Triple-Emulsion Microcapsules for Highly Efficient Multispectral Upconversion in the Aqueous Phase

This study reports a new triplet-emulsion-based architecture for highly efficient triplet–triplet annihilation (TTA) upconversion (UC) in the aqueous phase. This encapsulation system separates the upconversion-emitting solvent core from the polymeric shell phase by utilizing an inner water phase. As a result, undesirable phosphorescence interference and chromophore loss were eliminated to achieve the aqueous upconversion efficiency close to those attainable in typical deoxygenated organic solvent systems. This system further allows various unconventional spectral shifting schemes, i.e., multicolor emission from monochromatic excitation (e.g., red to green and blue) or, conversely, frequency amplification of broad-band visible spectra to near-monochromatic shorter wavelength emission (e.g., green and red to blue), with minimal spectral impurities and interferences, representing a significant advance in encapsulated TTA-UC systems suitable for various aqueous-based applications.