Xiudi Xiao

Preparation and optical properties of red, green and blue afterglow electrospun nanofibers

Utilizing convenient electrospinning techniques, CaTiO3 : Pr3+, SrAl2O4 : Eu2+,Dy3+ and CaAl2Si2O8 : Eu2+,Dy3+ nanofibers with afterglow emission were fabricated. X-ray diffraction (XRD), micro-Raman spectrometry (Raman) and scanning electron microscopy (SEM) were used to characterize the composition and morphology of electrospun nanofibers. The results showed that calcined samples were super-long nanofibers with a diameter of hundreds of nanometres. Fluorescence and afterglow properties were investigated by spectrofluorometery, which indicated that CaTiO3 : Pr3+, SrAl2O4 : Eu2+,Dy3+ and CaAl2Si2O8 : Eu2+,Dy3+ nanofibers show characteristic red, green and blue afterglow emission. The electrospun nanofibers with afterglow emissions of the three primary colors are expected to be applied in the field of miniature lighting, biological markers, multi-wavelength photo-detection, etc.

Morphology and phase control of fluorides nanocrystals activated by lanthanides with two-model luminescence properties.

The morphology, size and phase control of luminescent fluoride nanocrystals through doping has become a new research hotspot due to their improved properties. In this work, Yb(3+) ions, as one of the most efficient sensitizers for various lanthanide activators, were doped in NaGd(Y)F(4) nanocrystals. The results show that no obvious influence was observed for Yb(3+)-doped NaYF(4) nanocrystals, while the influence of Yb(3+) doping on NaGdF(4) nanocrystals was remarkable. The NaGd(1-x)Yb(x)F(4) nanocrystals were synthesized by a hydrothermal route and had a morphology of rice-like nanorods. By controlling the synthesis parameters, the average size and slenderness of the nanocrystals increased gradually with addition of Yb(3+) ions. In contrast, the NaGd(1-x)Yb(x)F(4) nanocrystals maintained a hexagonal phase, which is more beneficial for application as a luminescent host, until the content of Yb(3+) ions reached x = 0.9. The growth and transformation mechanism of NaGd(1-x)Yb(x)F(4) nanocrystals was proposed to be a result of the competition between ion diffusion and an Oswald ripening process. Photoluminescence (PL) spectra confirm the efficient up-conversion and near-infrared (NIR) two-model luminescence properties of Er(3+) (Tm(3+)) activated NaGd(Y)(1-x)Yb(x)F(4) nanocrystals. Simulated analysis results indicate that a colloidal solution of mixed luminescent nanocrystals is expected to find application as the activated medium of three dimensional displays and a broadband optical amplifier.

Photoluminescence of Ag nanoparticle embedded Tb3+/Ce3+ codoped NaYF4/PVP nanofibers prepared by electrospinning

Ag nanoparticle embedded NaYF(4):0.05Tb.xCe/PVP (PVP stands for poly(vinyl pyrrolidone)) composite nanofibers have been prepared by electrospinning. A field emission scanning electron microscope and x-ray diffraction have been utilized to characterize the size, morphology and structure of the as-prepared electrospun nanofibers. Obvious photoluminescence (PL) of NaYF(4):0.05Tb.0.05Ce/PVP electrospun nanofibers due to the efficient energy transfer from Ce(3+) to Tb(3+) ions is observed. The PL intensity of the electrospun nanofibers decreases gradually with the addition of Ag nanoparticles. No obvious surface plasmon resonance enhanced luminescence is observed. The reasons for the weakening of the emission intensity with the addition of Ag nanoparticles have also been discussed in this work.

Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties.

VO2 (M) STF through reduction of V2O5 STF was prepared. The results illustrate that V2O5 STF can be successfully obtained by oblique angle thermal evaporation technique. After annealing at 550°C/3 min, the V2O5 STF deposited at 85° can be easily transformed into VO2 STF with slanted columnar structure and superior thermochromic properties. After deposition SiO2 antireflective layer, Tlum of VO2 STF is enhanced 26% and ΔTsol increases 60% compared with that of normal VO2 thin films. Due to the anisotropic microstructure of VO2 STF, angular selectivity transmission of VO2 STF is observed and the solar modulation ability is further improved from 7.2% to 8.7% when light is along columnar direction. Moreover, the phase transition temperature of VO2 STF can be depressed into 54.5°C without doping. Considering the oblique incidence of sunlight on windows, VO2 STF is more beneficial for practical application as smart windows compared with normal homogenous VO2 thin films.

Size-dependent polarized photoluminescence from Y3Al5O12: Eu3+ single crystalline nanofiber prepared by electrospinning

After one-step calcination of the as-prepared electrospun nanofibers, single crystalline YAG (Y3Al5O12) nanofibers were successfully synthesized in situ even when the diameter reached 800 nm. X-Ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results confirmed that the calcined YAG nanofibers were pure body-centered cubic (bcc) YAG phase. The crystallography of single crystalline YAG nanofibers was perfect. After doping with Eu3+ ions, notable polarized photoluminescence (PL) was observed from an individual YAG: Eu3+ nanofiber, which was predominately owing to the dielectric mismatch between the nanofiber and its surroundings. The PL polarization ratio (ρ) showed a strong diametrical dependence as a factor of ∼1/R when the diameter (R) is comparable to the light wavelength. The large scale, super-long, single crystalline YAG nanofibers with notable polarized PL are promising to be applied as one dimensional nanofiber lasers, linearly polarized light resources, polarized sensors, photodetectors, etc.

Synthesis and optical properties of chromium-doped spinel hollow nanofibers by single-nozzle electrospinning

Novel spinel hollow nanofibers were synthesized by a convenient single-nozzle electrospinning technique. Based on the composition and morphology results by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), a ‘gas-push’ model was proposed to elucidate the formation mechanism of hollow nanofibers during calcination. Photoluminescence (PL) properties of calcined ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers were investigated systematically. Under an excitation of 400 nm or 530–550 nm (4A2g→4T1g or 4A2g→4T2g transitions of Cr3+ ions), an emission band at 675–725 nm including a sharp emission line (R-line) at ∼687 nm with several vibrational sidebands was obtained. Compared with the spectroscopic properties of ZnAl2O4: xCr3+ nanofibers, the emission band was broadened and the decay lifetime was shortened for MgAl2O4: xCr3+ nanofibers. By calculation of crystal field strength, the value of Dq/B is estimated to be 3.25 and 2.72 for ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers, respectively. The difference of crystal field strength gives a good explanation of the spectroscopic and decay evolution between ZnAl2O4: xCr3+ and MgAl2O4: xCr3+ nanofibers.

Tunable Emission of BCNO Nanoparticle-Embedded Polymer Electrospun Nanofibers

Using low temperature synthesized BCNO phosphors as raw materials, monodispersed BCNO nanoparticles (∼10 nm) are obtained successfully after a two-step centrifugation. X-ray diffraction results indicate that these BCNO nanoparticles are mainly hexagonal BN phase. These BCNO nanoparticle-embedded polymer nanofibers with an average diameter of 300 nm are prepared by electrospinning. Photoluminescence spectra of these nanofibers indicate that the emission can be readily tuned by adjusting the C concentration in the BCNO phosphors. These nontoxic nanofibers with intense tunable emission may find potential applications in the fields of lighting, biological marker, optoelectronic nanodevices, etc.

A facile process to prepare one dimension VO2 nanostructures with superior metal–semiconductor transition

VO2 nanobelts with metal–semiconductor properties were prepared through low temperature hydrothermal reaction and post annealing. X-Ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC) and UV-vis-NIR spectrophotometry were employed to investigate the evolution of structure, morphology and properties of the VO2 nanobelts. The results illustrate that the pure VO2 (B) nanobelts can be obtained by hydrothermal reaction. The shape of the nanobelts evolves with hydrothermal temperature, time and reactant concentration. With the increasing of hydrothermal temperature from 160 °C to 200 °C, the nanobelts become homogenous and regular. The regular nanobelts are also obtained by the decrease of V2O5 concentration. Samples prepared at 200 °C over 48 h have superior morphology and crystallinity. After annealing, VO2 (B) can be transformed into VO2 (M), which is dependent on the hydrothermal conditions. Samples prepared at 160 °C over 48 h and 180 °C over 48 h can be transformed into VO2 (M) at 450 °C over 2 h, while samples obtained at 200 °C over 48 h should be annealed at 500 °C for 2 h. The nanobelts are transformed into irregular nanostructures, nanorods and nanobelts at the hydrothermal temperatures of 160 °C, 180 °C and 200 °C, respectively. However, samples prepared at 200 °C over 48 h with a V2O5 concentration of 0.0125 M can keep the intact nanobelts after annealing. The DSC analysis proves that the VO2 (M) shows good phase transition behavior around 68 °C and the phase transition temperature can be reduced to 58 °C by 0.5 at% tungsten doping. After mixing the VO2 (M) with acrylic resin, the visible transmission of the VO2 composite coating on glass is up to 52.2% and the solar modulation at 2000 nm is up to 31.5%, which means that it is a good candidate for smart windows.

Synthesis of thermochromic W-doped VO 2 (M/R) nanopowders by a simple solution-based process

Thermochromic W-doped VO2 nanopowders were prepared by a novel and simple solution-based method and characterized by a variety of techniques. We mainly investigated the effect of tungsten dopant on the structural properties and phase transition of V1-xWxO2. The as-obtained nanopowders with tungsten content of ≤ 2.5 at% can be readily indexed as monoclinic VO2 (M) while that of 3 at% assigned into the rutile VO2 (R). The valence state of tungsten in the nanopowders is +6. TEM and XRD results show that the substitution of W atom for V in VO2 results in a decrease of the d space of the (011) plane. The phase transition temperature is determined by differential scanning calorimetry (DSC). It is found, for the first time, that the reduction of transition temperature reaches to 17 K per 1 at% of Wdoping with the tungsten extents of ≤1 at%, but only 9.5 K per 1 at% with the tungsten extents of >1 at%. The reason of this arises from the difficulty of the formation of V3+-W4+ and V3+-W6+ pairs by the increasing of Wions doping in the V1-xWxO2 system.

Optical properties and microstructure of Ta 2 O 5 biaxial film

This study investigates the optical properties and microstructure of Ta(2)O(5) film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method. Based on the Cauchy model, the dispersion equations of optical constants of film are determined from the transmittance spectra measured at normal and oblique incidence over 400-800 nm. The starting values derived with an envelope method quicken the optimization process greatly. The dispersion of the principal indices N(1), N(2), and N(3) and the thickness d of thin film are presented statistically. A good agreement between the measured optical properties and theoretical calculation is obtained, which validates the model established for thin film produced by glancing angle deposition.