Direct observation of three-photon resonance in water-soluble ZnS quantum dots

Abstract

We report on large three-photon absorption (3PA) in thioglycol-capped ZnS semiconductor quantum dots (QDs) at different wavelengths with femtosecond Z-scan technique. Both the intrinsic 3PA coefficients and cross sections of the 1.3nm sized ZnS QDs in aqueous solution are nearly one order of magnitude greater than that of ZnS bulk crystal. The 3PA resonance in ZnS QDs is observed at the lowest excitonic transition of 1S(e)-1S3∕2(h).