Colloidal Synthesis of Luminescent Quantum Dots in Macadamia Oil
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Colloidal Synthesis of Luminescent Quantum Dots in Macadamia Oil
Menglu Li, Weng Leong Chan and Hannah C. Gardner Biomedical Engineering Group, School of Engineering, Nanyang Polytechnic, 180 Ang Mo Kio Ave 8, Singapore 569830.
ABSTRACT Semiconductor nanocrystals or quantum dots are becoming increasingly popular in research fields as wide ranging as cancer therapies, solar energy and disease detection. Colloidal synthesis provides a low-cost method of producing high quality quantum dots with narrow size distributions. The controllable nature of colloidal synthesis allows researchers to design the size, shape and surface functionalization of the resulting particles. Here we investigate a simple low temperature method to produce CdSe quantum dots. The quantum dots were grown in solution by dissolving the CdO precursor in a mixture of macadamia oil, and oleic acid. Elemental Se was heated separately before the two mixtures were combined under an inert atmosphere. The injection temperature, reaction temperature and oleic acid concentration were all varied. Optical absorption and photoluminescence spectroscopies showed the size of the quantum dots increased with time, temperature and oleic acid concentration. Dynamic light scattering has shown the hydrodynamic particle size to range from 7 to 22nm and the samples for up to 6 months.
INTRODUCTION For use in any application nanoparticles need to be of a high quality. Desirable properties in a nanoparticle are high stability, high crystallinity and high quantum yield. The ability to select the size of nanoparticles and ensure a narrow size distribution is also important along with the option of controlling the surface properties of the particle. Colloidal chemical synthesis provides a method of reaching all these targets. The desire to produce nanoparticles with the properties outlined has led to a vast amount of research and several synthetic techniques. Nanoparticles can be produced from both group II-VI and group III-V compounds and the wavelength of emission can be tuned from the ultra violet to the near infra-red1.
Prior to 1993 nanoparticles were mainly synthesised via aqueous route2 but the nanoparticles produced had poor crystallinity and low uniformity in both size and shape having a root mean square greater than 15%3,4. However, in 1993 and 1994 Murray et al5 and Bowen Katari et al6 developed highly cited organometallic syntheses of cadmium chalcogenides. Trioctylphosphine (TOP) or tributylphosphine and trioctylphosphine oxide were used as highboiling coordinating solvents. Recently Sapra et al7 developed a novel synthesis route using olive oil as the co-ordinating solvent. This eliminates the need for the toxic TOP.
EXPERIMENTAL DETAILS Chemicals: Cadmium oxide 99.5%, selenium 99.5%, oleic acid 99% and acetone ACS reagent grade were obtained from Sigma Aldrich whilst analytical reagent grade toluene was obtained from Fisher; all were used as received. Macadamia oil was purchased from a local supermarket (Fairprice macadamia cold pressed oil 100% pure) and u
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