Optically bifunctional heterostructured nanocrystals

Abstract

We show that an attempt to synthesize nanocrystal alloys of Cd_1−xZn_xS_ySe_1−y in a single-step reaction leads naturally to a heterostructured nanocrystal system with CdSe-rich core and CdS-ZnS hybrid shell because of differences in chemical reactivities of the different constituents. These nanocrystals exhibit very high (~65%) photoluminescence (PL) efficiency. The band-edge excitonic energy and the corresponding band-edge emission can be tuned over a range of the visible spectrum by changing the composition. These samples show very strong two-photon absorption cross section (σ₂=1.923×10⁻⁴⁷ cm⁴·s/photon or 1923 GM), establishing a very rare example of an optically bifunctional material with tunability and a very high quantum efficiency for linear optical properties, namely, PL, and strong nonlinear properties, namely, two-photon absorption.