Drastic photostability improvement of silica particles impregnated with multiple emitting CdSe quantum dots prepared through efficient surface silanization

Numerous studies have been performed on silica coated quantum dots (QDs) for the retention of photostability of QDs over long period of time. However, the photostability of silica coated QDs has been found to be inferior to that of polymer coated QDs under some circumstances, and the quantitative data is missing in prior arts. Here, we report the drastic improvement of photostability of CdSe QDs encapsulated into silica particles by optimizing the preparation conditions. We have prepared silica particles (ca. 60 nm in size) encapsulated with multiple, over dozens of emitting CdSe QDs. The key step is a surface silanization of QDs, where the original ligands are replaced by a partially hydrolyzed alkoxide in hydrophobic solution. The evaluation using single particle detection methods shows that the photostability increases up to 8 times as compared with the polymer coated counterparts by optimizing the molar ratio of alkoxide against QDs upon the silanization. When the ratio is optimum, the packing density of QDs in the silica particle becomes the maximum accompanied by the most obvious red shift of ensemble photoluminescence peak. This indicates a developed silica network in close proximity to the QD surface on the particle is formed. The knowledge acquired from this work is universal, and can be extended to other emitting QDs such as InP and perovskites.