Near-Infrared Phosphors with Persistent Luminescence over 1000 nm for Optical Imaging

Persistent phosphors with “self-sustained” light emission are considered to be one of the most promising candidates for the new-generation “background-free” optical imaging. In particular, near-infrared (NIR) persistent luminescence (PersL) over 1000 nm has demonstrated the superior power to obtain deep penetration depth and high-fidelity imaging due to the avoidance of real-time external excitation. In this chapter, we will give comprehensive insights into the state-of-the-art of NIR (>1000 nm) persistent phosphors, starting from the introduction of basic principles of light-matter interactions, followed by the description of NIR autofluorescence phenomena of bio-tissues and related filtering approaches. Then, the mechanism of PersL, including charge carrier trapping-detrapping phenomena, persistent energy transfer (ET) process, and photostimulation-induced trap redistribution approaches, will be explained to give a general picture of how PersL works and how we can play with the information of energy-level locations of host bands, activators and traps. The reported over 1000-nm NIR-persistent phosphors, basically divided into lanthanide and transition-metal ions-activated ones will be summarized with highlighted examples to introduce design concepts of these phosphors. Finally, we draw a prospective of key challenges and feasible improvements in the future following the current trends of this research field.