最新刊期
卷 36 ， 期 8 ， 2015
- 摘要：The study of carbon quantum dots used as either photoluminescence functional components or nano carriers for magnetic resonance-fluorescence multimodal molecular imaging probe is just beginning. In the paper, the gadopentetate monomeglumine was used as a precursor which provides simultaneously carbon sources and Gd3+ sources. The influences of pyrolysis temperature, holding time and heating rate on the carbonization degree of the precursor, the quantum yield and the Gd3+ content of the products were studied. When the precursor was pyrolized under reasonable condition (the pyrolysis temperature was not higher than 350 ℃), Gd3+ chelates dopped carbon quantum dots were facilely prepared. The carbon quantum dots not only possessing high luminous power (quantum yield ~7.6%), but also showing good magnetic resonance response (longitudinal relaxation rate ~6.5 mmol-1·L·s-1) can be used as a magnetic resonance/fluorescence multimodal molecular imaging probe.关键词：carbon quantum dots;Gd3+ chelates;fluorescence;magnetic resonance;molecular imaging probe105|206|1更新时间：2020-08-12
- 摘要：Sm3+-doped TiO2(TiO2 :Sm3+)nanocrystals were synthesized by the sol-hydrothermal method and the down-conversion positive glow were prepared with the matrix of P25 doped with different mass fraction of the as-prepared TiO2 :Sm3+ powder, which was used to assemble the dye-sensitized solar cell (DSSC) to improve the photoelectric properties. The fluorescence spectroscopy indicates that the TiO2 :Sm3+ possess down-conversion feature of converting ultraviolet light to 570－700 nm visible light. When the doped content of the as-prepared TiO2 :Sm3+ powder in the photo anode was 80%, the short circuit current density reached to 13.12 mA/cm2, increased by 26.5% compared with the pure P25 photo anode, and the efficiency was also increased by 23.5%.关键词：dye-sensitized solar cells;sol-hydrothermal method;TiO2:Sm3+;down-conversion photoanode;short circuit currents168|83|2更新时间：2020-08-12
- 摘要：The energy level alignment, film growth and molecular orientation of C8-BTBT on MoS2 were studied by ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and atomic force microscopy (AFM). The molecules adopt standing-up orientation on MoS2 and the island growth mood were confirmed. The ionization potential (IP) decrease and highest occupied orbital (HOMO) down-shift were observed as the film thickness increased. IP decrease is ascribed to the gradual increase of the surface electric dipole pointing inwards when the molecular tilt angle (θ) about the substrate normal decreases with the increasing of film thickness. The energy level shift results in an analogy P-N junction effect, which provides important guidance for C8-BTBT based electronic device design.关键词：photoemission spectroscopy (PES);C8-BTBT;energy level alignment;molecular orientation;film growth176|28|0更新时间：2020-08-12
- 摘要：YVO4 :Eu3+ nanoparticles of about 8 nm were synthesized by precipitation reactions and coated with SiO2 by a reverse microemulsion method. Powder X-ray diffraction (XRD) patterns indicate that these nanoparticles are purely tetragonal phase. Transmission electron microscope (TEM) images show that YVO4 :Eu3+ nanoparticles are successfully coated with silica to form core-shell structured nanocomposites. The thicknesses of SiO2 shells can be altered by changing the volume of tetraethoxysilane (TEOS) used in the reaction. The ultraviolet-visible (UV-Vis) absorption spectra of YVO4 :Eu3+@SiO2 nanocomposites agree well with that of the YVO4 :Eu3+ nanoparticles colloid. Both the excitation and emission spectra are the same for YVO4 :Eu3+ nanoparticles and the nanocomposites. With the increasing of the thickness of SiO2 shell, the intensity ratio of 5D0-7F2/5D0-7F1 decreases, indicating that SiO2 shells can increase the local symmetry of Eu3+. All samples can emit bright red light under ultraviolet irradiation. The photoluminescence quantum yield decreases after SiO2 coating. With the increasing of the thickness of SiO2 shell, the photoluminescence quantum yield becomes lower and lower.关键词：YVO4:Eu3+;SiO2;microemulsion;core-shell;luminescence99|38|0更新时间：2020-08-12
- 摘要：Ni/SnO2 films were prepared by spin coating Ni/SnO2 gel on the glass substrates. The effects of the doping amount of nickel and calcination temperature on the structure and morphology of Ni/SnO2 films were discussed. The structure and morphology of Ni/SnO2 composite film were characterized by using XRD, IR, SEM and other testing methods. The results show that the particles of the film calcined at 500 ℃ have high crystallization, small size, and distribute uniformly. The right amount of Ni2+ doping can improve the absorbance in the near ultraviolet region of SnO2 film, and the absorbance in the near ultraviolet region of Ni/SnO2 film decreases with the increasing of Ni2+ mole fraction from 5% to 10%. The conductivity of Ni/SnO2 film is the best when Ni2+ mole fraction is 6%.关键词：Ni/SnO2;composite thin films;sol-gel;functional materials92|99|2更新时间：2020-08-12
- 摘要：Y2O3 :Yb/Tm/Gd@Y2O3 microcrystals with core-shell structure were prepared by homogeneous precipitation method and then annealed at high temperature. The microparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and luminescent spectra. Upconversion spectra and excitation power dependence indicate that the energy transfer from Tm3+ to Gd3+ plays a crucial role in populating the excited states of Gd3+. The shortest wavelength of upconversion emissions in Y2O3 matrix is converted from the infrared region. Meanwhile, the core-shell structure greatly improved the upconversion fluorescence intensity of Gd3+ in Yb3+-Tm3+-Gd3+ codoped system.关键词：Y2O3;Gd3+ doping;upconversion luminescence112|100|2更新时间：2020-08-12
- 摘要：The photoelectrochemical (PEC) performance and photocatalytic activity of TiO2 nanorod arrays (NRs) loaded with carbon quantum dots (CQDs) were investigated. In comparison with TiO2 NRs, the absorption ability of TiO2 NRs loaded with CQDs was enhanced. The transient photocurrent and open-circuit potential under visible light illumination were increased of 300% and 2.5%, respectively. After loaded with CQDs, the photocatalytic degradation efficiency of methylene blue (MB) under visible light illumination was increased from 25% to 33%. The electrochemical impedance spectra (EIS) and Mott-Schottky plots were measured to investigate the charge movement under the visible light illumination. The results suggest that the charge transfer resistance is reduced and the electron lifetime is increased for TiO2 NRs loaded with CQDs. The loading of CQDs can induce the flat-band potential negative shift and the conduction band position raise, resulting in the enhancement of electron reduction properties.关键词：arbon quantum dots;TiO2 nanorod arrays;flat-band potential;photocatalysis113|183|5更新时间：2020-08-12
- 摘要：Gallium oxide(Ga2O3) thin films were depsited by radio frequency magnetron sputtering on sapphire(0001) substrates with a range of substrate temperatures from 500 to 1 000 ℃. The norphological characteristics, optical bandgaps, electrical properties and photoresponsivity of the grown thin films were researched.With the increasing of the growth temperature, the crystallinity and conductivity of the films increase at first and then decrease slightly. Ultraviolet-visible spectra indicate that the transmittance of β-Ga2O3 film depsited on 800 ℃ is over than 90%, and it's absorption edge is located at about 255 nm, meaning that the optical bandgap was about 4.8 eV. The metal-semiconductor-metal photodetector based on β-Ga2O3 film shows dark current of ~1 nA and photocurrent of ~800 nA under 254 nm light illumination at 10 bias voltage. The maximum responsivity of the photodetector is 0.3 A/W at 260 nm, 40 times as much as the responsivity at 290 nm.关键词：β-Ga2O3;RF magnetron sputtering;UV detector193|170|4更新时间：2020-08-12
- 摘要：Organic light emitting devices (OLEDs) were fabricated with yttrium fluoride (YF3) as the electron injection layer instead of lithium fluoride (LiF) and aluminum as the cathode. The experiment results show that YF3 injection buffer layer with appropriate thickness can effectively enhance the electron injection ability of the cathode, leading to more balanced concentration of electrons and holes, and optimized electroluminescent properties of OLEDs. The device with 1.2 nm-thick YF3 layer has the minimum turn-on voltage of 2.6 V, the maximum current efficiency of 8.52 cd·A-1, and the maximum luminance of 36 530 cd·m-2. Compared with LiF reference sample, the maximum brightness and current efficiency are increased by 39% and 53%, respectively.关键词：organic light-emitting devices;yttrium fluoride;electron injection layer108|102|0更新时间：2020-08-12
- 摘要：Blue organic light-emitting device (BOLED) with a Bphen interlayer inserted between two hole transport layers was demonstrated. It utilized the hole blocking effect of Bphen interlayer to obtain more balance for electrons and holes in the recombination zone. It reduced the probability of exciton-polaron quenching, thereby improved efficiency and luminance of blue organic light-emitting device. The current efficiency improved about 27.30%, from 16.12 cd/A to 20.52 cd/A, and the power efficiency improved about 23.96% from 14.23 lm/W to 17.64 lm/W. The physical mechanisms on the improvement of efficiency were discussed in detail.关键词：BOLEDs;Bphen interlayer;exciton-polaron quenching;carriers balance106|234|4更新时间：2020-08-12
- 摘要：Period thickness-dependent GaNAs/InGaAs short-period superlattice and solar cells with an absorption edge of around 1 eV were grown by MBE. High-resolution X-ray diffraction (HRXRD) measurements indicate that the crystalline quality of SPSL is improved while the period thickness increases from 6 nm to 20 nm. However, when the period further rises, the period repeatability and interface quality of SPSL degrade. By using a proper thickness and optimization of thermal annealing, good optical properties of SPSL with higher N content in the superlattice are achieved. The samples show an absorption edge of around 1 eV. The p-i-n solar cell using the optimized SPSL as the active region was fabricated. The short-circuit current density of the device reaches 10.23 mA/cm2. The ideality factor extrapolated by concentrator test of the p-i-n soalr cells is in good agreement with that of J-V curves under darkness.关键词：GaNAs;superlattice;solar cells;MBE101|221|3更新时间：2020-08-12
- 摘要：The mode stability of shallow surface relief vertical cavity surface emitting laser (VCSEL) is constrained by the nonuniform current density distribution in the active region. In order to solve this problem, a new type of structure was put forward, in which indium tin oxide (ITO) transparent conductive layer was employed in shallow surface relief VCSEL. This structure not only can increase the threshold gain of the higher-order modes but also can improve the gain of fundamental model and strengthen the suppressive effect of fundamental mode on higher order mode. The influence of the ITO thickness on the threshold gain and the effect of ITO on the current density distribution in active region are studied. It is found that the suppressive effect of fundamental mode on higher order mode is strongest when the thickness of ITO is integral multiples of the half wavelength. The gain of fundamental mode increases and the gain of higher order decreases with the improving of the current density distribution in the active region of VCSEL, and at the same time, the series resistance and the voltage are also reduced.关键词：VCSEL;ITO film;surface relief;single mode120|258|0更新时间：2020-08-12
- 摘要：Cu was used as the source/drain (S/D) electrodes of amorphous indium-zinc-oxide (a-IZO) thin-film transistors (TFTs) in order to realize low-resistance metallization in oxide thin film transistors. Cu film with a resistivity as low as 2.0 μΩ·cm was deposited by optimizing the sputtering process. The crystal structure, adhesive property of Cu film as well as the interfaces of Cu/a-IZO were investigated. In addition, a-IZO TFTs with Cu S/D electrodes were fabricated. The Cu films were polycrystalline. The adhesion of Cu to glass substrate was enhanced by introducing an a-IZO film. Meanwhile, the diffusion of Cu atoms was suppressed in a-IZO. The fabricated TFT exhibited a saturated mobility of 12.9 cm2/(V·s), a subthreshold voltage of 0.28 V/dec and a threshold voltage of -0.6 V.关键词：thin-film transistor;indium-zinc-oxide;copper metallization114|172|3更新时间：2020-08-12
- 摘要：P3HT-based organic field effect transistors(OFETs) with PMMA gate dielectric were fabricated by solution process. The effects of the spinning speeds of both P3HT active layer and PMMA gate dielectric on the performance of the devices were investigated. The experiment results show that the fabricated OFETs exhibit the optimal performance at the spinning speeds of 2 000 r/min of both P3HT and PMMA, of which the field effect mobility is 6.84×10-2 cm2·V－1·s－1. This indicates that spinning speed is a technological parameter to improve the performance of solution-processed OFETs.关键词：organic field effect transistors;spinning speed;P3HT;PMMA157|118|0更新时间：2020-08-12
- 摘要：Top-contact thin-film transistors(TFTs) were fabricated using SiNx as the gate insulator and InGaZnO as the channel layer. The insulator was modified by Al2O3 layer and its effect on the performance of IGZO-TFTs was investagated. The results show that TFTs with 4-nm-thick Al2O3 film exhibits the best electrical performance. The best performance can be attributed to the suppression of maximum density of surface states at the channel-insulator interface which is reduced by 17.2% contrasting to the TFTs without Al2O3 buffer layers. The field effect mobility increases from 1.19 to 7.11 cm2/(V·s), and the threshold voltage decreases from 39.70 to 25.37 V. Under bias stress for 1 h, the threshold voltage shift decreases from 2.19 to 1.41 V/dec.关键词：IGZO thin film transistors;Al2O3;SiNx;the maximum density of surface states112|113|6更新时间：2020-08-12
- 摘要：LED light flux is affected not only by current, but also by the junction temperature change. The traditional LED dimming method typically only changes the current and ignores the junction temperature changes. In order to fix this downside, a mathematical model was established based on the relationship among the luminous flux, current and pin temperature that can show the junction temperature of LED. The luminous fluxes of HL001WY type GaN-based white LEDs were tested at different currents and pin temperatures, and the experimental data were quadratic term trend regression. By using calibration and normalization method, the mathematical model was established. The calculations show that the relative error between the calculated value and the actual measured value is less than 4.5%.关键词：smart dimming;model analysis;electro-optical conversion;thermal analysis141|199|2更新时间：2020-08-12
- 摘要：The chlorophyll content and distribution in the Gannan navel orange leaves were non-destructively measured by competitive adaptive reweighted algorithm (CARS) and successive projections algorithm (SPA) combined with hyperspectral imaging technology. 32 and 6 characteristic wavelengths were extracted by CARS and SPA, and then partial least squares (PLS) was used for modeling quantitative analysis. The results show that SPA-PLS and CARS-PLS model can obtain better results than PLS model through the analysis of prediction of 37 samples. The prediction set correlation coefficients were 0.90 and 0.91, the root mean square error is 1.53 and 1.60 respectively. The chlorophyll content of each pixel was calculated with SPA-PLS model, then the chlorophyll distribution map of navel orange leaves was visualized using imaging processing technology. Overall results sufficiently demonstrate that the variable selection method combined with hyperspectral imaging technology can be used to measure the chlorophyll content and distribution in navel orange leaves.关键词：chlorophyll content;hyper-spectral imaging;navel orange leaves;CARS;SPA101|117|7更新时间：2020-08-12
- 摘要：We proposed the 6-12-1 topology BP neural network according to the LED reliability and relevant element. The ideal factor, junction temperature, color temperature drift of the white LED chip and so on were measured as the input and the life as output to calculate the precision of the model. The model shows a good ability of extrapolation and robustness, and can predict the life of the LED in a short time. The linear correlation of ANN reaches 99.8%, and the inspection group error is less than 3%.关键词：LED;reliability;BP neural network;weight analysis108|245|5更新时间：2020-08-12
- 摘要：We report experimental investigations of nonlinear dynamics and optical nonlinearities of GaAs single crystal in the telecommunication windows. Femtosecond time-resolved degenerate pump-probe measurements indicate that the observed third-order nonlinear process originates from the instantaneous effect whereas the fifth-order effect arises from two-photon absorption (2PA) induced free-carrier nonlinearities. By performing the Z-scan experiments with femtosecond laser pulses at the wavelengths of 1 300 nm and 1 500 nm, we determine all nonlinear parameters of GaAs crystal, including 2PA coefficient, third-order nonlinear refraction index, 2PA-induced free-carrier absorption cross section, and 2PA-induced free-carrier refraction cross section. These results suggest that GaAs crystal is a promising candidate for applications on optical limiting and photodetector at the telecommunication wavelengths.关键词：two-photon absorption;free carrier absorption;GaAs crystal;telecommunication wavelengths127|144|1更新时间：2020-08-12
- 摘要：By means of density functional theory and self-consistent reaction field in B3LYP/6-311G(d) method, the 16 kinds of phthalate esters (PAEs): BBP,DBP,DCHP,DEHP,DEP,DIDP,DINP, DMP, DNOP, BMPP, DAP, DHP, DIPrP, DMEP, DPhP and DPP were selected and their structures were optimized. Their Raman vibrational frequencies and depolarization in atmosphere and 6 kinds of solvents were calculated. The results show that Raman vibrations of 16 PAEs are assigned to ring deformation,ester base deformation,C—C stretching,C—H wiggle,C—H stretching and of these several patterns. The peak position of the ester base functional group is relatively fixed in 1 700－1 780 cm-1. Raman peak of ester base vibration is stronger,and the polarization degree is lower (the symmetry of vibration was stronger). Therefore, the ester base vibration can be regarded as the characteristic vibration. But the minimum differential wave numbers of only 12 kinds of PAEs are larger than micro Raman spectrometer detection limit (0.2 cm-1), so the 16 kinds of PAEs can not be fully identified by depolarization and the Raman peak of ester base vibration frequency area. Solvent effect analysis shows that benzene solvent has obvious enhanced solvent effects on 16 kinds of PAEs. The minimum differential wave numbers of 16 kinds of PAEs increase to 0.2 cm-1 above and the Raman intensity increases to 23%－183%,which illustrate that the 16 kinds of PAEs can be fully identified by depolarization and the Raman peak of ester base vibration frequency area. It provides theoretical basis for the detection of PAEs Raman spectroscopy.关键词：phthalic acid ester;vibration assignment of Raman spectrum;Raman spectrum identification;solvent effect;depolarization156|310|3更新时间：2020-08-12
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