A review on defect engineered NIR persistent luminescence through transition metal ion (Cr, Mn, Fe and Ni) doping: Wider perspective covering synthesis, characterization, fundamentals and applications

Persistent luminescence is an optical phenomenon where materials continue to emit light after the cessation of the excitation source which leads to different applications in areas like bioimaging, information storage, anticounterfeiting, etc. This review focuses on the latest advancements in near-infrared (NIR) persistent luminescence (PersL) materials doped with Cr³⁺, Mn⁴⁺, Mn²⁺, Fe³⁺ and Ni²⁺along with recent advances in the synthesis and mechanisms associated with the afterglow. A comprehensive discussion on the various types of defects and their importance in NIR PersL materials is also included, along with a section dedicated to the techniques used to characterize these defects and application of NIR PersL materials in different areas. The review also examines the different strategies to improve the NIR PersL. It starts with a brief description of the history of the PersL and then discusses the reported NIR PersL phosphors activated by manganese, chromium, iron and nickel ions. Understanding the mechanism associated with PersL is very important to develop a novel PersL phosphor, so the review discussed the role of defects and traps in PersL along with different models which include the conduction band model, oxygen vacancy model, and quantum tunneling model which is followed by few main applications of PersL materials and culminated by concluding and associated challenges and future directions in this ever-growing field.