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 (Ln3+) 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 Ln3+ 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 photo-luminescent 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 Ln3+ activated inorganic micro-sized UC materials from the perspective of tailoring UC emission color and intensity for plastic recycling applications.