Silica Overcoating of CdSe/CdS Core/Shell Quantum Dot Nanorods with Controlled Morphologies

CdSe/CdS core/shell quantum dot nanorods (QDNRs) exhibit anisotropic optical properties. Overcoating QDNRs with silica (SiO 2 ) shells is desirable for protecting the surface of the inorganic core, imparting dispersibility in water, and allowing functionalization with silanes. While several methods have been developed for encapsulating spherical CdSe-based quantum dots in SiO 2, extension of these approaches to QDNRs has been limited. Here, we report a reverse microemulsion approach for controlled deposition of SiO 2 overcoatings with thicknesses of 2–12 nm onto CdSe/CdS QDNRs with aspect ratios of up to 19. Addition of poly(ethylene glycol) silane during SiO 2 deposition terminates the reaction and allows facile control over the shell thickness, especially for thinner shells. By independently controlling the amounts of tetraethyl orthosilicate, ammonium hydroxide (NH 4 OH), and water, morphological control is achieved, giving uniform SiO 2 shells or heterogenenous deposition onto the ends of QDNRs as lobed structures, nanolollipops (single lobe) or nanodumbbells (double lobes). Especially for high-aspect ratio QDNRs, we report breakage of the double-lobed structures. The SiO 2 overcoating process causes a reduction in the fluorescence quantum yield of approximately 20%, which we attribute to use of NH 4 OH as a catalyst in this reaction.