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Abstract: Novel SiO2 hierarchical nanostructure has been grown on SiC nanowires using thermal decomposition of a mixture of ethanol and titanium tetrachloride. Novel nanostructure was realized in one synthesis route. Based on SEM and TEM observations, the hierarchical nanostructure consists of core-shell SiC–SiO2 main stem nanowire and a lot of SiO2 nanorod branches grown on the main stem. A mean diameter of SiC central cores was about 40nm and their lengths reach about 100μm. The lengths and diameters of SiO2 nanorod-like branches were ranged in 400–800nm and 30–120nm, respectively. The growth of core-shell SiC–SiO2 nanowires obeyed vapor–liquid–solid mechanism and the SiO2 nanorod-like branches grew via vapor–solid mechanism. The infrared absorption and photoluminescence properties of the grown nanostructure were investigated. [Copyright &y& Elsevier]

Abstract: Large-scale SiC nanocables were synthesized on a Ni(NO3)2-catalyzed Si substrate by using a simple and cheap method based on thermal decomposition of methanol. Based on X-ray diffraction and high-magnification transmission electron microscopy, the as-grown nanocables consisted of crystalline SiC cores and amorphous SiO2 shells. The diameters of SiC cores were 5.7–10nm and the thicknesses of SiO2 shells were 9–20nm. Dividing of nanocables was observed and its origin was investigated. An asymmetric feature of SiC TO band with a shoulder at the high-frequency side was attributed to the contribution of SiC TO mode. The nanocables displayed strong violet–blue emission. A possible growth mechanism was proposed. [Copyright &y& Elsevier]

Abstract: Large-scale SiC–SiO2 core–shell nanowires decorated with carbon nanoparticles have been synthesized on Si substrate using thermal decomposition of ethanol. The amorphous carbon nanoparticles on SiO2 shell are of hemispherical configuration hiving a mean diameter of about 20nm. The average size of carbon nanoparticles estimated from Raman measurement is 23.4nm close to that evaluated from transmission electron microscopic observation. Strong enhancement of blue emission band and appearance of a new yellow emission band were observed in SiC–SiO2 core–shell nanowires decorated with carbon nanoparticles and their origins were discussed. A possible synthesis mechanism of SiC–SiO2 core–shell nanowires decorated with carbon nanoparticles was proposed. [Copyright &y& Elsevier]

Abstract: We report on the quantum confinement effect and field-emitting characteristics of ultrathin 3C–SiC nanobelts synthesized by a simple and low-cost microwave method. Morphological analysis indicates that the nanobelts are tens of micrometers in length, tens of nanometers in width and only several nanometers in thickness. Under 325nm excitation, a broad emission peaked at 391nm has been observed in the spectrum of the nanobelts, which reveals an obvious blueshift of bandgap. Field-emission measurements show that the nanobelts are promising field-emitting materials with a low turn-on field of ∼3.2V/μm. [Copyright &y& Elsevier]

Abstract: MoO3 nanoflowers were successfully synthesized on a Si substrate by a facility microwave hydrothermal method. The nanoflowers consisted of tens of nanobelts and the nanobelts were about several micrometers in length, several tens to several hundreds of nanometers in width, and tens of nanometers in thickness. Field-emission measurements showed that the nanoflowers had a relatively low turn-on field of ∼4.3V/μm and their emission was a barrier tunneling quantum-mechanical process. The fluctuations of the emission current were less than 10% over 3h. The low turn-on field and high stability of emission current indicate that the as-grown MoO3 nanobelts exhibit a good field-emission property and have great potential for applications in field-emission devices. [Copyright &y& Elsevier]

Abstract: Cubic and hexagonal NaYF4:Ln3+ (Ln=Eu and Yb/Tm) microcrystals were separately synthesized by an EDTA-assisted solvothermal method. Under 393-nm excitation, the emission spectra of NaYF4:Eu3+ microcrystals show the characteristic Eu3+ emissions. In the excitation spectra of the 610-nm emission, the 7F0 → 5D3 is dominant for the cubic microcrystals, while the 7F0 → 5L6 is dominant for the hexagonal sample. In addition, unusually strong ultraviolet emissions (1I6 → 3H6, 1I6 → 3F4, and 1D2 → 3H6) were observed in the hexagonal NaYF4:Yb3+/Tm3+ microcrystals under 980-nm excitation. In comparison with a cubic sample having the same chemical compositions, the hexagonal microcrystals had a markedly enhanced ability of emitting ultraviolet up-conversion luminescence. [Copyright &y& Elsevier]

Abstract: YF3:Yb3+(20%)/Tm3+(2%) octahedral nanocrystals were synthesized by a microemulsion method with NH4HF2. Pumped with a 980-nm diode laser, the nanocrystals emitted weak blue and intense ultraviolet light. Especially, unusual 3P2 → 3H6 (∼265nm) and 3P2 → 3F4 (∼309nm) emissions, coming from a five-photon excitation process, were observed. The emissions from 1D2 and 1I6 were much stronger than those from 1G4 and 3H4. The upconversion mechanism was discussed in detail. [Copyright &y& Elsevier]

Abstract: The upconversion luminescent properties of YF3:Yb3+(20%)/Tm3+(1%) nanobundles with different sizes (240–500nm in length) were studied under 980-nm excitation. Ultraviolet (1I6 → 3F4/3H6 and 1D2 → 3H6), blue (1D2 → 3F4 and 1G4 → 3H6), red (1D2 → 3H4, 1G4 → 3F4, and 3F3 → 3H6), and near infrared (3H4 → 3H6) emissions were observed. The results indicated that the relative intensity of the ultraviolet to the blue as well as the blue to the near infrared increased with decreasing the size of nanobundles. Especially, the position of the dominant red emission peak varied with the size of nanobundles. As the length of nanobundles increased to 500nm, unusual 3F3 → 3H6 transition was observed, which was theoretically explained considering the decrease of the nonradiative transition rate of 3F3 → 3H4. [Copyright &y& Elsevier]

Abstract: Pumped with a 980-nm diode laser, violet/ultraviolet upconversion fluorescence was presented in Y0.83Yb0.15Er0.02F3 nanocrystals. Observed emissions at 318nm and 379nm were affirmed coming from a four-photon excitation process. In comparison with a bulk sample having the same chemical compositions, the nanocrystals had a markedly enhanced ability of emitting violet/ultraviolet upconversion fluorescence. By employing Tm3+ ions as structural probes in the samples, we found that the enhancement could be attributed to the decrease of Judd–Ofelt parameter Ω 2. A model for revealing the four-photon excitation process was proposed based on spectral analysis. [Copyright &y& Elsevier]

Abstract: YF3:Eu3+ nanobundles were synthesized by a facile microemulsion method. Analysis of X-ray diffraction, scanning electron microscope, and transmission electron microscopy reveals that each nanobundle consists of numerous nanowhiskers with a mean length of ∼500nm and a mean diameter of ∼2nm. Under 393-nm excitation, the luminescence was dominated by 5D0 → 7F1 transition, indicating the inversion symmetry of Eu3+ site. The luminescence intensity increased with increasing Eu3+ concentration, up to about 30mol%, and then decreased abruptly. The peak positions and spectral shapes of emissions were independent of Eu3+ concentration. Finally, the critical distance of energy transfer was calculated. [Copyright &y& Elsevier]