Preparation of CdSe Quantum Dots in Ionic Liquids

Abstract

Quantum dots are nanocrystalline semiconductors that have potential applications across many fields ranging from electronics (LEDs, photovoltaics) to the life sciences (fluorescent tags for biological molecules). At the nano level, the band gap is tuneable because it is a function of the size of the nanoparticle so that the optical and electronic properties can be quite easily adjusted. Traditional semiconductors lack this versatility. To date, synthesis of semiconductor quantum dots such as CdSe has been reported in volatile organic solvents at high temperatures, which are costly and could be difficult to use if significant scale up operations are required in the near future for these materials. We have investigated the use of a new class of solvent, namely ionic liquids, for the synthesis of CdSe quantum dots. Ionic liquids offer a number of significant advantages over volatile organic solvents including low vapour pressure, low flammability and exceptional chemical and thermal stability. A series of phosphonium ionic liquids with different anions were examined in this work and it was found that, with non co-ordinating anions, CdSe quantum dots with identical spectroscopic properties to those produced in organic solvents could be easily synthesized.