最新刊期
卷 38 ， 期 6 ， 2017
- 摘要：White long persistent phosphors, Sr3Al2O5Cl2∶Eu2+, Tm3+, have been successfully prepared by the solid state reaction at 800 ℃. The as-prepared sample Sr2.91Al2O5Cl2∶0.04Eu2+, 0.05 Tm3+ shares single phase and regular nano-fiber morphology. This sample exhibits two broad emission bands located at ~ 448 nm and ~ 590 nm, respectively, and its white persistent duration is about 20 min (> 0.35 mcd/m2). At last, intense white light can be found from the white light-emitting diode with Sr2.91Al2O5Cl2∶0.04Eu2+, 0.05 Tm3+.关键词：long persistent properties;phosphors;photo-luminescent properties119|57|0更新时间：2020-08-12
- 摘要：To explore the changes of the optical properties for Ge in different orientations and different strains, we performed the first principle calculations based on density functional theory combined with GGA+U approach. The results show that Ge undergoes a transition from indirect- to direct-gap on uniaxially tensile strains (along [100], [110] and [111] directions) and biaxially tensile strains (parallel to (100), (110) planes).The band gaps of Ge with uniaxially strains (along [110] and [111] directions) are higher than those with biaxially strains, and the transition points of uniaxially strains are lower than those of biaxially strains. Under uniaxially and biaxially compressive strains, the changes of dielectric constants and loss factors of Ge between the frequency bands are both negligible. However, the dielectric constants and loss factors rise first and then fall in a definite range of strains when Ge is under uniaxially and biaxially tensile strains. Compared with unstrained Ge, Ge under [111] 1.22% strain possesses excellent optical properties: reasonable forbidden bandwidth, higher static dielectric, higher absorption coefficient, lower loss function and lower strains.关键词：Ge;first principle;strain;optical properties142|271|0更新时间：2020-08-12
- 摘要：π-conjugated semiconductor 9,10-bis(phenylethynyl) anthracene (BPEA) was chosen to synthesize single-crystal microwire arrays by the physical vapor transport (PVT) technique. The intermediate products were observed at different stages of the vapor transport in order to investigate the growth mechanism. The fabricated BPEA microwires can serve as the active optical waveguides that allow the locally excited photoluminescence to propagate along the length of the wires. Compared with that of the flat-lying microwire (R=0.033 dB μm-1), the optical-loss coefficient (R) of vertical BPEA wire is smaller (0.029 dB μm-1), demonstrating lower waveguide loss.关键词：vertical growth;organic micro/nanostructures;physical vapor transport;waveguide121|172|0更新时间：2020-08-12
- 摘要：Using colloidal chemical method, the CdSe QDs clusters were synthesized in oleic acid-paraffin system. The quantum dot clusters were modified by isopropyl alcohol, and the fluorescence spectroscopy (PL) and ultraviolet (UV) absorption spectra were studied by using the curve fitting method. Finally, the inner relationship of the changing of optical properties of CdSe QDs clusters was discussed by analyzing the AFM images and Fourier transform infrared spectroscopy of the samples. With the increase of the concentration of isopropanol, the fluorescence peak of QDs appears blue-shift of 11 nm and the blue-shift curve change stepwise. The relative fluorescence intensity increases first and then decreases, and the fluctuation amplitude can reach the maximum of 1 000 a.u.. The first and the second absorption peak of QDs appear red-shift with the increase of the concentration of isopropanol, and the largest red-shift is up to 12 nm.关键词：isopropyl alcohol;CdSe QDs;fluorescence peak;blue-shift;surface modification135|226|0更新时间：2020-08-12
- 摘要：This paper performed quantitative evaluation of the effects of light illumination environment on photobiological response of different age groups. From the perspective of light conversion, a biological rhythm factor model is proposed considering the ocular transmittances of different ages, pupil diameter and the illuminated area in the retina. Three kinds of white LED light sources (3 000, 4 000,6 000 K) with different color temperatures were selected and their spectral distributions were measured at the same illumination 500 lx. Then we calculate the rhythm factors, and make the linear fitting with the evaluation model which use the modified factor proposed in the former standard. The result shows that under the same color temperature, the biological rhythm factor value decreases with increasing age. For the same kind of age, the biological rhythm factor values increases with the increase of the color temperature. These results are consistent with some researcher's conclusion. In addition, according to the result of linear fitting, the linear correlation of two age-related rhythm factors in three different color temperatures were 0.958 08, 0.985 833 and 0.957 22, respectively, with a high correlation. Compared with the way in the standard, this article proposed another evaluation model considering difference in human eye age, and attempt to use absolute rather than relative effects of the transmittance.关键词：non-visual biological effects;biological rhythm factor;LED light source;age134|378|3更新时间：2020-08-12
- 摘要：In order to confirm the sub-wavelength grating parameters and the best position the sub-wavelength grating being placed in micro-electro-mechanical system (MEMS) wavelength tunable VCSEL(top DBR surface, top DBR bottom surface, inner cavity) range to realize stable polarization control, MATLAB was used to build MEMS wavelength tunable VCSEL model, then the reflectivity of three structures' top reflective mirror (top DBR, grating, air gap) changing with the sub-wavelength grating parameters were calculated by which the grating parameters range (high reflectivity) making TE/TM polarization of the three structures stable could be confirmed. The reflectivity difference for which the high reflective corresponding reflectivity minus the low reflective corresponding reflectivity in the same grating parameters range can determine the position where the sub-wavelength grating is placed to realize the most stable polarizations. The results show that the sub-wavelength grating on the bottom surface of the top DBR mostly can not control TM polarization, while not only TE polarization but also TM polarization is most stable when the grating is placed in the inner cavity. TE polarization threshold is less than TM polarization of 10 cm-1 within the grating parameters range to realize TE polarization stable, while TM polarization threshold is less than TE polarization of 5 cm-1 within the grating parameters range to realize TM polarization stable.关键词：MEMS wavelength tunable VCSEL;polarization stable;sub-wavelength grating;MATLAB build model127|207|4更新时间：2020-08-12
- 摘要：InGaN/AlGaN near-ultraviolet light emitting diode (near-UV LED) were grown on patterned Si substrate by metal-organic chemical vapor deposition (MOCVD). The effects of V-pit size on optical and electrical properties of InGaN/AlGaN near-UV LED (395 nm) were investigated systematically by manipulating the thickness of low temperature GaN interlayer to change the V-pit size. The results show that the low temperature GaN interlayer can enhance the formation of V-pit, and the V-pit size increases with the increasing of the thickness of low temperature GaN interlayer. In terms of electrical properties, with the increasing of the V-pit size, the leakage current at -5 V increases from 5.2×10-4 μA to 6.5×102 μA, and the forward voltage at 350 mA decreases from 3.55 V to 3.44 V initially and then increases to 3.60 V. In terms of optical properties, with the increasing of the V-pit size, the normalized external quantum efficiency (EQE) at 35 A/cm2increases from 0.07 to the maximum of 1 initially and then decreases to 0.53. The mechanism of the effects of V-pit size on optical and electrical properties of InGaN/AlGaN near-UV LED were analyzed. The analyzing results show that the optical and electrical properties of InGaN/AlGaN near-UV LED are closely related to V-pit size. The optimized V-pit size is approximately 120-190 nm, too large or too small will deteriorate the properties of devices seriously.关键词：Si substrate;near-UV LED;low temperature GaN interlayer;V-pit size;optical and electrical properties120|141|1更新时间：2020-08-12
- 摘要：In order to distinguish the characteristics of composite and traditional non-composite crystal used in the diode pumped solid state lasers (DPSSL)and improve the efficiency of DPSSL, the thermal effect of based on YAP/Tm∶YAP composite crystal was studied. The finite element method (FEM) was employed. The temperature and heat stress were simulated, and the relationship between the thermal lens and un-doped crystal length was analyzed. Experimental results indicate that the peak temperature and the thermal stress of YAP/Tm∶YAP composite crystal rod decrease to less than 80% and 70% comparing with the non-composite crystal. The length of thermal lens is still constant under the condition of the variation of un-doped crystal length, which verifies that using the composite crystal in the DPSSL can benefit for the laser properties of temperature and mechanics. Nevertheless, the beam quality of DPSSL can not be optimized using the composite crystal.关键词：composite crystal;thermal effect;diode pumped solid state lasers;finite element method140|286|7更新时间：2020-08-12
- 摘要：The Ti-based nano-diamond coatings were treated by tape-stripping, metallographic sandpaper friction, and RF hydrogen plasma process. The effects of the post processing technology on the samples were analyzed by testing the morphology, field emission property, and luminescence effect of the samples. The diamond powders were transferred to metal titanium sheet by electrophoresis method, and then the field emission cathode coating was formed after vacuum heat treatment and surface post-treatment technology. finally, the microscopic mophology, field emission properties and luminescence effect of the samples were characterized. For tape-stripping processing, the field emission current density increases from 50 μA/cm2 to 72 μA/cm2 at the electric field of 10 V/μm. For metallographic sandpaper friction, the current density increases from 48 μA/cm2 to 82 μA/cm2 at the electric field of 10 V/μm. Moreover, appropriate hydrogen treatment is helpful to reduce the work function of the surface. The dangling bonds of the diamond surface are saturated by hydrogen atom and C－H bonds form on the surface, which can reduce the electron affinity to improve the field emission properties and luminous uniformity of the samples.关键词：nano-diamond coating;surface treatment process;field emission characteristics;luminescence effect183|86|0更新时间：2020-08-12
- 摘要：Silicon-doped Al0.19Ga0.81N/Al0.37Ga0.63N DBRs were grown on n-type 6H-SiC substrates by metal organic chemical vapor deposition(MOCVD). To suppress the generation of cracks, a low-temperature AlN pre-deposition layer on 6H-SiC(0001) substrate was used as buffer. A smooth-surface 15-pair electrically conducting DBR with a reflectance of 68% at 369 nm was obtained. The stop-band bandwidth and RMS value of DBR are 10 nm and 0.4 nm, respectively. Furthermore, the vertical structure UV LEDs with and without n-DBR on 6H-SiC substrate were fabricated. By comparing EL spectra, it is shown that the introduction of DBR structure can effectively improve the UV emission.关键词：AlGaN;ultraviolet LED;distributed Bragg reflectors;metal organic chemical vapor deposition;vertical structure145|147|2更新时间：2020-08-12
- 摘要：High electron mobility transistors (HEMTs) based on GaN have a promising prospect in the fields of high frequency and high power due to their advantages of high output power density, high operating frequency and high operating temperature. At present, great progress has been made in material growth and fabrication processes of HEMTs. However, the trapping effect produced by the defect limits the development of HEMTs. In this paper, the surface states, interface defects and bulk defects of HEMT devices and the causes of these defects were discussed. The phenomenon caused by trap effect such as the current collapse, gate lag, drain lag and kink effect were also described in detail. The main approaches to improve the defects were summarized from structure design and process design. And the latest progresses focusing on the four aspects of the capping layer, surface treatment, passivation layer and field plate structure were reviewed. Further optimization in the defect of the GaN based HEMT devices was explored at the end.关键词：GaN;high electron mobility transistor (HEMT);defect;trapping effect290|1493|1更新时间：2020-08-12
- 摘要：We reported herein an ensemble C1-Cu2+ as a new displacement-based fluorescent probe for sulfide anion detection. Upon the addition of S2-, it displayed marked fluorescence enhancement under aqueous conditions and the detection limit was determined to be as low as 90 nmol/L. In addition to its high selectivity for sulfide anion rather than other common anions, C1 was successfully applied to the detection of sulfide anion in HeLa cells with ‘Turn-On’ fluorescent methods.关键词：displacement approach;fluorescence enhancement;sulfide anion;good solubility;bioimaging application123|112|0更新时间：2020-08-12
- 摘要：High-quality GaN films were grown on Si-plane 6H-SiC (0001) substrates with AlN buffer and step-graded AlGaN (AlxGa1-xN: x=0.8,0.5,0.2) buffer with different growth temperature and NH3 flux by metal-organic chemical vapor deposition (MOCVD). The properties of GaN films were examined by X-ray diffraction, atomic force microscopy, room temperature photoluminescence spectra and Raman spectra. Experimental results show that the lower tensile stress in the GaN films, the higher the crystallinity, surface morphologies and optical properties of the GaN films. Under the optimum conditions of AlGaN buffer, the stress value of GaN films is reduced to its minimum. The ω-rocking curves full-width at half-maximum (FWHM) of the (0002) and (1012) planes are ameliorated to 191 and 243 arcsec, respectively. The densities of screw and edge dislocations decrease to the best values of 7×107 and 3.1×108 cm-2. The root-mean-squared roughness value is 0.381 nm. It shows that the step-graded AlGaN buffer can change stress state in GaN films effectively and improve the crystallinity of GaN films significantly.关键词：GaN;step-graded AlGaN buffer;crystallinity;stress139|285|0更新时间：2020-08-12
- 摘要：In order to alleviate current crowding around p-electrode of high power blue light-emitting diodes (LEDs) and improve its external quantum efficiency (EQE), a SiO2 current blocking layer (CBL) was deposited between ITO transparent conductive layer and p-GaN by plasma enhanced chemical vapor deposition (PECVD). An interdigitated SiO2 CBL pattern was then fabricated by photolithography and BOE wet etching process. The effect of interdigitated SiO2 CBL on the current spreading performance of high power LED was analyzed using commercial SimuLED package. It is found that the current crowding around the p-electrode is effectively alleviated by employing the interdigitated SiO2 CBL. Comparing with the high power LED without interdigitated SiO2 CBL, the light output power is significantly improved. At 350 mA injection current, the external quantum efficiency of the high power LED with interdigitated SiO2 CBL is 18.7% higher than that of LED without interdigitated SiO2 CBL.关键词：high power LED;interdigitated SiO2 CBL;current crowding;external quantum efficiency146|268|1更新时间：2020-08-12
- 摘要：Organic electrical bistable devices based on MEH-PPV (poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenyl vinylene]) and PEG[poly(ethylene glycol)] bilayer films were demonstrated. The structure of the device is Al/MEH-PPV/PEG/ITO, and we optimize the device by changing the molecular weight, concentration and annealing temperature of PEG film. The electrical current ON/OFF ratio of the optimized device is over 103 between the high-conducting state (ON state) and low-conducting state (OFF state). The device remains in the high resistance state below the threshold voltage of 2.5 V and the device resistance abruptly decreases due to the trap-controlled space charge limit current, leading to a high conductivity state. The SEM measurements and I-V curve fitting indicate that the phase separation induced electrical charge trapping plays an important role for the electrical bistable behavior of the devices.关键词：PEG;MEH-PPV;organic bistable devices;trap;charge trapping theory105|103|1更新时间：2020-08-12
- 摘要：Hyperspectral imaging technology was used to extract the optimal wavelength for apple brix and firmness test. Firstly, the hyperspectral images of apples were acquired from double-sided sampling. The reflection waveforms of the regions of interest (RIOs) with similar brightness were acquired and smoothed by the second derivation and standard normal variate (SD+SNV) method. The brix and firmness values of RIOs were also tested. Then, the characteristic wavelengths of two indicators were extracted by using the successive projections agorithm(SPA). According to the distribution of characteristics wavelengths, two times SPA was proposed. Combined the feature of waveforms and the results of two projections, the optimal wavelengths of different sampling facets were determined. Finally, the genetic algorithm for back propagation(GA-BP) was used to build the prediction model. The best results were obtained from the double-sided sampling wavelengths (543 nm and 674 nm). The correlation coefficient of brix (R) is 0.847 6 and the mean square error (MSE) is 3.32, and for the firmness, R is 0.793 8 and MSE is 9.6. The results show that the brix and firmness can be detected by the same wavelength information.关键词：hyperspectral imaging;apple;optimal wavelength;two times SPA;GA-BP186|128|13更新时间：2020-08-12
- 摘要：Polycyclic aromatic hydrocarbons(PAHs) are a kind of organic pollutant which widely distribute in the environment and whose carcinogenicity is a great threat to human's health. It is necessary to find an efficient and accurate method to detect the concentration of PAHs. By analyzing the fluorescence spectra of the mixed solution of BkF、BbF and BaP, we can see that the fluorescence spectra of the mixed solution overlap seriously within the excitation wavelength range of 260－400 nm and emission wavelength range of 300－500 nm, respectively. There are large difference in fluorescence characteristics for different mixture concentration ratio of the mixed solution. Because the spectra can not directly reflect the concentration of each component in the mixture, we apply radial basis function (RBF) neural network with artificial bee colony (ABC) algorithm to the concentration detection. By comparing RBF and ABC-RBF neural network, we can draw a conclusion that the prediction error of ABC-RBF neural network is relatively small, and the average recovery rate of BkF, BbF and BaP is 99.20%, 99.12% and 99.23%, respectively.104|190|4更新时间：2020-08-12
- 摘要：Luminol-AgNO3-gold nanoparticles system has a strong chemical luminescence(CL) phenomena. When polyphenol compounds are added in the system, the cheminescence signals have different degrees of change. —OH in the phenolics can interact with the nanometer gold, and the interaction is related to the number and location of —OH in the phenolic compounds. Combined with the flow injection chemiluminescence method, hydeoquinone, catechol and phthalate were determined. The detection limits are 4.0×10-11, 8.0×10-10, 2.6×10-9 g/mL, respectively. The method was successfully used to determine catechol in water. The recovery is 97.5%－105%, and the relative standard derivations (RSD) is 1.4%－2.5%. The possible mechanism of the CL reaction was discussed, and the CL method for determination of the polyphenol compounds was proposed.关键词：polyphenol compounds;chemiluminescence;gold nanoparticls121|313|0更新时间：2020-08-12
- 摘要：In order to quickly determine the relationship between the correlated color temperature (CCT) of white LEDs and the corresponding yellow phosphor concentration, a method of‘intermediate parameter A’was proposed in this paper, which can reduce the workload, shorten the working time and improve the precision. First, the formula of the chromatic coordinate and the‘intermediate parameter A’was deduced by theoretical analysis. Then, six groups white LED samples with different yellow phosphor concentration were fabricated. After that, the‘A value’of each concentration was calculated. It is found that the relationship between the A value and the phosphor concentration is linear. The chromatic coordinates of the target CCT can be found on the chromaticity diagram, so the yellow phosphor concentration of the target CCT can be predicted by using this method. The experimental results show that the deviation between the CCT of white LED and the target CCT is less than 50 K by using this method. In the prediction of a high CCT, this method is more accurate by one order of magnitude than the method of‘direct exploration of the relationship between CCT and phosphor concentration’. And in predicting the phosphor concentration of a target CCT, the difference of phosphor concentration between the two groups of phosphor concentration samples and the six groups of samples is less than 0.5% by using this method. Therefore, the method of‘intermediate parameter A’has the advantages of short time, less workload and more accurate in determining the phosphor concentration of the white LED with target CCT.关键词：white LED;correlated color temperature;intermediate parameter A;phosphor concentration114|151|2更新时间：2020-08-12
- 摘要：The design of radiation hardening large scale integrated circuit based on the standard process is the development tendency in the future. Extracting the radiation effect parameters of the nano device is the foundation of improvement of the radiation hardening. In order to eliminate the influence introduced by encapsulation in the parameter extraction process, a set of equipment for irradiation parameters extraction of wafer level device was designed, which could realize the function of online X-ray irradiation and online parameter test and analysis with the advantage of strong commonality, wide measuring range. The X-ray energy spectra, dose rate, beam uniformity were measured with the tube voltage of 50 kV, as well as I-V, C-V and low frequency noise characteristics of the wafer level MOS device were test and analysis. The experiment results show that the equipment can satisfy the standard of ASTM F1467 test, and meet the requirements of the radiation effect parameters extraction of the wafer level device. The equipment can provide a good test condition for the design of radiation hardening large scale integrated circuit.关键词：radiation hardening;experiment equipment;wafer level device irradiation;X-ray irradiation;radiation effect;parameters extraction114|253|0更新时间：2020-08-12
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