Atomically Precise Doping In An Isolated Coreless Supertetrahedral Nanocluster For Tunable Photoelectric And Photoluminescent Properties

Metal chalcogenide supertetrahedral nanoclusters are the aggregates of tens or hundreds of covalent-bonded atoms and structurally regarded as precise fragments of the well-known cubic zinc sulfide semiconductors, which formally bridge the size gap between colloidal nano-scaled quantum dots and small molecular species in solution. Compared with traditional II-VI type of bulk semiconductors, open-framework metal chalcogenide semiconductors based on supertetrahedral nanocluster possess prominent superiorities. During the last decade, such nanoclusters have experienced a rapid development in the regulation on both composition ans size. However, introducing specific dopants to desired positions in such nanoclusters at atomic scale to realize their ordered distribution remains a big challenge. A better understanding of doped structures will make it possible to establish structure/activity relationships for materials design from a theoretical perspective rather than trial-and-error experimental approaches. This thesis focuses on the preparation of novel metal chalcogenide supertetrahedral nanoclusters, post modification through atomicially precise doping strategy and regulation on optical or photoelectric properties of those doped semicondutors. The main works are summarized as follows:(1) We applied a two-step strategy to realize ordered distribution of multiple components in one nanocluster with a crystallographically ordered core/shell structure. A semiconductor material(denoted as ISC-10-Cd In S) composed of coreless supertetrahedral chalcogenide Cd-In-S nanocluster was prepared through the superbase-involved solvothermal reaction, and then a copper ion was inserted at its void core site through a diffusion process to form a Cu-Cd-In-S quaternary nanocluster. This intriguing molecular cluster with mono-copper core and Cd-In shell exhibits enhanced visible-light-responsive optical and photoelectric properties compared to the parent nanocluster.(2) A two-step synthesis strategy was applied to realize an atomically precise doping of Mn2+ ion into the core site of Cd-In-S nanoclusters, and to achieve uniform distribution of Mn2+ dopants in the crystal lattice. The photoluminescence(PL), X-ray photoelectron(XPS), as well as the electron paramagnetic resonance(EPR) spectra reveal the successful incorporation of Mn2+ ion into the core site of the nanocluster. Different from the pristine host material with weak green emission(～490 nm), the Mn2+-doped material shows a strong red emission(630 nm at room temperature and 654 nm at 30 K), which is significantly red-shifted relative to the orange emission(～585 nm) observed in traditional Mn2+-doped II-VI semiconductors. Various experiments including extensive synthetic variations and PL dynamics have been performed to probe the mechanistic aspects of synthesis process and resultant unusual structural and PL properties.(3) We clarified the possibility of semiconductor ISC-10-Cd In S as single-phase material to produce phosphor-converted white-light emission diode excited by near-UV or blue light. The emission of this single-phase phosphor varied from green to reddish orange and yellowish though simply doping the monomanganese and monocopper into the coreless Cd-In-S nanocluster, respectively. By virtue of codoping strategy, Mn2+:Cu+ codoped sample exhibited a broad yellowish white-light emission range from 450 to 800 nm, which could be also generated by simply mixing the ISC-10-Cd In S precursor and two monodoped samples in a certain ratio.