Hongzhi Shen

Highly luminescent, stable, transparent and flexible perovskite quantum dot gels towards light-emitting diodes

By controlling the hydrolysis of alkoxysilanes, highly luminescent, transparent and flexible perovskite quantum dot (QD) gels were synthesized. The gels could maintain the structure without shrinking and exhibited excellent stability comparing to the QDs in solution. This in situ fabrication can be easily scaled up for large-area/volume gels. The gels integrated the merits of the polymer matrices to avoid the non-uniformity of light output, making it convenient for practical LED applications. Monochrome and white LEDs were fabricated using these QD gels; the LEDs exhibited broader color gamut, demonstrating better property in the backlight display application.

The gas-sensing and structure properties of Fe-doped In2O3 nanotubes by electrospinning technique

Fe-doped In2O3 nanotubes were successfully synthesized by electrospinning technique followed by subsequent heat treatment. The as-prepared samples appeared as an apparently open-end one-dimensional (1D) and tubular-like morphology with the diameter of approximately 150 nm and the wall thickness about 20 nm. The diffraction peak of the obtained nanotubes shifts toward bigger angle direction with the increase of the Fe content. Comparing to the In2O3 nanotubes, the Fe-doped In2O3 nanotubes exhibit better sensing characteristics toward ethanol gases, including higher sensing response, lower operating temperature and higher selectivity. Enhanced sensing properties are attributed to 1D hollow nanostructures and the role of doping Fe element.

Electrospinning synthesis and photoluminescence properties of SnO 2 : x Eu 3+ nanofibers

SnO2:xEu3+(x=0, 1%, 3%, 5%, molar fraction) fibers were synthesized by electrospinning technology. The size of the as-prepared fibers is relatively uniform and the average diameter is about 200 nm with a large draw ratio. The as-prepared Eu3+ doped SnO2 nanofibers have a rutile structure and consist of crystallite grains with an average size of about 10 nm. A slight red shift of the A1g and B2g vibration modes and an additional peak at 288 nm were observed in the Raman spectra of the nanofibers. The energies of bandgaps of the SnO2 nanofiber with Eu doping of 1% and 3% are 2.64 eV, and the energy of bandgap is 2.94 eV with Eu doping of 5%(molar fraction). There is only orange emission(5D0→7F1 magnetic dipole transition) for Eu doped SnO2 nanofibers, and no red emission could be observed. The orange emission upon indirect excitation splits into three peaks and the peak intensity at the excitation wavelength of 275 nm is higher than that at the excitation wavelength of 488 nm.

Epitaxial growth of highly infrared-transparent and conductive CuScO2 thin film by polymer-assisted-deposition method

As an important wide bandgap p-type conductive delafossite material, CuScO2 (CSO) has been intensively investigated for its wide applications in multi-functional optoelectronic devices. In order to obtain both high infrared (IR) transparency and low resistivity, we report on, for the first time, the experimental preparation of single phase epitaxial CSO thin film by using polymer-assisted-deposition (PAD) method. As a key point in the PAD process, the used polymer materials (PEI and EDTA) not only control the desired viscosity for the process, but also bind the metal ions to prevent premature precipitation and formation of metal oxide oligomers. The technique results in a homogeneous distribution of the metal precursors in the solution as well as the formation of uniform metal organic film. Due to the uniaxial locked epitaxy mechanism, the epitaxial growth of CSO (0001) thin film on a-plane sapphire is achieved, and the orientation relationship of the film with respect to the substrate are confirmed to be CSO[3R](0001)//a-Al2O3(110). The obtained CSO thin film from the PAD technique exhibits a low electrical resistivity of 1.047 Ω cm at room temperature, and a high transmittance of 65–85% in the near-IR range and more than 85% in the mid-IR range. The presented technique does provide the possibility of preparing high-crystallinity oxide films which can be applicable over a wide wavelength range from visible band to infrared band.

Highly infrared-transparent and p-type conductive CuSc1−xSnxO2 thin films and a p-CuScO2:Sn/n-ZnO heterojunction fabricated by the polymer-assisted deposition method

We fabricated a series of infrared (IR)-transparent and conductive Sn-doped CuScO2 thin films using a polymer-assisted deposition (PAD) method. Highly c-axis oriented films were grown on a-plane sapphire substrates, and the orientation relationship with respect to the substrates was confirmed to be CuScO2:Sn[3R](0001)//a-Al2O3(110). The films exhibited good p-type conductive characteristics, and a high conductivity of 17.86 S cm−1 was achieved for CuSc0.94Sn0.06O2 at room temperature, which is 19 times larger than the un-doped film at room temperature. The prepared films retain a transparency of >70% in the near-IR region and >90% in the mid-IR region, which are the best performing p-type IR transparent conductive thin films grown by chemical solution methods to date. As x changes from 0 to 0.06, the hopping activation energy varies within the range of 129–98 meV. As an application of such films, p-CuScO2:Sn/n-ZnO heterojunction diodes were fabricated using the PAD technique. The measured ∼2 V threshold voltage of the p-CuSc0.94Sn0.06O2/n-ZnO diode is in reasonable agreement with the bandgap energy of CuSc0.94Sn0.06O2. The resulting films can be used in optoelectronic devices over a wide wavelength range from the visible to IR band, due to their high electrical conductivity and optical transparency.

Study on thermal stability of single-phase YCoO3 nanoparticles

YCoO₃ is a important inorganic functional materials, which has a wide-spread application in gas-sensing devices. In this paper, the thermal stability of single-phase YCoO₃ is studied by XRD, TG-DTA and TEM. The single-phase YCoO₃ is prepared by a two-step process involving sol-gel technique and sintering method. The synthesis conditions of the single-phase YCoO₃ are 900-1000 °C for 10 h in air. The synthesis temperature is extended to 850-1100 °C and the sintering time is shortened to 5h in oxygen atmosphere. The experimental results show that the synthesized powders have orthorhombic structure, with the diameter about 30 nm, which is stable in air below 1050 °C and in oxygen atmosphere below 1100 °C. Above those temperatures, YCoO₃ decomposes into Y₂O₃ and Co₃O₄. Oxygen atmosphere inhibits the decomposition of YCoO₃ at high temperature, resulting in the decomposition temperature increasing by 50 °C.