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1.
β-NaYF 4:Ln 3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) hexagonal microrods have been successfully synthesized through a facile molten salt method without any surfactant. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. It is found that at a preferred reaction temperature of 400 °C, the structure of β-NaYF 4 can gradually transform from microtubes to microrods as reaction time extends from 0.5 to 4 h. Furthermore, as the molar ratio of NaF:RE 3+ (RE represents the total amount of Y 3+ and the doped rare earth elements such as Eu 3+, Tb 3+, Yb 3+/Er 3+, or Yb 3+/Tm 3+) increased, the phase of sample transforms from YF 3 into NaYF 4. Under the excitation of 395 nm ultraviolet light, β-NaYF 4:5 %Eu 3+ shows the emission lines of Eu 3+ corresponding to 5D 0-3 → 7F J ( J = 1–4) transitions from 400 to 700 nm, resulting in red down-conversion (DC) light emission. When doped with 5 % Tb 3+ ions, the strong DC fluorescence corresponding to 5D 4 → 7F J ( J = 6, 5, 4, 3) transitions with 5D 4 → 7F J (green emission at 544 nm) being the most prominent group that has been observed. Moreover, upon 980 nm laser diode excitation, the Yb 3+/Er 3+- and Yb 3+,Tm 3+- co-doped β-NaYF 4 samples exhibit bright yellow and blue upconversion (UC) luminescence, respectively, by two- or three-photon UC process. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed. 相似文献
3.
LaOCl:Yb 3+, Er 3+ nanofibers and hollow nanofibers were prepared by electrospinning combined with a double-crucible chlorination technique using NH 4Cl as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Yb 3+, Er 3+ nanostructures were tetragonal with space group P4/ nmm. Scanning electron microscope analysis and histograms revealed that diameters of LaOCl:Yb 3+, Er 3+ nanofibers and hollow nanofibers, respectively, were 117.87 ± 15.48 and 141.09 ± 17.10 nm under the 95 % confidence level. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Yb 3+, Er 3+ nanostructures exhibited strong green and red UC emission centering at 526, 548, and 671 nm, respectively, attributed to 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2, and 4F 9/2 → 4I l5/2 transitions of Er 3+ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the addition of Yb 3+ ions, and the optimized molar ratio of Yb 3+ to Er 3+ was 10:1 in the as-prepared nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Yb 3+, Er 3+ nanostructures were achieved under the excitation of a 532-nm laser. CIE analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Yb 3+ (and/or Er 3+) ions and morphologies of nanomaterials, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism and the formation mechanisms of LaOCl:Yb 3+, Er 3+ nanofibers and hollow nanofibers were also proposed. 相似文献
4.
LnBaFeCoO 5 + δ (Ln = Nd, Sm, Gd) layered oxides have been synthesized and their crystal structure, thermal stability, thermal expansion, electrical conductivity, thermoelectric power, and magnetic susceptibility have been studied. The oxides have a tetragonal structure (sp. gr. P4/ mmm) with unit-cell parameters a = 0.3909(2) nm and c = 0.7695(6) nm for Ln = Nd (δ = 0.65), a = 0.3908(3) nm and c = 0.7662(6) nm for Ln = Sm (δ = 0.37), and a = 0.3908(2) nm and c = 0.7613(6) nm for Ln = Gd (δ = 0.37). The LnBaFeCoO 5 + δ compounds are antiferromagnetic p-type semiconductors. With decreasing Ln 3+ ionic radius, their electrical conductivity and linear thermal expansion coefficient decrease and their thermoelectric power and antiferromagnetic ordering temperature increase. Near 518–653 K, the linear thermal expansion coefficient of the LnBaFeCoO 5 + δ oxides increases from (12.9–16.6) × 10 ?6 to (19.3–26.5) × 10 ?6 K ?1, which is due to the release of weakly bound oxygen from the oxides. We have determined parameters of charge transport in the [Fe(Co)O 2] layers in the crystal structure of the LnBaFeCoO 5 + δ phases. 相似文献
5.
Poly(vinyl pyrrolidone)/CoFe 2O 4 nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20 ± 7 nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10 K suggests the existence of the magnetically aligned core surrounded by spin- disordered surface layer. The reduced remanent magnetization value of 0.6 at 10 K (higher than the theoretical value of 0.5) shows the PVP/CoFe 2O 4 nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. 相似文献
6.
Journal of Materials Science - The CuFeCr0.5Ni0.5O4 (CFO) compound was synthesized using sol–gel reaction combustion technic. The structural analysis showed that the obtained composites have... 相似文献
7.
LaOCl:Yb 3+, Er 3+ nanobelts were prepared by electrospinning combined with a double-crucible chlorination technique using NH 4Cl as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Yb 3+, Er 3+ nanobelts were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that width of LaOCl:Yb 3+, Er 3+ nanobelts was 6.12 ± 0.18 μm under the 95% confidence level, and the thickness was 113 nm. Transmission electron microscope observation showed that as-obtained LaOCl:Yb 3+, Er 3+ nanobelts were composed of nanoparticles. LaOCl:Yb 3+, Er 3+ nanobelts emitted strong green and red up-conversion emission centring at 523, 551 and 667 nm, respectively, attributed to 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I l5/2 transitions of Er 3+ under the excitation of a 980-nm diode laser (DL) excitation. Moreover, the near-infrared characteristic emission of LaOCl:Yb 3+, Er 3+ nanobelts was achieved under the excitation of a 532-nm laser. Commission Internationale de L'Eclairage analysis demonstrated that colour-tuned luminescence can be obtained by changing doping concentration of Yb 3+ and Er 3+, which could be applied in the fields of optical telecommunication and optoelectronic devices. The up-conversion luminescent mechanism and the formation mechanism of LaOCl:Yb 3+, Er 3+ nanobelts were also proposed. 相似文献
9.
A novel LaMnO 3 photocatalyst with perovskite structure was prepared by sol–gel combustion method. The combustion reaction mechanisms of
nanocrystalline LaMnO 3 powders were investigated by thermal analysis, infrared spectra, and X-ray diffraction technique. The results showed that
the gels exhibited self-propagating behavior after ignition in air. Nanocrystalline LaMnO 3 powders can be synthesized in one step by using sol–gel combustion synthesis. The photocatalytic activity of the LaMnO 3 powders were evaluated by degradation of methyl orange (MO) in water under UV light irradiation. The results showed that
the LaMnO 3 powders exhibit good photocatalytic activities under UV light irradiation. The degradation percentage after 36 h on LaMnO 3 powders was about 76%. 相似文献
10.
Er 3+ and Pr 3+ codoped fluorotellurite glasses has been synthesized. The PL spectrum revealed that the intensity of Er 3+ characteristic emission was enhanced as Pr 3+ concentration increased. Due to small mismatch between the energy level of Er 3+: 4F 7/2 and Pr 3+: 3P 0 resonant energy was possibly transferred between them. While Pr 3+ concentration kept increasing, both Pr 3+ and Er 3+ concentration quenching occurred. These glasses with the controllable CIE coordinates might be a potential candidate for the widely application such as solid state multicolor display. 相似文献
12.
Rare earth-doped hexagonal NaGdF 4 nanocrystals were precipitated from a glass. The glass with the mol% composition 70.1SiO 2·4.3Al 2O 3·1.8AlF 3·2.3Na 2O·18.5NaF·3.0Gd 2O 3 doped with 8 × 10 19 Sm 3+ ions per cm 3 was already phase separated after casting. The formed droplets enriched in rare earths and fluoride had sizes in the range mainly from 50 to 90 nm. During annealing at temperatures ≥600 °C, multi core particles of hexagonal NaGdF 4 were formed inside the amorphous droplet phase. The fluorescence spectra show that Sm 3+ is incorporated into the NaGdF 4 lattice. This is confirmed by electron dispersive X-ray analyzes performed in a transmission electron microscope. 相似文献
16.
The interaction of the surface plasmons of gold nanoparticles on silicon nanowires with fluorophores, lanthanide ions (praseodymium ions, Pr 3+, neodymium ions Nd 3+, holmium ions Ho 3+, and erbium ions Er 3+) was investigated. In the presence of Au/Si nanomaterials, the fluorescence peaks were significantly enhanced, which resulted in about 2 orders of magnitude enhancement. The photoluminescence studies revealed that the enhanced fluorescence originates from the local field enhancement around Ln 3+ ions, caused by the electronic plasmons resonance of the gold nanoparticles. Results showed that this Au/Si nanostructure had larger enhancement factor than that caused by unsupported Au nanoparticles. These results might be explained by the local field overlap originated from the closed and fixed gold nanoparticles on silicon nanowires. 相似文献
17.
YPO 4:Ln 3+ (Ln = Eu and Sm) nanotubes were synthesized by a precipitation process in the presence of SDS. The XRD results showed that all samples have a xenotime type tetragonal structure, indicating that doped rare earth ions have no influence on the phase. The SEM and TEM images showed that all samples are nanotubes. On basis of the morphology of samples and the properties of SDS, the possible formation mechanism was speculated. YPO 4:Eu 3+ and YPO 4:Sm 3+ nanotubes showed characteristic emission bands of Eu 3+ and Sm 3+ ions, respectively. For YPO 4:Eu 3+/Sm 3+ nanotubes, the codoping Sm 3+ ions can enhance the emission intensity of Eu 3+ ions. 相似文献
19.
Polycrystalline powders of rare-earth doped La1?xGdxB3O6 (0?≤?x?≤?0.2) and La1?xSmxB3O6 (0.0?≤?x?≤?0.1) phosphors were successfully prepared by a B2O3 flux method. All the phosphor samples are well characterized by powder X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) methods and fluorescence lifetime of Sm3+ ion. The XRD patterns show that La1?xMxB3O6 (M?=?Gd and Sm) adopt monoclinic with the I2/a space group. The SEM–EDS results confirmed the doping of Gd and Sm into LaB3O6 lattice. The IR and Raman spectra of these solid solutions gave distinctive bands corresponding to planar BO3 and tetrahedral BO4 groups. The photoluminescence (PL) spectra of La1?xGdxB3O6 gave a strong emission band, 6PJ?→?8S7/2, at 310 nm. The PL spectra of La1?xSmxB3O6 phosphor showed orange-red emission at 598 nm when excited using light of wavelength of 402 nm. The results were obtained by the transition 4G5/2?→?6H7/2 of Sm3+ ions. The influence of dopant concentration on the emission profiles was studied. The ESR spectra of La1?xGdxB3O6 (x?=?0.02) gave a typical U-spectrum and spin-Hamiltonian parameters are deduced. 相似文献
20.
Mn 2+ and RE 3+ (RE = Tb, Eu, Nd) co-doped CdSiO 3 orange phosphors were prepared at 1050 °C by a sol–gel method. The phase and crystallinity of the synthesized materials were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The luminescence characteristics were analyzed using photoluminescence (PL) spectra, afterglow decay curves, long-lasting phosphorescence spectra, and thermoluminescence (TL) spectra. Due to the difference in co-doped rare earth ionic radii, it varied greatly in trap density and trap depth caused by the different defects deriving from RE 3+ ions co-doping into the CdSiO 3: Mn 2+ host. The afterglow intensity and time for these samples increased as follows: CdSiO 3: Mn 2+0.2%, Nd 3+0.8% < CdSiO 3: Mn 2+0.4%, Tb 3+0.8% < CdSiO 3: Mn 2+0.4%, Eu 3+0.3%. CdSiO 3: Mn 2+0.4%, Eu 3+0.3% had the best afterglow properties, which could be due to the proper traps formed by Eu 3+ ions co-doping into the host. The role of RE 3+ co-doped into the CdSiO 3: Mn 2+ matrix and the possible long-lasting phosphorescence process was also discussed in this paper. 相似文献
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