Focus control of wide-angle metalens based on digitally encoded metasurface

Based on the principle of super-symmetric lens with quadratic phase gradient transformation, combined with the principle of digital coding of metasurface, we propose a wide-angle coded metalens for focusing control in two-dimensional space. This metalens achieves focus shift in the x-direction by changing the oblique incidence angle of the incident wave,and focus control in the y-direction by combining with the convolution principle of the digitally coded metasurface to achieve flexible control of light focusing in the two-dimensional plane. The metasurface unit is mainly composed of threelayer of metal structure and two layers of medium, and the transmission phase is obtained by changing the middle layer of metal structure, which in turn obtains the required phase distribution of the metalens. The design of the metalens realizes the function of the lens with a large viewing angle at the x-polarized incidence, and realizes two-dimensional focus control. Experimentally, we prepared the designed coding metalens and tested the focus control function of the wide-angle coding metalens. The experimental results are in good agreement with the design results.

A Study of 10 Rotating Radio Transients Using Parkes Radio Telescope

Rotating Radio Transients(RRATs)are a relatively new subclass of pulsars that emit detectable radio bursts sporadically.We analyzed 10 RRATs observed using the Parkes telescope,with eight of these observed via the ultra-wide-bandwidth low-frequency(UWL)receiver.We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs.We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs.All of their integrated pulses follow a simple power law,consistent with the known range of pulsar spectral indices.Their average spectral indices of single pulses are-0.9,-1.2,and-1.0 respectively,which are within the known range of pulsar spectral indices.Additionally,we find that the spreads of single-pulse spectral indices for these RRATs(ranging from-3.5 to+0.5)are narrower compared to what has been observed in other RRATs.Notably,the average spectral index and scatter of single pulses are both relatively small.For the remaining five RRATs observed at the UWL receiver,we also provide the upper limits on fluence and flux density.In addition,we obtain the timing solution of PSR J1709-43.Our analysis shows that PSRs J1919+1745,J1709-43,and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.

Charicteristic of a novel optoelectronic polymer and related device fabrication

In this paper a preliminary investigation of a novel optoelectronic polymer, poly (p-phenylene N-4-n-butylphenyl-N,N-bis- 4-vinylenephenylamine) (PNB), is reported. A single layer structure of ITO/PNB/Al was prepared via spin-coating of PNB solution as a thin film on the top of an ITO substrate, while aluminum top electrode was vacuum evaporated. Dark current- voltage characteristics of this device showed a typical rectifying behaviour. Photovoltaic response under a monochromatic illumination at 420 nm was observed, with an open circuit voltage of 0.3 V and fill factor of 0.21. Spectral response and optical absorption were found to be matched well. It was also discovered that the device showed a green electroluminescent emission at a forward bias. Turn-on voltage of the device was about 6 V and light output about 22.6 nW at a forward bias of 10 V. The work demonstrated that the PNB material might possess dual exciton sites resulting in a competition for excitons to be either separated or recombined. Both effects were associated with each other, which limited the photovoltaic or electroluminescence to some degrees.

Hydrothermal preparation and persistence characteristics of nanosized phosphor SrS:Eu^(2+),Dy^(3+)

Nanosized long-persistent phosphors SrS：Eu^2＋, Dy^3＋ were prepared by the hydrothermal method.The samples were characterized by X-ray powder diffraction, transmission electron microscopy, and charge-coupled device spectrometry.The persistence characteristic was studied using the decay curves.The results showed that the emission intensity decreased sharply with temperature increasing, although the particle size increased.The S2-vacancies caused by oxidization served as shallow traps, and Dy3＋ served as deep traps in SrS：Eu^2＋, Dy^3＋.The afterglow intensity of SrS：Eu^2＋, Dy^3＋ was higher than that of SrS：Eu2＋ prepared at the same temperature.However, the minimization span of initial afterglow with temperature for the former sample was larger than that for the latter.Binary-doped phosphor decayed more slowly than the singly doped one.The afterglow of SrS：Eu^2＋, Dy^3＋ decayed more quickly with the increase of sintering temperature.

Preparation and Luminescent Properties of BAM Blue Phosphor for PDP and CCFL

The Ba x-0.05MgAl 10O 16+x∶Eu 2+ 0.05 (0.88≤x ≤1.02) phosphors with different Ba 2+ content and the Ba 0.85MgAl 10O 16.94∶Eu 2+ 0.09 phosphors with different fluxes (BaF 2, MgF 2, AlF 3, BaCl 2, MgCl 2, AlCl 3, H 3BO 3) were prepared by high temperature solid-state reaction method and their luminescence characteristics were studied under 254 nm excitation and vacuum ultraviolet (VUV) excitation. With the increase of the Ba 2+ content, there is an increase in the emission intensity, and when x=0.94, it reaches a maximum. Then, as the Ba 2+ content increases, the emission intensity slowly falls. The fluorides have better flux-effects than chlorides and H 3BO 3. The possible mechanism in the process of particle growth was discussed when fluorides were used as fluxes. The effect of the activator concentration on this system was also investigated. The quenching concentration is 0.13 mol in per mole host.

Photoconductive Properties of MEH-PPV/CuS-Nanoparticle Composites

Photoconductive properties of photodiodes based on composites of CuS nanoparticles and Poly[2-methoxy,5- （2＇-ethylhexyloxy）-p-phenylenevlnylene] （MEH-PPV） are investigated. By comparing composite devices with different MEH-PPV：CuS weight ratios of l：l （D2-1）, 1：1.25 （D2-2）, 1：2.5 （132-3） and 1：5 （D2-4）, it is found that the device D2 3 exhibited the best performance： the short-circuit current density of 17μA/cm^2 with the light intensity of 16.7mW/cm^2, the highest open-circuit voltage of 0,83 V, and the photosensitivity of 132 at reverse bias of - 1 V. The photosensitivity is improved by a factor of 5 compared with the undoped MEH-PPV device.

Effects of sputtering conditions on electrochemical behavior and physical properties of Ni-Mo alloy electrode

Sputtering method was used to prepare Ni-Mo alloy electrodes for hydrogen production in alkaline solution. The influences of the working pressure during deposition and the substrate temperature on the electrochemical behavior of electrode were characterized by steady-state polarization plot and Tafel polarization curve measurements. And the physical properties of electrodes were characterized by XRD, SEM, AFM and EDS. It is found that the overpotential is significantly influenced by the working pressure which affects critically the electrode surface morphology, and two Tafel regions are observed for each sample. The overpotential value does not change very much with the substrate temperature. The XRD results indicates that the electrodes should be considered nanocrystalline. Thornton model for the microstructure of sputter-deposited electrodes is referred to explain the observed microstructure change.

Study on Luminescence Properties of a Novel Rare Earth Complex Eu(TTA)_2(N-HPA)Phen

A novel rare earth complex Eu（TTA）2（N-HPA）Phen （TTA = thenoyltrifluoroacetone, N-HPA = N-phenylanthranilic acid, and phen = 1,10-phenathroline ）, which contains three different ligands, was synthesized. The Eu complex was blended with poly N-vinylcarbazole （PVK） in different weight ratios and spin coated into films. The luminescence properties of films were investigated and energy transfer between PVK and the complex was discussed. Multilayer structural devices consisting of ITO/PVK： Eu （TTA）2 （N-HPA） phen/BCP/Alq3/Al were fabricated with PVK ： Eu （TTA）2（N-HPA） as light-emitting layer. Increasing the concentration of Eu in the PVK thin film would inhibit the emission of PVK to different degrees. Finally, the pure red luminescence of europium（ Ⅲ ） was observed when the doping weight ratio was approximately 1 ： 5, which indicated an effective energy transfer from PVK to rare earth complex.

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with Fe_3O_4 particles

In order to investigate the impedance matching properties of microwave absorbers,the ternary nanocomposites of GO/PANI/Fe3O4（GPF） are prepared via a two-step method,GO/PANI composites are synthesized by dilute polymerization in the presence of aniline monomer and GO,and GO/PANI/Fe3O4 is prepared via a co-precipitation method.The obtained nanocomposites are characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,and Fourier transform infrared spectroscopy（FTIR）,respectively.The microwave absorbability reveals enhanced microwave absorption properties compared with GO,PANI,and GO/PANI.The maximum reflection loss of GO/PANI/Fe3O4 is up to-27 dB at 14 GHz with its thickness being 2 mm,and its absorption bandwidths exceeding-10 dB are more than 11.2 GHz with its thickness values being in the range from 1.5 mm-4 mm.It provides that GO/PANI/Fe3O4 can be used as an attractive candidate for microwave absorbers.

Syntheses and Characterization of Binuclear Complexes Tb_(1-x)Eu_x(TTA)_3 Phen

Rare earth ternary complexes Tb1-xEux（TTA）3Phen（x=0,0.25,0.5,0.75,1.0）were synthesized and characterized by DTA-TG,XRD and infrared（IR）.The photophysical properties of these complexes were studied in detail using ultraviolet absorption spectra and fluorescent spectra.Ultraviolet absorption showed that the energy absorption of the complexes mostly came from ligands.Infrared spectra of Tb1-xEux（TTA）3Phen complexes were similar to the pure complexes.TG curves proved that the complexes were stable.Tb3＋ emission was almost quenched and the Eu3＋ emission was enhanced by codoping the complexes.The Tb3＋ ion acted as an energy transfer bridge that helped energy transfer from poly（N-vinylcar-bazole（PVK）to Eu3＋.In addition,their PL and EL properties were systematically studied.

Emission Characteristics of PVK Doped TbY(o-MBA)_6(phen)_2 Systems

A rare earth complex TbY （o-MBA）6（phen）2 was synthesized, which was first used as an emitting material in electroluminescence. By doping it into the conjugated polymer PVK, single-layer and double-layer devices were fabricated with structures： device A ： ITO/PVK ： rpDY （o-MBA）6（phen）2/LiF/Al; B ： ITO/PVK ： rpDY （o-MBA）6（phen）2/AIQ/LiF/Al; C： ITO/PVK： TbY（o-MBA）6（phen）2/BCP/AlQ/LiF/Al. The characteristics of these devices were investigated. For single-layer and double-layer devices, the emission of PVK was completely restrained, and only the green emission from rpD^3＋ was observed in electroluminescence. The above mentioned observation is attributed to the different mechanism of electroluminescence and photoluminescence. In photoluminescence process, the energy of Tb complex may come from PVK through Forster energy transfer process, while in electroluminescence process direct sequential charge trapping appeares to be the main operating mechanism. From the optimized device B, brightly green emission can be obtained, and the highest EL brightness of the device reaches 213 cd·m^-2 at 14 V.

Electrical bistable devices using composites of zinc sulfide nanoparticles and poly-(N-vinylcarbazole)

N-dodecanethiol capped zinc sulfide（Zn S） nanocrystals were synthesized by the one-pot approach and blended with poly（N-vinylcarbazole）（PVK） to fabricate electrical bistable devices. The corresponding devices did exhibit electrical bistability and negative differential resistance（NDR） effects. A large ON/OFF current ratio of 104 at negative voltages was obtained by applying different amplitudes of sweeping voltage. The observed conductance switching and the negative differential resistance are attributed to the electric-field-induced charge transfer between the nanocrystals and the polymer,and the charge trapping/detrapping in the nanocrystals.

Characteristics and Time-Dependent Instability of Ga-Doped ZnO Thin Film Transistor Fabricated by Radio Frequency Magnetron Sputtering

We report on the fabrication and electrical characteristics of Ga-doped ZnO thin film transistors(TFTs).Low Ga-doped(0.7wt%)ZnO thin films were deposited on SiO_(2)/p−Si substrates by rf magnetron sputtering.The GZO TFTs show a mobility of 1.76 cm2/V⋅s,an on/off ratio of 1.0×10^(6),and a threshold voltage of 35 V.The time−dependent instability of the TFT is studied.The VTH shifts negatively.In addition,the device shows a decrease of the on/off ratio,mainly due to the increase of the off-current.The mechanisms of instability are discussed.

Effect of strain on exciton dynamics in monolayer WS2

The exciton dynamics in a WS2 monolayer with strain are studied by transient absorption measurements.We measure the differential transmission signal from monolayer WS2 as a function of the probe wavelength at different levels of strain applied to the sample.The differential transmission spectrum has a positive maximum value at about 614 nm and shows no significant strain dependence.By time-resolving the differential transmission signal,we find that the strain has a minimal effect on the exciton formation process.However,the exciton lifetime is significantly reduced by strain.These results provide useful information for applications of WS2 in flexible electronic and optoelectronic devices where strain is inevitable.

Dependence of Temperature on Upconversion Emission of YLiF_4:Er^(3+)

Intense upconversion emissions of YLiF 4∶Er 3+ synthesized by hydrothermal method were obtained. The upconversion intensity decreases with the increase of environment temperature. In different temperature, the upconversion mechanism is different. At room temperature, the green upconversion mechanism is the combination of two photon process and three photon process, and the red upconversion mechanism is two photon process.

Research on Performance of ZnS∶TbF_3 Thin Film Electroluminescence Device

The electroluminescence of ZnS doped with terbium fluoride thin films prepared b y ra dio frequency magnetron sputtering method was reported. The characteristics of t h e ZnS∶TbF 3 thin film electroluminescence devices, such as film characteristi cs of the ZnS∶Tb active layer, substrate temperatures during magnetron sputteri ng and Tb concentration of the active layer, were systematically investigated. The results show that annealing can evidently improve the luminescence performance of the luminescence device.

A Kind of Low Loss Birefringent Photonic Crystal Fibre with Increasing-Diameter Air-Holes

We report the results of our investigation on the loss property of a birefringent photonic crystal fibre （PCF） based on a particular periodic arrangement of air-holes and pure silica. The structure of the birefringent PCF, whose air-hole diameter in one ring is always larger than the next inner ring, presents an obviously low confinement loss than the one whose air-hole （except those on the horizontal line） diameter is constant. It is shown from numerical results that a four-ring PCF with birefringenee B=5×10^-4 and fast axis confinement loss of 4.5×10^-3 dB/km at wavelength of 1.55μm can be designed.

Transient demonstration of exciton behaviours in solid state cathodoluminescence under different driving voltage

In the solid state cathodoluminescence （SSCL）, organic materials were excited by hot electrons accelerated in silicon oxide （SiO2） layer under alternating current （AC）. In this paper exciton behaviours were analysed by using transient spectra under different driving voltages. The threshold voltages of SSCL and exciton ionization were obtained from the transient spectra. The recombination radiation occurred when the driving voltage went beyond the threshold voltage of exciton ionization. From the transient spectrum of two kinds of luminescence （exciton emission and recombination radiation）, it was demonstrated that recombination radiation should benefit from the exciton ionization.

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles

A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy(TEM) and Fourier transform infrared spectroscopy(FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/ GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss(RL) of GO/PANI/GAunano with a thickness of 2 mm is up to-24.61 d B at 15.45 GHz, and the bandwidth corresponding to RL at-10 d B can reach 4.08 GHz(from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.

Influence of Surface Quenching Effects on Luminescent Dynamics of ZnS：Mn^2＋ Nanocrystals

A model describing surface quenching of isolated ion centres in nanocrystals is proposed based on the energy transfer between the doped ions and the nanocrystalline surface quenching centres. The quenching rate depends on the position of the ions in the nanocrystal, hence the decay curve under non-selective excitation is generally nonexponential. The decay curve calculated with this model is in good agreement with that of the ^4T1→^6A1 emission in ZnS：Mn^2＋ nanocrystals.