Quantum dots as single-photon sources: Antibunching via two-photon excitation

Two-photon excitation induced photoluminescence (2PE-PL) microscopy of CdSe colloidal quantum dots at the single-entity level is demonstrated. We provide evidence for single nanoparticle microscopy in the two-photon excitation regime by varying the laser excitation average power, as well as by measuring the confocal point spread function in three dimensions with a single quantum dot. Model calculations of the point spread function are in good agreement with our experimental findings in the 2PE-PL nonsaturation regime. Ultimately, we observe photon antibunching and triggered single-photon emission at room temperature from those quantum nanostructures under two-photon excitation in a well-defined three-dimensional photonic volume.