共查询到20条相似文献,搜索用时 0 毫秒
1.
Zuoling Fu 《Journal of luminescence》2007,124(2):213-216
Y2O3:Eu3+ nanocrystals were prepared by combustion synthesis. The particle size estimated by X-ray powder diffraction (XRD) was about 10 nm. A blue-shift of the charge-transfer (CT) band in excitation spectra was observed in Y2O3:Eu3+ nanocrystals compared with bulk Y2O3:Eu3+. The electronic structure of Y2O3 is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation (GGA) within the scheme due to Perdew-Burke-Ernzerhof (PBE). The calculated results show that the energy centroid of 5d orbital in nanocrystal has increasing trend compared with that in the bulk material. The bond length and bond covalency are calculated by chemical bond theory. The bond lengths of Y2O3:Eu3+ nanocrystal are shorter than those of the bulk counterpart and the bond covalency of Y2O3:Eu3+ nanocrystal also has an increasing trend. By combining centroid shift and crystal-field splitting, the blue-shift of the CT band is interpreted. 相似文献
2.
Dheeraj Jain 《Journal of luminescence》2009,129(5):439-3684
Zinc phosphate glasses doped with Gd2O3:Eu nanoparticles and Eu2O3 were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P2O5 glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu3+ ions has been observed when Eu2O3 is incorporated in ZnO-P2O5 glasses. Lack of energy transfer from these defect centres to Eu3+ in Gd2O3:Eu nanoparticles doped ZnO-P2O5 glass has been attributed to effective shielding of Eu3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu3+ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd2O3:Eu nanoparticles or Eu2O3 incorporation. 相似文献
3.
The nanocrystalline Gd2O3:Eu3+ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O2−-Eu3+ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu3+ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu3+, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu3+ ions. 相似文献
4.
A nonhydrolytic hot solution synthesis technique was used to grow monodisperse ternary oxide nanocrystals of ZnGa2O4:Eu3+. The shape of ZnGa2O4:Eu3+ nanocrystals was a function of the type of precursor, and their size was controlled by changing the concentration ratio of Zn precursor to surfactant. The crystal structure of synthesized ZnGa2O4 nanocrystals was a cubic spinel with no detectable secondary phases. Photoluminescence of red-emitting ZnGa2O4:Eu3+ nanocrystals resulted in a high (5D0-7F2)/(5D0-7F1) intensity ratio, suggesting that the Eu3+ ions occupy tetrahedral Zn2+ sites or distorted octahedral Ga3+ sites with no inversion symmetry in ZnGa2O4 nanocrystals. 相似文献
5.
Auger electron/X-ray photoelectron and cathodoluminescent (CL) spectroscopic studies were conducted on pulsed laser deposited SrAl2O4:Eu2+,Dy3+ thin films and the correlation between the surface chemical reactions and the decrease in the CL intensity was determined. The Auger electron and the CL data were collected simultaneously in a vacuum chamber either maintained at base pressure or backfilled with oxygen gas. The data were collected when the films were irradiated for 14 h with 2 keV electrons. The CL emission peak attributed to the 4f65d1 → 4f7 transitions was observed at ∼521 nm and the CL intensity of the peaks degraded at different rates in different vacuum conditions. X-ray photoelectron spectroscopy (XPS) data collected from degraded films suggest that strontium oxide (SrO) and aliminium oxide (Al2O3) were formed on the surface of the film as a result of electron stimulated surface chemical reaction (ESSCR). 相似文献
6.
Uniform and crack free polycrystalline lutetium oxide (Lu2O3:(Eu,Pr)) films were fabricated by Pechini sol-gel method combined with the spin-coating technique. X-ray diffraction (XRD) and atomic force microscope (AFM) characterizations indicated that the obtained film was composed of polycrystalline cubic Lu2O3 phase with an average grain size around 30 nm. The photoluminescence(PL) spectra and decay performances of the Lu2O3:5 mol% Eu films co-doped by 0-0.5 mol% Pr3+ with different concentrations were characterized. It was found that the afterglow was reduced obviously due to the introduction of 0-0.5 mol% Pr3+ in the Lu2O3:5 mol% Eu films coupled by decrease in the emission intensity at 612 nm. The mechanism of afterglow diminishing was discussed based on the thermoluminescence measurements. 相似文献
7.
Thermoluminescence (TL) studies of Eu2+ and Mn2+ doped BaMgAl10O17 (BAM) are reported and discussed. The TL spectra that are measured after irradiation with ultraviolet (120-) show a series of TL peaks between 100 and . The TL spectra are similar for BAM with the two dopants, which suggest that the shallow traps are typical for the BAM host lattice. Using the Hoogstraaten analysis trap depths between 0.1 and are determined. A model is proposed based on thermally activated recombination in local TL centres (not via the conduction band). Further support for this model is obtained from the observation that the TL signal is strongest for excitation around the band edge of BAM . Upon heating the samples in air all low temperature TL peaks decrease in intensity. In addition a new peak appears in the TL spectrum, which is connected with a deeper trap and also a partial oxidation of Eu2+ to Eu3+ is observed. The luminescence efficiency is lower and the UV induced degradation is faster after annealing in air. These results indicate that the shallow traps are related to oxygen vacancies. The shallow traps do not have a negative influence on performance (efficiency and degradation) of BAM as a lighting phosphor. The luminescence efficiency and stability are strongly influenced by the formation of Eu3+ and a deeper trap during annealing in air. Subsequent annealing in a reducing atmosphere restores the original properties. 相似文献
8.
Jinping Huang Hongshan Luo Pingle Zhou Xibin Yu Yikang Li 《Journal of luminescence》2007,126(2):881-885
In this paper, a novel phosphor, Y6W2O15:Eu3+ was synthesized by thermal decomposition and phase transition of its decatungstate gel precursor. With stepwise increase of temperature to 750 °C, a crystalline phase of Y6W2O15:Eu3+forms that gives intense red emission when excited at 466 nm, the emission is attributed to the Eu3+ ions transitions from 5D0 excited states to 7FJ (J=0-4) ground states. The long excitation wavelength proves the Eu3+ transition follows the photoexcitation of the oxygen-metal (O→W lmct) charge transfer bands in yttrium tungstate. Some structural information regarding Y6W2O15 provided by luminescence is in accord with that characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The long-wavelength excitation properties of this material may find application in the production of red phosphors for white light-emitting diodes (LEDs). 相似文献
9.
Red-emitting Y2O3:Eu3+ and green-emitting Y2O3:Tb3+ and Y2O3:Eu3+, Tb3+ nanorods were synthesized by hydrothermal method. Their structure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The photoluminescence (PL) property of Y2O3:Eu3+,Tb3+ phosphor was investigated. In the same host (Y2O3), upon excitation with ultraviolet (UV) irradiation, it is shown that there are strong emissions at around 610 and 545 nm corresponding to the forced electric dipole 5D0-7F2 transition of Eu3+ and 5D4-7F5 transition of Tb3+, respectively. Different qualities of Eu3+and Tb3+ ions are induced into the Y2O3 lattice. From the excitation spectrum, we speculate that there exists energy transfer from Tb3+ to Eu3+ ions .The emission color of powders reveals regular change in the separation of light emission. These powders can meet with the request of optical display material for different colors or can be potentially used as labels for biological molecules. 相似文献
10.
V. Sudarsan 《Journal of luminescence》2010,130(8):1379-1383
Binary (ZnO)0.5(P2O5)0.5 glasses doped with Eu2O3 and nanoparticles of Gd2O3:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)0.5(P2O5)0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na2O-SiO2 glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu3+ ions leading to improved Eu3+ luminescence from such glasses. Based on the decay curves corresponding to the 5D0 level of Eu3+ ions in both Gd2O3:Eu nanoparticles incorporated as well as Eu2O3 incorporated glasses, a significant clustering of Eu3+ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)0.5(P2O5)0.5 glass doped with Gd2O3:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu3+ ions. Poor energy transfer from the defect centres to Eu3+ ions in Gd2O3:Eu nanoparticles doped (ZnO)0.5(P2O5)0.5 glass has been attributed to effective shielding of Eu3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu3+ ions. 相似文献
11.
H.C. Swart J.J. Terblans O.M. Ntwaeaborwa R.E. Kroon B.M. Mothudi 《Physica B: Condensed Matter》2012,407(10):1664-1667
Strontium aluminate phosphors are ideal for luminescent infrastructure materials. Their brightness and persistent glow time are much higher than previously used sulphide phosphors. Strontium aluminates prepared by the sol–gel and combustion methods are compared with commercially available strontium aluminate. High luminescent efficient SrAl2O4:Eu2+,Dy3+ pulsed laser deposited (PLD) thin films were also produced using the commercially available powder. Photoluminescence (PL) degradation studies showed that the phosphor intensity decreased about 20% over a period of 2 weeks under ultraviolet (UV) irradiation. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) showed that cathodoluminescence (CL) degradation is due to the formation of SrO due to electron stimulated surface reactions. The light output mechanism of the phosphor is also discussed in more detail. 相似文献
12.
Brandon Howe 《Journal of luminescence》2004,109(1):51-59
Host-lattice emission, energy transfer and degradation processes are characterized in undoped and Eu-doped BaMgAl10O17. Undoped BaMgAl10O17 exhibits a broad emission centered at 265 nm when excited at wavelengths shorter than 190 nm. This emission is assigned to exciton recombination at Ba-O groups in the cation layer of the lattice. The emission exhibits excellent overlap with the excitation band of Eu2+ in this host, providing a means of host-to-activator energy transfer in the doped phosphor. The exciton emission is relatively stable to thermal damage, but undergoes a peak shift and significant decrease in intensity after exposure to VUV radiation. Heating of VUV-damaged materials in air leads to some repair of the spectral properties. 相似文献
13.
H.C. Swart O.M. NtwaeaborwaP.D. Nsimama J.J. Terblans 《Physica B: Condensed Matter》2012,407(10):1660-1663
SrAl2O4:Eu2+, Dy3+ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O2) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O2 atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f65d1→4f7 Eu2+ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O2 atmospheres was most probably responsible for the quenching of the PL intensity after annealing. 相似文献
14.
B.M. Mothudi M.A. Lephoto O.M. Ntwaeaborwa J.R. Botha H.C. Swart 《Physica B: Condensed Matter》2012,407(10):1620-1623
BaAl2O4:Eu2+,Nd3+,Gd3+ phosphors were prepared by a combustion method at different initiating temperatures (400–1200 °C), using urea as a comburent. The powders were annealed at different temperatures in the range of 400–1100 °C for 3 h. X-ray diffraction data show that the crystallinity of the BaAl2O4 structure greatly improved with increasing annealing temperature. Blue-green photoluminescence, with persistent/long afterglow, was observed at 498 nm. This emission was attributed to the 4f65d1–4f7 transitions of Eu2+ ions. The phosphorescence decay curves were obtained by irradiating the samples with a 365 nm UV light. The glow curves of the as-prepared and the annealed samples were investigated in this study. The thermoluminescent (TL) glow peaks of the samples prepared at 600 °C and 1200 °C were both stable at ∼72 °C suggesting that the traps responsible for the bands were fixed at this position irrespective of annealing temperature. These bands are at a similar position, which suggests that the traps responsible for these bands are similar. The rate of decay of the sample annealed at 600 °C was faster than that of the sample prepared at 1200 °C. 相似文献
15.
A new nanostructure-mediated approach was demonstrated to synthesize Eu3+-doped yttrium oxysulfates Y2O2SO4:Eu3+ giving rise to abnormally enhanced Eu3+ emission. Yttrium and europium salts, sodium dodecylsulfate (SDS), and urea at various Eu3+ concentrations were reacted in aqueous solution at 80, 85, and 87 °C to yield Eu3+-doped dodecylsulfate-templated yttrium oxide mesophases with straight-layered (S-type), concentric-layered (C-type) and layer-to-hexagonal transient-layered (T-type) structures, respectively. On calcination at 1000 °C, all of these mesophases were converted into Y2O2SO4:Eu3+ to exhibit luminescence bands including the 5D0-7F2 transition with a tendency in intensity to saturate or reach a maximum at 10-12 mol% Eu doping. The Eu3+ emissions for Y2O2SO4:Eu3+ mediated by the T- and C-type mesophases were enhanced in intensity by a factor of about two and three times, respectively, stronger than those for not only compositionally the same sulfate Y2O2SO4:Eu3+ obtained from yttrium-based sulfates but also Y2O3:Eu3+ obtained in the SDS-free system. In contrast, the emission intensities for the S-type-mesophase-mediated Y2O2SO4:Eu3+ were close to those for the latter sulfates. The abnormally enhanced emission is likely based on specific deformation of sulfate groups induced through the conversion of concentric dodecylsulfate-layers to straight sulfate-layers in the oxysulfate framework upon calcination. 相似文献
16.
B.M. Mothudi O.M. Ntwaeaborwa A. Kumar K. Sohn H.C. Swart 《Physica B: Condensed Matter》2012,407(10):1679-1682
Long persistent SrAl2O4:Eu2+ phosphors co-doped with Dy3+ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl2O4 were observed in all the samples. The broad band emission spectra at 497 nm for SrAl2O4:Eu2+, Dy3+ were observed and the emission is attributed to the 4f65d1 to 4f7 transition of Eu2+ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy3+ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence. 相似文献
17.
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
18.
The 4f energy levels and crystal-field parameters for several clusters representing the local coordination surroundings of Eu3+ in the bulk and nanocrystalline cubic Y2O3: Eu3+ crystals are obtained by using a method based on the combination of the DV-Xα calculation and the effective Hamiltonian method initialized by M.F. Reid et al. (J. Phys.: Condens. Matter, 2011, 23: 045501). The results are in reasonable agreement with the measured energy levels and the crystal-field parameters obtained from the least-square fitting. The charge transfer energies are also obtained for all the clusters from the DV-Xα calculation. The results indicate that, compared with the bulk Y2O3: Eu3+ crystal, the charge transfer band in the excitation spectra is red-shifted in the nanocrystal. 相似文献
19.
Ryan Atkins 《Journal of luminescence》2008,128(9):1463-1470
We have completed a study of the optical properties of SrY2O4:Eu3+ under vacuum ultraviolet (VUV) excitation. Reflectance measurements on the undoped material yield a calculated band gap of about 6.1 eV. Studies on the doped material indicate that Eu3+ occupies the Y(1) and Y(2) sites in this host. Host-to-activator energy transfer calculations indicate a preference for transfer to Eu3+ at the Y(2) site. Modeling of the transfer efficiency data leads us to estimate that about 35% of absorbed radiation is lost to the surface under excitation near the band edge. 相似文献
20.
Sr2MgSi2O7:Eu2+, Dy3+ phosphors were prepared by the (aminopropyl)-triethoxysilane (APTES) co-precipitation method. Effects of synthesis temperature on the crystal characteristics, luminescent properties and afterglow performance of Sr2MgSi2O7:Eu2+, Dy3+ phosphors have been discussed in detail and compared with the corresponding commercial product. The experimental results indicated that the sample could be synthesized at a relatively lower temperature and had better performance on the above-mentioned properties using the co-precipitation method. 相似文献