Ultra-Narrow Homogeneous Photoluminescence Line Width of Zinc-Blende CdSe-Based Core/Shell Nanocrystals: Dominating Role of Lattice–Ligands Interface

Homogeneous photoluminescence (PL) line width of semiconductor nanocrystals is usually much greater than thermal broadening at room temperature (∼25 meV), limiting their applications as optical and optoelectronic materials. Here, homogeneous PL line width of zinc-blende CdSe nanocrystals with epitaxially grown CdS, ZnSe, and ZnS shells is studied using single-molecular spectroscopy, confirming that delocalization of electron and hole wave functions to the lattice-ligands interface dictates their PL homogeneous line width. Specially, epitaxial ZnSe (or ZnSe inner and ZnS outer) shells form type-I band offsets with CdSe cores, colocalizing both electron and hole wave functions within the ordered core lattice with minimum lattice strain. Without delocalization to the disordered lattice-ligands interface, these epitaxial shells reduce the homogeneous PL line width of CdSe nanocrystals by ∼70%. Exceptionally narrow homogeneous PL (∼25 meV) allows observation of the energy splitting (20∼60 meV) of two lowest optically active states of the ground-state exciton for 2-6 nm CdSe in right-triangular-bipyramidal shape. This energy splitting does not play a decisive role in determining the PL homogeneous line width but leads to dual-peak and polarized emission.