最新刊期
卷 35 ， 期 5 ， 2014
- 摘要：We systematically studied the low-temperature (12 K) photoluminescence (PL) spectroscopies of WSe2 nanosheets prepared by vapor deposition technique. It is found that PL intensity monotonically decreases with the increasing of WSe2 nanosheet layers. In particular, the PL intensity dramatically decreased when the thickness of WSe2 films changed from monolayer to bilayer, which indicated that there is a direct-to-indirect transition in the band gap of WSe2 nanosheets. Then we focused on the variable temperature photoluminescence of the bilayer structure. When the temperature increases from 12 K to 300 K, the temperature-dependent evolution of the direct transition energy (peak A) is approximately consistent with the common formula obeyed by bulk semiconductors, while the indirect transition energy (peak I) can only be described by a linear relationship with temperature. This indicates that peak A and peak I have different transition characteristics and these two transition characteristics coexist in bilayer WSe2 simultaneously.关键词：nanosheets;WSe2;photoluminescence;red shift310|370|0更新时间：2020-08-12
- 摘要：The structure and luminescence properties of Sr3-xCaxAl0.6Si0.4O4.4F0.6 (SCASOF) doped with Ce3+ are studied as a function of the Ca/Sr ratio. First-principle calculations conform that Ca preferentially occupies 8h sites in the host structure. With the increasing of Ca/Sr ratio, the excitation and emission spectra of Sr3-xCaxAl0.6Si0.4O4.4F0.6:Ce3+ phosphors show an obvious red shift, owing to the enhancement of crystal field. Under the excitation of 460 nm, the luminescence intensity of Ce3+ doped SCASOF phosphors is enhanced with the increase of Ca/Sr ratio. On the contrary, the emission intensity decreases with the increase of Ca/Sr ratio under the excitation of 400 nm. Accordingly, we infer that the incorporation of Ca might change the occupation sites of luminescence center. This assumption is verified by investigating the photoluminescence spectra, quenching concentration and fluorescence lifetime. Moreover, the thermal quenching and chromaticity coordinates variation are also studied. Results show that Ce3+ doped SCASOF phosphor has a great potentiality to be a near-UV or blue-convertible phosphor for white-light emitting diode.关键词：phosphors;Sr3-xCaxAl0.6Si0.4O4.4F0.6：Ce3+;quenching concentration;fluorescence lifetime108|90|0更新时间：2020-08-12
- 摘要：ZnMgO alloy allows for tunable optoelectronic devices. However, the compositional range between ZnO and MgO is interrupted by a crystalline miscibility gap where the wurtzite crystal structure of ZnO is structurally incompatible with the rocksalt structure of MgO. In this article, ten periods of ZnO/ZnMgO superlattice were produced by plasma-assistant molecular beam epitaxy on c-plane sapphire substrate with different oxygen condition. It is found that the sample grown at lower oxygen flow and radio-frenquency (RF) plasma power tends to form rocksalt phase. With the increase of oxygen flow and RF plasma power, wurtzite phase tends to dominate and phase segregation is enhanced. The phase transform affected by the oxygen atoms density is reasoned by the formation enthalpies of ZnO and MgO.关键词：MgZnO;ZnO;superlattice;Ⅱ-Ⅵ ratio;phase segregation109|134|1更新时间：2020-08-12
- 摘要：Monoclinic Gd2O3:Bi3+,Nd3+ phosphors were prepared by combustion method using glycine as a fuel. The structure of the phosphor was characterized by X-ray diffraction and TEM. The influences of Bi3+/Nd3+ concentration on the spectrum shape, fluorescence intensity and fluorescence lifetimes were investigated. The results show that there is an efficient energy transfer from Bi3+ to Nd3+ ions in Gd2O3:Bi3+,Nd3+. With optimized Bi3+ mole fraction of 6% and Nd3+ mole fraction of 2%, the monoclinic Gd2O3:Bi3+,Nd3+ phosphor has the strongest near-infrared luminescence intensity, which is about 20 times stronger than the sample without Bi3+ doping.关键词：combustion;near-infrared;energy transfer;Gd2O3：Bi3+;Nd3+105|139|0更新时间：2020-08-12
- 摘要：The applications of the upconversion (UC) phosphors in solar cells are still constrained because of their relatively low luminescence efficiency. In this work, LiYF4:Er3+/Yb3+ co-doped with different concentrations of Na+ was prepared by a simple and green hydrothermal procedure. The co-doping of Na+ was proposed to enhance UC luminescence of LiYF4:Er3+/Yb3+ microcrystals. The influence of Na+ on the crystal structure, morphology and luminescence of LiYF4:Er3+/Yb3+ was investigated. The results indicate that the co-doping of Na+ can tailor the local crystal field around Er3+. Compared with LiYF4:Er3+/Yb3+, the green and red emission intensities of LiYF4:Er3+/Yb3+ co-doped with 15% Na+ are enhanced by about 4.2 and 2.9 times, respectively. The distortion of the local symmetry and the reduction of OH groups are confirmed to be the origin of the improvement.关键词：solvothermal method;up-conversion;Na+ doped;LiYF4：Er3+/Yb3+112|116|2更新时间：2020-08-12
- 摘要：ZnO thin film that grows at low temperature benefits the sharp interface in heterostructure and enough doping level of acceptor in ZnO. In general, the smooth growth can be easily obtained at temperature higher than 600 ℃, but difficult in the case of low growth temperature. In this work, by controlling the growth ambient and growth rate, a series of ZnO thin films with smooth surface were grown on a-plane sapphire substrates at 450 ℃ by the plasma-assisted molecular beam epitaxy (P-MBE). The growth was performed in oxygen-rich atmosphere. To tune the growth rate, the zinc flux was changed by varying the K-cell temperature of zinc source (Tk) while keeping oxygen flux constant. The growth rate of the samples is only 40~100 nm/h. Scanning electron microscopy (SEM) images indicate that there are lots of irregular grains on the thin film surface at high zinc flux, and most of the grains disappear gradually from the surface with the zinc flux decreasing. This smooth growth with low growth rate is conducive to control finely the layer thickness and smoothness in the multilayer structure. The root mean square (RMS) surface roughness is only 0.238 nm, measured by atomic force microscopy (AFM). The smooth surface benefits from the low growth rate and small sub-lattice mismatch between the c-plane-ZnO thin film and a-plane-sapphire substrate.关键词：ZnO;molecular beam epitaxy;growth temperature;smooth growth119|121|1更新时间：2020-08-12
- 摘要：RE (RE=Eu3+ or Tb3+) single-doped α-SrHPO4 phosphors with nano-scale grain were synthesized by the hydrothermal method in this work. The morphological and optical properties of these phosphors were also investigated. The sizes of the α-SrHPO4 nanorods are found in the range of 90 to 200 nm in length and 24 to 36 nm in width. The introduction of doping agent ions of Eu3+ or Tb3+ decreases both the quality of the crystallinity and the aspect ratio of the matrix. Under the excitation of near ultraviolet light (395 nm), α-Sr0.97HPO4:0.03Eu3+ exhibits two main emission peaks at 590 nm and 614 nm, corresponding to the 5D0→7FJ(J=1, 2) transition of Eu3+, respectively. Under the excitation of near ultraviolet light (217 nm), α-Sr0.97HPO4:0.03Tb3+ shows only one predominant emission peak at 543 nm originated from the 5D4→7F5 transition of Tb3+. The CIE chromaticity coordinates for α-Sr0.97HPO4:0.03Eu3+ phosphor are presented in the orange yellow region and that of α-Sr0.97HPO4:0.03Tb3+ phosphor observed in the yellowish green region.关键词：rare earth;α-SrHPO4;hydrothermal synthesis;photoluminescence93|119|0更新时间：2020-08-12
- 摘要：Red long-lasting phosphor Y2O2S:Eu3+,M2+ (M=Mg, Ca, Sr, Ba),Ti4+ nanoarrays were synthetized by sol-gel template method. The nanoarrays were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). The results show that Y2O2S:Eu3+,Mg2+,Ti4+ nanotube arrays are highly ordered, regularly arranged and uniform. The doping ions do not change the crystal structure and the situation of emission peaks of phosphors, but have influence on the luminescence properties. Under 324 nm excitation, the strongest red-emission peaks at 626 nm assigned to 5D0 → 7F2 transition of Eu3+. The afterglow properties of phosphors doped with different divalent ions increase according to the order of Ba2+, Ca2+, Sr2+, Mg2+. For the sample doped with Mg2+, the decay time can last over 287 s (≥1 mcd/m2).关键词：Y2O2S：Eu3+;Mg2+;Ti4+;sol-gel template method;luminescence property106|33|3更新时间：2020-08-12
- 摘要：Based on the property that cyclodextrin substances can form supramolecular inclusion, we studied the ability of electroneutral β-cyclodextrin (β-CD) or electronegative carboxymethyl-β-cyclodextrin (CM-β-CD) for forming supramolecular inclusion with electrochemiluminescence (ECL) active substance Ru(bpy)32+ and their ECL enhancement. The results show that the supramolecular inclusions can enhance the ECL of Ru(bpy)32+. Compared with Ru(bpy)32+, CM-β-CD increases 1.42 times while only 1.28 times for β-CD. Using SiO2 nanoparticles with negative surface charge as carriers, their absorption capacity for Ru(bpy)32+ supramolecular inclusion was investigated. The results show that SiO2 nanoparticle carriers have a stronger adsorption capacity for β-CD supramolecular inclusion of Ru(bpy)32+. SiO2 composite nanoparticles of β-CD-Ru(bpy)32+ supramolecular inclusion with srtongest ECL signal amplification were prepared in this paper.关键词：electrochemiluminescence;signal amplification;Ru(bpy)32+;supramolecular inclusion;SiO2 composite nanoparticle89|113|3更新时间：2020-08-12
- 摘要：Er3+/Yb3+ codoped NaYF4 microcrystals were prepared via a facile hydrothermal approach assisted with oleic acid. The cubic-to-hexagonal phase transition and enhancement of up-conversion luminescence of Er3+ ions were simultaneously achieved by the gradual addition of Zr4+ ions in the reaction system. X-ray diffraction and SEM results indicated that the introduction of Zr4+ ions could remarkably accelerate the cubic-to-hexagonal phase transition process and pure hexagonal NaYF4 microcrystals were obtained, when Zr4+ mole fraction reached 5%. Strong green and red up-conversion luminescence of Er3+ ions was observed and the up-conversion intensity increased gradually with the addition of Zr4+ ions.关键词：optical materials;upconversion luminescence;Zr4+ impurity doping120|168|0更新时间：2020-08-12
- 摘要：An iridium(Ⅲ) complex of (DFPPM)2Ir(acac) was prepared, and characterized by X-ray single crystal diffraction. The photophysical properties of (DFPPM)2 Ir(acac) were investigated by UV-Vis spectroscopy and photoluminescence (PL) technique. X-ray diffraction studies have revealed that the complex belongs to triclinic system with space group of P-1 and cell dimensions a=14.444 4(7) nm, b=18.047 9(10) nm, c=19.220 0(9) nm, α=113.115(5)°, β=90.453(4)°, γ= 90.989(4)°, V=4 607.0(4) nm3. The complex of (DFPPM)2Ir(acac) emits blue light with a maximum peak at 496 nm in dichloromethane at room temperature. Moreover,(DFPPM)2Ir(acac) was utilized as phosphorescence dopant in OLEDs with the structures of ITO/NPB(40 nm)/CBP:(DFPPM)2Ir-(acac) (10%, 30 nm)/TPBi (15 nm)/Alq3 (50 nm)/Mg:Ag(150 nm, 10:1)/Ag(10 nm). The device showed blue emission at 494 nm, maximum brightness of 21 400 cd/m2,current efficiency of 12.0 cd/A, and power efficiency of 5.4 lm/W.关键词：iridium (Ⅲ) complex;pyrimidine;phosphorescent material;OLED149|136|0更新时间：2020-08-12
- 摘要：CaTiO3:Pr3+ based pearlescent pigments with fluorescent were prepared by ultrasonic-assisted dispersion technique. The samples were characterized by fluorospectro-photometer, laser particle size analyzer, X-ray diffraction, scanning electron microscopy and automatic colorimeter, respectively. The results show that the sample obtained from TiO2-mica pearlescent pigments with CaO coating ratio 5.3% and calcinating at 900 ℃ for 150 min gives a narrow particle size distribution (the average diameter is 24.34 μm) with a homogeneous, dense and smooth surface. It gives white color under the solar light. The characteristic color(L*, a*, b*) of the sample is (89.03, -1.29, 1.00). The maximum emission wavelength is a red light of 613 nm under the excitation of ultraviolet at 304 nm, corresponding to the transition for 1D2→3H4. The average fluorescent lifetime is 154.50 μs.关键词：ultrasonic-assisted dispersion;fluorescent;pearlescent pigments;CaTiO3：Pr3+108|189|0更新时间：2020-08-12
- 摘要：GaN nanoparticles with different sizes were prepared by direct nitridation method. The structure, morphology and optical property of the synthesized samples were characterized by XRD, SEM and PL spectra. The diameters of two kinds of GaN nanoparticles are around 100 nm and 300 nm, respectively. The emission at 357 nm can be ascribed to the band-edge emission. The emission band at 385 nm can be ascribed to the radiation recombination from shallow donor level of nitrogen vacancy (VN) to valence band. The emission band at around 560 nm can be ascribed to the DAP (Donor-acceptor pair) transition from shallow donor level of nitrogen vacancy (VN) to deep acceptor level.关键词：GaN nanoparticles;direct nitridation method;photoluminescence140|400|0更新时间：2020-08-12
- 摘要：Yb3+ doped multicomponent silicate used as photonic crystal fiber core material was prepared. Its refractive index is 1.586, efficient half width of the fluorescent spectrum band is 85.3 nm, and fluorescence lifetime is 1.30 ms. The influences of structural parameter on the normalized frequency (single mode cutoff condition), numerical aperture, effective mode area, nonlinear effect, and limit loss of the photonic crystal fiber were investigated. Using Yb3+ doped silicate as fiber core material, an octagonal and five layer air hole structure based photonic crystal fiber was designed. The performances of the photonic crystal fiber were digitally simulated using the limited element method. The calculated results indicate that the effective mode field area is 1 150 μm2 and the numerical aperture of the inner clad is 0.45 when the aperture of the air hole is 21.6 μm and the space between the air holes is 60 μm.关键词：fiber core material;structural parameter;effective mode;numerical aperture130|204|0更新时间：2020-08-12
- 摘要：A low-temperature hole-injection layer (LT-HIL) was inserted between multiple-quantum well and electron-blocking layer in GaN-based light-emitting diodes (LEDs) to improve the hole-injection efficiency. The effects of magnesocene (Cp2Mg) flow rate and process temperature of LT-HIL in MOCVD epitaxy were investigated. The surface reflectivity and dominant wavelength of epitaxial wafers were measured by photoluminescence spectrometer, the surface profiles were observed by microscope, and the light-output power and forward voltage of fabricated chips were tested by wafer-level auto-measurement system. As the Cp2Mg flow rate increases, the crystal quality, flatness, and uniformity of epilayer decrease. Due to the compensation effects in Mg-doped GaN material, the dominant wavelength shows red-shift at first and then blue-shift, the output power of the chip goes up to the maximum then falls down, and the forward voltage goes down to the minimum then rises up. Compared to conventional LED chips without LT-HIL, the output power and forward voltage of the LED chips with Cp2Mg moral flow rate of 1.94 μmol/min are enhanced by 20.3% and reduced by 0.1 V under the injection current of 20 mA. It is also shown that the gradually changing process temperature can also improve the crystal quality, flatness and uniformity of epilayer, although it is non-principal reason under the condition of large Cp2Mg moral flow rate.关键词：LED;MOCVD;low-temperature hole-injection layer;magnesocene;temperature101|179|0更新时间：2020-08-12
- 摘要：ZnO nanowires were synthesized by chemical vapor deposition method, and single ZnO nanowire semiconductor devices with Ohmic contact electrodes were fabricated using the micro grid template method. The electrical properties of the device were investigated at low temperatures. The results show that there are two types of transport mechanism: thermal activation and nearest-neighbor hopping mechanism from 300 to 60 K. The properties of ultraviolet light response and recovery of the device were tested at 300, 200, and 100 K, respectively. The results show that the sensitivity of the device to ultraviolet is improved at low temperature, and the current recovery time increases with the temperature falling down.关键词：ZnO nanowires;low temperature;transport mechanism;UV photosensitivity101|185|0更新时间：2020-08-12
- 摘要：Pure ZnO resistive switching and ZnO:2% Cu resistive switching with sandwich structure were fabricated in the same conditions. The bottom electrode was ZnO:Al, and the top electrode was Cu for the resistive switchings. The switching characteristics such as endurance, variations of threshold voltage as well as distribution of resistance were investigated. The results demonstrate that the ZnO:Cu devices exhibit more excellent switching performance than ZnO devices. In addition, the switching mechanism of ZnO:Cu resistive device were also studied in this paper. The I-V characteristics of the device indicate that the conduction mechanisms of high and low resistance states can be explained by trap-controlled space charge limited current (SCLC) and Ohmics law, respectively.关键词：ZnO：Cu;resistive switching;SCLC105|218|2更新时间：2020-08-12
- 摘要：A simple and facial carbothermal reduction method was utilized to prepare ultra-long ZnO nanowires with lengths of about 100 μm, diameters of about 500 nm, aspect ratio up to 200 without usage of any catalyst and carrier gas. The effects of the positions of Si substrate, deposition time and the amount of reactant materials on the morphology of ZnO nanowires were studied. The gas sensing results of ZnO nanowires show that ZnO nanowire sensors have a good performance to alcohol with good selectivity, fast response and recovery at the working temperature of 350 ℃, and the detectable volume fraction is as low as 5×10-6. In addition, a UV sensor based on ZnO nanowires was constructed through a simple and practical dielectrophoresis method. The photocurrent of the sensor increases about 13% under 365 nm UV illumination but has no changes under 254 nm UV irradiation, which indicates the good selectivity of the sensor.关键词：ultra-long ZnO nanowires;gas sensing;UV sensor124|188|1更新时间：2020-08-12
- 摘要：The sophisticated techniques of photolithography and wet-etching are used to fabricate GaN-based LED chips with surface-textured ITO layer to enhance the light output efficiency. It is shown that the light-output power can be efficiently improved by this surface-textured method. After the triangle-lattice of close-packed micro-holes are fabricated, the light-output power of LED chips under the injection current of 20 mA exhibits 11.4% enhancement comparing to the conventional LED chips. However, the forward voltage correspondingly increases 0.178 V. With our proposed micro-structures, the light-output power can also be enhanced by 8.2%, while the forward voltage increases only 0.044 V. It is also shown that the close-packed micro-hole pattern benefits high light-output under small injection current. However, this pattern would induce current-crowding if the injection current become high, and thus the light-output efficiency would decrease significantly. On the other hand, our optimized micro-structure is help for high electric-injection efficiency. This induces a high light-output efficiency, and the efficiency droop can be suppressed. The proposed micro-structure is preferred for high power LED chips under large current injection.关键词：light-emitting diodes;indium-tin-oxide;surface-textured;light-output efficiency133|88|7更新时间：2020-08-12
- 摘要：We presented a facile method to prepare uniform size and stable property graphene quantum dots (GQDs) from chemical cutting the double-walled carbon nanotube with blue light emission in a chlorobenzene solution. The double-walled carbon nanotube was firstly cut into graphene nano sheets (GNSs) in acidic in the condition of heating and stirring, then chlorobenzene was used to separate GQDs from GNSs in water. The chlorobenzene solvent enabled the preparation of GQD-PVK hybrid nanocomposite. Nonvolatile rewritable memory effect was observed for the GQD-based nanocomposite, suggesting the promising applications of GQDs in data storage. Moreover, due to the easy solution process, we demonstrated the design and realization of flexible GQD-based memory device. The memory has performance as follow: low driving-voltage, high ON/OFF ratio, high cycles, high repeatability and stability. This work may expand the application of GQDs to the portable electronic devices.关键词：graphene quantum dot;blue light;polymer;flexible memory104|158|2更新时间：2020-08-12
- 摘要：The bioluminescence was studied under the stimulation of ship noise using the acoustic transducer, and an experiment was carried upon Noctiluca sp. bioluminescence in a tank. The characteristics of Noctiluca sp. bioluminescence were recorded on images under different frequencies noise launched by acoustic transducer. The luminescent points were obtained through an analysis of these images. The statistical characteristics of Noctiluca sp. bioluminescence under stimulation of ship noise were obtained approximatively. The results show that the number of luminescent points increases with the acoustic transducer frequency and energy increasing.关键词：bioluminescence;Noctiluca sp.;ship noise103|166|1更新时间：2020-08-12
- 摘要：Taking diphenyl ether (DE) as the reference, the molecule activity on ground state, ultraviolet spectrum and ground-excited state electron transitions mechanism of other 9 para-halogenated diphenyl ethers were analyzed by the combination of Gaussian 09 software calculation, natural bond orbital theory, and transition density matrix. The results show that DE is most vulnerable to electrophilic substances in the ground state, meanswhile, CDE-15 is vulnerable to nucleophilic substances to lose electrons. The introduced para-halogen substituent can reduce the energy gap of DE, while the maximum absorption wavelength and absorption intensity of DE increase with the volume of substituents. Nine kinds of halogenated diphenyl ethers and DE have the similar ground-excited state electron transition mechanism.关键词：time-dependent density functional method;para-halogenated diphenyl ethers;ground state molecule activity;ultraviolet spectrum;electron transition mechanism106|144|0更新时间：2020-08-12
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