Preparation of photostable fluorescent InP/ZnS quantum dots embedded in TMAS-derived silica

Cd-free fluorescent InP/ZnS quantum dots (QDs) have attracted attention for use as color converters of liquid crystal displays. To protect InP/ZnS QDs from oxygen, which degrades them by photo-oxidation during excitation, we fabricated a transparent monolithic silica composite containing the QDs using an aqueous solution of tetramethylammonium silicate (TMAS) as a silica source. The TMAS solution was basic and readily dispersed the negatively charged QDs obtained by ligand exchange of 1-dodecanethiol for 3-mercaptopropionic acid (MPA). A highly transparent monolithic TMAS-derived silica composite containing the MPA-modified QDs (InP/ZnS-MPA@TMAS) was obtained from the aqueous QD dispersion through a sol-gel process. The photoluminescence (PL) quantum yield of InP/ZnS-MPA@TMAS was 21.7%. Changes in PL intensity under continuous 400-nm excitation were measured to evaluate the photostability of the QDs in InP/ZnS-MPA@TMAS. The PL intensity of InP/ZnS-MPA@TMAS was over 90% of the initial value after 180 min, while that of a reference polymethylmethacrylate film containing hydrophobic QDs decreased to 69%. The higher photostability of InP/ZnS-MPA@TMAS than that of the reference film was explained by the TMAS-derived silica acting as a gas barrier to protect the embedded QDs from photo-oxidation by oxygen in air.