Silica Modification of Quantum Dots for Fabrication of Thermally Stable Siloxane Encapsulated QD Composite

Abstract

The Quantum Dots (QDs) have gained enormous interests in the display industry in recent years due to their tunable optical properties depending on size, narrow emission spectra, and high photoluminescence quantum yield (PLQY). However, the QDs have some limitations derived from their high surface areas, such as thermal stability and oxidation problem under high temperature/high humidity conditions. For stabilization of surface and dispersion in organic solvents, the organic ligands such as oleic acid, trioctylphosphine (TOP) or trioctylphosphine oxide (TOPO) are usually used during synthesis process. Despite the ligand capping, the organic ligands are easily detached and decomposed by heat, air, and moisture. Many groups have studied about silica modification of the colloidal QDs or QD/polymer composites to protect QD surface from heat and moisture. [1] Recently, we reported a siloxane encapsulated QD (CdSe/CdZnS core/shell, ligand: oleic acid, from Ecoflux, Korea)) resin through in-situ sol-gel condensation reaction of 3-metharyloxypropyltrimethoxy silane (MPTS) and diphenylsilanediol (DPSD) in the QD existence. [2] The QDs were uniformly dispersed in the photo-cured QD-siloxane film, and the QD-siloxane film showed long-term stability in harsh environment (85--> in air and 85-->/85% RH conditions). To increase thermal stability of the QD-siloxane film, we additionally silica-modify the oleic acid-capped QDs using various silanes such as tetraethylorthosilicate (TEOS) and MPTS, which could be reacted during sol-gel condensation reaction. The oleic acid-capped QDs are clearly modified by formation the additional silica shell. The silica-modified QDs are well dispersed in siloxane matrix because QD-siloxane film is fabricated by in-situ sol-gel condensation reaction of MPTS and DPSD in the existence of QDs, and the silica-modified QD-siloxane film is also stable under the harsh condition (85--> in air and 85-->/85% RH). The silica-modified QD-siloxane film is even enhanced the thermal stability under 120--> in air condition, compared to previously reported oleic acid-modified QDs encapsulated in siloxane. Moreover, the silica modification of QDs passivated by organic-ligands will be further studied to improve photo-stability.