Preparation and photoluminescence properties of yellow-emitting CuInS₂/ZnS quantum dots embedded in TMAS-derived silica

The degradation of CuInS₂ (CIS) quantum dots (QDs) under excitation light due to photo-oxidization by O₂ has been a significant problem. Embedding QDs into a matrix to protect them against O₂ would improve their photostability. In this paper, hydrophilized CIS/ZnS/ZnS QDs prepared by a ligand exchange method were embedded in silica through a sol-gel method using tetramethylammonium silicate (TMAS) aqueous solution, in which negatively-charged nanoparticles can be well dispersed. QDs modified with 3-mercaptopropionic acid (MPA) were well dispersed into TMAS-derived silica. The obtained monolithic TMAS-derived silica composites containing embedded MPA-modified CIS/ZnS/ZnS QDs exhibited high photoluminescence (PL) quantum yields (43-47%). Changes in PL intensity under continuous excitation were measured to evaluate the photostability of the QDs. The PL intensity of the composite was 105% that of the initial value after 5 h irradiation, while the PL intensities of as-prepared QDs and a PMMA composite decreased to 88% and 92%, respectively. The good gas barrier properties of TMAS-derived silica likely caused the high photostability by preventing O₂ from reaching the surface of the embedded QDs.