Synthesis Of Doped Quantum Dots And Investigation Of Relative Mechanisms

Doped nanocrystals (d-dots) have recently become active mainstreammaterials in the field of materials chemistry and physics because of theirunique optical, electronic, and magnetic properties. D-dots with efficientemission can not only retain the good optical properties of intrinsic QDs, butalso possess additional advantages such as larger Stokes shift to avoidself-absorption/energy transfer, greatly enhanced thermal and chemicalstability, and longer excited state lifetime. And d-dots have stimulated a greatdeal of research interest owing to it possess considerable applications inbiomedical labeling, cellular effectors and reporters, light emitting devices,lasers, and sensors. Some highly emissive d-dots have been synthesized bychoosing the Ⅱ-Ⅵ semiconductorsas host materials for Cu2+or Mn2+. Wehave discussed the preparation methods and the mechanism of luminous. Thedetailed contents are as follows:1、A new sulfur precursor with a highly reactive chemical nature wasprepared with S powder and NaBH4at the high temperature of180℃in aclosed autoclave and made it possible to carry out the synthesis of high qualitymetal sulfide nanocrystals （NCs） with diverse composition and structure.Using this new sulfur source, we demonstrated aqueous synthesis of colloidalCu doped ZnCdS NCs (d-dots) with pure, color tunable photoluminescence(PL) in a wide spectral range (from517to650nm) based on the ‘co-nucleation doping’ strategy. The influences of the various experimentalvariables, including Cd/Zn ratio, Cu-doping concentration, pH value andamount of mercaptopropionic acid (MPA), on the optical properties ofCu-doped ZnCdS NCs were systematically investigated. Furthermore, highlyefficient and stable dopant emission from Cu:ZnCdS/ZnS core/shell d-dotswith PL quantum yield as high as40%was achieved by the deposition of aZnS shell around the bare Cu:ZnCdS cores; this is the highest reported to datefor aqueous doped NCs. The optical properties and structure of the d-dotswere characterized by UV–vis absorption spectra, PL spectra, x-rayphotoelectron spectroscopy, powder x-ray diffraction, and transmissionelectron microscopy. The experimental results indicated that this facilesynthesis route would provide a versatile approach for the preparation of otherwater-soluble sulfide d-dots.2、Water-soluble, highly emissive, color-tunable, and stable Cu:ZnSeS/ZnScore/shell d-dots with pure dopant emission have been synthesized through asimple aqueous synthetic route. The influence of various experimentalvariables, including introduction of chloride ions, amount of MPA, pH valueand Cu-doping concentration, on the optical properties of Cu dopant emissionhave been systematically investigated. Through epitaxial growth of a ZnSshell on Cu:ZnSeS cores, the fabricated Cu:ZnSeS/ZnS d-dots exhibit a highPL QY of up to40%, which is the highest ever reported for any type ofwater-soluble Cu-doped selenide-based II–VI semiconductor NCs. Moreover, the serious photostability problem of Cu-based d-dots in the presence of airand light is solved and the quenching of the excitonic emission is suppressedas well. The stable testing of these highly luminescent d-dots shows that theCu:ZnSeS/ZnS d-dots have better photostability and preserve more than～90%of the initial intensity in the presence of air and light30days later. Thisnew class of green emissive material shows their potential applications inbiolabeling, bioimaging, and light emitting devices.3、High-quality Mn:ZnS d-dots with photoluminescence quantum yield of50–70%have been synthesized based on nucleation-doping strategy bychoosing1-dodecanethiol (DDT) as the capping ligand. Controlling thegrowth of small-sized MnS core nanoclusters was successfully achieved bychanging the injection temperature of sulfur precursor, the growth time ofMnS nuclei, and the amount of DDT. Furthermore, MnS/ZnS core/shell d-dotswith a diffusion layer at the interface between the MnS core and the ZnS shellwere fabricated through an overcoating of the ZnS shell layer on thepresynthesized MnS core nanoclusters. The resulting monodisperse d-dotsexhibited spherical shape with a zinc-blende crystal structure. The criticaltemperature for lattice diffusion of Mn ions in the ZnS host lattice wasdetermined to be about260℃by annealing the presynthesized and purifiedMn:ZnS d-dots.