19 September 2005: Scaling up quantum dot production

US researchers have raised the possibility of scaling up quantum dot production by developing a cut-price method of synthesis. 

Large-scale manufacture of the nanometre-scale fluorescent dots has been held back by the high cost of the solvents used during synthesis. Quantum dots currently cost more than $2000 (?1100) per gram.

Scientists at Rice University, Houston, US, have replaced the solvents necessary, such as octadecene (ODE), with heat-transfer fluids, the kind used in chemical plant processing units to transfer heat. 

ODE is one of the least expensive solvents used in quantum dot manufacture, but it contributes 90 per cent of the raw materials costs for producing a quantum dot. In comparison, heat-transfer fluids cost about seven times less than ODE. Replacing ODE with a heat-transfer fluid called Dowtherm A reduced the overall cost of materials by approximately 80 per cent. 

Quantum dots are a valuable commodity: tiny semiconducting crystals with potential for applications such as bioimaging, colour displays and lasers. Cadmium selenide dots absorb high-energy photons of ultraviolet and re-emit visible light photons. Different sizes of dots glow different colours right through the spectrum from red to blue as the crystals get smaller.

The researchers not only synthesised the dots, but also devised a way of predicting their size. Nikos Mantzaris, assistant professor of chemical and biomolecular engineering at Rice University, Houston, US, developed a mathematical modelling approach that predicts particle size and growth behaviour using the solvent’s viscosity, surface free energy and solubility of bulk cadmium selenide powder. Fiona Salvage