Zhijun Ma

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.

Broadband spectral modification from visible light to near-infrared radiation using Ce3+–Er3+ codoped yttrium aluminium garnet

Broadband spectral conversion from visible light to near-infrared radiation in Ce(3+)-Er(3+) codoped yttrium aluminium garnet is reported. Excitation, emission, time-resolved luminescence spectra and fluorescence decay curves have been measured to prove the energy transfer from Ce(3+) to Er(3+). The broadband and strong absorption of Ce(3+), efficient energy transfer from Ce(3+) to Er(3+), and three-photon quantum cutting process in Er(3+) ions result in efficient near-infrared emission when excited by 400-500 nm broad visible light. The energy of the Er(3+) ((4)I(13/2)→(4)I(15/2)) transition matches well with the band gap of germanium (Eg ∼ 0.785 eV). Ce(3+)-Er(3+) codoped yttrium aluminium garnet is promising for the enhancement of conversion efficiency of germanium solar cells.

Intense infrared emission of Er 3+ in Ca 8 Mg(SiO 4 ) 4 Cl 2 phosphor from energy transfer of Eu 2+ by broadband down-conversion

We report on conversion of near-ultraviolet and visible radiation ranging from 250 to 500 nm into near-infrared emission by a Ca(8)Mg(SiO(4))(4)Cl(2): Eu(2+), Er(3+) phosphor. Efficient 1530-1560 nm Er(3+) emission ((4)I(13/2)-->(4)I(15/2)) was detected under the excitation of Eu(2+) (4f?5d) absorption band as a result of energy transfer from Eu(2+) to Er(3+), which is confirmed by both steady state and time-resolved emission spectra. The laser power dependent emission intensity changes were investigated to analysis the energy transfer mechanism. Energy transfer from Eu(2+) to Er(3+) followed by a multi-photon quantum cutting of Er(3+) is proposed. The result indicates that the phosphor has potential application in enhancement of conversion efficient of germanium solar cells because the energy difference of Er(3+): (4)I(13/2)-->(4)I(15/2) transition matches well with the bandgap of Ge (Eg~0.785 eV).

Fabrication and optical properties of Y2O3: Eu3+ nanofibers prepared by electrospinning

Y(2)O(3): Eu(3+) nanofibers with the average diameter of ~300 nm were in situ fabricated by electrospinning. X-ray diffraction (XRD) pattern confirmed that the Y(2)O(3): Eu(3+) nanofibers were composed of pure body-centered cubic (bcc) Y(2)O(3) phase. High-resolution transmission electron microscopy (HRTEM) results indicated that Y(2)O(3): Eu(3+) nanofibers were constituted of nonspherical crystalline grains, and these crystalline grains were orderly arranged along the axial direction of single nanofiber. These Y(2)O(3): Eu(3+) nanofibers showed a partially polarized photoluminescence (PL). The arrangement of crystalline grains and the mismatch of dielectric constant between Y(2)O(3): Eu(3+) nanofiber and its environment probably contributed together to the polarized PL from Y(2)O(3): Eu(3+) nanofiber.

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.

Unusual luminescence quenching and reviving behavior of Bi-doped germanate glasses

Here for the first time, we report an unusual annealing temperature dependent near-infrared (NIR) luminescence quenching and reviving behavior in Bi-doped MgO-Al₂O₃-GeO₂ glasses. Systematic characterizations of the samples by using differential thermal analysis (DTA), photoluminescence and absorption spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that this phenomenon is associated with the reversible reaction of Bi⁺ and Bi⁰ initiated by the change of local glass structure. Excitingly, wavelength tunable luminescence is also observed and it can be ascribed to selective excitation of active Bi⁺ center in different sites. These results not only open a new way for controlling luminescence properties of main group elements in glass but also provide great value for improving practical active-fiber drawing process.

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.

Persistent Near Infrared Phosphorescence from Rare Earth Ions Co-doped Strontium Aluminate Phosphors

SrAl 2 O 4 phosphors co-doped with Eu 2+ , Dy 3+ , and Nd 3+ ions are synthesized through a citric acid assisted sol-gel combustion process. The crystalline phases and crystallinity of the synthesized phosphors are studied by X-ray diffraction analysis. Strong persistent phosphorescence at 882 nm is observed as a consequence of irradiation by ultraviolet light at 370 nm due to the persistent energy transfer from excited Eu 2+ ions to Nd 3+ ions. The optimum doping concentration of Nd 3+ ions is estimated to be ~2%, when the concentration of Eu 2+ and Dy 3+ ions are 1 and 1.5%, respectively, considering the energy transfer efficiency and the near infrared phosphorescence intensity.

Large-scale preparation of strawberry-like, AgNP-doped SiO2 microspheres using the electrospraying method

In this paper, we report on a novel strategy for the preparation of silver nanoparticle-doped SiO(2) microspheres (Ag-SMSs) with an interesting strawberry-like morphology using a simple and efficient electrospraying method. SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (x-ray diffraction), EDS (energy-dispersive spectroscopy) and UV-vis spectra (ultraviolet-visible spectra) were applied to investigate the morphology, structure, composition and optical properties of the hybrid microspheres, and E. coli (Escherichia coli) was used as a model microbe to evaluate their antibacterial ability. The results showed that the Ag-SMSs were environmentally stable and washing resistant. The Ag-SMSs exhibited effective inhibition against proliferation of E. coli, and their antibacterial ability could be well preserved for a long time. The environmental stability, washing resistance, efficient antibacterial ability and simple but productive preparation method endowed the Ag-SMSs with great potential for practical biomedical applications.

Preparation and Optical Properties of Long Afterglow Europium-Doped Ca ( Sr ) Al2Si2O8 Electrospun Nanofibers

Eu 2+ -doped Ca(Sr)Al 2 Si 2 O 8 nanofibers with an average diameter of 500 nm were in situ synthesized by electrospinning and calcination in reduced ambience. X-ray diffraction results confirmed that the Ca(Sr)Al z Si 2 O 8 :Eu 2+ nanofibers were of the anorthite phase. An intense blue emission due to the 4f 6 5d 1 → 4f 7 transition of Eu 2+ ions was observed in the nanofibers. The emission band shifted to the blue region with the substitution of Ca by Sr due to the change in the crystal field surrounding Eu 2+ ions. The long afterglow decay curves of Ca(Sr)Al 2 Si 2 O 8 :Eu 2+ nanofibers contain rapid (∼ 13.86 s) and slow (∼ 157.12 s) components. By the co-doping of Dy 3+ ions, the emission and long afterglow duration of nanofibers were improved remarkably. These Ca(Sr)Al 2 Si 2 O 8 :Eu 2+ , Dy 3+ electrospun nanofibers with excellent emission and long afterglow properties were potentially applied in biological marker, disnlay, sensor, etc.