BAM Phosphor Research Articles

A micro-structural corrosion mechanism on the thermal degradation of BaMgAl10O17: Eu2+ phosphor

The thermal degradation is a vital issue that restricting luminous efficiency and service life of BaMgAl10O17: Eu2+phosphor for chromogenic and illuminating fields. The effects of heat-treatment temperature on the luminescence properties and micro-structure of BAM were researched to accurately elucidate the thermal degradation mechanism. Some pieces of evidence for micro-structural corrosion were detected according to the results of PL, TL, XPS and IR. With the heat-treatment temperature increasing, a decrease of blue-emitting intensity and new red-emitting peaks revealed thermal degradation and activator oxidation. The XPS results showed the surface chemical composition changes and the micro-structure adjustment. The defects elimination detected by TL could be responsible for this micro-structural corrosion. IR results further confirmed the changes on bond forms. These were direct evidence and specific forms for the micro-structural corrosion due to the thermal degradation. Based on the relationship between micro-structural corrosion and luminescence properties, a micro-structural corrosion mechanism was given for the thermal degradation of BAM phosphor. The thermal degradation was caused in parallel by the micro-structure corrosion and the activated ion (Eu2+) oxidation.

Ce3+/Mn2+-activated Ca7(PO4)2(SiO4)2: efficient luminescent materials for multifunctional applications.

To develop new efficient phosphors for LEDs based on multifunctional applications, a series of Ce3+/Mn2+ activated Ca7(PO4)2(SiO4)2 (CPS) samples were prepared by solid-state reaction method. Upon 365 nm excitation, a broad emission band around 439 nm in the Ce3+-single-doped CPS was observed. The optimal Ce3+ concentration was determined to be 3%, for which the quantum efficiency was obtained to be 90.4%, higher than that of the commercial BAM phosphor. By monitoring 458 nm, an intense and broad excitation band was found from 240 to 400 nm, which can match well with the near-ultraviolet (NUV) LED chip. For Ce3+-Mn2+ codoped CPS, a new red emission band belonging to Mn2+ appeared and an energy transfer from Ce3+ to Mn2+ was confirmed. It was also found that the emission spectra of Ce3+/Mn2+ could well cover the optical absorption bands of plants. The fabrication of the phosphors on NUV LED chip indicates that the present phosphors could be promising in solid lighting and plants growth.

BAM系蛍光体の構造劣化 : TEMによるX線、紫外線照射時の構造変化観察

BAM系蛍光体の構造劣化 : TEMによるX線、紫外線照射時の構造変化観察

Synthesis of High-Performance BaMgAl10O17:Eu2+Phosphor Through a Facile Aqua-Suspension Method

High-performance BaMgAl10O17:Eu2+ (BAM) phosphor was prepared by a facile aqua-suspension method, based on the in situ surface charge modification of starting powders with the aid of the γ-Al2O3 porous structure. When stirred in de-ionized water at 80°C, the starting powders of BaCO3, MgO, and Eu2O3 were positive surface charged, and attracted by the porous and negative charged γ-Al2O3 powders. Through the electrostatic effect, high uniformed BAM precursor was achieved after the aqua-medium was removed. Fourier transform infrared (FTIR) spectra indicated some new chemical bonds among the reactants of the BAM precursor, which improved the powder activity and made it possible to achieve high-performance BAM phosphor at a lower calcination temperature. The obtained BAM phosphor exhibited a narrow particle size distribution, enhanced crystallinity, and a short decay time.

High dispersibility and enhanced luminescence properties of BaMgAl10O17:Eu2+ phosphors derived from molten salt synthesis

BaMgAl10O17:Eu2+ (BAM) phosphors were prepared via the molten salt synthesis (MSS) method. The NaCl–KCl eutectic mixture and LiF were used as the molten salt and flux, respectively. X-ray powder diffraction (XRD) patterns indicate that the BAM phase is formed above 1200°C and that the addition of LiF leads to an obvious improvement in crystallinity. The emission intensity of the BAM phosphor with 10wt% LiF is about 85% higher than that of the phosphor without LiF and about 200% higher than that of the phosphor without molten salt and LiF. Scanning electron microscopy (SEM) reveal that the as-prepared phosphors have good crystallinity and regular morphology, and most importantly, they are not aggregated. Li+ doping is benefit for the thermal stability and results in a slightly longer decay times of 1.17μs.

Scheelite-type MWO4 (M = Ca, Sr, and Ba) nanophosphors: Facile synthesis, structural characterization, photoluminescence, and photocatalytic properties

Scheelite-type MWO4 (M=Ca, Sr, and Ba) nanophosphors were synthesized by the precipitation method. All compounds crystallized in the tetragonal structure with space group I41/a (No. 88). Scherrer’s and TEM results revealed that the average crystallite size varies from 32 to 55nm. FE-SEM illustrate the spherical (CaWO4), bouquet (SrWO4), and fish (BaWO4) like morphologies. PL spectra indicate the broad emission peak maximum at 436 (CaWO4), 440 (SrWO4), and 433nm (BaWO4) under UV excitation. The calculated CIE color coordinates of MWO4 nanophosphors are close to the commercial BAM and National Television System Committee blue phosphor. The photocatalytic activities of MWO4 were investigated for the degradation of methylene blue dye under UV illumination. At pH 3, BaWO4 nanocatalyst showed 100% dye degradation within 60min. The photocatalytic activity was in the decreasing order of BaWO4>CaWO4>SrWO4 under both neutral and acidic conditions.

Luminescence and Structural Properties of High Stable Si-N-Doped BaMgAl10 O17 :Eu2+ Phosphors Synthesized by a Mechanochemical Activation Route

Highly thermal stable Si–N-doped BAM (BaMgAl10O17: Eu2+) phosphors have been successfully synthesized by a mechanochemically assisted solid-state reaction method. Mechanical milling greatly improved the amount of Si–N pairs substituted for Al–O pairs in BAM lattice>. Si–N incorporation improves the photoluminescence (PL) properties and the color purity, reduces the thermal quenching, and most importantly, increases the thermal stability of the BAM phosphors significantly. The interpretation of the positive influence of Si–N doping was attributed to the local structure of the produced phosphors, which was analyzed with the aid of first-principles density functional calculations. This analysis showed that the substitution of Al–O pairs with Si–N pairs should preferentially occur in the boundary between the spinel layer and the conduction layer of the BAM phosphor, leading to a compression of the conduction layer. Eu2+ ions prefer to substitute the N-coordinated Ba2+ ions in the lattice of Si–N-doped BAM phosphors, leading to a strong Eu–N bonding. The results of these calculations agree fairly well with the results recorded experimentally, specifically the electron paramagnetic resonance (EPR) spectra, the X-ray absorption fine structure (XAFS), thermoluminescence spectra (TL), and decay behaviors.

Understanding and arresting degradation in highly efficient blue emitting BaMgAl10O17:Eu2+ phosphor—A longstanding technological problem

Blue emitting BaMgAl10O17:Eu2+ (BAM) phosphor is indispensable for Plasma Display panel and lighting because of high luminescence efficiency. However, thermal degradation (annealing in air at 500–600°C) of BAM (upto ∼30%) remains an intriguing problem for display industry worldwide. In the present study, a systematic approach is pursued to develop highly efficient BAM phosphor that exhibits least degradation, understand the role of Eu2+ site occupancy in such BAM phosphor and encapsulate individual phosphor grains with a shell of silica nanoparticles. The approaches lead to highly efficient BAM:Eu2+ phosphor that showed no degradation against thermal baking (annealing at 500°C in air) for both UV and VUV radiation under UV and VUV excitation. An optimum solid state chemical route including precursor phases, dopant concentration, and thermal regimes has been evolved to develop BAM. Emission from Eu2+ occupying three different sites is identified with energetically stable anti Beevers Ross as the dominant contributor. Coating by nano sized amorphous silica sol with subsequent sintering lead to uniform silica shell. This nano silica layer also helps to enhance the luminescence from phosphor grains.

Enhanced photoluminescence of BaMgAl 10O 17:Eu 2+ nanophosphor for PDP application

BaMgAl 10O 17:Eu 2+ nanorods were synthesized by sol–gel technique, and their luminescent properties were investigated upon the irradiation of vacuum ultraviolet (VUV) light. By introducing surfactant cetyl-tri-methyl-ammonium bromide (CTAB) in sol–gel process and additional Mg 2+ in the raw materials, the emission intensity and thermal stability of the nanophosphor were both enhanced. The above improvements made it possible that the nanosized BAM phosphor could be a good alternative for PDP application.

Host emission from BaMgAl10O17 and SrMgAl10O17 phosphor: Effects of temperature and defect level

Abstract— Understanding the mechanism of blue‐light emission in Eu‐doped BAM phosphor as well as its sensitive degradation is required because this is a very important material in fluorescent lamps and plasma‐display panels. In this study, both theoretical and experimental investigations on the host emissions in BaMgAl10O17 and SrMgAl10O17 were performed. Host emissions from BaMgAl10O17 and SrMgAl10O17 by photoluminescence and thermoluminescence spectra were observed. Photoluminescence spectra suggested that the host emission from SrMgAl10O17 was easily quenched by thermal vibrations. The thermoluminescence spectra showed the existence of shallow and deep defect levels in BaMgAl10O17 and SrMgAl10O17 phosphors. It was shown that SrMgAl10O17 and its conduction plane could undergo degradation during irradiation of vacuum‐ultra‐violet (VUV) lights based on the calculated energy of formation of an oxygen vacancy. Moreover, the structural defects, such as oxygen vacancies, would cause localizing levels in the upper level in the valence band and in theconduction band. The results suggest the contribution of the host emission to the energy transfer to the Eu atoms would not be significant and the oxygen vacancies would act as the traps for excited carriers.

Synthesis of nano-size BaMgAl 10O 17:Eu 2+ blue phosphor by a rapid exothermic reaction

Ultrafine particles of BaMgAl 10O 17:Eu 2+ (BAM) phosphor were synthesized by a solid-state combustion reaction in a powder bed of 0.9BaCO 3+MgO+5Al 2O 3+0.05Eu 2O 3+ k(KClO 3+1.5C) composition. A large exothermic reaction of the mixture (KClO 3+1.5C) leads to a self-sustaining combustion mode. Under optimized combustion conditions, the product consisted of BAM powder and KCl was obtained. BAM ultrafine particles resulting from the combustion process were easily obtained by simply washing the salt by-product with water. Combustion-processed BAM phosphor shows a homogeneous grain size of 100–500 nm, good dispersity, regular morphology, and improved luminescence properties.

Synthesis of BaMgAl<SUB>10</SUB>O<SUB>17</SUB>:Eu<SUP>2+</SUP> Blue Phosphor by Electro-Spray Aerosol Flame Deposition

Spherical and nano-sized BaMgAl10O17:Eu2+ (BAM) phosphor particles for plasma display panel (PDP) application were synthesized by Aerosol Flame Deposition (AFD) and subsequent heat treatment at 1250 degrees C for 4 h under reducing atmosphere. The effects of various atomization methods, precursor solution and various deposition position along flame axis were investigated in order to control the morphology and size of the phosphor. Characteristics of BAM phosphor were investigated for products prepared under various condition and they were compared with those of the commercial BAM. It was found that electro-spray gas-assisted atomization produce the most fine particle, while the optimum particle size for real application in phosphor devices (200-400 nm) was produced by the gas-blast atomizer.

Effects of the surface coating of BaMgAl 10O 17:Eu 2+ phosphor with SiO 2 nano-particles

BaMgAl 10O 17:Eu 2+(BAM) phosphors were coated with SiO 2 nano-particles by a modified sol–gel method. In order to elucidate the effects of SiO 2 coating onto BAM phosphor, the luminescent decay time is measured before and after SiO 2 coating. It was revealed that surface coating of BAM phosphors with SiO 2 leads to an increase in luminescent decay time and quantum efficiency, due to the suppression of nonradiative decay via surface defects. The experimental results suggest that the nonradiative decay via surface defects is an important relaxation process, related to the optical properties of display devices such as plasma display panels (PDP) and lamps.

Microstructure and luminescence of surface-coated nano-BaMgAl 10O 17:Eu 2+ blue phosphor

MgF 2 coating on BaMgAl 10O 17:Eu 2+ (BAM) particles was obtained by an emulsion method. The chemical compositions, microstructure, and luminescent performance of surface-coating BAM were characterized by XRD, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), energy dispersion spectrum (EDS) and vacuum ultraviolet (VUV) excitation, respectively. The results indicate that a compact homogeneous MgF 2 film is successfully coated on the surface of BAM particles by forming a chemical bond. Lengthening of fluorescence lifetimes were observed in surface-coated BAM phosphor attributed to less non-radiative rate due to coating. The luminescent performances of surface-coated BAM is improved due to the hanging-bonds and defects on the surface of nano-scale BAM particles being removed as well as non-radiative transition probability decreasing.

Thermal treatment effects on degradation of BaMgAl 10O 17:Eu 2+ phosphor for PDP

The thermal degradation mechanism of the BaMgAl 10O 17:Eu 2+ (BAM) phosphor used in plasma display panel (PDP) is not yet fully clarified. We studied the dependency of the luminance and chromaticity y-value of BAM phosphor on baking temperature, handling time, atmosphere and thermal treating process. The luminance and chromaticity y-value increased after baking at around 400 °C but decreased at 600 °C or higher temperatures. The thermal degradation was obviously aggravated in oxidative atmosphere. The shift of y-value was reversed when thermal treated in non-oxidative atmosphere. We considered that the mechanism of thermal degradation of BAM phosphor was firstly due to the migration of Eu 2+ ions and then due to the effect of oxygen. We also proposed a post-treatment for BAM phosphor to reduce the thermal degradation during panels’ fabrication.

Synthesis of BaMgAl10O17:Eu2+ particles with small grain size and regular morphology

Abstract BAM (BaMgAl 10 O 17 :Eu 2+ ) is widely used in plasma display panel (PDP) as a blue-emitting phosphor. It is necessary to improve the grain size, morphology and dispersibility of BAM phosphor because of the development of high definition PDP. Moreover, the crystal growth mechanism during the synthesis process of BAM particle is not fully clarified. In this paper, we synthesize BAM phosphor by solid-state reaction method. The primary raw material α-Al 2 O 3 powder was prepared by precipitation method. The phase transitions and crystal growth process during the formation of BaMgAl 10 O 17 have been studied. The intermediate product BaAl 2 O 4 phase was synthesized at 1000 °C on the surface of α-Al 2 O 3 particles as coating. When temperature increased to 1300 °C, BaMgAl 10 O 17 phase was formed. The BaMgAl 10 O 17 particles keep the shape and dispersibility of α-Al 2 O 3 powder. The results show that BAM phosphor synthesized in this paper has a homogeneous grain size at around 2.5 μm, good dispersibility, regular morphology and good luminescence properties.

Luminescent properties of BaMgAl10O17:Eu2+ phosphor layer prepared with phosphate ester

The preparation of BaMgAl10O17:Eu2+ (BAM) blue phosphor layer for a plasma display panel by the addition of a newly designed energetic dispersant (hereafter referred to as SAIT7) and its resulting photoluminescence (PL) efficiency is investigated. The addition of SAIT7 increases the maximum solids loading of BAM phosphor paste from 27.91 to 35.87 vol% and yields a highly packed microstructure of the phosphor layer. The PL intensity is increased by 7.57% compared to the BAM blue phosphor layer prepared without SAIT7. In conclusion, the addition of SAIT7 increased the packing density of the phosphor layer and resulted in improved luminescent properties of the phosphor layer.

Genetic Algorithm-Assisted Combinatorial Search for New Blue Phosphors in a (Ca,Sr,Ba,Mg,Eu)xByPzOδ System

Genetic algorithm-assisted combinatorial chemistry (GACC) was implemented to search for new blue phosphors in seven cation systems, including CaO, MgO, BaO, SrO, B2O3, P2O5, and Eu2O3. The GACC process was followed by a series of fine-tuning processes based on conventional high-throughput screening employing quaternary and ternary libraries, to pinpoint promising compositions. GACC was found to be useful as a preliminary step for final screening. This series of processes involving computations and actual syntheses led us to (Sr1-x-yCaxBay)2P2O7:Eu2+ (0.32 < x < 0.72, y < 0.04) phosphors. It was found that the boron addition played a significant role in enhancing the luminance but it was completely evaporated during the synthesis, and an excessive amount of alkali earth elements was essential for better luminescence. The luminance of (Sr1-x-yCaxBay)2P2O7:Eu2+ (0.32 < x < 0.72, y < 0.04) phosphors reached 70% of a commercially available BAM phosphor at 254 nm excitation. The color chromaticity was in the deep blue region, x = 0.15, y = 0.05. The structure of these phosphors was found to be Sr2P2O7 (Pnma, 62), but the luminescent property was far better than the Sr2P2O7:Eu2+ phosphor.

Effect of TRITON™ X‐based dispersants bearing a carboxylic terminal group on rheological properties of BAM/ethyl cellulose/terpineol paste

AbstractIn this study, we attempted to use TRITON™ X (or octyl phenol ethoxylate (OPE) of different oxyethylene units (i.e., n = 2, 5, and 10))‐based dispersants containing a carboxylic group in the oxyethylene chain end for the formulation of BAM phosphor paste. Thus, a three‐component system employing OPE‐COOH as a dispersant, terpineol as a solvent, and ethyl cellulose as a binder was compounded with BAM particles, and the rheological properties of the paste were investigated in detail. Among three acidic TRITON X‐based compounds we tested (i.e., [OPE2‐COOH], [OPE5‐COOH], and [OPE10‐COOH]), OPE10‐COOH containing the highest number of oxyethylene units in the backbone was found to be the dispersant showing the lowest viscosity of BAM paste under identical conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Crystallinity and luminescent properties of citrate sol–gel derived BAM phosphor

By adopting a facile citrate sol–gel process, pure well-crystallized BaMgAl 10O 17:Eu 2+(BAM) blue phosphors were successfully prepared. The crystallinity, particle size, morphology, chemical composition and luminescent properties were characterized by XRD, FE-SEM, EDS and spectrofluorometer respectively. The results indicated the precursor was amorphous below 800 °C, and begun to crystallize at 1100 °C. The synthesis temperature decreased by about 300 °C compared to solid-state method to prepare BAM. FE-SEM images showed a well-crystallized, platelet morphology with a particle size of 1–3 μm. The obtained BAM phosphors were fine powders and had higher luminescent intensity compared to solid-state derived BAM phosphors due to high purity and perfect crystalline morphology.