 The discovery of senior al-204EU-2+, di-3+, and 1996 marked a major breakthrough in the field of persistent luminescence. This material is now one of the most commonly used persistent luminescent materials due to its high brightness and stability. Despite its widespread use, however, the exact mechanism behind the persistence of light emission remains unknown. Several theories have been proposed to explain the phenomenon, including the presence of deep traps, the formation of defects, and the presence of oxygen vacancies. The purpose of this review is to summarize the current understanding of persistent luminescence in EU-2+, based materials, and to discuss the potential mechanisms involved.