Temperature-modulated photoluminescence of quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) grafted with thermoresponsive poly(N-isopropylacrylamide) chains have been prepared. As the temperature increases, PNIPAM chains shrink and aggregate so that the QDs exhibit enhanced fluorescence emission. At a temperature around the lower critical solution temperature (LCST) of PNIPAM, the fluorescence exhibits a maximum intensity. Our experiments reveal that the fluorescence emission is determined by the interactions between QDs as a function of the interdot distance. The optical interdot distance for the maximum luminescence intensity is similar to 10 nm. The chain length of PNIPAM also has an effect on the luminescence. Short PNIPAM chains are difficult to associate, leading to a large interdot distance. so that the luminescence intensity changes slightly with temperature.