Development of a new blue CaMgSi2O6:Eu2+ phosphor for PDPs

Abstract— A blue‐light‐emitting Eu²⁺‐doped CaMgSi₂O₆ phosphor having a long lifetime for a plasma‐display panel (PDP) was developed. The CaMgSi₂O₆:Eu²⁺(CMS:Eu) phosphors show no luminance degradation during the baking process, and an equivalent photoluminescence peak intensity compared to that of the conventional blue‐phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM) after baking. CMS: Eu shows a poor luminescent characteristic for the Xe excimer band excitation due to the lack of absorption. To introduce the absorption center for the Xe excimer band, we performed Gd‐codoping of CMS: Eu as a sensitizer and found a new excitation band around 172 nm, which originated from Gd³⁺. The test PDPs panels using synthesized CMS: Eu phosphor and CMS: Eu, Gd phosphor were examined to investigate the luminescent and aging characteristics of a Xe‐discharge excitation source. The CMS: Eu panel shows an emission peak intensity comparable to that of the BAM panel (i.e., a comparable stimuli L/CIEy, 93% of BAM), while the CMS: Eu, Gd panel shows poorer blue emission intensity compared to the BAM panel (up to 53% of total stimuli of BAM). The CMS: Eu panel and the CMS: Eu, Gd panel show less luminance degradation than the BAM panel under the aging test, and the panel retains 90% of its luminance after 300 hours of driving. It was found that CMS: Eu appears to be a candidate for a new blue PDP phosphor because of its longevity in a Xe‐discharge plasma environment.     

Quantum chemistry and QSPR study on relationship between crystal structure and emission wavelength of Eu2+‐doped phosphors

Abstract— The relationship between crystal structures and emission properties has been computationally investigated for Eu²⁺‐doped phosphors. The electronic structure of the Eu²⁺‐doped BaMgAl¹⁰O¹⁷ phosphor was analyzed by using the quantum chemistry method. The different effects of O and Ba atoms on the Eu 5d states were determined. The presence of O and Ba atoms increases and decreases the energy level of the Eu 5d orbital by forming anti‐bonding and bonding interactions, respectively. According to the electronic‐structure analysis, the structure index that represents the local geometrical information of the Eu atom was defined. The relationship between the crystal structures and the emission wavelengths of the 1 6 Eu²⁺‐doped oxide phosphors were studied by using the quantitative structure‐property relationship (QSPR). The QSPR model suggested that the both O and alkaline‐earth atoms around the Eu atom are of importance in the determination of the emission wavelength. The interaction between the Eu and the nearest O atoms make the Eu²⁺ emission wavelength short. On the other hand, the interaction from the alkaline‐earth atoms around the Eu atom lengthens the Eu²⁺emission wavelength. This evaluation method is useful in selecting the host material that indicates a desirable emission wavelength of the Eu²⁺‐doped phosphors.     

Study of the effect of water on thermal and operating degradation of BaMgAl10O17: Eu2+ (BAM) blue phosphor

Abstract— From the adsorption and desorption characteristics of water, we showed that water can intercalate into BaMgAl₁₀O₁₇: Eu²⁺ blue phosphor. ESR, XANES, and XPS analyses confirmed that oxidation by water causes thermal degradation of BAM. We also demonstrated that intercalated water accelerates luminance degradation under VUV irradiation and showed oxidation of Eu²⁺ during panel operation by means of μ‐XPS. We concluded that the cause of thermal and operating degradation of BAM is the oxidation of Eu²⁺ due to water.     

Effect on deoxidation of doped europium in oxidized BaMgAl10O17

Abstract— We studied the effect of the deoxidation of oxidized blue‐light‐emitting europium‐doped BaMgAl₁₀O₁₇ (BAM) phosphor in a plasma‐display panel by making photoluminescence and powder X‐ray diffraction measurements and by X‐ray absorption fine structure analysis. Photoluminescence spectra, powder X‐ray diffraction, and X‐ray absorption near‐edge structure, and extended X‐ray absorption fine structure spectra of BAM at the europium L₃‐edge suggest that the oxidized BAM annealed in air is revived by heating in a H₂/N₂ (5% H₂) reducing atmosphere above 500°C.     

Oxidation of doped europium in BaMgAl10O17 by annealing studied by x‐ray‐absorption fine‐structure measurements

Abstract— We studied the influence of annealing in air on doped europium in BaMgAl₁₀O₁₇ by performing x‐ray absorption fine‐structure measurements. We determined the oxidation of doped divalent europium by annealing in air at over 500°C. The interatomic distance between the europium and the surrounding oxygen atoms was compressed by oxidation. It also appears that the oxidation process of europium is determined by the diffusion of oxygen into BaMgAl₁₀O₁₇.     

Influence of x‐ray irradiation on doped europium in BaMgAl10O17 studied by x‐ray absorption fine structure and x‐ray diffraction

Abstract— We studied the influence of x‐ray irradiation on the doped europium ion in BaMgAl₁₀O₁₇ (BAM) by x‐ray absorption fine structure measurement and x‐ray diffraction. We found that x‐ray irradiation promoted oxidation of doped europium and fading emissions. However, no difference was found in x‐ray diffraction patterns before and after x‐ray irradiation. We concluded that the fading of BAM after x‐ray irradiation was mainly caused by oxidation of the doped europium in the BAM.     

A study on the chromaticity shifts of blue phosphor for color plasma displays

The dependency of the chromaticity shifts on the concentration of Eu²⁺ doped in BaMgAl₁₀O₁₇ (BAM) was investigated under heat‐treatment and vacuum ultraviolet (VUV) irradiation. The Eu²⁺ ions in BAM show an asymmetrical broad emission band with a maximum at ～452 nm under excitation of VUV light at room temperature, showing that multiple crystalline cationic sites exist in the host. It was found that the chromaticity shifts greatly decrease with increasing heat‐treatment temperature. Regardless of the Eu²⁺ concentration, the chromaticity shifts caused by heat‐treatment are greater than that caused by VUV irradiation. Compared with conventional BAM, a solid solution of BAM with barium aluminate as a powder and film was also studied, and very few chromacity shifts were observed. It is suggested that the distribution of Eu²⁺ ions in different sites in a BAM lattice results in different chromaticity coordinates. By increasing the Eu²⁺ concentration in BAM, or under heat‐treatment and VUV irradiation, the emission band shifts towards longer wavelengths.     

Identification of charge‐transfer transition between Gd3+ to O2− in gadolinium‐containing oxide phosphors in VUV region

Abstract— The broad bands at around 155 nm for GdAl₃(BO₃)₄:Eu, at 184 nm for Ca₄GdO(BO₃)₃:Eu, at 183 nm for Gd₂SiO₅:Eu, and at 170 nm for GdAlO₃:Eu were observed. These bands were assigned to the charge‐transfer (CT) transition of Gd³⁺‐O^2?. In the excitation spectrum of (Gd,Y)BO₃:Eu, a broadened excitation band was observed in VUV region. It could be considered that this band was composed of two bands at about 160 and 166 nm. The preceding band was assigned to the BO₃ group absorption. The later one at about 166 nm could be assigned to the CT transition of Gd³⁺‐O^2?, according to the result of GdAl₃(BO₃)₄:Eu, Ca₄GdO(BO₃)₃:Eu, Gd₂SiO₅:Eu, and GdAlO₃:Eu. The excitation spectra overlapped between the CT transition of Gd³⁺‐O^2? and BO₃ groups absorption. It caused the emission of Eu³⁺ to take place effectively in the trivalent europium‐doped (Gd,Y)BO₃ host lattice under 147‐nm excitation.     

Detrimental effects of O2 and CO2 on the cathode performance of flat‐matrix CRTs used for large‐scale flat displays

Abstract— The detrimental effects of O² and CO² on the cathode emissions of a flat‐matrix (FM) CRT and some methods which increase its life are described. Cathode emission gradually decreases over long‐term operation when an FM‐CRT is used as a tiling element in a large‐scale flat display. It is necessary that for the FM‐CRT the reduction of the emission current be within 10% in order to keep the operational life longer than 10,000 hours. The reason for the degradation of the cathode emission was clarified by experiments using high‐vacuum equipment. It was found from experiments that O² and CO², which are produced by the dissolution and activation of the oxide‐coated cathodes, are very harmful to emissions. It is, therefore, very important to lower the partial pressure of O² and CO² in the FM‐CRT in order to reduce their harmful influence on the oxide cathodes. Two methods were used to reduce their partial pressure in the FM‐CRT. One was to make the diameter of the evacuation tube larger and the other was to increase the quantity of the getters. It was found that the adoption of twice as many getters in the FM‐CRT was most useful in lowering the partial pressure of O² and CO². This has ensured that the life of an FM‐CRT is longer than 10,000 hours.     

Dependency of luminescence properties of Y2O3: Eu on the activator incorporation degree and lattice parameter

Abstract— Samples of yttrium oxide doped with trivalent europium have been prepared by ceramic techniques, under different synthesis conditions; barium chloride (BaCl₂) and sodium tetraborate (Na₂B₄O₇) were tested as flux. The improvement of the luminescence properties dependency on the substitution of Eu³⁺ for Y³⁺ in the host lattice under electron and UV excitations is demonstrated. The lattice parameter as a quantitative assessment of activator incorporation degree is proposed. The obtained results are discussed with respect to the employed processing method.     

Phosphors for plasma‐display panels: Demands and achieved performance

Almost two‐thirds of the discharge cells in plasma‐display panels (PDPs) are covered with phosphors. Beyond the efficient conversion of vacuum UV photons into visible light, the phosphor layer serves as a reflective mirror transporting light in the desired viewing direction. The quantum efficiency of state‐of‐the‐art PDP phosphors is, at its upper limit, 80–95%. Today's improved blue‐emitting BaMgAl₁₀O₁₇:Eu (BAM) phosphor still deteriorates during panel processing and operation, resulting in a loss of efficiency and color purity. A reduction in the phosphor particle size below 2 μm is suited to ease panel manufacturing and to improve light output.     

A new perspective for the thermal degradation mechanism of blue BAM

A new thermal degradation mechanism for blue BAM (BaMgAl₁₀O₁₇:Eu²⁺) under thermal treatment in the presence of water is proposed. The water can be originated either from the thermal treatment steps, such as organic binder baking steps, or from the atmosphere under which blue BAM is being heated. Under such thermal treatment conditions, water molecules can be easily intercalated into the conduction layers of blue BAM, resulting in not only the depreciation of luminance but also in the emission color change toward green. The intercalated water molecules in the conduction layer, where Eu²⁺ ions are located along with Ba²⁺ ions, are strongly associated with Eu²⁺ ions, creating different coordination environments around Eu²⁺ ions. In this paper, the details of changes in emission behaviors along with water content in the water intercalated blue BAMs are discussed.     

Enhanced PL and VUV absorption of BaZr(BO3)2:Eu3+ by Al3+ incorporation

Abstract— The photoluminescence (PL) and vacuum‐ultraviolet excitation (VUV) properties of BaZr(BO₃)₂ doped with the Eu³⁺ activator ion were studied as a new red phosphor for PDP applications. The excitation spectrum shows strong absorption in the VUV region with an absorption band edge at 200 nm. The charge‐transfer excitation band of Eu³⁺ was enhanced by co‐doping with an Al³⁺ ion into the BaZr(BO₃)₂ lattices. The PL spectrum shows the strongest emission at 615 nm, corresponding to the electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺ in BaZr(BO₃)₂, which results in good red‐color purity.     

Eu2+‐doped barium thioaluminate EL devices prepared by two‐target pulsed‐electron‐beam evaporation

Abstract— New blue‐emitting thin‐film‐electroluminescent (TFEL) devices that satisfy the requirements for full‐color TFEL displays were developed. Eu²⁺‐doped BaAl²S⁴ thin films were used for the emission layer. BaAl²S⁴:Eu thin films were prepared by two‐target pulsed‐electron‐beam evaporation suitable for the deposition of multinary compounds that have difficulty in obtaining stoichiometoric thin films. The EL spectrum only had a peak at around 470 nm. The Commission Interantionale de l'Eclairge (CIE) color coordinates were x = 0.12 and y = 0.10. The luminance level from a 50‐Hz pulses voltage was 65 cd/m².     

Eu2+‐doped AlN—SiC solid‐solution phosphors: Synthesis and cathodoluminescence properties

Abstract— Eu and Si co‐doped AlN was reported to be an interesting blue phosphor for field‐emission displays (FEDs). In this paper, SiC instead of Si³N⁴ was used as the Si source. Eu²⁺‐doped AlN—SiC phosphors were prepared by firing the powder mixtures of AlN, SiC, and Eu²O³ at 2050°C for 2 hours under 1‐MPa N². Solid solutions between AlN and SiC were formed in a wide range, promoting the solution of Eu²⁺ in AlN. The phosphors showed intense blue emissions under electron‐beam excitation, indicative of potential phosphors for FEDs.     

Phase relationship in V2O3-rich region of the V2O3–CaO system between 1573–1773 K at PO2 = 10−10 and 10−11 atm

V₂O₃–CaO system is one of the fundamental systems in the fields of vanadium extraction and vanadium-containing alloys production. Due to the insufficient experimental study, the data of this system was limited. The present study was carried out between 1300 and 1500 °C (1573–1773 K) at the V2O3-rich region (>56 wt% V₂O₃), with the controlled partial pressure of oxygen (PO2) at 10-10 and 10–11 atm. High-temperature equilibration experiments, quenching technique and electron probe micro-analyser (EPMA) were adopted to determine the microstructures and compositions of phases at high temperature. The results of phase compositions obtained were used to plot a sub-solidus phase diagram, which showed a great discrepancy with existing publications, and 4 solid-phase regions with their phase boundaries were identified in the present study. The solubility of CaO in V2O3 was found to increase slightly with the temperature under both PO2. The study is expected to fulfil the gaps of thermodynamics information in the V₂O₃-containing systems.     

White LEDs using the sharp β‐sialon: Eu phosphor and Mn‐doped red phosphor for wide‐color gamut display applications

The sharp β‐sialon (Si_6‐zAl_zO_zN_8‐z : 0 < z < 0.1):Eu green phosphor, combining with a blue LED and CaAlSiN₃:Eu red phosphor, is suitable for the wide‐color gamut white LEDs backlighting system, because of its sharp and asymmetric emission spectrum shape. However, the color gamut and the brightness of the aforementioned display is restricted because of the wide emission band of the CaAlSiN₃:Eu red phosphor. In this work, we used K₂SiF₆:Mn as an alternate red phosphor, which has a sharp emission spectrum. The display with the white LED using sharp β‐sialon:Eu and K₂SiF₆:Mn shows a wide‐color gamut, which covers the hole NTSC triangle. The use of K₂SiF₆:Mn enables to realize not only a wider color gamut but also a higher brightness of displays, compared with the use of CaAlSiN₃:Eu. Furthermore, it is confirmed that the white LED using sharp β‐sialon:Eu and K₂SiF₆:Mn is stable against temperature and also durable under the accelerated drive conditions.     

Cooperative downconversion in Y3Al5O12 : RE3+,Yb3+ (RE = Tb,Tm, and Pr) nanophosphors

Abstract— Efficient near‐infrared (NIR) quantum cutting (QC) through cooperative downconversion in Y₃Al₅O₁₂ : RE³⁺,Yb³⁺ (RE = Tb, Tm, and Pr) nanophosphors has been demonstrated, which involves the conversion of the visible photon from RE³⁺ into the NIR emission of Yb³⁺ with the optimal quantum efficiency approaching 200%. The authors have analyzed the measured luminescence spectra and decay lifetimes and propose a mechanism to rationalize the NIR QC effect. The results indicate the potential of developing RE³⁺‐Yb³ dual‐ion‐based nanophosphors for the downconversion of high‐energy photons to multiple photons with an energy greater than the bandgap of silicon‐based‐photonics display devices.     

Critical evaluation and thermodynamic optimization of the V–O system

The V–O system has been critically evaluated and thermodynamically assessed based on the available phase diagram and thermodynamic data using the CALPHAD method. The liquid phase over the whole composition range from metallic liquid to oxide melt is described by the modified quasichemical model with five species: V^II, V^III, V^IV, V^V and O, which takes short-range ordering in liquid solution into account. All solid solutions are modeled considering respective crystal structures. A set of self-consistent thermodynamic parameters of the V–O system is obtained and the available experimental data are reproduced well within experimental error limits. Especially for the VO_x solid solution, the site fractions of vacancies in both vanadium and oxygen sublattices are reproduced well using the present model and parameters.     

Synthesis of Bi and Gd doped ZnB2O4 for evaluation as potential materials in luminescent display applications

A series of Bi³⁺ and Gd³⁺ doped ZnB₂O₄ phosphors were synthesized with solid state reaction technique. X-ray diffraction technique was employed to study the structure of prepared samples. Excitation and emission spectra were recorded to investigate the luminescence properties of phosphors. The doping of Bi³⁺ or Gd³⁺ with a small amount (no more than 3 mol%) does not change the structure of prepared samples remarkably. Bi³⁺ in ZnB₂O₄ can emit intense broad-band purplish blue light peaking at 428 nm under the excitation of a broad-band peaking at 329 nm. The optimal doping concentration of Bi³⁺ is experimentally ascertained to be 0.5 mol%. The decay time of Bi³⁺ in ZnB₂O₄ changes from 0.88 to 1.69 ms. Gd³⁺ in ZnB₂O₄ can be excited with 254 nm ultraviolet light and yield intense 312 nm emission. The optimal doping concentration of Gd³⁺ is experimentally ascertained to be 5 mol%. The decay time of Gd³⁺ in ZnB₂O₄ changes from 0.42 to 1.36 ms.