Qingru Wang

Enhancing blue luminescence from Ce-doped ZnO nanophosphor by Li doping

Undoped ZnO, Ce-doped ZnO, and (Li, Ce)-codoped ZnO nanophosphors were prepared by a sol-gel process. The effects of the additional doping with Li ions on the crystal structure, particle morphology, and luminescence properties of Ce-doped ZnO were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and photoluminescence spectroscopy. The results indicate that the obtained samples are single phase, and a nanorod shaped morphology is observed for (Li, Ce)-codoping. Under excitation with 325 nm light, Ce-doped ZnO phosphors show an ultraviolet emission, a green emission, and a blue emission caused by Zn interstitials. The spectrum of the sample codoped with a proper Li concentration features two additional emissions that can be attributed to the Ce3+ ions. With the increase of the Li doping concentration, the Ce3+ blue luminescence of (Li, Ce)-codoped ZnO is obviously enhanced, which results not only from the increase of the Ce3+ ion concentration itself but also from the energy transfer from the ZnO host material to the Ce3+ ions. This enhancement reaches a maximum at a Li content of 0.02, and then decreases sharply due to the concentration quench. These nanophosphors may promise for application to the visible-light-emitting devices.PACS78.55.Et; 81.07.Wx; 81.20.Fw

Improved electrical transport properties of an n-ZnO nanowire/p-diamond heterojunction

A heterojunction of n-ZnO nanowire (NW)/p-B-doped diamond (BDD) was fabricated. The rectifying behavior was observed with the turn on voltage of a low value (0.8 V). The forward current at 5 V is 12 times higher than that of a larger diameter n-ZnO nanorod (NR)/p-BDD heterojunction. The electrical transport behaviors for the comparison of n-ZnO NWs/p-BDD and n-ZnO NRs/p-BDD heterojunctions are investigated over various bias voltages. The carrier injection process mechanism for ZnO NWs/BDD is analyzed on the basis of the proposed equilibrium energy band diagrams. The ZnO NWs/BDD heterojunction displays improved I–V characteristics and relatively high performance for the electrical transport properties.

Improvement of structural and optical properties of ZnAl 2 O 4 :Cr 3+ ceramics with surface modification by using various concentrations of zinc acetate

AbstractThe influence of surface modification with various concentrations of zinc acetate solution on the structural and optical properties of ZnAl2O4:Cr3+ particles was studied. The X-ray diffraction peaks assigned to the spinel structure of ZnAl2O4:Cr3+ powders revealed a tiny shift towards the lower angle, and ZnO phase was detected when ZnAl2O4:Cr3+ crystals surface was modified. The results of X-ray photoelectron spectra confirmed that the antisite defects related to tetrahedral Al existed in the surface lattices of zinc aluminate crystals. The signal intensity of XPS assigned to tetrahedral Al decreased after surface modification, while that of XPS assigned to octahedral Zn increased. The results of transmission electron microscope showed that the surface lattices of ZnAl2O4:Cr3+ particles became more ordered after surface modification, and zinc oxide nanocrystals were observed as a coating layer or dispersed particles surrounding ZnAl2O4:Cr3+ particles when the concentration of Zn(AC)2 solution increased up to 1.5 mol/L. The red emission assigned to Cr3+ ions in spinel lattices was detected at room temperature, and the emission intensity was enhanced when ZnAl2O4:Cr3+ crystals was modified. While the emission intensity was reduced when the concentration of Zn(AC)2 solution increased up to 1.5 mol/L. ZnAl2O4:Cr3+ crystals were modified by using with various concentrations of zinc acetate (0.5 M, 1.0 M and 1.5 M). These crystals surfaces showed different morphologies, and the crystallinity and photoluminescence performances were enhanced.HighlightsThe crystallinity of ZnAl2O4:Cr3+ crystals is improved by using surface modification.The defects transform from AlZn to ZnAl after surface modification.The PL intensity is 2.5 times than that of crystals without surface modification

Enhanced color purity of blue OLEDs based on well-design structure

We have fabricated blue organic light-emitting devices (OLEDs) with higher color purity and stability by optimizing the structure of the Glass/ITO/NPB(50 nm)/ BCzVBi (30 nm)/ TPBi (x nm)/Alq3(20 nm)/LiF/Al. The results show that the introducing of hole blocking layer(HBL) TPBi greatly can improve not only the color purity but the color stability, which owe to its higher the Highest Occupied Molecular Orbital (HOMO) energy levels of 6.2 eV. We expect our work will be useful to optimizing the blue OLEDs structure to enhancing the color property.

Improvement of amplified spontaneous emission performance in organic waveguides

Metal film is an essential part of the electrically pumped organic semiconductor lasers. But the large loss is the most important factor restricting the electrical pumping. In this paper, we investigate optically pumped amplified spontaneous emission (ASE) in the presence of metal films. The ASE threshold of device with metallic film is reduced by 2.5 times in comparison with that of the metal-free devices. The SiO2 space layer with optimizing thickness between gain media and metal film can effectively prevent absorption loss but also provides a proper waveguide effect. Furthermore, the metal film can prevent the light leaking to the substrate and reflect the lights back into the media, which increases the intensity of pumping and emission again.