Preparation And Unique Properties Of Semiconductor Quantum Dot Fluids

Semiconductor quantum dots (Qdots) have the properties of broadband absorption with narrow, symmetric photoluminescence spectra, high quantum yield, size-dependent spectrum, large effective Stokes shifts, high resistance to photobleaching and exceptional photochemical stability. These properties make Qdots have great advantages in biological labeling, optical sensing, nano-photovoltaic devices and optical coding compared to organic fluorophore.As a solid, the inorganic Qdots are hard to integrate with organic polymers at the interface when they are compound. In this dissertation, we successfully functionalized the Qdots and then prepared solvent-free Qdot ionic liquid. The structures and properties of Qdot ionic liquid were characterized by UV-vis absorption spectra (UV-vis), Photoluminescence spectra (PL), Transmission Electron Microscopy (TEM), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and Fourier-transform Infrared (FT-IR).The Cadmium Selenium Qdots were prepared by injecting TBP-Se precursor into Cd-SA stock solutions at high temperature. The core/shell Qdots with different emission wavelength, high quantum yield and chemical stability were prepared by growing a certain layer and different types of shell materials. The technical parameter and condition in the synthesis of core/shell Qdots were systematically investigated. The oil-soluble Qdots were then functionalized with 3-mercaptopropionic acid (MPA), degraded gelatin and hyperbranched polyethylenimine (PEI), respectively. Water-soluble Qdots with different function groups and charges were prepared and the process technics of surface modification for Qdots was optimized. The optical properties and microstructures of Qdots after modification were well discussed by TEM,UV-vis,PL,FTIR,EDX and other characterization.The technology of phase transfer catalysis was introduced into the preparation of Qdot ionic liquid. The cationic quaternary ammonium salt with PEG chain (NPEQ) was chosed as phase-transfer reagent and was coated on the surface of anionic stabilized water-soluble Qdots through ion exchange. The solvent-free oil-soluble Qdot ionic liquid with monodispersity and high quantum yield was prepared. The rheological results of Qdot ionic liquid showed that the loss modulus (G") was higher than the storage modulus (G') throughout the measured temperature range. The viscosity of Qdot ionic liquid was as low as 0.08 Pa-s at 80℃which demonstrated good fluidity. TGA showed that the Qdot ionic liquid was virtually solvent-free with organic content of 88% w/w and decomposition temperature of about 200℃which suggested high thermal stability. The NPEQ functionalized Qdots was well soluble in nonpolar solvents and insoluble in polar solvents Amphiphilic polyoxyethylene octadecylamine was chosed to prepare amphiphilic Qdot ionic liquid by acid-base reaction. The nanocrystals were dispersed as random linear manner on the copper grid with no aggregation and it has well crystalline with high quantum yield. The amphiphilic Qdot ionic liquid has good solubility in different polar solvents.