Revealing the Band-Edge Exciton Fine Structure of Single InP Nanocrystals

Weinvestigate the fundamental optical properties of single zinc-blendeInP/ZnSe/ZnS nanocrystals (NCs) using frequency- and time-resolvedmagneto-photoluminescence spectroscopy. At liquid helium temperature,highly resolved spectral fingerprints are obtained and identifiedas the recombination lines of the three lowest states of the band-edgeexciton fine structure. The evolutions of the photoluminescence spectraand decays under magnetic fields show evidence for a ground dark excitonlevel 0(L) with zero angular momentum projection along theNC main elongation axis. It lies 300 to 600 & mu;eV below the & PLUSMN;1(L) bright exciton doublet, which is finely split by the NC shapeanisotropy. These spectroscopic findings are well reproduced witha model of exciton fine structure accounting for shape anisotropyof the InP core. Our spectral fingerprints are extremely sensitiveto the NC morphologies and unveil highly uniform shapes with prolatedeviations of less than 3% from perfect sphericity.