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.