High-power diode-end-pumped Tm：YAP and Tm：YLF slab lasers

Diode-end-pumped continuous-wave(CW) Tm:YAP and Tm:YLF slab lasers are demonstrated. The a-cut Tm:YAP and Tm:YLF slabs with doping concentrations of 4 at.-% and 3.5 at.-%,respectively,are pumped by fast-axis collimated laser diodes at room temperature. The maximum CW output powers of 72 and 50.2 W are obtained from Tm:YAP and Tm:YLF,respectively,while the pump power is 220 W,corresponding to the slope efficiencies of 37.9% and 26.6%,respectively.     

Single-molecule surface-enhanced Raman scattering of R6G in aqueous environment under non-resonance conditions

The single-molecule surface-enhanced Raman scattering(SERS) spectra of Rhodamine 6G(R6G) in an aqueous environment under non-resonance conditions are studied.Series of spectra are recorded in timemapping mode,and intensity fluctuations of SERS signals and spectral diffusion are observed.The correlations between the presence frequency of SERS spectra and number of hot spots as well as the quantity of molecules in scattering volume are examined thoroughly.The results indicate that only molecules located at hot spots produce good signal-to-noise ratio Raman spectra and the origin of fluctuating SERS signals are mainly ascribed to the movement of hot spots.     

Novel red perovskite phosphor Ca2AlNbO6:Eu for white light-emitting diode application

Eu³⁺-doped perovskite phosphors of Ca₂AlNbO₆ were synthesized from a solid state reaction. A small amount of the Li₂CO₃ flux was found to greatly shorten calcination time and reduce reaction temperature. The structural and optical properties of the samples were systematically investigated. The excitation spectra of Ca₂AlNbO₆:Eu³⁺ reveal two excitation bands at 398 (⁷F₀→⁵L₆) and 466 nm (⁷F₀→⁵D₂), which match well with the two popular emissions from near-UV and blue LED chips. Under blue light excitation, the red emission of Ca₂AlNbO₆:0.05Eu³⁺ is twice more intense than that of (Y_0.95Eu_0.05)₂O₃. The chromaticity coordinates of (Ca_0.95Eu_0.05)₂AlNbO₆ (x=0.654, y=0.346) are close to the standard values (x=0.670, y=0.330) of National Television Standard Committee (NTSC). The optical properties suggest that Ca₂AlNbO₆:Eu³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

Influence of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu2O3:2%Yb, 0.2%Tm nanopowders

Lutetium oxide nanopowders codoped with Tm³⁺ and Yb³⁺ were synthesized by the reverse-strike co-precipitation method. Effects of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu₂O₃:2%Yb, 0.2%Tm nanopowders had been investigated. The results show that pH value of the precipitant (NH₄HCO₃) solution has a significant effect on the particle size, morphology and upconversion emission intensity of the Lu₂O₃:2%Yb, 0.2%Tm nanopowders. All the samples obtained from different pH value of precipitant solution can be readily indexed to pure cubic phase of Lu₂O₃, indicating good crystallinity. The upconversion emission intensity of Lu₂O₃:2%Yb, 0.2%Tm nanopowders obtained from the precipitant solution with pH=11 is the strongest. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing the number of OH⁻ groups and the enlarged nanopowder size. The strong blue, weak red and near infrared emissions from the prepared nanopowders were observed under 980 nm laser excitation, and attributed to the ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ ion, respectively.     

Effect of dibutyl phthalate as plasticizer on high-molecular weight poly(vinyl chloride)–lithium tetraborate-based solid polymer electrolytes

A series of different composition of polymer electrolytes-based on poly(vinyl chloride) (PVC) as host polymer, lithium tetraborate (Li₂B₄O₇) as dopant salt, and dibutyl phthalate (DBP) as plasticizer were prepared by solution casting method. The interaction between the PVC, Li₂B₄O₇, and DBP were studied by Fourier transform infrared. The shifting, broadening, and splitting of transmission peaks were the evidences of complexation. The highest ionic conductivity polymer electrolyte of 2.83 × 10⁻⁶ S/cm was achieved at ambient temperature upon addition of 30 wt.% of DBP. In addition, the temperature-dependent conductivity, frequency-dependent conductivity, dielectric permittivity, and modulus studies were performed. The temperature-dependent conductivity of the polymer electrolytes was found to obey the Arrhenius behavior. The thermal stability of polymer electrolytes was verified by thermogravimetric analysis. The lower in glass transition temperature was proven in differential scanning calorimetry, whereas the higher amorphous region within the polymer matrix was demonstrated in X-ray diffraction.     

具有不同取代基团的香豆素系列分子二阶非线性光学性质的DFT研究

本文设计了具有不同取代基团的7-苯乙烯基香豆素和4-苯乙烯基香豆素的A、B两个系列共14个化合物分子.采用密度泛函理论B3LYP/6-31G方法对其几何构型进行了全结构优化.在所得优化结构的基础上对这些分子的稳态二阶非线性光学(NLO)系数β值进行计算分析,同时用含时密度泛函理论(TD-DFT)对这些分子的电子性质进行了研究.结果表明:此类香豆素化合物具有较大的分子β值,其中A类分子的共面性好,共轭链长,β值均比B类分子的大.14个化合物中前线分子轨道能级差越小的化合物,其βwt值越大.各分子前线分子轨道跃迁对二阶NLO效应有明显的贡献.     

Synthesis of salicylaldehyde Schiff base modified Cu nanocrystals by thermal treatment in liquid paraffin

Cuboid copper nanocrystals were synthesized by thermal treatment in liquid paraffin without any inert gas protection with salicylaldehyde Schiff base copper (II) (Cu (II)-Salen) complex as precursor. Liquid paraffin was used as solvent and reductant. The obtained copper nanocrystals are morphology-controlled and stable when exposed to air for one year. The nanocrystals were characterized by X-ray diffraction measurements (XRD), UV-visible spectroscopy (UV-vis), transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FT-IR). The results showed that the stable cuboid copper nanocrystals are synthesized by using Salen as capping agents.     

Frequency dispersive complex permittivity and permeability of ferromagnetic metallic granular composite at microwave frequencies

We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vf_CIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vf_CIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ.     

Tunable I-shaped metamaterial by loading varactor diode for reconfigurable antenna

A tunable metamaterial by employing I-shaped metamaterial with loaded varactor diode is presented in this paper and the phase of emitting wave modulated by the varactor diode is demonstrated. We have proved that the energy loss is relatively low when the working frequency is chosen to be away from the resonance frequency of the I-shaped metamaterial. By using the metamaterial, a pattern reconfigurable antenna is designed based on arrayed antennas theory. Simulations results show that the radiation pattern can be tuned to different angles by properly arranging the linear phase difference of adjacent regions.