Doped Nanocrystals/Polymer Composites And Their Application In Luminescent Solar Concentrators

Two significant scientific problems were studied.The first one is transition-metal(TM)ions doped II-VI semiconductor nanocrystals.Here,trace tributylphosphine(TBP)was employed to initiate cation exchange and generate single crystalline II-VI NCs with trace TM ions,which was Cu ions in this paper,residue inside.The second one is preparation and characterization of doped nanocrystals and polymer composites,PMMA or PDMS,via in-situ polymerization.The properties and the applications in Luminescent Solar Concentrators was disscuessd.Firstly,the substitutional Cu(I)dopants with controllable concentrations in CdS nanocrystals were confirmed by local atom-specific fine structure from X-ray absorption near edge structure(XANES),extended X-ray absorption fine structure(EXAFS)spectroscopy,elemental analysis characterizations from X-ray photoelectron spectroscopy(XPS)and the Geometric phase analysis(GPA)measurement.The doped nanocrystals had a nice nonodispersity and uniform size distribution confirmed by the transmission electron microscop(TEM).Resolution transmission electron microscopy(HRTEM)and x-ray powder diffraction(XRD)indicated the doped nanocrystals were pure cubic phase nanocrystals.The dominant and strong Cu(I)dopant fluorescence were verified by their absorption and photoluminescence(PL)spectra,and PL lifetime.The 620 nm kinetic curve could be well fitted with a two-exponential model,resulting in two lifetimes of 0.2 ?s and 1.3 ?s,respectively.This long-lived fluorescence further supported the dominance of Cu dopant related emission.The self-quenching problem was solved here due to the large Stokes shift of 0.88 eV.Finally,the band positions and the p-type conductivities of as-prepared Cu(I)doped CdS NCs were identified by ultraviolet photoelectron spectroscopy(UPS)measurements.The high monodispersity of NCs enabled their strong film-scale self-assembly and would hasten their subsequent applications in device.Besides,several doped nanocrystals including Cu(I)doped CdS nanocrystals were composited with PMMA via in-situ polymerization.Doped nanocrystals didn't affect the structure of PMMA,as confirmed by the results of proton nuclear magnetic resonance spectra(PNMR),infared spectra(FT-IR)and thermogravimetriv(TG).The molecular weight of PMMA became bigger tested by the gel permeation chromatography(GPC).The reason of this consequence may be the ineraction of the amorphous segment in PMMA and surface ligand capped under the nanocrystals.Microscopic fluorescent spectral indicated the nanocrystals gathed with 0.1-0.5?m,and keep the well luminescence property.Ultraviolet-visible(UV-Vis)spectra,photoluminescence spectra,PL lifetime and quantum yield(QY)characterizations indicated that the compsites keep the well luminescence properties of the doped nanocrystals.Redshift happened in PL spectrua which was caused by reabsorbtion.