Thermosensitive luminescent gold quantum dots: Synthesis, optical characterization and applications

Abstract

This chapter reviews the synthesis and optical characterization of gold quantum dots (QDs) as well as their potential applications. In addition, a one-pot synthesis for the preparation of luminescent gold QDs is presented, without expensive ligands involved and without the need for processing at high temperatures. The influence of the alkyl chain length of the surface ligands (alkyl thiols), the concentration of tetrachloroauric ions and the influence of preparation temperature on the optical properties of the gold QDs have been investigated. The fabrication of different gold QD polymer nanocomposites for use as optical security devices is presented. For example, cellulose triacetate gold QD nanocomposites have been synthesized and integrated into paper. Furthermore, acrylic gold QD nanocomposites with holographic structures have been fabricated by softlithography. It has been found that the synthesized gold QDs show thermosensitive photoluminescence. An increase of pho toluminescence quantum yield was observed, when cooling the gold QD solutions or nanocomposites, whereas the photoluminescence quantum yield decreased, when heating the solutions or nanocomposites. The return to room temperature after cooling or heating leads to a relaxation of photoluminescence quantum yield to their initial room temperature values. Heating and cooling cycles have been repeated several times and the photoluminescence quenching/enhancement processes proved to be fully reversible. Investigations of gold QDs in solution showed highest photoluminescence quantum yield of 17 % at room temperature. This value could be improved to 29 % by cooling down the gold QD solution to-7 °C. The synthesized thermosensitive luminescent gold QDs are promising candidates for optoelectronic devices, medical imaging, sensing and security labels