摘要:Powdered samples NaYF4∶Eu3+ and NaYF4∶Eu3+, Tb3+ are successfully prepared by high temperature solvothermal method. The obtained samples are characterized by X-ray power diffraction(XRD), field emission scanning electron microscopy (FESEM), and photoluminescence(PL) spectra. Experiment results revealed that as-prepared NaYF4∶Eu3+ and NaYF4∶Eu3+, Tb3+ crystallized in hexagonal phase without cubic phase, and the size was about 80 nm×100 nm (side length×thickness). When the doping concentration of Eu3+ and Tb3+are various, the lattice structure of samples do not change, indicating that the Eu3+ and Tb3+ ions are completely dissolved in the NaYF4 host lattice by substitution for the Y3+. The emission from 5D0→7F1 (595 nm) and 5D0→7F2 (618 nm) of Eu3+ ions was observed under excitation of 394 nm light from Xe lamp. The visible light intensity changes with the doping ions of Eu3+ concentration and the influence to crystal structure of Tb3+ ions concentration have been investigated. These results show that the doping ions of Tb3+ change the coordination environment of Eu3+, resulting to stronger red emissions, and electric dipole transition occupied the main contribution.
关键词:down-conversion; β-NaYF4;high temperature solvothermal method;dipole transition
摘要:Uniform NaYF4∶18%Yb,0.5%Tm nanocrystals were synthesized via thermal decomposition method following high temperature, and then a change of the nanocrystals was made from oil-soluble to water-soluble by ligand-exchanged method. X-ray diffraction (XRD) analyses showed that the samples were β-NaYF4 nanocrystals. The TEM images exhibited that the nanocrystals had an average size of 35 nm. Under 980 nm near-infrared laser excitation, the samples showed intense ultraviolet upconversion emission. 5-photon upconversion fluorescence of the Tm3+ ions in the nanocrystals was stronger than 4-photon and 3-photon upconversion fluorescence. Due to special optical properties and small size, the water-soluble nanocrystals would show potential applications in the biomedical field.
摘要:The influence of crystal phases on the downconversion quantum processes is studied experimentally. One high-energy ultraviolet photon (Tb3+ :7F6 →5L1, 294 nm) is quantumly cut into two lower energy photons: one in the near-infrared region (Er3+ :4I9/2→ 4I15/2, 800 nm) and the other in the blue region (Tb3+:5D4 →7F6, 467 nm), both of which can be efficiently absorbed by GaAs solar cells. The hexagonal microcrystal and cubic nanoparticles NaYF4∶Tb3+,Er3+ were prepared by hydrothermal method. The thermodynamically stable and ordered hexagonal phase is favorable for the quantumcutting processes, however, the dowconversion can not be observed in our cubic phase samples. Using different excitation wavelengths of 294 and 355 nm to excite the hexagonal phase NaYF4∶Tb3+,Er3+, the spectra indicate that the cross-relaxation (Tb3+:5L1, Er3+:4I15/2) → (Tb3+:5D4, Er3+:4I9/2) is required for down conversion. It is shown that the quantum yields in the medium prepared by hydrothermal method are lower compared with that by melting method.
摘要:Ce3+∶BaF2 nanoparticles prepared via co-precipitation have been investigated for reaction sequence and concentration of reactants. Nano-particles were characterized by means of X-ray diffraction, SEM, TEM, ICP respectively. The results indicate that the powder synthesized by the condition of reverse reaction (anionic drip into the cationic) and high F- concentration is single phase and the actual doping value is close to the theoretical value. The transparent ceramic was prepared by hot-pressed way at 900 ℃ and 30 MPa. It can be seen that some closed pores existed in the grains from the picture of cross section. After superficial corrosion, grain boundary could be clearly seen from the microscope images. The X-ray induced luminescence intensity reached a maximum when the doping mole fraction of Ce3+ was 0.1%, lower than the Ce3+ content in the crystal.
摘要:A new bipolar blue phosphorescent host material was synthsized and applied to phosphorescent organic light emitting diodes with Firpic(iridium(Ⅲ)[bis(4,6-difluorophenyl)-pyridinato-N,C2']picolinate), the maximum current efficiency was 40 cd/A, maximum brightness was 19 691 cd/m2, maximum luminous efficiency was 12 lm/W. The results suggest that the host materials which we synthesized can better balance carrier injection and transport with appropriate triplet energy and goodly thermal stability.
摘要:Na2WO4∶Sb3+ phosphors were prepared with a sol-gel method. The samples were characterized with X-ray diffraction, reflectance spectra, emission and excitation spectra. The phosphor can be excited with ultrovilet light in the range of 250~320 nm and give intensitive emission in the range of 410~550 nm. The maximum emission and excitation wavelength is 470 nm and 280 nm, respectively. The optimized sintered temperature is 800 ℃ and samples with a Sb3+ concentration of 0.01 give the strongest emission. The luminescence mechanism of Na2WO4∶Sb3+ phosphors were also briefly discussed.
摘要:Zn2SnO4 nanocubes have been synthesized via a simple and facile one-pot hydrothermal process. The X-ray diffraction (XRD) pattern demonstrates that the products are fine single crystals Zn2SnO4 with the inverse spinel crystal structure. The FESEM and TEM images confirm that Zn2SnO4 microcrystallines are cube-like structure with the side length of 100~400 nm. In addition, the photoluminescence (PL) spectra of Zn2SnO4 nanocubes at room temperature show a broad blue-green emission around the 380~820 nm wavelengths with a maximum center at 590 nm. The PL property of the Zn2SnO4 nanocubes can be obviously reduced by annealing at 400 ℃ for 1 h due to the improvement of the crystal quality and the reduced concentration of oxygen vacancy.
摘要:The electronic structures and optical properties of Zn1-xCdxS ternary mixed crystals have been investigated using the first-principle plane-wave pseudopotential method. Comparison of calculations with different Cd doping concentration, the band gap shows gradually decrease with Cd doping concentration increasing. This band-narrowing phenomenon is ascribed to the reduction of bottom of conduction band determined by low energy electrons of Zn4s orbit and the elevation of top of valence band which was formed by the electrons of S3p states. Also the sulfur vacancy level was calculated and showed a shift near to the Fermi level with an increased of Cd doping concentration. The dielectric function and absorption coefficient of Zn1-xCdxS are also studied. For the absorption coefficient calculation of Zn1-xCdxS, we found that absorption onset in UV-Vis spectrum shifts to low energy with x increase. Moreover, the XRD, fluorescence spectrum and experimental absorption spectra of Zn1-xCdxS prepared by chemical synthesis and annealing treatment are obtained. The results exhibit agreement with the calculations.
摘要:Ba2Ca(BO3)2∶Eu2+ phosphor was synthesized by a high temperature solid-state method. CaCO3 (A.R), BaCO3 (A.R), H3BO3 (A.R) and Eu2O3 (99.99%) were used as raw materials. Its crystal structure, luminescent characteristics and Commission International de lEclairage (CIE) chromaticity coordinates values were measured. Under the ultraviolet to visible light irradiation, Ba2Ca(BO3)2∶Eu2+ shows an asymmetrically single green emission band with a maximum at 537 nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The emission intensity of Ba2Ca(BO3)2∶Eu2+ was influenced by Eu2+ molefraction, at first, it increases with the increase of Eu2+ mole fraction, and reaches a maximum value at 2%Eu2+, then decreases with further increasing its concentration because of the concentration quenching effect. And the concentration quenching mechanism is verified to be dipole-dipole interaction. According to the crystal structure data and the experimental spectral data, the critical distances(Rc) can be obtained, and are 2.64 nm and 2.11 nm, respectively. Moreover, with increasing the Eu2+ doped content, the CIE chromaticity coordinates of the samples were slightly varied. For Ba2Ca(BO3)2∶2%Eu2+, the quantum efficiency is approximately 72%.
摘要:ZnS∶Cu quantum dots have been synthesised via a water-soluble route, then the ZnS shell coated for surface modification. The influence of shell thickness on the optical properties of ZnS∶Cu quantum dots has been studied. The samples were characterized by TEM, XRD, PL, PLE and UV-Vis. The results showed that the ZnS∶Cu/ZnS quantum dots were cubic sphalerite, uniform spherical-shaped and had a narrow size distribution. The average particals size increased from 2 nm to 3.2 nm after the shell modification. The PLE and UV-Vis spectra showed a gradual red shift with the shell thickening, which suggested that the quantum dots was growing with the ns/nc increased. It can proved that the ZnS shell growed on the ZnS∶Cu quantum dots surface and formed the ZnS∶Cu/ZnS core/shell structure quantum dots. The PL intensity related with Cu2+ increased at the beginning and decreased with further growth of the ZnS shell. The intensity of emission peak achieved the maximum when ns/nc=2.5.
摘要:HAZO films were prepared on quartz substrates by RF magnetron sputtering in Ar+H2 gas ambient at room temperature. The effects of post-annealing in pure Ar atmosphere on the structural, optical and electrical properties of the HAZO films were investigated. It was found that post-annealing treatment was beneficial to crystallization of HAZO thin films, while caused a large degradation of the conductivity. The increase in the resistivity of HAZO thin films was attributed to the doped hydrogen atoms diffuse out after annealing. It was showed that interstitial hydrogen atoms (Hi) and substitutional hydrogen atoms (HO) at an O site removed from films, as well as the effect of H passivating deep acceptors and dangling bonds gradually eliminated as the heating temperature was increased.
摘要:A novel tunable filter featuring the defect mode of the TM wave from one-dimensional photonic crystals doped by magnetized plasma is investigated. Firstly, based on the continuous condition of boundary, the transfer matrix is deduced for magnetized plasma where external magnetic field is perpendicular to wave vector. Then by the transfer matrix method (TMM), we find out that the frequency of the defect mode can be modulated by plasma frequency or external magnetic field. Without changing the structure of the photonic crystal, the location of the defect mode can be modulated in a larger frequency range, and the number of the defect modes can also be controlled.
摘要:Bi3.15Eu0.85Ti3O12 (BEuT) thin films were prepared on fused silica substrates by using chemical solution deposition technique. The structural and optical properties of thin films were stu-died in this work. XRD results show that BEuT thin films exhibit a polycrystalline bismuth-layered perovskite structure, and the average grain sizes increase with the annealing temperatures, which is consistent with the SEM results. Raman spectra of BEuT samples indicate that Eu3+ mainly replace Bi3+ in perovskete layer. In the wavelength of above 500 nm, BEuT thin films exhibit high optical transmittance, and the band gaps of all samples are nearly about 3.69 eV. The emission intensities of BEuT thin films increase with the annealing temperatures, which could be due to the improvement of crystallization for the samples annealed at higher temperature.
摘要:A low-cost approach for fabricating Si/ZnO branched nanowire arrays was reported. The Si nanowire arrays were prepared on Si(100) substrate using a metal-assisted chemical etching process at room temperature. The diameter and distribution are uniform, and the length of Si nanowire could be tuned by varying the etching time. The ZnO film on the surface of Si nanowire was obtained by magnetron sputtering method and then the ZnO nanowires were prepared via hydrothermal method. The samples were characterized by field-emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy(EDS) and photoluminescence (PL). The Si/ZnO branched nanowire arrays are suitable for applications in photovoltaic and photocatalysis.
关键词:ZnO;Si;metal-assisted chemical etching;hydrothermal method;nanowire arrays
摘要:ZnO nanorods were grown on a thin Au layer by hydrothermal method. In the photoluminescence (PL) spectrum, a strong UV emission and a weak deep-level emission were observed. The optically pumped lasing could be detected in ZnO nanorods. The integrated intensity of the spectra increases nonlinearly with the excitation power density, which indicated there exists the stimulated emission. And multi-mode emission peaks emerged when the excitation power density exceeded the threshold. Using Au layer as mirror, the light loss was further decreased, which resulted in the decrease of the laser threshold to 31.2 kW/cm2.
摘要:This paper deals with the characteristics of aluminium nitride (AlN) films doped by silicon (Si) thermal diffusion. The films are analyzed by energy dispersive X-ray spectroscopy (EDS) and high-temperature dependent electrical conductivity. The results of EDS show that the Si element is successfully doped into the AlN films using SiNx as the diffusion source at the temperature of 1 250 ℃. The high-temperature current-voltage (I-V) measurements show that the electrical properties of the AlN films can be prominently improved by Si thermal diffusion, and at the measured temperature of 460 ℃ their electrical conductivities increase from 1.9×10-3 S·m-1 to 2.1×10-2 S·m-1 after the Si thermal diffusion. The high-temperature dependence of thermal conductivity suggests that the activation energies of V3+N and Si are about 1.03 eV and 0.45 eV, respectively.
摘要:The active region of high power VCSEL at 1 060 nm is calculated and designed. The performances of highly-strained InGaAs quantum wells with GaAsP, GaAs and AlGaAs barriers are compared. A comprehensive model taking self-heating effect into consideration is presented to determine the parameters of quantum well and barrier. It is found that the best value of width and number of In0.28Ga0.72As quantum wells in our design is 9 nm and 3, respectively. And high output power up to Watt-level is achieved. In addition, the temperature performances are also compared among the three different barriers, which show that the devices with GaAsP barriers have higher output power and better temperature stability. Finally, the InGaAs/GaAsP QWs are grown used MOCVD and the PL spectrum is tested, the experimental data agrees with the theoretical results very well.
摘要:Silicon-rich silicon nitride film was deposited by plasma enhanced chemical vapor deposition (PECVD) on (100)-oriented monocrystalline silicon, according to silicon solar cell process. Photoluminescence (PL) performance of the films at annealing temperatures in N2 ambient was studied, showing that temperatures had great effect on the characteristics. Excited by 325 nm line, PL from defect-related states was only observed in the film and Si clusters has not been formed at annealing temperature 900 ℃. After annealed at different temperature, PL intensity decreased with increasing temperature. PL peak originated from defect energy Si dangling bond (K center). In this work, At 900 ℃, disappearance of PL peak was attributed to increasing non-radiation recombination and silicon clusters has not been formed. Structure of silicon nitride has been measured by X-ray photo-electron spectroscopy (XPS) showing binding energy at 101.8 eV and indicated that silicon phase has not been separated from silicon nitride. Infrared (FTIR) measurement provided a good confirm to PL analysis.
摘要:We reported the photoconductivity of Mg-doped p-InN layers, which were grown by molecular beam epitaxy (MBE). The surface of these samples was very flat which were observed by both reflection high energy electron diffraction (RHEED) and atomic force microscope (AFM). We studied the temperature-dependent photoconductivity of Mg-doped p-InN layers. We found out that the photosensitivity decreased with increasing temperature, which resulted from both the variation of photon-generated carrier concentration and the residual carrier concentration with increasing temperature.
关键词:molecular beam epitaxy(MBE);reflection high energy electron diffraction(RHEED);Mg doped p-InN;photosensitivity
摘要:A novel dansyl sulfonamide-based fluorescence probe, (E)-5-(dimethylamino)-N-(4-(2-(quinolin-2-ylmethylene)hydrazinecarbonyl)phenyl)naphthalene-1-sulfonamide (DW1) was synthesized for detection of Zn2+. UV-Vis, fluorescence and ESI-MS spectra of DW1 were measured to investigate the selective recognition. The results show that the fluorescence intensity increase significantly with high quantum yield (Φf=0.32) and blue-shift emission from 545 nm to 515 nm after the coordination of DW1 with Zn2+, manifesting DW1 could detect Zn2+ sensitively. Moreover, the selective and competitive fluorescent experiments show that DW1 is highly selective for recognition of Zn2+ over other common metal ions. Spectrophotometric titration and ESI-MS spectrum indicate the formation of a 1∶1 DW1-Zn2+ complex and the association constant K was calculated as 1.75×104 (mol/L)-1.
摘要:It was found that ZnSe quantum dots (QDs) could enhance the chemiluminescence(CL) of the luminol-K3Fe(CN)6 system. The CL from luminol-K3Fe(CN)6-ZnSe QDs system is strongly inhibited under the presence of hydroquinone. Based on this inhibition, a novel CL method with a lower detection limit and wider linear range was developed for determining diethylstilbestrol. The possible CL mechanism was also discussed. Under the selected experimental conditions, the CL intensity was linear with the concentration of diethylstilbestrol from 6.0×10-9 mol/L to 4.0×10-5 mol/L with a detection limit of 2.0×10-9 mol/L(S/N=3). The relative standard deviation(RSD)(n=11)for the determination of 4.0×10-6 mol/L diethylstilbestrol was 1.4%.The proposed method was successfully applied to analyze diethylstilbestrol in milk samples with recoveries of 94.47%~ 107.61%.