摘要
纳米材料由于具有与体相材料不同的新异物理与化学性质,在可再生能源、环保等领域具有特殊的应用。本文报道了采用溶剂热法在180-200℃制备出三元黄铜矿结构CuFeS2纳米颗粒和基于气-液-固(Vapor-Liquid-Solid)生长机理的气相法制备ZnCdSe合金纳米线的结果。利用扫描电镜、高分辨透射电子显微镜、X射线衍射仪对两种样品的形貌与晶体结构进行了细致的表征,证明所制备的CuFeS2纳米颗粒和ZnCdSe合金纳米线都是纯度很高的单相。同时还报道了反应条件对CuFeS2纳米材料形貌的控制作用,改变ZnSe与CdSe两种反应物的比例和反应时间,可以制备出尺寸不同的ZnCdSe纳米线,并且对于两种样品的生长机理进行了分析。利用紫外-可见光吸收光谱仪、近场扫描光学显微镜、荧光光谱仪对合成三元半导体材料进行光学性质的研究。结果发现,CuFeS2纳米颗粒的带隙由于粒径很小发生了一定的改变,比以前报道的(0.6eV)要略大(0.673 eV),而且纳米颗粒形状的CuFeS2在325nm激光的作用下发出漂亮的蓝色光,这是由于在CuFeS2中存在Cu+发生了3Eg→1A1g的跃迁现象所致,与所得到的PL谱的峰值对应。而对于合金ZnCdSe纳米线,根据PL谱的结果,利用维加德定律(Vegard law)分别计算出各个元素在化合物中的组分,并且实现了波长在521nm-717nm之间的发光可调谐性。当合金中Zn的含量较多时,PL峰值的变化不是很明显,出现在521nm-533nm之间,而且存在着很强的缺陷发光现象,当Cd的含量增加后,没有出现缺陷发光,发生此现象的原因是由于ZnSe的缺陷能级一般包括Zn离子和Se离子的空位、间隙离子或者其他的杂质缺陷,Se空位形成一种双施主能级,而Zn空位是一种受主型缺陷,新生长的ZnSe晶体,发光层中必然有Zn空位,发光峰是导带电子与Zn空位所俘获空穴的复合发光。具有光学性质可调谐的ZnCdSe三元半导体纳米线在纳米激光器方面有很大的应用价值。
Nano-materials with novel physical and chemical properties different from bulk materials, become more important in the fields, such as renewable energy, environmental protection and so on. In this article, the synthesis of ternary CuFeS2 nanoparticles with chalcopyrite structure which viaed the solventothermal reaction route at 180-200℃, and the growth of ZnCdSe alloy nanowires with hexagonal structure which viaed gas phase method with Vapor-Liquid-Solid (VLS) mechanism are reported. The morphology and structure of two nanomaterials were characterized by scanning electron microscopy, high-resolution transmission electron microscope and X-ray diffraction. The as-prepared CuFeS2 nanoparticles and alloy ZnCdSe nanowires are all high phase-purity. The morphology of CuFeS2 nanoparticles were varied significantly according to reaction conditions. The diameter of ZnCdSe nanowires was also affected by variation of ratio of two reactants of ingredients. The optical properties of the CuFeS2 nanoparticles and ZnCdSe nanowires have been studied by UV-visible absorption spectroscopy, near-field scanning optical microscopy, fluorescence spectroscopy. The band gap of CuFeS2 nanoparticles has been detected to be 0.673 eV, slightly larger than previously reported (0.6 eV). The wider gap possibly resulted from the nano-size effect. The observed blue emission of CuFeS2 nanoparticles irradiated by the 325nm laser beam was originated from the inner shell transition of 3Eg→1A1g in the Cu+of CuFeS2 and coincided to the PL image. For alloy ZnCdSe nanowires, the each component in the compound was calculated by Vegard Law based on the PL spectrum. The tunable wavelength of the emission light between the 521nm-717nm is achived in this study. A strong defect luminescence was found as increase of Zn content in the alloy ZnCdSe nanowires, while the PL peak between 521nm-533nm did not change obviously. Increase of the Cd content did not result in the defect luminescence. The reasons for this phenomenon may due to the defect levels in ZnSe generally include Zn ions and Se ion vacancies, interstitial impurity ions or other defects,Se vacancy to form a double-donor level, while the Zn vacancy is an acceptor-type defects The new growth of ZnSe crystals, light-emitting layer is bound to Zn vacancies, emission peak is Zn vacancy conduction band electron and hole recombination by trapping. The ternary semiconductor nanowires with the tunable optical properties may have potential application in the nano-lasers technology.
引文
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