Unraveling the dual emission of single quantum-dot by single particle spectroscopy

Abstract

Two-color emissive 0D–2D quantum-dot quantum-well (QD-QW) heteronanocrystals has created profound research activities. First multicolor emission in the visible region has been reported by Peng and co-workers in CdSe(core)–ZnS(barrier)-CdSe(shell) (core-barrier-shell) based heteronanostructures where the both CdSe phases (core and the shell) are emissive and tuneable as well. Owing to this enhanced and tuneable functionality, the QD-QW systems colloidal nanocrystals has fuelled their optical and imaging applications. Single particle spectroscopy has taken a giant step toward unravelling the features of individual particles and thus to provide direct information on their heterogeneity. To elucidate the dual emission characteristic of individual nanocrystals we performed energy mapped photoluminescence imaging. Surprisingly, the pseudo color PL intensity image shows that not all single particles are dual emissive in nature, few are either green emitting or red emitting. Photoluminescence spectrum of individual nanocrystals further confirms that individual nanocrystals can be dual emissive in nature. However, single color emissive dots are also present indicating the ensemble heterogeneity at single particle levels. The temporal evolution PL spectra of a single quantum shows spectral diffusion. The single dot experiments on the dual emissive QD-QW system unravels hidden photophysics which are otherwise not observed by ensemble spectroscopy.