Danyu Jiang

MgxZn1−xO-based photodetectors covering the whole solar-blind spectrum range

A series of MgxZn1−xO thin films has been prepared by metalorganic chemical vapor deposition and metal-semiconductor-metal structured ultraviolet photodetectors are fabricated from these films. The cutoff wavelengths of the photodetectors can cover the whole solar-blind spectrum range (220–280 nm) by varying Mg content in the MgxZn1−xO thin films. As a representative, the photodetector fabricated from Mg0.52Zn0.48O shows an ultraviolet/visible rejection ratio of about four orders of magnitude, and the dark current is 15 pA at 10 V bias. These results demonstrate that high-performance photodetectors operating in the whole solar-blind spectrum range can be realized in MgxZn1−xO films.

Controlled Synthesis of ZnS Quantum Dots and ZnS Quantum Flakes with Graphene as a Template

Novel ZnS quantum dots (QDs) and ZnS quantum flakes (QFs) were successfully prepared with graphene nanosheets (GNs) as a special template, and two unique heterostructures of ZnS/GNs were also obtained. Due to the structure-directing template effect of GNs, the as-synthesized ZnS with different morphologies, dots or flakes, were uniformly distributed on the surface of GNs by controlling nucleation and growth. The two different heterostructures of ZnS/GNs exhibited obvious photovoltaic response, and ZnS/GN QFs-on-sheet heterostructures show higher photovoltage than that of ZnS/GN QDs-on-sheet.

High temperature creep of a hot-pressed β-sialon

The four-point bending creep properties of a hot-pressed β-sialon with Sm–melilite solid solution (denoted as M′) as intergranular phase have been studied in the temperature range 1250–1350°C in air. Creep rates plotted against stresses gave stress exponents of 1.45, 1.51 and 1.72 at 1250, 1300 and 1350°C, respectively, and Arrhenius plot between creep rate and temperature yielded a creep activation energy of 576 kJ mol−1. Cavities were found to be mainly on the triple grain junctions. Diffusion coupled with grain boundary sliding and accompanied by the formation of wedge-shaped cavities was identified as the dominant creep mechanism.

The effect of creep deformation of a β sialon on Vickers hardness, fracture toughness and Weibull modulus

Abstract The influence of creep deformation of a β sialon with Sm-melilite solution (denoted as M′) as intergranular phase on Vickers hardness, indentation fracture toughness and Weibull modulus was investigated in this article. For samples crept at different temperatures and stresses, Vickers hardness and fracture toughness fell in the range of 14.1–15.5 GPa and 5.73–7.04 MPa m 1/2 , respectively. For virgin sample, the Vickers hardness and toughness were 15.8 GPa and 6.08 MPa m 1/2 , respectively. Weibull moduli on Vickers hardness were 36 and 39 for the samples crept at 1300xa0°C (sample 5, see Table 1 ) and 1350 °C (sample 9, see Table 1 ), respectively, compared to 23 for the virgin sample. Weibull moduli on fracture toughness were 18 and 21 for sample 5 and sample 9, respectively, compared to 19 for the virgin sample. The discrepancy of Vickers hardness, fracture toughness and Weibull modulus between the virgin and crept samples was due to the more compact microstructure, the decrease in the amount and devitrification of intergranular phase and cavities during creep. Aging effect study shows that Vickers hardness values on the ends of crept specimens are lower than those within the deformation zones.

Neodymium zirconate (Nd2Zr2O7) transparent ceramics as a solid state laser material

Transparent neodymium zirconate (Nd2Zr2O7) ceramics have been fabricated from nanoparticles prepared by combustion synthesis. Emission at 1054.5 nm has been demonstrated using a laser diode pump at 800 nm. A transmittance of 60% at wavelengths longer than ∼900u2002nm was achieved. A consequence of the very high concentration of Nd ions (1.32×1028u2002ions/m3) is that the absorption bands are wider than those of Nd doped Y3Al5O12 (Nd:YAG) facilitating pumping over a broader range of wavelengths. The full width at half maximum of the emission peak is also larger than that of Nd:YAG, and the decay time is 460u2002μs making Nd2Zr2O7 an excellent candidate for efficient high-power microchip lasers emitting at 1054 nm with diode pumping at ∼800 or ∼900u2002nm.

Novel luminescent yttrium oxide nanosheets doped with Eu3+ and Tb3+

Novel single-layer rare-earth oxide nanosheets were obtained by the exfoliation of Y(1−X)REXOBr (RE = Eu/Tb) layer. First, the Br− ions in Y(1−X)REXOBr were exchanged by benzoate ions under microwave conditions. The interlayer benzoate can chelate RE ions in the oxide layer, and change the structure and luminescence properties of the new layer compound. Then, a colloid of yttrium oxide nanosheets was obtained in n-butanol after the ultrasonic treatment of the benzoate-inserted layer for 30 min. The size and thickness of the yttrium oxide nanosheets were ∼800 nm and 0.8 nm, as measured by transmission electron and atomic force microscopies, respectively. A transparent thin film of the yttrium oxide nanosheets on indium tin oxide glass was prepared by electrophoretic deposition. The thin film showed strong red or green emission upon UV-light excitation based on Eu3+ and Tb3+ ions, respectively.

High temperature bending creep of a Sm-α-β Sialon composite

The four-point bending creep behavior of a Sm-α-β Sialon composite, in which Sm-melilite solid solution (denoted as M′) was designed as intergranular phase, was investigated in the temperature range 1260–1350°C and stresses between 85 and 290 MPa. At temperatures less than 1300°C, the stress exponents were measured to be 1.2–1.5, and the creep activation energy was 708 kJ mol−1, the dominant creep mechanism was identified as diffusion coupled with grain boundary sliding. At temperatures above 1300°C, the stress exponents were determined to be 2.3–2.4, and creep activation energy was 507 kJ mol −1, the dominant creep mechanism was suggested to be diffusion cavity growth at sliding grain boundaries. Creep test at 1350°C for pre-oxidation sample showed a pure diffusion mechanism, because of a stress exponent of 1. N3− diffusing along grain boundaries was believed to be the rate controlling mechanism for diffusion creep. The oxidation and α → β Sialon phase transformation were analyzed and their effect on creep was evaluated.

Microstructure and creep behavior of an Y-α-β sialon composite

Abstract Flexural creep behavior of a Y-α-β sialon composite was studied in air at temperatures of 1250–1350°C and stresses of 110–290 MPa. The composite in which YAG was designed as intergranular phase has an original α/β ratio of 65/35. The stress exponents in Norton equation were determined to be 1.31±0.12, 1.49±0.15 and 1.62±0.10 at 1250, 1300 and 1350°C, respectively, and creep activation energy was 677±25 kJ mol −1 . Combining the microstructure observations, grain boundary diffusion accommodated by grain boundary sliding was identified as the rate-controlling creep mechanism for the composite. The creep rate exponent p in Monkman–Grant relation was found to be 1.6, and the nucleation and growth of cavities in triple grain pockets was responsible for the creep rupture.

Microwave Intercalation Synthesis of WO3 Nanoplates and Their NO-Sensing Properties

AbstractnTungsten(VI) oxide (WO3) nanoplates were successfully synthesized by microwave intercalation. Through microwave processing, an intermediate product H2W2O7·xH2O was prepared quickly to greatly decrease the time used to prepare WO3 nanoplates. The crystal structure and morphology of WO3 were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The morphology of WO3 changed with an increase in calcining temperature. A mixed-potential NOx sensor using planar yttria-stabilized zirconia and WO3 as the sensing electrode (SE) was fabricated, and its performance in NOx detection at high temperature was examined. It was determined that at 500xa0°C, the sensor with the WO3-nanoplate SE had higher sensitivity to NO than the sensor with a SE consisting of WO3 microparticles. The response of the NO sensor with a WO3-nanoplate SE was linear with the logarithm of NO concentration in the range of 100-1000xa0ppm. The electrochemical impedance measurements indicate that the electrode reaction that occurred at the triple-phase boundary (TPB) of the sensor with WO3-nanoplate SE was stronger than the reaction that occurred at the TPB of the sensor with WO3-microparticle sensing electrode.

Enhanced fluorescence of europium-doped yttrium hydroxide nanosheets modified by 2-thenoyltrifluoroacetone

A novel luminescent inorganic/organic hybrid nanosheet [Y2(1−x)Eu2x(OH)5(TTA)n]+ was successfully synthesized. The photoluminescence of the hybrid nanosheet was significantly different from that of the unmodified nanosheet. The main charge transfer band Eu–O of the nanosheet was replaced by the more efficient π–π* electron transition band of the organic ligands in the hybrid. The emission bands of the 5D0–7F2 electric dipole transition in the hybrid were enhanced greatly. We also prepared a novel transparent thin film of the luminescent inorganic/organic hybrid on FTO glass by electrophoretic deposition. On being excited by ultraviolet radiation, the thin films show strong red emission.