Third-order nonlinear optical properties of CdSe/ZnS/CdSe core-shell-shell quantum dots

We report the synthesis of CdSe, CdSe/ZnS core-shell and CdSe/ZnS/CdSe core-shell-shell quantum dots (QDs) and their optical properties. These core-shell QDs are characterized by using TEM, absorbance and photo-luminescence emission. The absorption spectra of QDs reveals that blue and red shift observed as shells capped onto the core. The luminescence spectra of core-shell QDs have shown two bands, one is due to the coupling of core and shell and the second band is because of defect states. From TEM, the size of the core and shell are found. Nonlinear optical properties such as nonlinear absorption and nonlinear refraction of the QDs are investigated by the Z-scan technique using 532 nm with picosecond laser. The nonlinear absorption of QDs show reverse saturable absorption due to two-photon absorption and have large nonlinear refractive indexes. CdSe/ZnS and CdSe/ZnS/CdSe core-shell QDs have high third-order susceptibility about on order of 10(-12) esu. The large optical nonlinearities allow these QDs to be one kind of candidate materials for fluorescence label, bioimaging, optical limiting and all-optical switching of photonics.