Fig. 1.

Coupled CQD molecules. a Scheme for fabrication of coupled CdSe/CdS CQD molecule. b The dimer@SiO₂ CQD structure. The dimer 1.9/4.0 nm CQD molecules c before and d after the fusion procedure. e The 1.4/2.1 nm fused CdSe/CdS CQD molecules. Schematic structures are illustrated. Scale bars (b–e) are 50 nm and insets show higher magnification images. f The potential energy landscape and a cross-section of the calculated first electron wave function without Coulombic interaction ${\mathrm{\Psi }}_{\mathrm{e}}$ (red), with Coulombic interaction ${\mathrm{\Psi }}_{\mathrm{e}}^{\prime }$ (green) and of the hole wave functions ${\mathrm{\Psi }}_{\mathrm{h}}$ (blue) of the coupled CQD molecules. g Calculated bonding and anti-bonding two-dimensional electron wave functions without (cross-section of the bonding state is the red curve in f), and h with Coulombic interaction (cross-section of the bonding state is the green curve in f). i Absorption (dashed lines) and fluorescence spectra (solid lines) of monomers (blue), unfused (green), and fused 1.4/2.1 nm CdSe/CdS CQD molecules (red). j Calculated (red asterisk) and experimental (blue circles) band gap redshift of monomer-to-respective-homodimer structures for CQD molecules with different core/shell dimensions.