Fluorescence quantum efficiency of CdSe/ZnS quantum dots functionalized with amine or carboxyl groups

The thermo-optical parameters of cadmium selenide/zinc sulfide (CdSe/ZnS) core-shell quantum dots (QDs) suspended in aqueous solutions were measured using a Thermal Lens (TL) technique. TL transient measurements were performed using the mode-mismatched dual-beam (excitation and probe) configuration. A He-Ne laser at lambda(p) = 632.8 nm was used as the probe beam, and an Ar+ laser (at lambda(e) = 514.5 nm) was used as the excitation beam to study the effect of the core sizes (2-4 nm) of CdSe/ZnS nanocrystals functionalized with amine (R-NH2) or carboxyl (R-COOH) groups. The average values of the thermal diffusivity D = (1.48 +/- 0.06) 9 10(-3) cm(2)/s obtained for QDs samples are in good agreement with the pure water solvent result. The fraction thermal load (phi) and radiative quantum efficiencies (eta) of the functionalized CdSe/ZnS QDs were determined and compared with non-functionalized CdSe/ZnSQDs. The obtained eta values for non-functionalized CdSe/ZnS are slightly higher than those for the QDs functionalized with amine or carboxyl groups.