Highly water resistant surface coating by fluoride on long persistent Sr4Al14O25:Eu/Dy phosphor

A novel and efficient method of providing moisture resistance of inorganic particles such as divalent europium activated strontium aluminate phosphors (Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺) was developed by firing the phosphor in the presence of appropriate amount of ammonium fluoride at a temperature of 600-700 °C. Scanning electron microscopy, X-ray diffraction, FT-IR, EDAX and Photoluminescence measurements were carried out to characterize the uncoated and coated samples. The pH measurements were carried out for the water resistivity measurements. The phosphor particles became coated with a moisture-impervious thin coating that did not suppress the luminescence of the phosphor and can withstand complete immersion in water for long periods of time, showing very high water resistivity.     

Luminescence in trivalent rare earth activated Sr4Al2O7 phosphor

In this paper we report the combustion synthesis of trivalent rare-earth (RE³⁺ = Dy, Eu and Ce) activated Sr₄Al₂O₇ phosphor. The prepared phosphors were characterized by the X-ray powder diffraction (XRD) and photoluminescence (PL) techniques. Photoluminescence emission peaks of Sr₄Al₂O₇:Dy³⁺ phosphor at 474 nm and 578 nm in the blue and yellow region of the spectrum. The prepared Eu³⁺ doped phosphors were excited by 395 nm then we found that the characteristics emission of europium ions at 615 nm (⁵D₀?⁷F₂) and 592 nm (⁵D₀?⁷F₁). Photoluminescence (PL) peaks situated at wavelengths of 363 and 378 nm in the UV region under excitation at around 326 nm in the Sr₄Al₂O₇:Ce³⁺ phosphor.     

Oxide coatings on Y3Al5O12:Tb particles

A coating method with precipitating process was developed to reduce the particle size and to improve the particle dispersion of Y₃Al₅O₁₂:Tb³⁺ phosphor prepared by sol-gel method. The particle morphology was observed by using SEM and TEM; and the particle size and its dispersion was measured by using laser scattering technique. Several coating materials were tested. Among them, Al₂(SiO₃)₃ coating not only reduced the particle size from several micrometers to ∼1 μm and improved the particle dispersion, but also well kept luminescent intensities and improved the duration of the phosphor under the bombardment of cathode ray. The mechanism of the particle size reduction was proposed.     

Photoluminescence and thermoluminescence of Ce and Eu in Ca2Al2SiO7 matrix

The Ca₂Al₂SiO₇ samples doped with Ce³⁺ and Eu²⁺ are synthesized via a high temperature solid-state reaction. Ca₂Al₂SiO₇: Ce³⁺ emits a strong UV-violet emission while Ca₂Al₂SiO₇: Eu²⁺ emits a blue-green emission. The Stokes shift of the latter is greater due to a stronger crystal repulsion from ligands to Eu²⁺ ions. Ca₂Al₂SiO₇: Ce³⁺ exhibits a stronger initial intensity and longer duration of afterglow due to the higher liberated probability of the trapped carriers. The thermoluminescence curves reveal that at least three traps exist in the phosphors. Ca²⁺ vacancies may enhance the electron trapping and then lead to a stronger afterglow. A possible explanation will be provided.     

Acetate reduction synthesis of Sr2Si5N8:Eu phosphor and its luminescence properties

A novel synthesis method was developed for the efficient red phosphor, Eu²⁺-activated Sr₂Si₅N₈, by employing the strontium acetate as both the reducing agent and strontium source. The phase purity of final product was strongly dependent on the heating rate of the precursors. Sr₂Si₅N₈:Eu²⁺ (2 at%) phosphor presented a broadband excitation spectrum in the range 300–500 nm, matching well with the blue emission (400/460 nm) of current InGaN light-emitting diodes (LEDs). The red emission peaking at 619 nm gave the relatively high (about 155%) intensity compared with the Y₃Al₅O₁₂ (YAG) (P46-Y3) standard phosphor. In addition, the saturated chromatic coordinates (0.638, 0.359) allowed it a promising candidate as a red phosphor in white LEDs application for illumination or display.     

ErP5O14非晶玻璃的红外量子剪裁

研究了Er_1.0P₅O₁₄铒非晶玻璃的红外量子剪裁现象. 从吸收谱和激发光谱的计算比较中肯定了Er_1.0P₅O₁₄非晶 玻璃的1537.0 nm红外荧光为多光子量子剪裁荧光. 从Er_1.0P₅O₁₄非晶玻璃的可见和红外荧光发射光谱中发现激发²H_11/2, ⁴G_11/2和⁴G_9/2能级所导致的⁴I_13/2→⁴I_15/2量子剪裁红外荧光很强;基于自发辐射速率、无辐射弛豫速率和能量传递速率等参数的计算,对其量子剪裁机理进行了分析.发现起源于基态的强下转换能量传递{²H_11/2→⁴I_9/2,⁴I_15/2→⁴I_13/2},{⁴G_11/2→⁴I_13/2, ⁴I_15/2→²H_11/2},{⁴G_9/2→⁴F_7/2,⁴I_15/2→⁴I_13/2}和{⁴G_9/2→⁴I_13/2, ⁴I_15/2→²H_11/2}是导致Er_1.0P₅O₁₄非晶玻璃具有强的三光子和四光子量子剪裁红外荧光的原因.研究结果对改善太阳能电池效率有一定意义.     

Energy transfer and luminescent properties of Ce, Cr co-doped Y3Al5O12

The phosphors in the system Y_3−xAl_5-yO₁₂:xCe³⁺,yCr³⁺ were synthesized by solid-state reactions and their photoluminescence properties were investigated. These phosphors have absorption in the visible light region and give luminescence in the far-red region (∼688 nm), which are suitable for the application in the device of luminescent solar concentrator (LSC). In these phosphors, Ce³⁺ located at Y³⁺ site can effectively transfer its absorbed energy to Cr³⁺ at Al³⁺ site.     

Enhanced luminescence of Dy in Y3Al5O12 by Bi co-doping

In the present paper, phosphors with the composition Y_3−x−yAl₅O₁₂:Bi³⁺_x, Dy³⁺_y were synthesized with solid state reactions. The luminescence properties of Bi³⁺ and Dy³⁺ in Y₃Al₅O₁₂(YAG) and the energy transfer from Bi³⁺ to Dy³⁺ were investigated in detail. Bi³⁺ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states ³P_{0, 1} to ground state ¹S₀. Dy³⁺ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state ⁴F_9/2 to ground states ⁶H_15/2 and ⁶H_13/2. The co-doping of Bi³⁺ enhances the luminescent intensity of Dy³⁺ by ∼7 times because Bi³⁺ can transfer the absorbed energy to Dy³⁺ efficiently. The mechanism of energy transfer was also discussed.     

Emission analysis of Pr and Tm: Ca2Gd2W3O14 phosphors

5 mol% of Pr³⁺ and Tm³⁺ ions activated calcium gadolinium tungstate (Ca₂Gd₂W₃O₁₄₎ phosphors were synthesized by traditional solid state reaction method. Crystalline phase structure was identified from the X-ray diffraction (XRD) profiles. From the scanning electron microscopy (SEM) images, we have observed the agglomeration of the particles, and average grain size is around 40-300 nm. Using the energy dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectra, identified the elements and functional groups present in the prepared phosphors. The emission spectrum of Pr³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown an intense red emission at 615 nm with the excitation wavelength λ_exci=450 nm and thus these red color emitting powder phosphors are used as one of the components in the preparation of WLEDs. The excitation spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ powder phosphor has shown a ligand to metal charge transfer (W-O) band (LMCT) within the WO₄²⁻ group. Emission spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ phosphors have shown blue emissions at 453 nm (¹D₂→³F₄).     

Synthesis and Sm/Sm doping effects on photoluminescence properties of Sr4Al14O25

Complete and partial samarium reduction was achieved under strong reducing atmosphere by solid-state and combustion synthesis of Sr_3.96Sm_0.04Al₁₄O₂₅. Dependence of different fluxing agents on the formation of various strontium aluminates was examined. The samples were investigated by X-ray powder diffraction, temperature dependent luminescence decay and photoluminescence measurements. Excitation with UV radiation resulted in sharp and well resolved emission lines of samarium ions. Distinct temperature behavior for Sm²⁺ and Sm³⁺ were detected in the range of 100-500 K. Estimated emission thermal quenching values (TQ_1/2) for divalent samarium were approximately 270 K while for trivalent state around 660 K. Measured luminescence decay values of Sm²⁺ are substantially lower than for Sm³⁺,≈1.7 and ≈2.7 ms, respectively. The spectral feature of Sm²⁺ emission spectrum indicates that dopant occupies low symmetry site in Sr₄Al₁₄O₂₅ compound.     

Synthesis of nano-size BaMgAl10O17:Eu blue phosphor by a rapid exothermic reaction

Ultrafine particles of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphor were synthesized by a solid-state combustion reaction in a powder bed of 0.9BaCO₃+MgO+5Al₂O₃+0.05Eu₂O₃+k(KClO₃+1.5C) composition. A large exothermic reaction of the mixture (KClO₃+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.     

Al NMR studies of NpPd5Al2

We present ²⁷Al NMR studies for a single crystal of the Np-based superconductor NpPd₅Al₂. We have observed a five-line ²⁷Al NMR spectrum with a center line and four satellite lines separated by first-order nuclear quadrupole splittings. The Knight shift clearly drops below T_c. The temperature dependence of the ²⁷Al nuclear spin-lattice relaxation rate shows no coherence peak below T_c, indicating that NpPd₅Al₂ is an unconventional superconductor with an anisotropic gap. The analysis of the present NMR data provides evidence for strong-coupling d-wave superconductivity in NpPd₅Al₂.     

First-principles calculations of structural and thermodynamic properties of Y 3Al5O12

The pseudo-potential plane-wave method using the generalized gradient approximation (GGA) within the framework of the density functional theory is applied to study the structural and thermodynamic properties of Y ₃Al₅O₁₂. The lattice constants and bulk modulus are calculated. They keep in good agreement with other theoretical data and experimental results. The quasi-harmonic Debye model, in which the phononic effects are considered, is applied to the study of the thermodynamic properties. The temperature effect on the structural parameters, bulk modulus, thermal expansion coefficient, specific heats and Debye temperatures in the whole range from 0 to 20 GPa and temperature range from 0 to 1500 K.     

超声喷雾共沉淀法制备的Lu3Al5O12∶Eu3+ 纳米粉体发光特性

采用新型超声喷雾共沉淀法技术,以Lu₂O₃、Eu₂O₃、Al(NO₃)₃·9H₂O为原料,制备了不同浓度Eu³⁺离子掺杂的Lu₃Al₅O₁₂纳米粉体.用X射线粉末衍射表征了获得纳米粉体的相,用扫描电镜观察了纳米粒子的形貌.测定了粉体的激发光谱、⁷F₀-⁵D₂声子边带谱与发射光谱.研究了不同高温烧结温度与Eu³⁺掺杂浓度对纳米粒子的发光强度与粒子形貌的影响规律.研究表明,当烧结温度高于900 ℃时,粉体发光强度明显增强,并且随着煅烧温度的增加,发光强度有所增强.Eu³⁺离子的最佳掺杂浓度为5~7 mol%.根据稀土离子Eu³⁺光学跃起矩阵元的特点,从发射光谱获得Eu³⁺光学跃起的J-O参量Ω₂与Ω₄.在Eu³⁺掺杂浓度均为5 mol%时,其强度参量达最小,电-声子耦合最强.然后随着掺杂浓度的进一步提高,强度参量略有增加,电-声子耦合减弱.说明Eu-O键强增加,共价性增强,Eu³⁺的局域环境对称性降低.Ω₂值低于Eu³⁺在玻璃与晶体基质中的情况,这是由于纳米粒子中存在着大量的缺陷以及晶体的结构畸变导致纳米粒子的对称性下降所致.     

Effects of dopant concentrations on phosphorescence properties of Eu/Dy-doped Sr3MgSi2O8

Long afterglow Sr₃MgSi₂O₈: Eu, Dy phosphor with high brightness was prepared by sintering at high temperature and weak reductive atmosphere. The luminescent properties of this photoluminescent pigment were studied systematically by investigating concentration effects. The analytical results indicated that the main emission peaks appear at 482 nm. The excitation and emission spectra of this phosphor show that both of them are broadband. This is ascribed to the 4f⁷→4f⁶5d¹ transition of Eu²⁺ in the pigment matrix, which is in good agreement with the calculated value of 470 nm, and implies that luminescent centers Eu²⁺ occupy the deca-coordinated Sr²⁺ sites with the host of Sr₃MgSi₂O₈.     

The structure and luminescence properties of a novel orange emitting phosphor Y3MnxAl5−2xSixO12

A series of phosphors with the composition Y₃Mn_xAl_5−2xSi_xO₁₂ (x=0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6) was prepared through solid state reactions. X-ray powder diffraction analysis of samples shows that when co-doping content does not exceed 16% of Al³⁺, equimolar co-doping of Mn²⁺ and Si⁴⁺ does not change the garnet structure of phosphors, but makes the interplanar distance to decrease a certain extent. However, if the co-doping content exceeds 16%, new phases will form in the samples. The excitation and emission spectra of samples show that Mn²⁺ in Y₃Mn_xAl_5−2xSi_xO₁₂ emits broadband orange light (peak wavelength varies from 586 to 593 nm). With an increment in co-doping content, the emission intensity of the phosphors increases when the value of x is lower than 0.1 while it decreases when it is higher than 0.1 and the emission peak moves to a longer wavelength.     

The structure and luminescence properties of long afterglow phosphor Y3−xMnxAl5−xSixO12

A series of phosphors with the composition Y_3−xMn_xAl_5−xSi_xO₁₂ (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn²⁺ and Si⁴⁺ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn²⁺ in Y₃Al₅O₁₂ emits yellow-orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn²⁺ and Si⁴⁺ co-doped samples emit yellow-orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18 min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content.     

Low thermal quenching and high-efficiency Ce, Tb-co-doped Ca3Sc2Si3O12 green phosphor for white light-emitting diodes

Low thermal quenching and high-efficiency Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSSO:Ce³⁺) phosphors with co-doping Tb³⁺ ion were prepared by a solid state method and the properties of these phosphors were investigated. The results showed that co-doping of Tb³⁺ not only enhances the photoluminescence remarkably and decreases the thermal quenching of the phosphor, but also heightens the performances of the LEDs fabricated with the phosphor. A high-efficiency and low color temperature white LED was fabricated with the prepared CSSO:1%Ce³⁺, 0.5%Tb³⁺ and a red phosphor, indicating that CSSO:1%Ce³⁺,0.5%Tb³⁺ phosphor is a suitable green phosphor for the fabrication of high-efficiency white LEDs.     

Luminescent properties of a new green emitting Eu doped CaZrSi2O7 phosphor for WLED applications

CaZrSi₂O₇ (CZS), a modification of the thortveitite family, was prepared as a polycrystalline powder material by the conventional solid-state reaction method. Structural, thermal and photoluminescence (PL) properties of the prepared material were investigated in order to evaluate its potentiality. XRD patterns confirm the monoclinic phase of CaZrSi₂O₇: Eu²⁺ phosphors.. Emissions arising from transitions between the 5d and 4f orbital gaps of Eu²⁺ are manifested in the broadband excitation and emission spectra with major peaks at 363 and 512 nm, respectively. The excitation wavelength matches well with that of the emission of the ultraviolet-light emitting diode (UV-LED). Concentration quenching occurs when the Eu²⁺ concentration is beyond 0.05 and the dipole-dipole interaction was the reason for the corresponding quenching mechanism. The temperature dependence of emission intensity of CZS: Eu²⁺ phosphor was investigated and it showed better thermal stability than the standard YAG: Ce³⁺ phosphor.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.