Synthesis And Optical Characterization Of MInS2 Semiconductor Nanocrystals And Their Composite Structures

Semiconductor nanocrystals have unique optical and electrical properties, due to quantum size effect and dielectric confinement effect. In comparison with dyes, semiconductor nanocrystals have good photo stability and negligible photobleaching. The synthesis and application ofâ… -â…¢-â…¥2 group semiconductor nanocrystals have attracted much research interests these days. In those materials, CuInS2 and AgInS2 have been focused on by researchers because of the characteristics for potential applications, which could be called MInS2 semiconductors.In this dissertation, chemical solution methods are explored to realize the functional-adjustment of semiconductor-based nanostructures and modulate novel properties, accompanied by understanding the structural and functional correlations of separate constituents. A series of cation-disordered nanosructure and tetrahedral coordination II-VI/I-III-VI2 group semiconductor composite structural unit are successfully synthesized, and their optical properties are systematically studied. Further study shows that the fluorescence properties of these controllable nanostructures have been largely enhanced or modified, or even resulting in novel functions. The summary are as follows:1. Fabrication of MInS2 semiconductor nanocrystals with different crystal structures via chemical solution methods.Monodispersed metastable cubic AgInS2 nanocrystals with an average size of around 2.5 nm are obtained via a solution-phase reaction. In contrast with the usual chalcopyrite and orthorhombic phase, Ag+and In3+cations in metastable cubic AgInS2 are randomly coordinated by four S2-anions. A phase transition from cation-disordered cubic to orthorhombic AgInS2 occurs with the increased reaction temperature or elongated reaction time. The photoluminescence quantum yield of cation-disordered cubic AgInS2 nanocrystals could reach 10% at room temperature, which is much higher than that of orthorhombic AgInS2 nanocrystals obtained via a similar approach. Cubic and hexagonal structural CuInS2 nanocrystals are synthesized via a similar method, and characterized by HRTEM, XRD, UV-Vis and PL, which offers structural bases to the research of tetrahedral coordinationâ…¡-â…¥/â… -â…¢-â…¥2 group semiconductor composite nanostructures.2. Fabrication of tetrahedral coordinationâ…¡-â…¥/â… -â…¢-â…¥2 group semiconductor composite nanostructures with modified fluorescence properties.â… -â…¢-â…¥2 group semiconductors have complex energy band structures, such as CuInS2 and AgInS2 belong to narrow band gap semiconductors. According to the close comparability of crystal structures and the differences of energy band gaps among CuInS2, AgInS2 and ZnS semiconductor nanocrystals, size controllable ZnS/AgInS2, ZnS/CuInS2 solid solution and heterostructural nanocrystals with modified energy band gaps are synthesized and characterized by spectrum functions. Because these semiconducors have common tetrahedral coordination structures, similar crystal lattice parameters and different energy band structures, it is possible to realize that the absorption and flourescence spectra which match the modified band gaps are enhanced and adjusted in the range of visible light section.In conclusion, this dissertation via chemical solution synthesis methods combines the structural control and characteristic promotion of nanocrystals, which could provide applicable materials in many fields, such as fluorescence labeling, life detecting, nanostructural heterojunction solar cell, etc.