Anomalous Stokes Shift of Colloidal Quantum Dots

We report an anomalous Stokes shift effect (SSE) observed in colloidal solutions containing down-shifting Carbon quantum dots (CQDs) of different sizes that is expected to have a positive influence on the power conversion efficiency of photovoltaic structures. Specifically, with an excitation wavelength of 390 nm, individual colloidal solutions of CQDs whose diameter was determined by the applied current during synthesis, exhibited photoluminescent (PL) emission wavelength peaks centered at 420 nm. However, the colloidal solution comprising the mixture of all the previously synthesized CQDs of different diameters was observed to have an anomalous PL Stokes shift centered at 515 nm Furthermore, the aforementioned anomalous SSE was also observed in CdTe QDs when added to the CQD mixed-solution (CMS). Thus, whereas a mixture of CdTe QDs of different sizes, exhibited a down-shifted photoluminescence centered at 555 nm, the peak was observed to have an anomalous Stokes shift centered at 580 nm when combined with the CMS. Quantum dot characterization included crystal structure analysis as well as photon absorption and photoluminescence wavelengths.