12 - Rare-earth doping in afterglow oxide phosphors: Materials, persistence mechanisms, and dark vision display applications

Abstract

Materials that absorb high energy electromagnetic radiations of high energy such as X-rays, γ-rays, and UV rays and preferably convert them into visible light are called luminescent materials or phosphors. Afterglow phosphors are a special type of luminescent materials that readily absorb and store up the incident photon energy and show photoluminescence emission even after the source of excitation has been ceased off. After a lot of deliberations, a majority of the researchers agreed that the excitation energy gets captured at the various trapping levels associated with intrinsic or intentional defects and later released thermally. As the source of excitation is eliminated, trapped charge carriers may acquire sufficient thermal energy from ambient surroundings resulting into recombination of the charge carriers. In literature, one can find an innumerable number of adjectives for explaining this phenomenon such as long afterglow, persistence luminescence, phosphorescence, long lasting, long decay, long duration, and long persistence. Long afterglow (LA) phenomenon is associated with extended lifetime or decay (typically ranging from 10−8s to few hours) of the luminescence process.