Effects of poly-N-isopropylacrylamide on fluorescence properties of CdS/Cd(OH)2 nanoparticles in water

Effects of poly-N-isopropylacrylamide (polyNIPAM) on the fluorescence properties of core/shell type CdS/Cd(OH)2 nanoparticles (NPs) have been studied in water. The NPs show strong fluorescence at low temperature, but the intensity decreases at >32 °C, allowing an on–off fluorescence switching by temperature. The heat-induced fluorescence quenching is due to the phase transition of polyNIPAM from coil to globule state. The NPs in solution associate with polyNIPAM via a hydrogen bonding interaction. Upon heating the solution, the NPs are confined within the polymer matrices during polymer aggregation. The aggregated polymer suppresses the incident absorption of inner NPs, resulting in fluorescence quenching. A notable feature obtained by the polyNIPAM addition is the enhanced thermal stability of NPs. The NPs confined within the polymer matrices are separated from each other. This therefore suppresses the coalescence of NPs, resulting in high stability even at high temperature.