FRET from core and core-shell quantum dots to laser dye: A comparative investigation

A remarkable progress has been made in the recent past in fluorescence resonance energy transfer (FRET) studies using semiconductor quantum dots (QDs) and application of QD-based FRET to probe specific biological processes. Here we report a systematic study of FRET from CdSe (core) and CdSe/ZnS (core-shell) quantum dots (donor) to sulforhodamine B (SRB) dye (acceptor) using steadystate and time resolved fluorescence spectroscopy. The results obtained demonstrate occurrence of efficient energy transfer from QDs to dye and are discussed in the light of the Förster theory. Time resolved decay curves of QDs obtained in the presence and absence of sulforhodamine B dye are analyzed. The values of spectral overlap, Förster distance and transfer efficiency have been determined using steady-state and time-resolved fluorescence spectroscopic data. It is observed that the transfer efficiency does not follow a linear dependence on spectral overlap integral and quantum yield of donor as predicted by the Förster theory for molecules. This nonlinear dependence of transfer efficiency on overlap integral as well as quantum yield of donor; and the possibility of surface states and defect states of QDs causing this are discussed.