Multiexciton fluorescence from semiconductor nanocrystals

We use transient photoluminescence to spectrally resolve the emission from 1, 2, and 3 electron-hole pairs states in CdSe colloidal nanocrystals with radii ranging between 2.3 and 5.2 nm. Temporally and spectrally resolved multiexciton emission from single NCs is also observed. The observation of multiexciton emission enables new experiments and potential applications at both the single NC level and using ensembles of NCs. First we discuss the use of single CdSe(CdZnS) core(shell) colloidal NCs (spheres and rods) to generate triggered photon pair emission at room temperature, with specific ordering of the pair's constituent photons. Second, we incorporate CdSe/ZnS core-shell nanocrystals into a TiO₂ host matrix and observe simultaneous two-state amplified spontaneous emission and lasing from both multiexcitonic transitions (1S _3/2-1S_e and 1P_3/2-1P_e) in a surface-emitting distributed feedback CdSe NC laser. From our data we deduce radiative lifetimes, quantum yields, stimulated emission gain, and power dependencies for the multiexciton transitions.