Controllable Synthesis of Upconversion Nanophosphors toward Scale-Up Productions

Upconversion nanophosphors (UCNPs) are considered as an important synthesis arm within biomedical and energy sectors due to their unique optical characteristics, which can convert near-infrared light into higher energy emissions. However, key challenges, cost, compatibility of the materials, etc. have to be taken into serious consideration to transform this in-lab UCNPs technology into scale-up production for wider commercial needs. This review highlights the fundamental concepts of synthetic approaches for UCNPs and recaps recent advances in terms of large-scale production. A number of typical synthesis routes in both batch and continuous processes are reviewed, alongside their limitations and potential improvements when being considered for mass production. By discussing and exploiting the technical compacity for the potential synthetic trends, key challenges, and expectations of future synthesis methods for UCNPs are also outlined.