Precise Controlling Of Hetero-nanostructures, Doping And Self-assembly Of â…¡-â…¥ Semiconductor Nanocrystals And Their Optoelectronic Properties Research

â…¡-â…¥ semiconductor quantum dots and their hybrid nanostructures to noble metalhave attracted broad attentions in fundamental science and technological applications due totheir unique optical and electrical properties, including visible light harvest, solar energyconversion and transfer, enhanced luminescence, LED et.al. In this paper, by chemicalthermodynamic directed cation exchange reaction reported by Zhang etc, the precisecontrol of Au/CdX hetero-nanocrystals, CdX Qds doping, and their large-scale self-assembly are realized. Their optoelectronic properties, including efficient photocatalytichydrogen evolution, doped luminescence and p/n electronic impurities properties have beenstudied.1. The structural symmetries of heterostructures Au-CdX （X represents S, Se, Te）which consisting of gold nanoparticle core and monocrystalline semiconductor shell havebeen controlled well. By controlling the crystallinity of the Ag₂X shell and reactiontemperature, the morphologies evolution of Au/CdX hetero-nanocrystals, namely fromisotropic core/shell to anisotropic heterodimer structures have been realized. By UV-Visabsorption spectra and finite difference time domain （FDTD） simulation, it is found that theAu-CdX heterostructures have good visible light harvesting because of strong Plasmon-exction coupling in these hybrid nanostructures. The different degrees of phase separationof Au-CdS heterostructures lead to different photocatalytic hydrogen evolutionperformances. It is found that by the mechanism of SPR enhanced electron-hole separationand collection, the heterodimer structured Au-CdS nanocrystals has better H2evolutionactivity, that manifest a dramatic photoactivity enhancement of730times (up to7.3mmol·h^-1·g^-1) than Au@CdS core/shell nanocrystals.2. Monovalent doped CdS, CdSe, CdS_xSe_1-xQds with good monodispersity wereprepared successfully by a new, facile and versatile low temperature out-to-in cationexchange method. It was confirmed that Ag⁺and Cu⁺occupy the position of Cd atoms inCdS lattice to be substitutional doping by XANES, EXAFS and XPS analysis. Futhermore,the doping concentration of Ag⁺and Cu⁺could be tailored by controlling of the out-to-incation exchange reaction. As a result, the exciton related absorption and PL emissionsbecame very weak or even disappear. There is only strong doped dominant red fluorescenceat about640nm with large Stokes shift0.77eV. The absolute quantum yields of Ag⁺andCu⁺doped CdS reached42.0%and28.9%respectively. The domiant fluorescence peak at 640nm exhibits ultralong decay behavior. The640nm kinetic curve fitted well with a twoexponential model and results in two lifetimes of0.2μs and1.3μs. By substitutional Ag⁺and Cu⁺doping, the n-type and p-type CdS semiconductor Qds were prepared successfully.3. The large-scale superlettices of Au@Ag₂S hetero-nancrystals and doped Cu2S,CdS, CdSe, CdSSe Qds have been realized easily. The high monodispersity of Qds and theappropriate Van der Waal force of capping ligands enable the self-assembly of Qds intosuperlattice. By low reaction temperature, short reaction time, the CdX Qds couldself-assemle into bulk sized superlattice on rigid/flexible substrates by hexagonal closepacking （hcp） order easily. The UV-Vis absorption spectra of CdS, CdSSe films exhibitefficient solar absorption and the films have high luminescent fluorescence under365nmultraviolet lamp irradiation. This effective bottom-up self-assembly laid the foundation fortheir large-area film applications, such as LED, p/n hetero-junction Qds solar cell and otherelectronic devices.