Papers by Keyword: Phosphor

Abstract: Ho³⁺/Yb³⁺ co-doped ZnO-TiO₂ composite system were synthesized by powder-solution mixing method and their upconversion (UC) luminescence characteristics were investigated under the 980 nm laser excitation. The effect of various ZnO/TiO₂ mixing ratios, and Ho³⁺ and Yb³⁺ concentrations were also studied. The XRD patterns showed that the product fired at 1300 °C consisted of Zn₂TiO₄, TiO₂, RE₂Ti₂O₇, and RE₂TiO₅ (RE = Ho³⁺ and/or Yb³⁺) phases. The green emission centered at 538 nm wavelength was detected as the strongest emission intensity which it was in accordance with the ⁵F_4, ⁵S₂ → ⁵I₈ transition of Ho³⁺ ion. The emission intensity of the product changed by varying ZnO/TiO₂ mixing ratios, and Ho³⁺ and Yb³⁺ concentrations. Brightest UC emission was observed in the sample of 1ZnO:1TiO₂ (in mole) doped with 0.03 mol% Ho³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h. Besides, the dependence of the UC emission intensity on the excitation power indicated that the two-photon process was responsible for this UC system.

Abstract: A novel blue-emitting phosphor, Li₃Gd₃Te₂O₁₂:Tm³⁺ for white light-emitting diodes (W-LEDs) was prepared by solid-state synthesis and its structure and luminescence properties were investigated. This phosphor shows a satisfactory blue performance (peak at 458 nm) due to the ¹D₂ → ³F₄ transition of Tm³⁺ excited by 361 nm light. Investigation of Tm³⁺ content dependent emission spectra indicates that x = 0.03 is the optimum doping content of Tm³⁺ ions in the Li₃Gd₃Te₂O₁₂ host. The critical distance and the concentration quenching mechanism were also investigated. In particular, the color purity of as-prepared sample is close to that of the commercial blue phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺). The present work suggests that the Li₃Gd₃Te₂O₁₂:Tm³⁺ phosphor is a potential blue-emitting candidate for the application in the near-UV WLEDs.

Abstract: Well-grown Ba₉Sc₂Si₆O₂₄:Ce³⁺ phosphors were synthesized by a novel melt quenching synthesis method. Sintered phosphor balls with excellent luminescent characteristics were obtained. This method is useful tool for rapid screening of phosphor materials.

Abstract: A series of novel luminescent materials Ca₁₀M(PO₄)₇:Eu²⁺ (M: Li, Na, K) were synthesized by the solid-state reaction. The previous literatures indicate that the doped different alkali metal ions can only lead to regular shift of the emission and excitation spectra. Howerver, in this paper, we found the result that these three kinds of phosphors showed huge differences between the emission spectra intensity as well as the positions of the excitation and emission spectra peaks. No any regulars can be found. In order to explore it, crystal structure, the performance of photoluminescence spectra and CIE coordinates have been systematically investigated and discussed. In Ca₁₀Li (PO₄)₇, Ca₁₀Na (PO₄)₇ and Ca₁₀K(PO₄)₇ host lattices, the positions of the cations are different, leading to three different crystal structures. Besides, the coordination conditions of the luminescent centers Eu²⁺ ions are also changed by the incorporation of the alkali metal ions. Thus the enormous disparity on the luminescence intensity as well as the excitation and emission peak positions may be ascribed to these three quite different crystal fields and different coordination numbers of the luminescent central ion in the Ca₁₀M(PO₄)₇:Eu²⁺ (M: Li, Na, K) phosphors.

Abstract: The Ce doped Strontium Magnesium silicate phosphor Sr₂MgSi₂O₇:Ce is compounded by using high temperature roasting process, and the plane sample of prepared phosphor is obtained by tablet press method. A modified MCJ-01A friction tester with the friction pair of glass bar against on the plane phosphor sample is used to determine the triboluminescence property of Ce doped Strontium Magnesium silicate phosphor in the linear contact sliding friction. Examination on the triboluminescence of Ce doped Strontium Magnesium silicate phosphor indicates that a quality triboluminescent phosphor with 448nm± blue spectrum emission can be obtained only in the 1200°C calcining temperature, and only 0.010 molar Ce doping concentration in the Sr₂MgSi₂O₇:Cex can promote the prepared phosphor to generate a higher triboluminecent emission and a smaller full width at half maximum (FWHM). The suitable level of applied load is beneficial to hold a balance between wear increment and spectrum intensity. Finally a triboluminescent unit with squirrel cage structure is constructed to realize the triboluminescence of multiple glass bars against on the cylindrical phosphor in the manner of sliding friction. This can satisfy the light emitting of 360o azimuth, and generate more tribological luminous flux.

Abstract: The aim of this research was to find out the way of the synthesis temperature reduction without deterioration of the phosphors optical properties. Since crystallization of Eu,Ca-α-sialon occurs by means of sialon crystallization from the oversaturated oxynitride liquid, thus a rise of the liquid phase amount could be performed not only via an increase of temperature but also through the application of the low eutectic additives. Al₂O₃ and AlF₃ additives have been chosen as the sources of liquid at the reaction temperature. The syntheses were carried out in a graphite furnace at 1650°C and the powders were characterized for their phase composition, particles morphology, excitation and emission properties and their quantum yield of luminescence was compared. It has been found that alumina addition to the initial mixture of nitrides was the most effective in formation of sialon solid solution with a minor contamination with AlN. Emission intensity of sialon phosphor was doubled if they were synthesized with each of additives. Quantum yield of tested phosphors was over 0.85 if excited at 380 nm for alumina and similar for AlF₃ modified composition. A significant particles refinement was observed if AlF₃ was applied.

Abstract: The red phosphor (TiZn₂O₄) is formed from TiO₂ and ZnO via simple solid-state reaction. This red phosphor is prepared by chemically stable as well as inexpensive oxide materials. Emission and excitation spectra are investigated for this phosphor. Photoluminescence (PL) measurements reveal that this phosphor emits bright red emission at 611 nm, which is associated with ⁵D₀ – ⁷F₂ transition, with near UV (395 nm) and blue light excitation (470 nm). The measured decay time of this red emission can be fitted well with a fast decay time of 67 ms and a slow decay time of 208 ms, respectively. A broad grain size distribution is observed for TiZn₂O₄ phosphor. Further, photoluminescence excitation (PLE) shows a good absorption band near UV, and the blue spectral region of visible spectrum as well. The optical properties, X-ray diffraction (XRD) measurements, and scanning electron micrographs (SEM) of this TiZn₂O₄ phosphor are studied.

Abstract: The Lu₂SiO₅ dried gel was prepared by the sol-gel reaction followed by a 24h drying at 90°C.The thermogravimetry–differential scanning calorimetry (TG-DSC) analysis curves of the dried gel demonstrates mass and enthalpy changes as temperature raised.The obtained dried gel was calcined at 900°C,1000°C,1100°Cand1200°C each for 2h to prepare polycrystalline Eu³⁺-dropped Lu₂SiO₅ phosphor.The phase composition and crystal structure was identified with an X-ray diffractometer (XRD).The dried gel was crystallized into A-type LSO phase at 1000°C, and transferred to B-type LSO phase when temperature was raised above 1050°C.The obtained LSO grain size is 200-300nm revealed in Field-emission scanning electron microscopy (FE-SEM) images.The photoluminescence spectrum of the obtained 2mol% Eu³⁺-dropped Lu₂SiO₅ phosphor showed a broad excitation band around 263nm and a sharp emission peak at 613nm.

Abstract: Well-grown M₃MgSi₂O₈ (M = Ca, Sr and Ba):Eu²⁺ phosphors were synthesized by novel melt quenching synthesis method. The luminescence property of the Sr₃MgSi₂O₈:Eu²⁺ phosphor synthesized by the melt synthesis method is comparable to those of the sample synthesized by a conventional solid state reaction. Sintered phosphor balls with excellent luminescent characteristics were obtained.

Abstract: A novel blue-emitting Sr₃NaLu (PO₄)₃F:Eu²⁺ phosphor for white light-emitting diodes (w-LEDs) have been successfully prepared via the solid-state reaction. The crystal structure and phase of the prepared phosphors were investigated using X-ray diffraction (XRD). The band gap of Sr₃NaLu (PO₄₎₃F was estimated to be about 5.79 eV from the diffuse reflection spectrum. The Sr₃NaLu (PO₄)₃F:0.05Eu²⁺ phosphor exhibits an intense and broad excitation band ranging from 200 to 450 nm in the near ultraviolet region and produces a bright blue emission band with the CIE chromaticity coordinates of x = 0.133 and y = 0.148 under the excitation of 365 nm, which were ascribed to the 4f-5d transitions of Eu²⁺. Moreover, the fluorescence decay curves were also investigated in detail. All the results suggest that Sr₃NaLu (PO₄)₃F:Eu²⁺ might be a promising blue-emitting phosphor used in w-LEDs.