Hong-Di Zhang

Flexible inorganic membranes used as a high thermal safety separator for the lithium-ion battery

A flexible SiO2 porous fiber membrane (SF) is prepared by electrospinning followed by calcination in this work. Compared with an organic substrate separator, the SF used as a separator will be an absolute guarantee of the battery thermal safety. The porosity of the SF is 88.6%, which is more than twice that of a regular PP separator. Hydrophilic SF shows better electrolyte wetting ability and its high porosity enables the SF to absorb 633% liquid electrolyte on average, while the lithium-ion conductivity reaches 1.53 mS cm−1. The linear sweep voltammogram testing of PP and SF suggested that SF, with great electrochemical stability, can meet the requirements of lithium-ion batteries. The cyclic and rate performances of batteries prepared with SF are improved significantly. Such advantages of the SF, together with its potential in mass production, make the SF a promising membrane for practical applications in secondary lithium-ion batteries.

Effect of Ce doping on the optoelectronic and sensing properties of electrospun ZnO nanofibers

Pure n-type ZnO nanofibers and p-type Ce-doped ZnO nanofibers were prepared by electrospinning followed by calcination. Their surface morphology, elemental composition, crystal structure, and optical and electronic properties were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and photoluminescence and UV-visible spectroscopy techniques and by their current–voltage (I–V) curves. The energy-dispersive X-ray spectroscopy and X-ray diffraction spectra showed that Ce was successfully incorporated into the ZnO crystal lattice and that the atomic percentage of Ce to Zn was 1.46%. The photoluminescence integrated intensity ratio of the UV emission to the deep-level green emission for Ce-doped ZnO nanofibers was over twice than that of pure ZnO. The UV-visible absorption edge of the Ce-doped ZnO nanofibers red-shifted by 2.6 nm compared with the pure ZnO nanofibers. The ZnO nanofibers had a good response to ultraviolet radiation. The sensitivity (Imax/I0) of the Ce-doped ZnO nanofibers was 102, which was one order higher in magnitude than that of pure ZnO nanofibers. The field-effect curve suggested that the synthesized Ce-doped ZnO nanofibers were p-type semiconductors. A p–n homojunction device was prepared using the ZnO nanofibers and showed good rectifying behavior. The turn-on voltage reduced by about 10 V under UV irradiation. Both the ZnO nanofibers and the ZnO p–n homojunction had excellent UV sensibilities. These results suggest that Ce-doped ZnO nanofibers may have widespread applications in optical and electronic devices.

Piezoluminescence from ferroelectric Ca 3 Ti 2 O 7 :Pr 3+ long-persistent phosphor

A variety of up-and-coming applications of piezoluminescence in artificial skins, structural health diagnosis, and mechano-driven lightings and displays recently have triggered an intense research effort to design and develop new piezoluminescent materials. In this work, we deduced and verified an efficient piezoluminescence in ferroelectric Ca3Ti2O7:Pr3+ long-persistent phosphor, in view of three fundamental elements forming piezoluminescence - piezoelectricity, luminescent centers and carrier traps. Under the stimulation of mechanical actions including compression and friction, Ca3Ti2O7:Pr3+ shows an intense red emission from 1D2-3H4 transition of Pr3+. On the basis of investigations on structural and optical characteristics especially photoluminescence, persistent luminescence and thermoluminescence, we finally proposed a possible piezoluminescent mechanism in Ca3Ti2O7:Pr3+. Our research is expected to expand the horizon of existing piezoluminescent materials, accelerating the development and application of new materials.

Effects of Ce doping and humidity on UV sensing properties of electrospun ZnO nanofibers

Pure ZnO and Ce-doped ZnO nanofibers were synthesized via electrospinning-calcination technique. The morphology, composition, structure, humidity sensing and photoelectric properties were characterized. The field-effect curves showed that a single pure ZnO nanofiber is an n-type semiconductor and an individual Ce-ZnO nanofiber is a p-type semiconductor. The Ce doping and humidity have strong influence on the UV sensing properties of ZnO-based nanofibers. In the dark, the responses [(IVarious RH − I43% RH)/I43% RH] of pure ZnO increased gradually with the increase of humidity, while the responses of Ce-doped ZnO nanofibers decreased. When exposed to UV radiation, the response of pure ZnO nanofibers decreased with increasing humidity, while that of Ce-doped ZnO increased. And the highest responses are around 88.44 and 683.67 at 97% humidity for pure ZnO and Ce-ZnO nanofibers under UV irradiation. In addition, the UV response of Ce-ZnO with good stability and repeatability increases by two orders of magnitud...

Multicolor Tuning in Room‐Temperature Self‐Activated Ca2Nb2O7 Submicroplates by Lanthanide Doping

Self-activated phosphors are capable of generating optical emissions from the internal ion groups of host lattice before externally introducing luminescent ions. However, numerous self-activated phosphors only show luminescence at low temperature due to the thermally activated energy migration among ion groups at room temperature, severely confining their application conditions. In this letter, we propose a strategy to converting the low-temperature luminescence to a room-temperature one through changing the synthesis conditions to induce structural distortions and thus to limit energy migration. Room-temperature self-activated luminescence of Ca2 Nb2 O7 was accordingly achieved in submicroplates synthesized using the sol-gel method. By further coupling the blue broadband emission from Ca2 Nb2 O7 submicroplates with the characteristic luminescence of Ln3+ (Pr3+ , Sm3+ , and Dy3+ ) dopants, multicolor emissions were successively tuned through adjusting the concentration of Ln3+ . Our results are expected to expand the scope of designing room-temperature self-activated phosphors and tuning multicolor emission.

Fabrication and formation mechanism of closed-loop fibers by electrospinning with a tip collector*

Electrospun nanofibers with designed or controlled structures have drawn much attention. In this study, we report an interesting new closed-loop structure in individual cerium nitrate/polyvinyl alcohol (Ce(NO3)3/PVA) and NaCl/PVA fibers, which are fabricated by electrospinning with a nail collector. The electrospinning parameters such as voltage and Ce(NO3)3 (or NaCl) concentration are examined for the formation of the closed-loop structure. The results suggest that the increase of the spinning voltage or addition of Ce(NO3)3 (or NaCl) is favorable for the formation of the closed-loop structure, and the increase of loop numbers and the decrease of loop size. Further analyses indicate that the formation mechanism of the closed-loop fibers can be predominantly attributed to the Coulomb repulsion in the charged jets.