算子框架的稳定性

算子框架是广义的框架,它包括框架序列和子空间框架.本文分别讨论了在Bessel算子列和算子框架的扰动下,其对偶框架的稳定性.得到了一些新结果,这些结果是序列框架稳定性的推广.     

Nd3+ doped fluorochlorozirconate glass:3.9 μm MIR emission properties and energy transfer

The Nd3+ doped fluorochlorozirconate (FCZ) glass was prepared by melt-quenching method. The 3.9 μm emission from Nd3+ ions is attributed to the two-photon absorption process. The strong emission transition at 3.9 μm fluorescence peak intensity, corresponding to the 4G11/2→2K13/2 transition, is directly proportional to the NaCl concentration. With the increase of the Cl- ions amount, the mid-infrared (MIR) luminescent intensity is significantly enhanced. Additionally, the Judd-Ofelt (J-O) parameter Ω2 is larger than that of the fluorozirconate (FZ) glass, which indicates the covalency of the bond between RE ions and ligand is stronger as Cl- ions substitution of F- ions in chloride FZ glass. The X-ray diffraction (XRD) patterns show that the amorphous glassy state keeps the FZ glass network structure. In brief, the advantageous spectroscopic characteristics make the Nd3+-doped FCZ glass be a promising candidate for application of 3.9 μm emission.     

Zn1-xCdxS三元混晶的电子结构及光学性质计算与实验验证

基于密度泛函理论的平面波超软赝势法,计算了Zn_1-xCd_xS三元混晶的电子结构和光学性质。计算结果表明,Cd进入ZnS晶格后,禁带宽度变窄,硫空位(V_S)缺陷能级随x值增大逐渐向费米能级移动,在紫外和可见波段的吸收截止波长随着x值增大逐渐红移。采用共沉淀法制备了Zn_1-xCd_xS三元混晶,XRD图谱表明形成了Zn_1-xCd_xS合金相,吸收光谱显示了与理论计算相符的能带和吸收截止边的移动规律,荧光光谱显示与V_S相关的发射峰随x增大逐渐红移,与计算得到的V_S缺陷能级的移动规律相同。     

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

NaCCH自由基低能电子态的理论研究

采用CASSCF/CASPT2方法研究了NaCCH自由基的低能电子态,在C2v对称性下给出了NaCCH自由基9个低能激发态的几何、组态、CI系数、振子强度、垂直激发能和绝热激发能.研究结果表明,NaCCH自由基的基态X1Σ+几何和转动系数与实验值是一致的;谐振频率与其他理论方法得到的值也符合的很好;HOMO和LUMO轨道的能量间隔为3.80eV,对应着13Σ+的绝热激发能;除13Π外,其它低能激发态均是稳定状态;基态到三重态是自旋禁阻的.     

ZnS∶Zn,Pb宽带蓝色发光和发光机制

用固相反应法制备了一系列ZnS∶Zn,Pb荧光粉.改变不同的灼烧温度和激活剂的掺杂量,通过对灼烧后荧光粉进行光谱分析,我们发现Pb2+在ZnS基质中的发光与制备条件有关:灼烧温度为800～950℃时,能得到Pb2+在ZnS基质中的蓝色发光.测量了其光致发射光谱、激发光谱,以及灼烧后荧光粉的成分.研究了阴极射线下ZnS∶Zn,Pb荧光粉的相对发光亮度与荧光粉电压的关系,ZnS∶Zn,Pb的相对亮度比ZnS∶Ag,Cl的高,比ZnS∶Zn更高.研究了发光衰减时间与温度的关系,得到了ZnS∶Zn,Pb的蓝色发光可能来源于Pb2+的D波段发射的结论.并对其发光机制进行了一些探讨.这种新型蓝粉可应用于VFD和FED等低压显示屏.     

优化反式平面钙钛矿太阳电池性能的简便方法——利用PEDOT:PSS与DMSO共混空穴传输层

优化界面接触、增强界面处载流子传输对于提高钙钛矿电池性能具有重要意义。本研究将适量二甲基亚砜（DMSO）添加到聚（3,4-乙烯二氧噻吩）-聚（苯乙烯磺酸盐）(PEDOT∶PSS)空穴传输层中,改善了空穴传输层的导电性和空穴传输特性,有效提高了反式平面钙钛矿太阳能电池光伏性能。短路电流(J_sc)从21.29 mA/cm²提高到22.15 mA/cm²,填充因子（FF）从76.35%提高到80.09%,转换效率（PCE）从16.02%提高到17.01%。薄膜与器件性能综合测试结果表明,DMSO的掺入使PEDOT∶PSS发生适度相分离,形成更好的PEDOT导电通道,增强了PEDOT∶PSS的导电特性。稳态光致发光光谱呈现出显著的荧光猝灭效应,也表明掺杂DMSO后PEDOT∶PSS的空穴提取能力得到提高,钙钛矿活性层与阳极之间的空穴传输更加顺畅,有助于实现高达80%以上的填充因子。本研究为改善反式平面钙钛矿太阳电池或有机太阳电池光伏性能提供了一种高效、简便的方法,具有很好的现实意义。     

Si4+掺杂对Gd1.6WO6:Eu3+0.4荧光粉发光特性的影响

采用高温固相法合成了不同Si⁴⁺掺杂比例的 Gd1.6(W1－xSix)O 6:Eu³⁺0.4荧光粉,分析了Si⁴⁺掺杂对 Gd1.6(W1－xSix)O 6:Eu³⁺0.4荧光粉晶格结 构的影响,研究了不同Si⁴⁺掺杂比例下的XRD谱、激发光谱、发射光谱和衰减曲线。 结果发现:Si⁴⁺的掺杂改变了基质的结构,使得激活剂离子Eu³⁺周围的晶体场 改变,从而改变了荧光粉的发光效率,当Si⁴⁺ 的掺杂浓度达到0.4mol时,晶体对称性最差,粉体发光强度最大 。根据发射光谱和衰减曲线计算了样品的J-O强度参数 和无辐射跃迁几率,结果表明适量的Si⁴⁺掺杂可以抑制无辐射跃迁,提高发光强度。 计算结果与实验结果相符。     

基于Laws模板与CSLBP的人脸识别

针对CSLBP对人脸图像的局部特征提取不充分问题,提出一种基于Laws模板的CSLBP算法。该算法首先选取Laws模板对原始图像进行滤波,获得多幅纹理单一图像。其次,引进CSLBP算子对各纹理图像进行特征提取,再将图像分成若干子区域,通过连接这些子区域的CSLBP直方图生成人脸特征向量。最后,针对Laws-CSLBP中存在的高维向量问题,做了进一步研究分析,引入了局部保持投影（LPP）的流行算法进行降维,并采用最近邻分类器进行判别分类。该算法在ORL、FERET人脸库中都取得了较好的识别效果,证明了该算法的有效性。     

A novel joint technique for PAPR reduction in CO-OFDM systems

For the high peak-to-average power ratio （PAPR） of coherent optical orthogonal frequency division multiplexing （CO-OFDM） system, a novel joint technique which is the combination of iterative partial transmit sequence （IPTS） and clipping technique is proposed. Simulation results demonstrate that the PAPR and bit error rate （BER） performance of the proposed technique both outperform those of the single techniques. Under the same conditions, the threshold value and peak power of IPTS clipping joint technique are optimized by 3.44 dB and 0.86 dBm compared with those of IPTS techinque, respectively. At the BER of 103, the optical signal to noise ratios （OSNRs） of the novel joint technique after 320 km and 400 km single-mode fiber （SMF） transmission are 0.68 dB and 1.18 dB smaller than those of clipping technique, respectively.