共查询到20条相似文献,搜索用时 62 毫秒
1.
Y.H. Song 《Journal of Physics and Chemistry of Solids》2010,71(4):473-475
This study evaluated potential applications of green to yellow-emitting phosphors (Sr1−xSi2O2N2: Eu2+x) in blue pumped white light emitting diodes. Sr1-xSi2O2N2: Eu2+x was synthesized at different Eu2+ doping concentrations at 1450 °C for 5 h under a reducing nitrogen atmosphere containing 5% H2 using a conventional solid reaction method. The X-ray diffraction patterns of the prepared phosphor (Sr1-xSi2O2N2: Eu2+x) were indexed to the SrSi2O2N2 phase and an unknown intermediate phase. The photoluminescence properties of these phosphors (Sr1−xSi2O2N2: Eu2+x) showed that the samples were excited from the UV to visible region due to the strong crystal field splitting of the Eu2+ ion. The emission spectra under excitation of 450 nm showed a bright color at 545-561 nm. The emission intensity increased gradually with increasing Eu2+ doping concentration ratio from 0.05 to 0.15. However, the emission intensity decreased suddenly when the Eu2+ concentration ratio was >0.2. As the doping concentration of Eu2+ was increased, there was a red shift in the continuous emission peak. These results suggest that Sr1-xSi2O2N2: Eu2+x phosphor can be used in blue-pumped white light emitting diodes. 相似文献
2.
Chengkang Chang Wen Li Xiaojun Huang Zhiyu Wang Xi Chen Xi Qian Rui Guo Yuelei Ding Dali Mao 《Journal of luminescence》2010,130(3):347-350
This paper reports the photoluminescence and afterglow behavior of Eu2+ and Eu3+ in Sr3Al2O6 matrix co-doped with Dy3+. The samples containing Eu2+ and Eu3+ were prepared via solid-state reaction. X-ray diffraction (XRD), photo luminescent spectroscope (PLS) and thermal luminescent spectroscope (TLS) were employed to characterize the phosphors. The comparison between the emission spectra revealed that Sr3Al2O6 phosphors doped with Eu2+, Dy3+ and Eu3+, Dy3+ showed different photoluminescence. The phosphor doped with Eu3+, Dy3+ showed an intrinsic f-f transition generated from Eu3+, with two significant emissions at 591 and 610 nm. However, the phosphor doped with Eu2+, Dy3+ revealed a broad d-f emission centering around 512 nm. After the UV source was turned off, Eu2+, Dy3+ activated Sr3Al2O6 phosphor showed excellent afterglow while Eu3+, Dy3+ activated phosphor almost showed no afterglow. Thermal simulated luminescence study indicated that the persistent afterglow of Sr3Al2O6: Eu2+, Dy3+ phosphor was generated by suitable electron traps formed by the co-doped rare-earth ions (Dy3+) within the host. 相似文献
3.
Needle-like SrAl2O4:Eu2+, Dy3+ phosphors had been prepared by calcining the precursors obtained from hydrothermal process at the temperature of 1100 °C in a weak reductive atmosphere of active carbon. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction (XRD) patterns illustrated that the single-phase SrAl2O4 was formed at 1100 °C, which is much lower than that prepared by the traditional method. The transmission electron microscope (TEM) observation revealed the precursors and the resulted SrAl2O4:Eu2+, Dy3+ phosphors had well-dispersed distribution and needle-like morphology with an average diameter about 150 nm at the center and the length up to 1 μm. After irradiation by ultraviolet radiation with 350 nm for 5 min, the phosphors emit green color long-lasting phosphorescence corresponding to the typical emission of Eu2+ ion, both the PL spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties. 相似文献
4.
Eu2+ and Dy3+ co-doped calcium aluminate, barium aluminate and strontium aluminate phosphors were synthesized at an initiating combustion temperature of 500 °C using urea as an organic fuel. The crystallinity of the phosphors was investigated by using X-ray diffraction (XRD) and the morphology was determined by a scanning electron microscope (SEM). The low temperature monoclinic structure for both CaAl2O4 and SrAl2O4 and the hexagonal structure of BaAl2O4 were observed. The effect of the host materials on the photoluminescence (PL) and phosphorescence properties were investigated by using a He-Cd Laser and a Cary Eclipse fluorescence spectrophotometer, respectively. The broad band emission spectra observed at 449 nm for CaAl2O4:Eu2+, Dy3+, 450 nm (with a shoulder-peak at 500 nm) for BaAl2O4:Eu2+, Dy3+ and 528 nm for SrAl2O4:Eu2+, Dy3+ are attributed to the 4f65d1 to 4f7 transition in the Eu2+ ion in the different hosts. 相似文献
5.
Blue-light emitting Sr2CeO4 phosphors were successfully prepared via a microwave-assisted solvothermal method employing ethylene glycol as a solvent. The formation of Sr2CeO4 phase began when the solvothermally derived precursors were heated at 800 °C. With increase in heating temperatures, significantly enhanced excitation and emission intensities were observed because of an increase in the amount of Sr2CeO4. Heating at 1200 °C led to a substantial decrease in mission intensity due to thermal decomposition of Sr2CeO4 at elevated temperatures. The solvothermally derived Sr2CeO4 was found to exhibit higher emission intensity than the solid-state-reaction-derived phosphors. According to the deconvoluted emission spectra, two emission peaks are attributed to two metal-to-ligand charge-transfer states. Based on the deconvoluted results, a qualitative energy-level diagram of Sr2CeO4 was proposed. VUV-excited luminescence studies for Sr2CeO4 indicate that one peak at 193 nm is assigned to the charge-transfer transition between Sr2+ and O2−. 相似文献
6.
Zhiguo Xia Daimei Chen Min Yang Ting Ying 《Journal of Physics and Chemistry of Solids》2010,71(3):175-180
YVO4:Eu3+,Bi3+ phosphors have been prepared by the high-temperature solid-state (HT) method and the Pechini-type sol-gel (SG) method. Spherical SiO2 particles have been further coated with YVO4:Eu3+,Bi3+ phosphor layers by the Pechini-type SG process, and it leads to the formation of core-shell structured SiO2/YVO4:Eu3+,Bi3+ phosphors. Therefore, the phase formations, structures, morphologies, and photoluminescence properties of the three types of as-prepared YVO4:Eu3+,Bi3+ phosphors were studied in detail. The average diameters for the phosphor particles are 2-4 μm for HT method, 0.1-0.4 μm for SG method, and 0.5 μm for core-shell structured SiO2/YVO4:Eu3+,Bi3+ particles, respectively. Photoluminescence spectra show that effective energy transfer takes place between Bi3+ and Eu3+ ions in each type of as-prepared YVO4:Eu3+,Bi3+ phosphors. Introduction of Bi3+ into YVO4:Eu3+ leads to the shift of excitation band to the long-wavelength region, thus the emission intensities of 5D0-7F2 electric dipole transition of Eu3+ at 615 nm upon 365 nm excitation increases sharply, which makes this phosphor a suitable red-emitting materials that can be pumped with near-UV light emitting diodes (LEDs). 相似文献
7.
This paper reports the preparation of long persistent Sr2Al2SiO7:Eu2+ and Sr2Al2SiO7:Eu2+, Dy3+ phosphors and the comparison of their photoluminescent properties. The silicate phosphors prepared by solid-state reaction routine showed a broad blue emission peaking at 484 nm when activated by UV illumination. Such a bluish-green emission can be attributed to the intrinsic 4f-5d transitions of Eu2+. After the UV source was switched off, long persistent phosphorescence could be observed by naked eyes for both samples in darkness. Afterglow measurements revealed that Eu/Dy codoped phosphor possesses better afterglow properties than the Eu single doped one, since the maximum lifetime (τmax=99 s) of the photons calculated from the decay profile is much larger than that of the Eu single doped phosphor (τmax=82 s). TSL results suggested that the difference in afterglow properties was caused by the difference in the electron traps within the crystal lattice. For Eu/Dy codoped phosphor, the doping of Dy ions produced electron traps with trap depth of 0.52 eV, which is suitable and therefore leads to good persistence. However, in the case of Eu single doped phosphor, the trap depth is 0.88 eV, which is really too deep an energy barrier to overcome, and therefore a poor persistence was observed in the experiment. 相似文献
8.
Sr3MgSi2O8:Eu2+ and Sr2MgSi2O7:Eu2+ phosphors find uses in applications such as plasma display panel (PDP), solid-state lighting, longafter glow. Preparation of these phosphors by a modified combustion synthesis is described in this paper. As-prepared samples did not show photoluminescence. After reducing the samples at 900 °C, characteristic Eu2+ emission was observed. Preparation of these phosphors by using similar methods helped clarifying various results obtained for Sr3MgSi2O8:Eu2+ by different investigators. 相似文献
9.
Youjie Hua Degang Deng Shilong Zhao Huanping Wang Lihui Huang 《Optics Communications》2011,284(1):27-29
(Ca1 − x, Srx)Al2Si2O8:0.06Ce3+, M+ (M+ = Li+, Na+, K+) phosphors have been prepared by conventional solid-state reaction method. The structural and optical properties of the phosphors were characterized by X-ray diffraction (XRD) technique and spectrophotometer, respectively. A regular variation was found among the XRD patterns of (Ca1 − x, Srx)Al2Si2O8:0.06Ce3+ phosphors based on the changing of Sr content. With the increase of Sr content, the maximum of emission band presented slight blue shifts (~ 15 nm). The luminescence intensity of CaAl2Si2O8:0.06Ce3+ and SrAl2Si2O8:0.06Ce3+ were significantly enhanced when K+ and Li+ were incorporated, respectively. 相似文献
10.
The spectroscopic properties in UV-excitable range for the phosphors of Sr3La2(BO3)4:RE3+ (RE3+=Eu3+, Ce3+, Tb3+) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr3La2(BO3)4:RE3+ were investigated. The f-d transitions of Eu3+, Ce3+ and Tb3+ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr3La2(BO3)4:Eu3+ is 611 nm, and Sr3La2(BO3)4:Ce3+ shows dominating emission peak at 425 nm, while Sr3La2(BO3)4:Tb3+ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr3La2(BO3)4:Tb3+ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation. 相似文献
11.
Lei Zhou 《Journal of Physics and Chemistry of Solids》2008,69(11):2877-2882
In this paper, seven kinds of silane coupling reagents were employed as silicate sources to prepare CaSiO3:Eu3+ phosphors by the sol-gel method. The different silicate precursors were used to adjust the microstructure and size of the resulting phosphors. The crystallite size of phosphors is in the range of 30-35 nm and some of them show regular microstructure after high-temperature thermolysis. The photoluminescence properties show that all of them exhibit the characteristic fluorescence 5D0→7FJ (J=0, 1, 2, 3, 4) of the Eu3+ ion and the strongest one is the red emission at 610 nm. Furthermore, the emission quantum efficiency (η) of the 5D0 Eu3+ excited state has been calculated to be around 33% from the emission spectrum and the lifetime of the Eu3+ first excited level (τ, 5D0). 相似文献
12.
Yong Sun Won 《Journal of Physics and Chemistry of Solids》2010,71(12):1742-1745
The supercells of pure and Eu-doped Sr2SiO4 were theoretically analyzed by density functional theory (DFT) calculations to investigate the typical two-peak emission of Sr2SiO4:Eu2+, which originates from two different Sr2+ (or Eu2+) sites in the Sr2SiO4 host structure. The Perdew-Wang generalized-gradient approximation (GGA) functional and the double numerical plus d-functions (DND) basis set with effective core potentials (ECP) were employed in the calculations of electronic properties. The electron transfer between Eu2+ ions placed at two different crystallographic Sr2+ sites was understood based on the accurate assignment of deconvoluted peaks of the two-peak emission to their corresponding crystallographic sites. This study ought to be instructive as a basic guideline to improve the color chromaticity of Sr2SiO4:Eu2+ for use in white light emitting diodes (WLEDs). 相似文献
13.
Qiaoli Wu 《Physica B: Condensed Matter》2009,404(16):2499-2502
Stabled hexagonal phase Sr1−xBaxAl2O4:Eu2+ (x=0.37-0.70) was prepared by solid-state method. Result revealed that the structure behavior of the SrAl2O4:Eu2+ calcined at 1350 °C in a reducing atmosphere for 5 h strongly depended on the Ba2+ concentration. With increasing Ba2+ concentration, a characteristic hexagonal phase can be observed. When 37-70% of the strontium is replaced by barium, the structure of the prepared sample is pure hexagonal. Photoluminescence and excitation spectra of the samples with different x and doped with 2% Eu2+ were investigated. Changes in the emission spectra were observed in the two different phases. The green emission at 505 nm from Eu2+ was found to be quite strong in the hexagonal phase. The intensity and peak position of the green luminescence from Eu2+ changed with increasing content of Ba2+. The strongest green emission was obtained from Sr0.61Ba0.37Al2O4:Eu2+. The decay characteristics of Sr1−xBaxAl2O4:Eu2+ (x=0.37-0.70) showed that the life times also varied with the value of x. Furthermore, the emission colors and decay times varying with x could be ascribed to the variation of crystal lattice. 相似文献
14.
Ran Pang Chengyu Li Lili Shi Qiang Su 《Journal of Physics and Chemistry of Solids》2009,70(2):303-306
By introducing the Y3+ into Sr2P2O7:Eu2+, we successfully prepared a kind of new phosphor with blue long-lasting phosphorescence by the high-temperature solid-state reaction method. In this paper, the properties of Sr2P2O7:Eu2+,Y3+ were investigated utilizing XRD, photoluminescence, luminescence decay, long-lasting phosphorescence and thermoluminescence (TL) spectra. The phosphor emitted blue light that was related to the 4f65d1-8S7/2 transition of Eu2+. The bright blue phosphorescence could be observed by naked eyes even 8 h after the excitation source was removed. Two TL peaks at 317 and 378 K related to two types of defects appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.61 and 0.66 eV. Also, the mechanism of LLP was discussed in this report. 相似文献
15.
Rahul Ghildiyal 《Journal of luminescence》2007,124(2):217-220
Nano crystalline powder of Sr2CeO4 has been synthesized by sol-gel technique. The luminescence properties of the material were compared with the one synthesized by conventional solid state reaction technique. The homogeneity and uniformity of the particle prepared by this method is much better than that prepared by the solid state reaction technique. This blue emitting phosphor was characterized by X-ray diffraction, scanning electron microscopy images and luminescent measurements. The emission spectrum of the material exhibits a broad band around ∼480 nm. The photoluminescence spectra of the Sr2CeO4 reveals that the strong blue emission is assigned to the Ce4+-O2− charge transfer transition (CTT) of Sr2CeO4 and not related to lattice defect. The Commission International de l’Eclairage coordinates are x=0.16 and y=0.25. 相似文献
16.
Chunyan Cao Hyun Kyoung Yang Byung Kee Moon Jung Hyun Jeong Kwang Ho Kim 《Optics Communications》2011,284(23):5453-5456
By controlling the pH values of prepared solutions, the 10 mol% Ce3+, 5 mol% Tb3+ co-doped KGdF4 (synthesized with pH = 3) and the 10 mol% Ce3+, 5 mol% Tb3+ co-doped GdF3 (synthesized with pH = 1) submicro/nanocrystals have been synthesized based on a citric acid assisted hydrothermal method. For comparison, the samples synthesized by co-precipitation method (without hydrothermal treatment) with pH = 3 and 1 were also collected. The X-ray diffraction data illustrate that the hydrothermal treated KGdF4 sample crystallizes in the cubic phase and the GdF3 sample crystallizes in the orthorhombic phase. However, the samples synthesized by co-precipitation method with pH = 3 and 1 are both cubic phase KGdF4. The field emission scanning electron microscopy images suggest that the hydrothermal treated KGdF4 submicro/nanocrystals present spherical morphology and the GdF3 submicrocrystals are rhombic-shaped. And the photoluminescence excitation and emission spectra as well as the luminescent dynamic curves demonstrate the difference in optical properties of the two hydrothermal treated samples. 相似文献
17.
The crystalline structure and photoluminescence (PL) properties of europium-doped cerium dioxide synthesized by the solid-state reaction method were analyzed. CeO2:Eu3+ phosphor powders exhibit the pure cubic fluorite phase up to 10 mol% doping concentration of Eu3+. With indirect excitation of CeO2 host at 373 nm, the PL intensity quickly increases with increasing Eu3+ concentration, up to about 1 mol%, and then decreases indicating the concentration quenching. While with direct excitation (467 nm), much more stronger PL emissions, especially the electric dipole emission 5D0-7F2 at 612 nm, are observed and no concentration quenching occurs up to 10 mol% doping concentration of Eu3+. The nature of this behavior and the cause of the concentration quenching were discussed. 相似文献
18.
Xiaoming Teng 《Journal of luminescence》2010,130(5):851-854
The Sr2Si5N8:Eu2+ phosphors, both undoped and doped with Tm3+, were synthesized by high temperature solid-state method. The XRD pattern shows that only Sr2Si5N8 phase is formed whatever Tm3+ was doped or not. The peak positions of both phosphors are centered at 612 nm which is assigned to the 4f65d→4f7 transition of Eu2+. It implies that the crystal field, which affects the 5d electron states of Eu2+, is not changed dramatically after the phosphor is doped with Tm3+. The afterglow time is about 10 min after Tm3+ ion is introduced into the phosphor. The concentration of Tm3+ has little influence on the afterglow time of the phosphor. The depths of trap energy level of the two phosphors were calculated based on the TL spectra. The depths of Sr2Si5N8:Eu2+ and Sr2Si5N8:Eu2+, Tm3+ are 1.75 and 1.01 eV, respectively. 相似文献
19.
Xi Chen 《Journal of luminescence》2011,131(12):2697-2702
In this work, we report preparation, characterization and luminescent mechanism of a phosphor Sr1.5Ca0.5SiO4:Eu3+,Tb3+,Eu2+ (SCS:ETE) for white-light emitting diode (W-LED)-based near-UV chip. Co-doped rare earth cations Eu3+, Tb3+ and Eu2+ as aggregated luminescent centers within the orthosilicate host in a controlled manner resulted in the white-light phosphors with tunable emission properties. Under the excitation of near-UV light (394 nm), the emission spectra of these phosphors exhibited three emission bands: one broad band in the blue area, a second band with sharp lines peaked in green (about 548 nm) and the third band in the orange-red region (588-720 nm). These bands originated from Eu2+ 5d→4f, Tb3+5D4→7FJ and Eu3+5D0→7FJ transitions, respectively, with comparable intensities, which in return resulted in white light emission. With anincrease of Tb3+ content, both broad Eu2+ emission and sharp Eu3+ emission increase. The former may be understood by the reduction mechanism due to the charge transfer process from Eu3+ to Tb3+, whereas the latter is attributed to the energy transfer process from Eu2+ to Tb3+. Tunable white-light emission resulted from the system of SCS:ETE as a result of the competition between these two processes when the Tb3+ concentration varies. It was found that the nominal composition Sr1.5Ca0.5SiO4:1.0%Eu3+, 0.07%Tb3+ is the optimal composition for single-phased white-light phosphor. The CIE chromaticity calculation demonstrated its potential as white LED-based near-UV chip. 相似文献
20.
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. 相似文献