Weiren Zhao

Luminescence properties of red phosphors Ca10Li(PO4)7:Eu3+

A series of red phosphors Ca10Li(PO4)7:Eu3+ were synthesized by high temperature solid-state reaction method. Their luminescence properties were characterized by means of photoluminescence excitation and emission spectra, CIE chromaticity and quantum efficiency. Results indicated that the phosphors could be effectively excited by the near ultraviolet (NUV) light (393 nm). The main emission peaks of the phosphor were ascribed to the transition 5D0-7F2 (613 and 617 nm) of Eu3+ ion when samples were excited by 393 nm. The CIE chromaticity (x, y) of Ca9.9Li (PO4)7:0.10Eu3+ was x=0.638, y=0.361 and the quantum efficiency of this phosphor was 75% excited by 393 nm. Therefore, this phosphor could be a promising red component for the applications in white LEDs.

Photoluminescence characterization of Ca10Na(PO4)7:Eu3+ red-emitting phosphor

Eu3+-doped Ca10Na(PO4)7 phosphors were successfully synthesized by solid-state reaction techniques. Their structures and photoluminescence characteristics were carefully studied. An efficient red emission under near-ultraviolet excitation is observed. The maximum intensity of luminescence was observed at the Eu3+ concentration around 9 mol%. The quadrupole-quadrupole interaction between Eu3+ ions is the dominant mechanism for concentration quenching of fluorescence emission from Eu3+ ions in Ca10-xNa(PO4)7:xEu3+. Due to the excitation spectrum is well coupled with near UV light, Ca10-xNa(PO4)7:xEu3+ phosphors have potential application as red phosphors in near UV chip-based white light emitting diodes.

Hydrothermal synthesis and luminescence properties of Eu3+ and Sm3+ codoped BiPO4

Abstract Eu3+/Sm3+ codoped BiPO4 phosphors were synthesized via a facile hydrothermal method with surfactant-free environment. The X-ray diffraction analysis demonstrated that the samples possessed the standard BiPO4 monoclinic structure. Scanning electron microscopy images showed that all samples composed of well-dispersed, micrometer-sized crystals with shuttle-like shape. Energy transfer from Sm3+ to Eu3+ was confirmed by the luminescence spectra and the decay processes of Sm3+ 4G5/2→6H5/2 emission. Orange-red luminescence could be obtained in Eu3+/Sm3+ codoped BiPO4 phosphors. The average lifetime of Sm3+ 4G5/2→6H5/2 emission decreased from 2.70 ms in BiPO4:0.03Sm3+ to 2.37 ms in BiPO4:0.03Sm3+,0.05Eu3+. The strong and wide absorption band around 395 nm, originating from both 7F0→5L6 transition of Eu3+ and 6H5/2→4K11/2 transition of Sm3+, endowed BiPO4:Eu3+,Sm3+ phosphors with the potential application in the fields of near UV-excited white-light-emitting diodes.

Photoluminescence characterization and energy transfer of NaBa1−x−yPO4:xCe3+, yTb3+ phosphors

Abstract A series of NaBa 1− x−y PO 4 : x Ce 3+ , y Tb 3+ phosphors were synthesized by solid-state reaction method. The crystal structure, photoluminescence emission and excitation spectra and decay times of the phosphors were carefully investigated. The results revealed that an efficient energy transfer occurred from Ce 3+ to Tb 3+ ions in NaBaPO 4 host by means of dipole-dipole interactions and the critical distance of the energy transfer was about 0.638 nm. Moreover, the phosphor emitted strong green emission under UV excitation, indicating that the phosphors are potentially useful as a highly efficient, green-emitting phosphor.

A novel long lasting phosphor Sr5 (PO4)3FxCl1-x:Eu2+,Gd3+ prepared in air condition

Abstract A series of blue long afterglow mixed halide-phosphate phosphors Sr5 (PO4)3 FxCl1−x:Eu2+,Gd3+ were synthesized in air by traditional solid-state reaction route. The crystal structures, photoluminescence, thermoluminescence properties and afterglow properties of the phosphors were characterized systematically using X-ray diffraction (XRD), luminescence spectrophotometer, microcomputer thermoluminescence dosimeter and single photon counter, respectively. Under 280 nm excitation, the broadband emissions of Eu2+ ions were observed at 445 nm (blue) due to the 4f7→4f65d transition. It was demonstrated that there existed the self-reduction of the Eu3+ to Eu2+ ions in this special halide-phosphate matrix in air condition. The addition of Gd3+ ions obviously enhanced the afterglow properties of the single doped Eu2+ ions in the halide-phosphate phosphors. And the content of the fluoride anions also had significant influence on the afterglow properties. All results indicated that Sr5 (PO4)3 FxCl1−x:Eu2+,Gd3+ might be potential phosphors for long lasting phosphorescence (LLP) materials.

Synthesis, electronic structures, and photoluminescence properties of an efficient and thermally stable red-emitting phosphor Ca3ZrSi2O9:Eu3+,Bi3+ for deep UV-LEDs

A series of red-emitting Ca3ZrSi2O9:Eu3+,xBi3+ phosphors was synthesized using a conventional high temperature solid-state reaction method, for the purpose of promoting the emission efficiency of Eu3+ in a Ca3ZrSi2O9 host. The site preference of Bi3+ and Eu3+ in the Ca3ZrSi2O9 host was evaluated by formation energy. The effects of Bi3+ on electronic structure, luminescent properties, and related mechanisms were investigated. The inner quantum yield of the optimized sample increased to 72.9% (x = 0.08) from 34.6% (x = 0) at 300 nm ultraviolet light excitation. The optimized sample (x = 0.08) also showed excellent thermal stability, and typically, 84.2% of the initial emission intensity was maintained when the temperature increased to 150 °C from 25 °C, which is much higher than that without Bi3+ doping (70.1%). The mechanisms of emission properties and thermal stability enhancement, as well as the redshift of the charge transfer band (CTB) induced by Bi3+ doping in the Ca3ZrSi2O9:Eu3+ phosphor, were discussed. This study elucidates the photoluminescence properties of Bi3+-doped Ca3ZrSi2O9:Eu3+ phosphor, and indicates that it is a promising luminescent material that can be used in ultraviolet light-emitting diodes.

Highly efficient red emission and multiple energy transfer properties of Dy3+/Mn4+ co-doped Ca14Zn6Ga10O35 phosphors

Novel Dy3+/Mn4+ co-doped Ca14Zn6Ga10O35 phosphors have been synthesized by a solid state reaction technique. Strong blue emission ranging from 370 nm to 500 nm was observed for the Ca14Zn6Ga10O35 host, attributed to the recombination of a donor–acceptor pair through a tunneling process. High internal and external quantum efficiencies of 64.4% and 56.2% respectively were obtained under the excitation of 310 nm in Mn4+ doped Ca14Zn6Ga10O35. This external quantum efficiency is the highest one reported for Mn4+ doped oxides. The temperature-dependent quantum efficiency of Ca14Zn6Ga10O35:Mn4+ is also measured, indicating the unchanged absorption of the excitation light with temperature. In Ca14Zn6Ga10O35:Dy3+, Mn4+ phosphors, multiple energy transfer from the host to Dy3+ and from Dy3+ to Mn4+ is observed and is confirmed to be a result of the dipole–dipole interaction. The emission changes from deep blue to white to deep red according to the different Dy3+/Mn4+ concentration ratio, and the warm white emission can be realized with the chromaticity coordinate (0.345, 0.275), CCT 3525 K and CRI 87. These results suggest that Ca14Zn6Ga10O35:Mn4+ phosphors have potential application as high efficiency red phosphors for solid-state lighting, while Dy3+/Mn4+ co-doped Ca14Zn6Ga10O35 phosphors can be used as a single-phased white phosphor.

The Preparation and Optical Properties of Novel LiLa(MoO4)2:Sm3+,Eu3+ Red Phosphor

Novel LiLa1−x−y(MoO4)2:xSm3+,yEu3+ (in short: LL1−x−yM:xSm3+,yEu3+) double molybdate red phosphors were synthesized by a solid-state reaction at as low temperature as 610 °C. The optimal doping concentration of Sm3+ in LiLa1−x(MoO4)2:xSm3+ (LL1−xM:xSm3+) phosphor is x = 0.05 and higher concentrations lead to emission quenching by the electric dipole—electric dipole mechanism. In the samples co-doped with Eu3+ ions, the absorption spectrum in the near ultraviolet and blue regions became broader and stronger than these of the Sm3+ single-doped samples. The efficient energy transfer from Sm3+ to Eu3+ was found and the energy transfer efficiency was calculated. Under the excitation at 403 nm, the chromaticity coordinates of LL0.95−yM:0.05Sm3+,yEu3+ approach to the NTSC standard values (0.670, 0.330) continuously with increasing Eu3+ doping concentration. The phosphor exhibits high luminous efficiency under near UV or blue light excitation and remarkable thermal stability. At 150 °C, the integrated emission intensity of the Eu3+ remained 85% of the initial intensity at room temperature and the activation energy is calculated to be 0.254 eV. The addition of the LL0.83M:0.05Sm3+,0.12Eu3+ red phosphors can improve the color purity and reduce the correlated color temperature of WLED lamps. Hence, LL1−x−yM:xSm3+,yEu3+ is a promising WLED red phosphor.