QD-Salt Mixed Crystals: the Influence of Salt-Type, Free-Stabilizer, and pH

Abstract

Colloidal quantum dots (QDs) bear a huge potential in different application fields due to their unique properties. Unfortunately, their limited stability against environmental influences and the limited processability of the colloidal solutions restricts, among other factors, their widespread implementation. Incorporating the QDs into an inorganic matrix allows overcoming of these barriers. In this manuscript, we demonstrate the reproducible incorporation of high quality CdTe QDs capped with thioglycolic acid into NaCl and KCl salt crystals. In comparison to previous reports, here we avoided the production of powder-like, weakly emitting mixed crystals and/or a loss of large amounts of QDs due to aggregation. The optimum conditions for this process were found by the variation of the amount of additional free-stabilizer and the pH of the saturated salt solutions. Both variables exhibit high influence on the colloidal stability of the QDs, ensuring the electrostatic forces on their surface to be high enough to prevent agglomeration. Incorporation in NaCl as host matrix is accompanied with pronounced etching of the QDs, causing a blue shift of the photoluminescence (PL)-spectra upon incorporation while KCl preserves the original optical properties of the QDs. Under optimized conditions, even the matrix-induced red shift of the emission upon incorporation can be overcome, resulting in a higher predictability of the mixed crystal preparation.