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.     

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.     

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.     

A new long-lasting phosphor Zr and Eu co-doped SrMg2(PO4)2

Zr⁴⁺- and Eu³⁺-codoped SrMg₂(PO₄)₂ phosphors were prepared by conventional solid-state reaction. Under the excitation of ultraviolet light, the emission spectra of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.0005-0.07) are composed of a broad emission band peaking at 500 nm from Zr⁴⁺-emission and the characteristic emission lines from the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4) transitions of Eu³⁺ ions. These phosphors show the long-lasting phosphorescence. The emission color varies from red to white with increasing Zr⁴⁺-content. The white-light emission is realized in single-phase phosphor of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.07) by combining the Zr⁴⁺- and Eu³⁺-emission. The duration of the persistent luminescence of Sr_0.95Eu_0.05Mg_2−2xZr_2xP₂O₈ (x = 0.07) reaches nearly 1.5 h. The time at which the long-lasting phosphorescence intensity is 50% of its original value (T_0.5) is 410 s. The afterglow decay curves and the thermoluminescence spectra were measured to discuss this long-lasting phosphorescence phenomenon. The co-doped Zr⁴⁺ ions act as both the luminescence centers and trap-creating ions.     

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.     

Effect of alkali metal ions co-doping on the structure and luminescent properties of phosphor Zn3(BO3)2:Eu3+

A series of the Zn₃(BO₃)₂:Eu³⁺ without or with alkali metal ions doping at a low sintering temperature were synthesized by the solid-state reaction method. The XRD pattern shows that all samples exhibit Zn₃(BO₃)₂ crystalline phase. The samples co-doped with alkali metal ions have better crystallinity compared with the un-compensated ones. The different charge compensation approaches have no influence on the shape and position of the emission and excitation spectra. However, the luminescent intensity of samples has been obviously enhanced with different alkali metal ions co-doping. The introduction of Li⁺ can increase the red emission of Eu³⁺ compared with the others. Thus, the volume compensation and the equilibrium of mole number can be taken into consideration by charge compensated (CC) approaches.     

Experimental and theoretical luminous efficacies of phosphors used in combination with blue‐emitting LEDs for lighting and backlighting

Abstract— Phosphors that absorb blue light and emit in the green, yellow, and red have been synthesized, and their experimental and theoretical luminous efficacies are compared. It is proposed that a blue‐emitting LED in combination with red‐emitting Sr₂Si₅N₈: Eu²⁺ and green‐emitting SrGa₂S₄: Eu²⁺ phosphors is used as an energy‐efficient white‐light source for display backlighting applications.     

Investigation of spectroscopic properties of Sm-Eu codoped phosphate glasses

Phosphate glasses with chemical compositions of 74.5NaH₂PO₄–20ZnO–5Li₂O–0.5Sm₂O₃ and 74NaH₂PO₄–20ZnO–5Li₂O–0.5Sm₂O₃–0.5Eu₂O₃ were synthetized by melt quenching method. We investigated the influence of Sm³⁺/Eu³⁺ doping on the optical properties of phosphate glasses. X-ray Diffraction indicates that the samples have an amorphous structure. DSC measurements show a good thermal stability of phosphate glasses. Using the absorption spectra, Judd–Ofelt analysis was applied to absorption bands of Sm³⁺ (4f⁵) to carry out the three phenomenological parameters of Judd–Ofelt (JO). According to the obtained values of Ω₂, Ω₄ and Ω₆, some radiative properties were theoretically determined. We report both the photoluminescence (PL) and the PL lifetime measurements of a prominent emission transition ⁴G_5/2 → ⁶H_5/2 (604 nm) of Sm³⁺ both in absence and in presence of Eu³⁺. It is shown that Eu³⁺ ions act as sensitizers for Sm³⁺ ions and contribute largely to the improvement of the radiative properties of phosphate glasses. An improvement of the PL lifetime value after adding Eu³⁺ ions (4.58 ms) is reported. The predicted lifetime (τ_rad) calculated by Judd–Ofelt theory and the experimental lifetime (τ_meas) for the prepared phosphate glasses were compared with those of other works. Photoluminescence (PL) intensity of ⁴G_5/2 → ⁶H_5/2 (604 nm), ⁴G_5/2 → ⁶H_7/2 (567 nm), ⁴G_5/2 → ⁶H_9/2 (650 nm) and ⁴G_5/2 → ⁶H_11/2 (706 nm) and the quantum efficiency (η) for the excited ⁴G_5/2 level were enhanced after adding Eu³⁺. The radiative properties obtained for (Sm, Eu) codoped phosphate glasses suggest that the present material can be a potential candidate for the development of color display devices.     

Investigation on luminescence of Na3Ca6(PO4)5:Eu2+ phosphor for LEDs

In this paper, a series of Na₃Ca_6(1−x)(PO₄)₅:xEu²⁺ (NCP:xEu²⁺, 0 ≤ x ≤ 4%) phosphors were prepared by conventional solid-state reaction method, and their photoluminescence properties were studied. Upon 365 nm excitation, the typical NCP:2%Eu²⁺ phosphor shows an asymmetric bluish green emission band with the dominant peak at 498 nm which could be attributed to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. By measuring the time-resolved photoluminescence spectra, it reveals more than one Eu²⁺ emission center in the Eu²⁺-activated NCP phosphors. By monitoring 498 nm, the excitation spectrum of NCP:2%Eu²⁺ demonstrates a broad excitation band ranging from 240 to 450 nm, which can match well with the emission wavelength of the NUV LED chip. The SEM image shows that the average particle size of NCP:2%Eu²⁺ is about 19.4 µm. The above results imply that the NCP:Eu²⁺ phosphor could have potential application in LEDs.     

Red emitting MTiO3 (M = Ca or Sr) phosphors doped with Eu3+ or Pr3+ with some cations as co-dopants

Ca (or Sr)TiO₃:Eu³⁺, M (Li⁺ or Na⁺ or K⁺) and CaTiO₃:Pr³⁺, M (Li⁺ or Na⁺ or Ag⁺ or K⁺ or Gd³⁺ or La³⁺) powders were prepared by combustion synthesis method and the samples were further heated to ～1000 °C to improve the crystallinity. The structure and morphology of materials were examined by X-ray diffraction (XRD) and a scanning electron microscopy (SEM). The morphologies of SrTiO₃:Eu³⁺, CaTiO₃:Eu³⁺ or CaTiO₃:Pr³⁺ powders co-doped with other metal ions were very similar. Small and coagulated particles of nearly cubical shapes with small size distribution having smooth and regular surface were formed. Photo-luminescence spectra of CaTiO₃:Pr³⁺ and co-doped either with Li⁺, Na⁺, K⁺, Ag⁺, La³⁺ or Gd³⁺ ions showed red emissions at 613 nm due to the ¹D₂ → ³H₄ transition of Pr³⁺. The variation of intensity of emission peak with different co-doping follows the order: K⁺ > Ag⁺ > Na⁺ > Li⁺ > La³⁺ > Gd³⁺. The characteristic emissions of CaTiO₃:Eu³⁺ lattices had strong emission at 614 and 620 nm for ⁵D₀ → ⁷F₂ with other weak transitions observed at 580, 592, 654, 705 nm for ⁵D₀ → ⁷F_n transitions where n = 0, 1, 3, 4 respectively in all host lattices. Photoluminescence intensity in SrTiO₃:Eu³⁺ is more than CaTiO₃:Eu³⁺ lattices. A remarkable increase of photoluminescence intensity (in ⁵D₀ → ⁷F₂ transition) was observed if co-doped with Li⁺ ions in CaTiO₃:Eu³⁺ and SrTiO3:Eu³⁺.     

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.     

Design and characterization of new lanthanide fluorides and their optical properties

Three kinds of lanthanide phosphors (La_xLu_1−xF₃: Eu³⁺, LaF₃–CaF₂:Eu³⁺ and LaF₃: Eu³⁺) have been successfully synthesized based on three different ways such as molten salts, co-precipitation, supersonic and microwave irradiations. The as-prepared powder materials all exhibited red luminescence. Their crystal structures or morphologies were studied by means of X-ray powder diffraction and scanning electronic microscope. Eu³⁺-doped LaF₃–CaF₂ phosphor can be emissive under excitation at longer wavelengths (466 and 533 nm) excitations. Supersonic and microwave irradiations have shortened the reaction time of LaF₃: Eu³⁺ crystals in 40 min under very low temperature (50 °C).     

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.     

Influences of substituting Na+ ions in Eu2+, Mn2+ doped Ba9Y2Si6O24 phosphors

Near-ultraviolet (NUV)-excitable phosphors composed of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0–0.8) and Ba_8.7-qNa_0.4Eu_0.1Mn_qY₂Si₆O₂₄ (q = 0–0.4) were prepared via a solid-state reaction in a reducing atmosphere. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. After Na⁺ substitution for Ba²⁺ in the Ba_8.9Eu_0.1Y₂Si₆O₂₄ host lattice, the clear shift from green to yellow emission was observed. The Gaussian components of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0, 0.4, and 0.8) phosphors were exploited by using the three different Eu²⁺ ion sites in the host lattice. The dependence of the luminescent intensity of the Mn²⁺ co-doped (q = 0–0.4) host lattices on the fixed Na⁺ and Eu²⁺ contents was also investigated. Co-doping Na⁺ with Mn²⁺ and Eu²⁺ emitters in the host structure enabled efficient energy transfer from Eu²⁺ to Mn²⁺. The mechanism underlying this energy transfer was also discussed. The Commission Internationale de I’Eclairage (CIE) coordinates near the yellow and red regions of the obtained phosphors were observed. Each of Ba_8.9Eu_0.1Y₂Si₆O₂₄, Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄, and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors with a 405 nm LED chip was fabricated. The color rendering index (CRI, R_a) at correlated color temperature (CCT) with the CIE coordinates was exhibited for the LEDs. The thermal quenching and activation energy for the Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄ and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors were measured.     

CaMoO4:RE3+,Yb3+,M+ phosphor with controlled morphology and color tunable upconversion

CaMoO₄:RE³⁺,Yb³⁺ (RE = Er, Ho, Tm) phosphors were successfully synthesized by a facile hydrothermal method. XRD patterns confirmed tetragonal structure under different RE³⁺ and M⁺ ions doping conditions. Particles shapes and sizes were confirmed by SEM and TEM analyses. Particles shape and size were well tuned by control of solution pH; spherical balls consisting of nano-grains at low pH of ∼2, rice grain shapes at moderate pH of ∼6, and thin flakes at higher pH of ∼12, were observed. Fine tunability of upconversion (UC) emission color was achieved by doping multiple RE³⁺ ions within a single CaMoO₄ host. Blue, green and orange upconverted emission were observed by doping Tm³⁺, Er³⁺ and Ho³⁺ in the CaMoO₄, respectively. Further, the emission colors were well tuned by the combination of Tm, Er and Ho ions and their concentrations. CaMoO₄:Tm³⁺,Ho³⁺,Yb³⁺ exhibited perfect white emission with well tunability from cool white to warm white colors. Substitution of part of Ca ions by M⁺ (M = Li, Na, K, Rb) ions affected the crystal field symmetry around RE³⁺ ions and hence changed the transition probabilities between their f–f transition levels, consequently intensified the UC intensities. The blue (Tm³⁺), green (Er³⁺), and orange (Ho³⁺) upconversion intensities of CaMoO₄:RE³⁺,Yb³⁺,0.10 K⁺ phosphors increased by 60, 50 and 40 folds compared to the unsubstituted analogues, respectively. The K substituted CaMoO₄:RE³⁺,Yb³⁺,K⁺ phosphors exhibited intense UC emissions visible by naked eye even pumped by less than 1 mW laser power and can have potential application in displays and variety of other applications.     

Enhancement of red fluorescence and afterglow in CaWO4:Eu3+ by addition of MoO3

In this study, Eu³⁺ doped Ca(WO₄)_1?x(MoO₄)_x phosphors were synthesized via high temperature solid-state reaction. Compared with the Eu³⁺ activated CaWO₄ sample, an increment of MoO₃ doping concentration could improve the emission intensity. Improved red afterglow originating from the ⁵D₀ to ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ was observed after appropriate amount of MoO₃ was added, and the optimal MoO₃ doping concentration was experimentally determined to be 0.02. The proposed explanation for the afterglow property was also discussed.     

Red phosphor Li2Mg2(WO4)3: Eu3+ with lyonsite structure for near ultraviolet light-emitting diodes

A series of Eu³⁺-activated Li₂Mg₂(WO₄)₃ (LMW) materials were synthesized by high temperature solid state reactions. The phosphor can be effectively excited by 394 nm near ultraviolet light and emit intense red light with high color purity. Prepared phosphors can be indexed to LMW with particular lyonsite structure. The occupation of Eu³⁺ in LMW is selective. Most of Eu³⁺ comes into ¹A sites without inversion symmetry. The present research suggests that LMW is a suitable host for luminescence applications and Eu³⁺-activated LMW is a promising phosphor for phosphor-converted white light-emitting diodes.     

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.     

Facile synthesis of lanthanide vanadates and their luminescent properties

GdVO₄:Eu³⁺, Bi³⁺ with tetragonal phase has been successfully synthesized by employing efficient irradiations. The assembly of composites with fine grains based on acoustic energy and microwave radiation requires low temperature (90 °C) and short reaction time (60 min). All the compounds exhibited red emissions and they can be sensitized through the doped Bi³⁺ ions. The dependence of pH changes and doping concentration on the fluorescence features has been discussed. The photoluminescence measurements show that the optical properties achieved the best results at pH = 9 for GdVO₄:Eu³⁺(5 mol%), Bi³⁺(1 mol%) or pH = 7 for GdVO₄:Eu³⁺.     

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.