Photoluminescence study of the annihilation process of donor-bound excitons in ZnO： observation of quantum mechanical interference

We report a photoluminescence observation of the coupling of donor-bound excitons and longitudinal optical phonons in high-quality ZnO crystals at 5 K. The first-order phonon Stockes line of donor-bound excitons exhibits a distinct asymmetric line shape with a clear dip at its higher energy side, suggesting that quantum mechanical interference occurs during the annihilation of donor-bound excitons. The donor binding energy is determined to be 49.3 meV from spectral featural.     

不同气氛下SiOx纳米线的制备及形貌、红外、光致发光研究

以N₂/H₂、N₂或NH₃为载气,利用碳辅助化学气相沉积法,常压1140℃下在石英衬底上制备了大量直径为20—300 nm,长数百微米的非晶SiO_x纳米线.制备得到的纳米线具有高度定向生长的特性.利用透射电子显微镜、扫描电子显微镜及电子能谱对SiO_x纳米线的形貌及组分进行了分析,Si与O原子之比为1∶18.傅里叶红外吸收谱显示了非晶氧化硅的三个特征峰（482,806和1095 cm^-1）及1132 cm^-1无序氧化硅结构的强吸收峰.SiO_x纳米线光致发光光谱（PL）在440 nm（283 eV）处具有较强的荧光峰;N₂为载气生长的SiO_x纳米线的PL峰强比NH₃为载气生长的SiO_x纳米线峰强大四个数量级. 关键词： x纳米线')" href="#">SiO_x纳米线 碳辅助化学气相沉积法 傅里叶红外吸收 光致发光     

Growth and properties of wide spectral white light emitting diodes

Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system. Three quantum wells with blue-light-emitting, green-light-emitting and red-light-emitting structures were grown according to the design. The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells. The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region. The room temperature photoluminescence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained. The light spectrum covers 400-700 nm, which is almost the whole visible light spectrum.     

Multipeak-structured photoluminescence mechanisms of as-prepared and oxidized Si nanoporous pillar arrays

Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O₂ atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.     

邻菲咯啉铜微纳米棒的制备及其影响因素研究

以五水硫酸铜和1,10-邻菲咯啉为原料,采用液相沉淀法制备邻菲咯啉铜(Ⅱ)微纳米棒,研究 pH 值和温度对产物形貌和尺寸的影响.通过 XRD、SEM、UV-Vis、FT-IR、元素分析和荧光光谱表征产物的结构与性能.结果表明,硫酸铜溶液的 pH 值显著影响室温时反应产物的物相和形貌.当起始 pH 值为 2.0和5.0时,分别生成了微米级的花状和长片状的单斜品系[Cu(phen)(H2O)2]·SO4;当 pH 值上升至 9.0和11.0时,分别生成了平均直径172 nm 和253 nm 的[Cu(phen)(OH)]2SO4·5H2O 棒状结构.在 pH 值为9.0条件下,棒状产物的直径随着反应温度的降低而减小,4℃时可获得平均直径为87 nm 的纳米棒.此外,片状[Cu(phen)(H2O)2]·SO4 的荧光光谱相对于纳米棒状[Cu(phen)(OH)]2SO4·5H2O 出现蓝移和发射增强现象.     

化学气相沉积法制备ZnSe微球

采用化学气相沉积方法,以MiSe2为前驱体,制备出尺寸均匀、分散度好的ZnSe微球.通过XRD、EDS和FESEM对产物的结构、成分和形貌进行了测试与表征.结果表明:所得ZnSe微球为立方闪锌矿结构,直径在800～1000 nm之间,具有近于理想的化学计量比.变温光致发光谱研究表明,ZnSe微球在550～640 nm处存在与Zn空位及杂质能级相关的发光峰.     

YVO4∶Eu3+纳米荧光粉的水热法合成及其光致发光性能的研究

以NaVO3,Y2O3,Eu2O3为原料,采用水热法在不同pH值(pH =6.5,8.2,10.1,13)条件下合成了具有不同形貌与颗粒尺寸的YVO4∶ Eu3+纳米荧光粉.利用XRD,TEM和荧光光谱仪对样品的结构、形貌和光致发光性能进行了研究.实验结果表明:所合成样品均为具有四方锆石结构的YVO4∶Eu3+纳米晶,溶液pH值对所合成样品的形貌与颗粒大小均有明显影响,而且光致发光性能与样品的形貌有关,YVO4∶Eu3棒状纳米荧光粉因具有较高结晶度而具有较高的荧光强度.     

水热法制备ZnS∶Cu,Al纳米X射线发光粉及其光谱特性

采用水热法低温(200 ℃)处理12 h直接制备ZnS∶Cu, Al纳米晶, 并探讨其光致(PL)和X射线激发(XEL)光谱特性及后续退火处理的影响. XRD和TEM分析表明, 水热法直接制备的ZnS∶Cu, Al粒径约为15 nm, 尺寸分布窄, 分散性好, 具有纯立方相的球形结构. 其PL和XEL光谱均为宽带谱, n(Cu)/n(Zn)=3×10^-4和n(Cu)/n(Al)= 0.5时PL和XEL光谱强度最大, XEL峰值在470 nm处. 在此条件下, 水热处理3 h直接合成的纳米晶在氩气保护下于800 ℃退火1 h后样品的XEL发光进一步增强. XEL光谱强度约是退火前样品的8倍, 此时峰值波长在520 nm, 团聚形成径为200～500 nm的类球形六方相结构. 发光强度增强, 但粒径很小, 对提高成像系统分辨率非常有意义. 通过比较样品的XEL和PL光谱, 讨论了XEL和PL光谱的发光机理和激发机制及退火对其特性的影响.