Various approaches have been reported for hybridization of silica colloids and quantum dot (QD) nanocrystals due to their useful applications in many fields, such as light emitting diode, display, bio-imaging, and sensing, etc. Most of the approaches require a ligand exchange process of the as-prepared nanocrystals which is hydrophobic due to the protecting ligands, before or during their hybridization. The ligand exchange process frequently brings about a complicated situation, such as aggregation of nanocrystals or optical deterioration. A direct assembly without the ligand exchange process can be greatly prospective, but has been challenging. A weak physical interaction, the van der Waals (vdW) force has been considered incapable of making a stable assembly of two different hydrophobic colloidal particles. They can be associated and dissociated reversibly. However, in a nanoscale regime, the reinforced vdW force due to an enlarged contact area can have a substantial impact. To prove it, we prepared hydrophobic colloidal silica (So, ~114 ± 11 nm) from tetraethoxysilane and octadecyltrimethoxysilane (TEOS and ODTMS) mixture precursors. The So is constructed by controlled aggregation of 15~25 nm-sized hydrophobic silica particles and thus, has many crevices where the QDs can sit on. The hybridization works nicely as long as the QD size fits within the concave regions of OD-silica. The hybridized structure is securely covered by silica with/without functional groups and exhibits greatly enhanced photoluminescence (up to 690%) than their free QDs under an identical QD concentration. The current approach was successfully extended to three different sized QD nanocrystals (≤ 10 nm). To the authors’ knowledge, this is the first report showing versatile hybridization of hydrophobic nanocrystals with colloidal silica using the vdW force only. A brief application for a white LED is also provided, with a promising optical performance.

Direct assembly of hydrophobic quantum dots with colloidal silica via van der Waals interaction

256th National Meeting (2018)

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