Strong two-photon absorption of CuInS2/ZnS quantum dots with various Cu/In ratios

The CuInS2 (CIS)/ZnS quantum dot (QD) samples with various Cu/In ratios have been synthesized and characterized. The effective two-photon absorption (TPA) coefficients for a series of CIS/ZnS core/shell QDs were measured by Z-scan technique. It was found that the TPA coefficients and quantum yields (QYs) of these samples were enhanced dramatically as the Cu/In ratio was decreased, and saturated at a Cu/In ratio of 1/4. A QY as high as 79% was achieved at a Cu/In ratio of 1/4. The effects of surface states and photon-induced dipole moment were demonstrated to be responsible for the optical nonlinear features of the colloidal core/shell QDs.