Radiative exciton recombination dynamics in QD-tagged polystyrene microspheres

Fluorescent polystyrene microspheres are prepared by the incorporation of fluorescent CdSe/CdS core/shell semiconductor nanocrystals (quantum dots, QDs) using the emulsification/solvent evaporation method. The radiative exciton recombination dynamics is investigated by nanosecond time-resolved fluorescence spectroscopy at ambient conditions. The time constants of fast and slow fluorescence decay in QDs, dispersed in toluene, were 3.5 and 17.8 ns, respectively. For the QD-tagged microspheres, the time constants of fast and slow processes were similar to 2-3 and similar to 11-12 ns, respectively, and did not depend significantly on the QD-content of the microspheres. The fast decay component could be attributed to the recombination of delocalized exciton in the internal core states, and the slow component was attributed to the localized exciton in the surface states. It was found that the ratio of amplitudes of the fast and slow processes also changed after incorporation of QDs in microspheres. The observed differences in fluorescence decay between non-entrapped QDs and QD-tagged microspheres were probably due to energy transfer between the nanocrystals, which were in close proximity inside the microspheres. The obtained fluorescent QD-tagged microspheres are characterized by the other methods as well, which makes them of value for various applications as optical materials.