Papers by Keyword: Luminescence

Abstract: Ten kinds of terbium doped inert yttrium complexes with 2,3-pyrazinedicarboxylate (2,3-pzdc^2-) have been synthesized. Characterization results indicate that the complexes have the compositions of Tb (pzdc)_1.55H₂O and Tb_xY_y(pzdc)_1.55H₂O (x:y=0.10:0.90; 0.20:0.80; 0.30:0.70; 0.40:0.60; 0.60:0.40; 0.70:0.30; 0.80:0.20; 0.90:0.10). IR spectra show that the lanthanide ions coordinate with the carboxylic oxygen atoms and nitrogen atoms of the ligands. Luminescence spectra show that the Y(III) ions can remarkably increase the luminescent intensities of terbium complexes. And Tb_0.7Y_0.3(pzdc)_1.55H₂O exhibits the strongest luminescent emission. Furthermore, the doped lanthanide complexes show longer luminescence lifetimes and higher quantum yields. The enhanced luminescence efficiencies of Tb³⁺ ions in the doped complexes may result from intramolecular energy transfer as well as the decrease of the self-quench of the Tb³⁺ ions induced by the doped Y(III) ions.

Abstract: Luminescent Ln³⁺ (Ce³⁺, Tb³⁺) doped hydroxyapatite (HAp: Ce, Tb) phosphors were successfully fabricated via the modified hydrothermal process. The structure, morphology, and luminescent properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectra respectively. The XRD results reveal that the obtained HAp: Ce, Tb phosphors show the characteristic peaks of hydroxyapatite in a hexagonal lattice structure and the import of Ce³⁺and Tb³⁺ causes small change in the crystalline structure and leads to the peaks shifting and declining. It is observed that the as-prepared luminescent samples exhibit nearly equiaxial morphology of dispersed particles about 50-150 nm in size. Under 254 nm UV radiation excitation, the phosphors demonstrate the characteristic ⁵D₄⁷F₃₆ emission lines of Tb³⁺and the excitation of Tb³⁺ is mainly caused by the energy transfer from Ce³⁺. PL intensity of Tb³⁺ doped HAp remarkably strengthened with increment of Ce³⁺ concentration and reached the maximum at the concentration of 4 mol%.

Abstract: For the demand of high color rendering W-LED, we chose (SrCaBa)₃(PO₄)₂SrCl₂:Eu²⁺ blue-emitting phosphor powder as the object of our study, and use high-temperature solid-state reaction method to prepare the phosphor powders in a weak reducing atmosphere. A detailed investigation on the reaction parameters, including kinds and relative ratio of raw materials, sintering temperature and Eu²⁺ activator concentration was conducted in terms of luminescent properties of phosphors powder. Research findings show that optimal reaction parameters are: sintering temperature is 1200°C, Eu²⁺ doping level is 0.15mol. By these parameters, the (SrCaBa)₃(PO₄)₂SrCl₂:Eu²⁺ phosphor powder show bright blue emission around 450nm and can be efficiently excited by violet and ultraviolet light (200nm-440nm). Further we employed the energy transfer between Tb³⁺ and Eu²⁺ and prepared a series of phosphors using (SrCaBa)₃(PO₄)₂SrCl₂ as host material_. Research findings show that emission color can be adjusted from blue to blue green by the ratio of Tb³⁺ to Eu²⁺, with line-like Tb³⁺ green emission overlapped on band-like Eu²⁺ blue emission.

Abstract: The Zn_0.2Ca_0.8TiO₃:0.1Pr³⁺ luminescent materials were prepared by sol-gel technology. The phase transformation of gel was studied by TG-DTA and XRD in heat treatment process. The luminescent properties of phosphor in different calcination temperatures were determined by fluorescence spectrophotometer, and then the best sintering temperature was confirmed. The luminescent properties of phosphor was obtained through the emission/ excitation spectra. The surface appearance measured with SEM. The results showed that the nanoZn_0.2Ca_0.8TiO₃:0.1Pr³⁺ phosphor could be obtained by sol-gel, sintering at 900°C. It sent out red fluorescent under the Ultra Violet. This characteristic emission peak at 614nm is associated with the typical ¹D₂³H₄ transition of Pr³⁺ion.

Abstract: In this study, a novel phase change material was prepared by coordinating rare earth Tb³⁺ ions to the carboxylate groups of a poly (ethylene glycol).The properties of the material were characterized by differential scanning calorimetry (DSC), infrared spectroscopy (IR) and fluorescence spectroscopy. The synthesis and characterization a novel phase change luminescent Tb-PEG/SA material were described in this paper. The result show that this modified PEG material show both good phase change properties and excellent luminescent properties.

Abstract: Binary organic-inorganic mesoporous hybrid materials were prepared by covalntly grafting Lanthanide (III) (Eu) trifluoroacetylaceton (TAA) complexes to the ordered meosoporous silica SBA-15 via hydrothermal method and hydrolysis and co-polycondensation method with the surfactant P123 and TEOS. Besides, Novel ternary lanthanide (III) (Eu) organic-inorganic-polymeric mesoporous hybrid materials have been synthesized as well through the introduction of the organic polymer PMAA to the binary system with covalent bond. We investigated the thermal stability and luminescence properties of hybrids and found that the ternary hybrid materials exhibit better thermal stability and stronger emission intensity. Furthermore, compared with the binary mesoporous material Eu (TAA-SBA-15)₃, the ternary mesoporous material Eu (TAA-SBA-15)₃PMMA exhibits the characteristic emission of the Eu³⁺ ion with a higher luminescence Intensity, suggesting that the introduction of polymer PMMA into the mesoporous matrix is of benefit for the sensitization of Eu³⁺ luminescence, by replacing H₂O groups that can quench the luminescence of Eu³⁺ ion.

Abstract: In this work, the photoluminescence properties of bismuth borate glass doped with Dy³⁺ have been studied. Glasses were prepared using the glass composition formula 30Bi₂O₃ : (70-x)B₂O₃ : xDy₂O₃, where x is 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%. Glass samples were fabricated by the use of the normal melt-quenching technique at the melting temperature of 1,100 °C at 3 hour time intervals. Glass samples were annealed at the temperature of 500 °C at 3 hour time intervals to remove thermal strain. From photoluminescence study, the emission spectra (excited at 451 nm) were observed three emission peaks, which are assigned to ⁴F_9/2⁶H_15/2 (484 nm), ⁴F_9/2⁶H_13/2 (574 nm), and ⁴F_9/2⁶H_11/2 (661 nm) transitions, respectively. The luminescence intensities of all glasses are comparable and the strongest intensity peak at 574 nm was obtained.

Abstract: Anatase TiO₂ nanosheets with different percentage of exposed high-reactive {001} facets were synthesized successfully. Besides the FESEM and TEM anslysis, XRD, Raman, and PL analysis were also conducted systematically to give a new insight on analyzing the as-prepared {001} facets dominated TiO₂ photocatalysts. Photocatalytic activities of the photocatalysts were tested by the degradation of methylene blue (MB) aqueous solution under UV irradiation. The results indicated that there was an optimal percentage of the exposed {001} facets existed to give the highest photocatalytic activity of as-prepared TiO₂ nanosheets. A possible mechanism for the enhanced photocatalytic activity of the {001} facets dominated anatase TiO₂ was also proposed.

Abstract: ZnO single crystals were prepared and then sequentially annealed from 573 to 1073 K in air atmosphere. Optical transmittance spectra (OTS), X-ray excited luminescence (XEL), and photoluminescence (PL) were measured before and after each step of annealing. The lower temperature annealing can enhance the emission but hardly affect the optical transmittance. Contrarily, higher temperature treatments ameliorated the transmittance but degraded emission. Based on experimental results, the blue and green emissions, as well as the 400-500-nm absorption were assigned to isolated zinc interstitial, zinc vacancy and oxygen vacancy in ZnO, respectively. In addition, the defect complexes play important role on optical properties of ZnO crystal. Our results provide further insight into understanding defects and defect complexes in ZnO crystals.

Abstract: Sr₃SiO₅:Eu²⁺ nanophosphors for white LEDs were synthesized by solgel method. The crystalline phases were examined with X-ray diffraction (XRD). Luminescence properties were studied, and effects of the Sr/Si ratio on the emission spectra were also studied. The nanophosphor showed a broad excitation band from 300 to 500 nm and a broad band emission peaking at 593 nm due to the typical electron transition of Eu²⁺ 4f⁷4f⁶5d¹. Remarkable enhancement in luminescence characteristics was observed when excesses silica was used. This phenomenon may be attributed to the improvement of Si sensitized the luminescence of Eu²⁺ in the Sr₃SiO₅ nanophosphor.