A Ligand Exchange Route to Highly Luminescent Surface-Functionalized ZnS Nanoparticles and Their Transparent Polymer Nanocomposites

A facile ligand exchange approach for surface-functionalized ZnS nanoparticles (NPs) with 5-(2-methacryloylethyloxymethyl)-8-quinolinol (MQ) is described. The MQ-ZnS NPs, with a cubic crystal structure, have the same diameter as ZnS NPs without MQ about 3.0 nm. The MQ-ZnS NPs exhibit strong fluorescence emission at about 500 nm and a high photoluminescence (PL) quantum yield (QY), up to 40%, with a decreasing ratio of MQ to ZnS NPs. The PL decay study reveals that the lifetimes of the different MQ-ZnS NPs with a single exponential decay are in the nanosecond time domain for emission at about 500 nm, which is obviously different from that of ZnS NPs with a biexponential decay for defect-state emission at 420 nm. The functionalized MQ-ZnS NPs are successfully incorporated into the polymer matrix by in situ bulk polymerization to fabricate transparent bulk nanocomposites with good thermal stability and processability. Transmission electron microscopy results show that the NPs are uniformly dispersed in the polymer matrix without aggregation. The good PL properties of MQ-ZnS NPs are preserved in the bulk nanocomposites. It is observed that the nanocomposites have red-shifted excitation and emission wavelengths compared with those of both the polymer matrix and MQ-ZnS NPs, possibly because of the cooperative interaction between MQ-ZnS NPs and the polymer matrix with blue emission.