found to maintain the luminescence intensity as high as before PLAL, indicating no contamination of impurities from processing devices. In addition, PLAL was also applied to KSrPO4:Eu3+ and KBaPO4:Eu3+ before H2 reduction and found not only to maintain the luminescence intensity but also to reduce the valence of Eu ions (Eu3+ → Eu2+). These results show not only the effectiveness of the micronization but also the feasibility of laser induced photo reduction of Eu ions in phosphate crystals for the W-LED applications by PLAL.

Effect of size variation and gamma irradiation on thermoluminescence and photoluminescence characteristics of CaSO4:Eu micro- and nanophosphors

Microcrystalline CaSO4:Eu phosphor particles prepared by the acid re-crystallization method were grinded by ball-milling method and reduced to small particles of sizes ~50 nm, 200 nm, 400 nm and 5 μm. For comparison, nanocrystalline CaSO4:Eu phosphor of size ~20 nm was also prepared by chemical coprecipitation method. The recorded photoluminescence emission and excitation spectra revealed that Eu is doped in CaSO4:Eu in the form of Eu2+ and Eu3+ in all the samples of microcrystalline and nanocrystalline powders. The samples of CaSO4:Eu, with different particle sizes, were irradiated with gamma rays over a range of doses ranging from 1 Gy to 100 kGy. The results of characterization by thermoluminescence method show that the intensity of the thermoluminescence peak for a given dose of gamma-rays decreases with the decrease in the particle size of CaSO4:Eu. A comparison shows that CaSO4:Eu of size 50 nm exhibited linear response between the thermoluminescence peak and the gamma-ray dose in the range of 1 Gy–10 kGy. This phosphor can, therefore, be used for the measurement of gamma ray dose in medical and industrial applications. A comparative study also showed that the sensitivity of thermoluminescence to gamma ray dose for the nanophosphor prepared by the ball milling technique is better than that of the nanophosphor prepared by chemical co-precipitation method.

In situ immobilization of YVO4:Eu phosphor particles on a film of vertically oriented Y2(OH)5Cl·nH2O nanosheets.

A heterostructured photoluminescence 'turn-off' film was developed using vertically oriented LYH:Eu nanosheets as a partial sacrificial layer for isolated YVO4:Eu3+ nanophosphor layers and was used for the convenient detection and removal of Cu2+ ions with excellent sensitivity and recyclability.

Controlled synthesis and photoluminescence behaviors of Lu2O3:Eu and Lu2O2S:Eu phosphor particles

Rounded Lu2O3:Eu phosphor powder with an average particle size of ~90 nm was synthesized via pyrolyzing the precipitation precursor prepared by a facile co-precipitation technique using ammonium hydrogen carbonate (AHC) as the precipitant, followed by direct sulfurization at 950 °C under a reducing atmosphere to yield two-dimensional plate-like Lu2O2S:Eu phosphor with a thickness of several micrometers. The photoluminescence (PL) behaviors of the two resultant phosphor powders were systematically investigated. The oxide and oxysulfide phosphors displayed characteristic red-light emissions of Eu3+ at ~612 and 630 nm, respectively, which were derived from 5D0,1→7FJ (J = 0, 1, 2, 3) transitions of Eu3+. The luminescence quenching types of both phosphors were dominated by exchange interactions and the optimum Eu3+ concentrations were found to be ~2.5 at.% for Lu2O3:Eu and ~1.0 at.% for Lu2O2S:Eu. The oxysulfide phosphor had a PL intensity ~3.5 times stronger than the oxide powder. The Lu2O3:Eu and Lu2O2S:Eu phosphors had CIE color coordinates of (0.65, 0.35) and (0.61, 0.39), which fall into the categories of reddish-orange and orange colors, respectively. A shorter fluorescence lifetime (~602.9 μs) and a higher percentage of excitation absorption (η ≈ 71%) were observed for the oxysulfide relative to those of the oxide (~2.4 ms and η ≈ 35%).

Effects of Y/Gd Ratio and Boron Excess on Vacuum Ultraviolet Characteristics and Morphology of (Y,Gd)BO3:Eu Phosphor Particles Prepared by Spray Pyrolysis

(Y1-xGdx)BO3:Eu (0≤x≤1) phosphor particles were prepared by spray pyrolysis. The optimal amount of boric acid for the high photoluminescence intensity of there particles differed depending on the molar ratio of Y to Gd. With decreasing Y/Gd molar ratio, an increasing amount of excess boric acid was required. The difference in excess quantity of boric acid, which was demanded for the highest photoluminescence intensity according to the Y/Gd ratio, influenced the morphology and mean size of the (Y,Gd)BO3:Eu phosphor particles. The (Y1-xGdx)BO3:Eu (0≤x≤1) phosphor particles had a regular morphology. The mean sizes of the GdBO3:Eu and YBO3:Eu phosphor particles were 1.4 and 1 µm, respectively. The high reactivity of boron and yttrium components produced YBO3:Eu phosphor particles with high photoluminescence intensities by spray pyrolysis using a spray solution with a stoichiometric amount of boric acid.

Morphology and luminescence of (Y,Gd)BO 3:Eu phosphor particles prepared by urea-assisted spray pyrolysis

Red phosphor of (Y,Gd)BO 3:Eu was prepared by urea-assisted spray pyrolysis through the polymeric reaction. The synthetic route was adopted to enhance optical characteristics of spherical phosphors. In particular, the phosphors synthesized with urea showed quite different morphology and luminous efficiency compared to those without urea. It was certain that precursor with the urea had a positive effect on the particle formation and the surface status of particles. To enhance the luminescence intensity and mechanical characteristics, synthesizing conditions were investigated and optimized, which included the concentration of urea, the synthesis temperature, and the activator concentration. As a result, the red emission intensity of the spherical (Y,Gd)BO 3:Eu phosphor obtained a remarkable improvement by optimal urea-assisted spray pyrolysis, compared to that by conventional solid-state technique.

Photoluminescence Characteristics of Gd 2Mo 3O 9:Eu Phosphor Particles by Solid State Reaction Method

Eu 3+-doped Gd 2Mo 3O 9 was prepared by solid-state reaction method using Na 2CO 3 as flux and characterized by powder X-ray diffractometry. According to X-ray diffraction, this material belonged to a tetragonal system with space group I4 1/ a. The effects of flux content and sintering temperature on the luminescent properties were investigated with the emission and excitation spectra. The results showed that flux content and sintering temperature had effects on the luminescent properties, the optimized flux content and the best temperature was 3% and 800°C, respectively. The excitation and emission spectra also showed that this phosphor could be effectively excited by C-T band (280 nm), ultraviolet light 395 nm and blue light 465 nm. The wavelengths at 395 and 465 nm were nicely fitting in with the widely applied output wavelengths of ultraviolet or blue LED chips. Integrated emission intensity of Gd 2Mo 3O 9: Eu was twice higher than that of Y 2O 2S:Eu 3+ under 395 nm excitation. The Eu 3+ doped Gd 2Mo 3O 9 phosphor may be a better candidate in solid-state lighting applications.

Formation of BaMgAl10O17:Eu Phosphor Particles with Spherical Shape and Filled Morphology in the Flame Spray Pyrolysis

Fine-sized, spherical BaMgAl10O17:Eu2+ phosphor particles with filled morphologies were prepared by flame spray pyrolysis. Precursor particles prepared by flame spray pyrolysis at a low-temperature diffusion flame and a short particle residence time within the diffusion flame were of large size and had hollow structures. On the other hand, precursor particles prepared at optimum preparation conditions were fine sized, had filled structures, and narrow size distributions. The melting of large-sized intermediate particles with hollow structures within the high-temperature diffusion flame formed fine-sized, spherical precursor particles with filled structures. The BaMgAl10O17:Eu2+ phosphor particles prepared by flame spray pyrolysis at optimum preparation conditions were fine-sized and had regular morphologies after post-treatment at 1400°C. The mean size of the BaMgAl10O17:Eu2+ phosphor particles was 1.0 μm. The photoluminescence intensity of fine-sized, spherical BaMgAl10O17:Eu2+ phosphor particles with filled structures was higher than that of large-sized phosphor particles with hollow structures excited by the vacuum ultraviolet light at the wavelength, 147 nm.

Effect of Boric Acid Flux and Drying Control Chemical Additive on the Characteristics of Y2O3:Eu Phosphor Particles Prepared by Spray Pyrolysis

Y2O3:Eu phosphor particles with a spherical shape, a fine size, and high brightness under vacuum ultraviolet (VUV) illumination were prepared by spray pyrolysis. The polymeric precursors were needed to modify the spray solution to prepare spherical particles. The use of only flux with the polymeric precursors did not produce dense and spherical Y2O3:Eu particles; that is, the produced particles were very porous. The addition of both a drying control chemical additive (DCCA) and boric acid to a spray solution containing polymeric precursors was found to produce Y2O3:Eu phosphor particles with a dense structure while maintaining the spherical morphology. According to X-ray diffraction (XRD) analysis, the DCCA induced an enhancement of crystallinity. The use of boric acid flux improved the photoluminescence (PL) intensity under VUV illumination. In addition, the use of both boric acid flux and a DCCA with polymeric precursors further improved the PL intensity owing to the enhancement of the morphology and the crystallinity.

Size Dependence of the Photo- and Cathodo-luminescence of Y2O2S:Eu Phosphors

Y 2 O 2 S:Eu phosphors were synthesized via solid-state reactions. Y 2 O 2 S:Eu phosphor particles of various sizes were obtained by varying the firing temperature and firing time. The photoluminescence properties of these Y 2 O 2 S:Eu phosphors were examined. In addition, the cathodoluminescence properties of the Y 2 O 2 S:Eu phosphors were examined for applied voltages of 3-8 kV. The relationship between the luminescence intensity and particle size of the Y 2 O 2 S:Eu phosphors was investigated. The photoluminescence and cathodolurninescence of the Y 2 O 2 S:Eu phosphors are affected differently by variations in particle size.

Morphology Control of Gd2O3:Eu Phosphor Particles with Cubic and Monoclinic Phases Prepared by High-Temperature Spray Pyrolysis

Gd2O3:Eu phosphor particles with cubic and monoclinic phases were directly prepared by high-temperature spray pyrolysis from aqueous, polymeric precursor and colloidal solutions. The colloidal solution with nanosized silica was effective for the preparation of Gd2O3:Eu phosphor particles with a cubic phase, a high photoluminescence intensity and a good morphology. The phosphor particles prepared from colloidal solutions with nanosized silica obtained by hydrolysis had a small size, a narrow size distribution, a spherical shape and a filled morphology. The optimum doping concentration of nanosized silica particles was 0.5 wt % of the product particles. The phosphor particles prepared by spray pyrolysis from colloidal solutions at temperatures below 1580 °C had the photoluminescence spectrra of the cubic phase and a maximum photoluminescence intensity at a temperature of 1560 °C.

Effect of preparation temperature on the characteristics of Eu-doped borate phosphor particles in the spray pyrolysis

Eu-doped gadolinium borate (GdBO 3:Eu) phosphor particles with fine size and uniform morphology were prepared by spray pyrolysis. The effects of the preparation temperatures on the characteristics of the GdBO 3:Eu phosphor particles prepared by spray pyrolysis were analyzed. The precursor particles obtained at preparation temperatures below 1400 °C had hollow and porous inner structures. On the other hand, the precursor particles obtained at preparation temperature of 1600 °C had dense structure and uniform morphologies. The precursor particles with glass phases were formed at high-preparation temperatures above 1400 °C. The precursor particles prepared at preparation temperature of 1400 °C turned into GdBO 3:Eu phosphor particles with fine size and regular morphology after post-treatment. The GdBO 3:Eu phosphor particles prepared from the precursor particles obtained at a preparation temperature of 1400 °C had the maximum photoluminescence intensity, which was similar to that of the commercial (Y,Gd)BO 3:Eu phosphor particles.

The enhancement of photoluminescence characteristics of Eu-doped barium strontium silicate phosphor particles by co-doping materials

Green light emitting (Ba,Sr) 2SiO 4:Eu phosphor particles with high photoluminescence intensity under long wavelength ultraviolet (UV) were prepared by spray pyrolysis from colloidal spray solution. Yttrium, cerium and holmium components were introduced as co-doping materials to improve the photoluminescence characteristics of (Ba,Sr) 2SiO 4:Eu phosphor particles in the spray pyrolysis. The photoluminescence intensities of co-doped (Ba,Sr) 2SiO 4:Eu phosphor particles were about 120∼143% of (Ba,Sr) 2SiO 4:Eu phosphor particles without co-dopant. The highest photoluminescence intensity was achieved when the doping concentration of yttrium was about 1.7 times of the doping concentration of europium. The photoluminescence intensity of the sieved phosphor particles using 20 μm sieve was comparable to that of the original (Ba,Sr) 2SiO 4:Eu phosphor particles.

Gd2O3:Eu phosphor particles prepared from spray solution containing boric acid flux and polymeric precursor by spray pyrolysis

Abstract Micron size Gd2O3:Eu phosphor particles with spherical shape and dense morphology were prepared from spray solution containing boric acid, citric acid and polyethylene glycol by spray pyrolysis. Boric acid used as flux material was effective in improving the photoluminescence intensity of micron size Gd2O3:Eu phosphor particles prepared by spray pyrolysis. Boric acid did not affect on the morphology of the phosphor particles prepared from spray solution containing citric acid and polyethylene glycol after post-treatment at high temperature. The optimum content of boric acid in the preparation of Gd2O3:Eu phosphor particles from spray solution containing polymeric precursors by spray pyrolysis was 1 wt.%. The optimum post-treatment temperature of Gd2O3:Eu phosphor particles showing the maximum photoluminescence intensity was 1050 °C. The Gd2O3:Eu phosphor particles post-treated at 1050 °C had complete spherical shape, non-aggregation characteristics and high crystallinity. The photoluminescence intensity of the Gd2O3:Eu phosphor particles prepared from spray solution containing polymeric precursors and boric acid flux was 149% of the phosphor particles prepared from spray solution without polymeric precursor and boric acid flux.

Effect of surface area and crystallite size on luminescent intensity of Y2O3:Eu phosphor prepared by spray pyrolysis

The luminescent intensity of Y2O3:Eu phosphor prepared by spray pyrolysis was monitored as a function of the surface area and crystallite size. In order to control the surface area or the crystallite size, some organic additives and flux materials were introduced in the spray solution. The reduction of surface area, which was achieved by only controlling the quantity of the organic additive, was found to be helpful for the improvement of luminescent intensity of Y2O3:Eu particles. The addition of Li2CO3 flux to the spray solution with the organic additive of 0.3 M enlarged the surface area of Y2O3:Eu particles as a consequence of the reduction of particle size. Then, the increase of surface area did not lower the luminescent intensity of Y2O3:Eu phosphor particles since the added Li2CO3 flux increased the crystallinity, simultaneously. It was found that the Y2O3 particles with larger crystallite size had higher photoluminescence regardless of the surface area. Therefore, we concluded that the crystallinity is more important factor than the surface area and increasing the crystallite size is essentially needed to enhance the luminescent intensity of Y2O3 phosphor prepared by spray pyrolysis.

Formation mechanisms and morphology dependent luminescence properties of Y 2O 3:Eu phosphors prepared by spray pyrolysis process

Y 2O 3:Eu phosphors were prepared by a spray pyrolysis process followed by post annealing. Morphology control of Y 2O 3:Eu phosphor particles in the spray pyrolysis process was attempted by using citric acid (CA) and polyethylene glycol (PEG) as additives in the spray precursors. Three different morphologies of Y 2O 3:Eu phosphor particles, viz. smooth spheres, rods and flakes, were obtained in the presence of PEG with different molecular weights or without the presence of PEG, respectively. Possible mechanisms for the formation of Y 2O 3:Eu particles with the different morphologies have been proposed. It is shown that the spherical Y 2O 3:Eu phosphors have higher photoluminescent intensity than those with other morphologies.

Densification and Photoluminescence Improvement of Y[sub 2]O[sub 3] Phosphor Particles Prepared by Spray Pyrolysis

Spray pyrolysis was used to prepare high luminous Y 2 O 3 :Eu phosphor particles with spherical shape. In this work, we introduce a simple but effective preparation strategy for enhancing the photoluminescence intensity of Y 2 O 3 :Eu particles. The key idea was the solution technique used to densify the porous structure and simultaneously enhance the crystallinity of Y 2 O 3 :Eu particles. When the yttrium nitrate solution was modified using the organic additive, the nonhollow particles could be obtained but they were very porous and the luminescence intensity was not improved. To solve this drawback, we used a drying control chemical additive (DCCA) as a secondary additive. It was found that the surface area was greatly reduced and the crystallite size was increased by the use of DCCA. As a result, the densified Y 2 O 2 :Eu particles showed great improvement in the photoluminescence intensity.

Nano-sized Y 2O 3:Eu phosphor particles prepared by spray pyrolysis

Y 2O 3:Eu phosphor particles with nano-sized and non-aggregation characteristics were prepared by spray pyrolysis using spraying solution containing polymeric precursors and Li 2CO 3 flux material. The post-treated phosphor particles with fine size and high brightness were ball milled to reduce the aggregation degree of the nano-sized Y 2O 3:Eu phosphor particles. The mean particle size, morphology, and brightness of Y 2O 3:Eu phosphor particles were strongly affected by contents of the additives and post-treatment temperature. The Y 2O 3:Eu phosphor particles prepared from the solution containing 0.3 M citric acid, 0.3 M ethylene glycol and 5 wt.% Li 2CO 3 had fine size and good morphology after post-treatment. The Y 2O 3:Eu phosphor particles post-treated at 1000 °C for 3 h had the mean size of 300 nm. Nano-sized Y 2O 3:Eu phosphor particles prepared by spray pyrolysis had similar photoluminescence intensity to the micron-sized Y 2O 3:Eu commercial product prepared by solid state reaction method. The Y 2O 3:Eu phosphor particles had aggregation-free and regular morphology characteristics even after 30 min ball milling process.

Red-Emitting Phosphor Particles with Spherical Shape, Dense Morphology, and High Luminescent Efficiency under Ultraviolet

Gd2O3:Eu phosphor particles of spherical shape, filled morphology, and high brightness were prepared by large-scale spray pyrolysis. The morphology control of Gd2O3:Eu particles was attempted by adding organic precursors in a spray solution. The influence of chain length of organic additives and introduction of esterification reaction within the droplet on the morphological and luminescent characteristics of Gd2O3:Eu particles was studied. The particles prepared from aqueous solution with no organic additive showed the hollow and porous shell structure and poor brightness, while those particles prepared from solutions with only polyethylene glycol (PEG) exhibited relatively filled structure and high brightness. The longer the chain length of added PEG is, the better morphological and luminescence characteristics the particles showed. The introduction of esterification reaction within the droplet by adding citric acid (CA) and ethylene glycol (EG) or PEG with various molecular weight enhanced the morphological characteristics and significantly improved photoluminescence characteristics regardless of chain length of PEG. The particles prepared from solution containing 0.1 M CA and 0.1 M PEG (M.W. 1500) showed the maximum photoluminescence intensity, which was 148% that of commercial product.

The synthesis of (Y1-xGdx)2O3:Eu phosphor particles by flame spray pyrolysis with LiCl flux

(Y1-xGdx)2O3:Eu phosphor particles with dense morphology were prepared by flame spray pyrolysis and the effect of LiCl flux on the crystallinity, morphology, and photoluminescence characteristics of the particles was investigated. All as-prepared particles had monoclinic phase regardless of flux and had different luminescence characteristics from those of commercial Y2O3:Eu particles of cubic phase. The addition of LiCl flux reduced the post-treatment temperature by 300 °C for phase transformation from the monoclinic phase to the cubic phase. The post-treatment temperature of (Y0.75Gd0.25)2O3:Eu particles for phase transformation decreased from 1100 °C to 700 °C when LiCl flux was used. The morphology of the particles was also influenced by the Y/Gd ratio and the LiCl flux. The as-prepared particles had spherical shape and non-aggregation characteristics regardless of Y/Gd ratio and flux. The sphericity of the as-prepared particles prepared without flux was maintained after post-treatment for phase transformation in all Y/Gd ratios. However, LiCl addition promoted the aggregation between product particles. The prepared particles had high photoluminescence intensities comparable to that of the commercial product.