Controlling the Durability and Optical Properties of Triplet-Triplet Annihilation Upconversion Nanocapsules

Precisely generating high energy photons beyond the surface at depth can significantly transform optically controlled processes like photocatalysis or 3D printing, but direct irradiation with high energy photons is not a feasible method due to absorption and optical scatter. Using triplet-triplet annihilation upconversion (TTA-UC), a nonlinear optical process, we can bypass this challenge by converting two low energy photons into one high energy photon. We recently demonstrated the use of silica-encapsulated oleic acid-cored nanoparticles with upconversion materials dispersed inside for high energy photon generation at depth, with good durability within a variety of chemical environments. To ensure the formation of a durable silica shell, we engineered the synthesis using tetraethyl orthosilicate and 10K MPEG-silane precursors to minimize nanoparticle leakage and aggregation. Simple structural modifications to the TTA-UC materials dispersed inside of the nanoparticle core can increase the overall upconverted light output. Additionally, we use charge detection mass spectrometry to directly monitor the nanocapsule growth kinetics, which helps us understand diverse nanocapsule morphologies. These results show that simple synthetic controls allow us to obtain robust, well-dispersed, bright upconverting nanoparticles for subsequent integration and engineering in light-controlled technologies.