Dongxu Zhao

Improved performance of electroluminescent devices based on an europium complex

Electroluminescent (EL) devices using an europium complex Eu(DBM)3 bath as the electron-transport emitting layer were fabricated. The quenching effect of the metal cathode and the unstable nature of the Eu complex under EL operation markedly influence the EL efficiency. By keeping the emitting area far from the metal cathode and partly doping the Eu(DBM)3 bath layer with a hole-transport material, the EL performance was significantly improved. Sharp-band red emissions with turn-on voltage of 3 V, brightness of 820 cd/m2, and external quantum efficiency of 1% were achieved.

Visible and ultraviolet light alternative photodetector based on ZnO nanowire/n-Si heterojunction

Closely packed ZnO nanowire array was fabricated on a n-type Si (100) substrate by a magnetron cosputtering method. The ZnO nanowire/n-Si heterojunction showed good diode characteristics with rectification ratio of above 1.6×102 at 4V in the dark. Experiments demonstrated that the diode could be used to detect either visible or ultraviolet light by easily controlling the polarity of the voltage applied on the heterojunction. The spectral response of the device will be discussed in terms of the band diagrams of the heterojunction and the carrier diffusion process.

Solar-Blind Avalanche Photodetector Based On Single ZnO–Ga2O3 Core–Shell Microwire

High-performance solar-blind (200-280 nm) avalanche photodetectors (APDs) were fabricated based on highly crystallized ZnO-Ga2O3 core-shell microwires. The responsivity can reach up to 1.3 × 10(3) A/W under -6 V bias. Moreover, the corresponding detectivity was as high as 9.91 × 10(14) cm·Hz(1/2)/W. The device also showed a fast response, with a rise time shorter than 20 μs and a decay time of 42 μs. The quality of the detectors in solar-blind waveband is comparable to or even higher than that of commercial Si APD (APD120A2 from Thorlabs Inc.), with a responsivity ∼8 A/W, detectivity ∼10(12) cm·Hz(1/2)/W, and response time ∼20 ns. The high performance of this APD make it highly suitable for practical applications as solar-blind photodetectors, and this core-shell microstructure heterojunction design method would provide a new approach for realizing an APD device.

Gold nanoparticles modified ZnO nanorods with improved photocatalytic activity

Well-aligned ZnO nanorods (NRs) were grown on indium-tin-oxide (ITO) slide by the hydrothermal method and used as templates for preparing ZnO/Au composite nanoarrays. The optical and morphological properties of ZnO/Au composites under various HAuCl(4) concentrations were explored via UV-vis absorption spectroscopy, photoluminescence (PL) and scanning electron microscopy (SEM). The density and size of gold nanoparticles (Au NPs) on ZnO NRs can be controlled by adjusting the concentration of HAuCl(4). The optimal ZnO/Au composites display complete photocatalytic degradation of methyl blue (MB) within 60 min, which is superior to that with pure ZnO NRs prepared by the same method. The reason of better photocatalytic performance is that Au NPs act as electron traps and it prevents the rapid recombination of electrons and holes, resulting in the improvement of photocatalytic efficiency. The photocatalytic performance of ZnO/Au composites is mainly controlled by the density of Au NPs formed on ZnO NRs. The application in rapid photodegradation of MB shows the potential of ZnO/Au composite as a convenient catalyst for the environmental purification of organic pollutants.

Photoluminescence properties of MgxZn1-xO alloy thin films fabricated by the sol-gel deposition method

The photoluminescence properties of MgxZn1−xO alloy thin films fabricated by the sol-gel deposition method were studied. The Mg2+ content in the films was up to 0.36 and they had the ZnO wurtzite structure. The band gap of the films can be controlled between 3.40 and 3.93 eV by adjusting the Mg2+ proportions. Transmittance spectroscopy was used to characterize the excitonic structure of the alloys, which the excitonic character is clearly visible at room temperature. The intense ultraviolet photoluminescence was observed at room temperature. This emission is indicative of the excitonic nature of the material.

Europium complexes as emitters in organic electroluminescent devices

Abstract Using two different trivalent europium (Eu 3+ ) complexes, europium(dibenzoylmethanato) 3 (bathophenanthroline) [Eu(DBM) 3 bath] and europium (dibenzoylmethanato) 3 (monophenanthroline) [Eu(DBM) 3 phen], with different ligands for emission-layer materials, various types of electroluminescent (EL) devices have been fabricated. Combined with a triphenylamine derivative (TPD) and an oxadiazole derivative (OXD7) as hole-transport-layer materials, two-layer- and three-layer-type devices have been fabricated. We find that these two emission-layer materials have similar EL spectra, but their EL performances are different. The EL capability of the Eu complexes and their carrier-transporting characteristics are largely dependent on the ligands.

Self-Powered Solar-Blind Photodetector with Fast Response Based on Au/β-Ga2O3 Nanowires Array Film Schottky Junction

Because of the direct band gap of 4.9 eV, β-Ga2O3 has been considered as an ideal material for solar-blind photodetection without any bandgap tuning. Practical applications of the photodetectors require fast response speed, high signal-to-noise ratio, low energy consumption and low fabrication cost. Unfortunately, most reported β-Ga2O3-based photodetectors usually possess a relatively long response time. In addition, the β-Ga2O3 photodetectors based on bulk, the individual 1D nanostructure, and the film often suffer from the high cost, the low repeatability, and the relatively large dark current, respectively. In this paper, a Au/β-Ga2O3 nanowires array film vertical Schottky photodiode is successfully fabricated by a simple thermal partial oxidation process. The device exhibits a very low dark current of 10 pA at -30 V with a sharp cutoff at 270 nm. More interestingly, the 90-10% decay time of our device is only around 64 μs, which is much quicker than any other previously reported β-Ga2O3-based photodetectors. Besides, the self-powering, the excellent stability and the good reproducibility of Au/β-Ga2O3 nanowires array film photodetector are helpful to its commercialization and practical applications.

White light emitting organic electroluminescent devices using lanthanide dinuclear complexes

Abstract Organic electroluminescent devices with Eu x Tb 1− x (aca) 3 phen dinuclear complex as the emitting layer were fabricated. When the devices are operated under proper voltage the white light can be obtained. It consists of three parts: red from Eu 3+ , green from Tb 3+ and blue from TPD (or NPB).

Enhanced electroluminescence of europium(III) complex by terbium(III) substitution in organic light emitting diodes

Abstract A binuclear complex Tb0.5Eu0.5(aca)3phen was synthesized and used as the emission material. It was found that there is an efficient energy transfer from Tb3+ to Eu3+ in the emitting layer.

The enhancement of ZnO nanowalls photoconductivity induced by CdS nanoparticle modification

10 nm sized hexagonal CdS nanoparticles were decorated on the surface of well-aligned ZnO nanowall through a facile hydrothermal approach. The effects of CdS-cap layer on the optical and photoelectrical properties of ZnO nanowalls have been studied. It was found the CdS acted not only as a passivation layer to suppress the detrimental surface states of ZnO nanowalls, which reduced the deep-level emissions, but also as an interfacial carrier transport layer to reduce the probability of carrier recombination. Due to this effect a significant enhancement in ultraviolet photoconductivity of ZnO nanowalls was observed by the surface modification with CdS nanoparticles.