Up-Conversion Fluorescent Labels for Plastic Recycling: A Review

The demand for more efficient and complete sorting techniques for plastic waste is growing, and one possible solution isbased on fluorescent labeling. Novel fluorescent labels based on trivalent lanthanide (Ln(3+)) activated inorganic up-conversion (UC) materials offer a promising technological solution for plastic recycling. UC is a nonlinear, anti-Stokes process of combining two or more low energy near-infrared (NIR) photons to obtain the emission of a single higher energy photon. While Ln(3+) based UC materials possess one key disadvantage -low quantum yield, they also exhibit many unique features, such as high signal/noise ratio, tailored emission color, long photoluminescent lifetime, and low toxicity. These unique features endear them for a diverse range of applications and offer many new opportunities. Herein, we review the recent advances in the Ln(3+) activated inorganic micro-sized UC materials from the perspective of tailoring UC emission color and intensity for plastic recycling applications.