Persistent luminescence in rare-earth doped wide band-gap materials

On March 12, 1993, after two years of trial and error, Murayam, Takeuchi, Aoki, and Matsuzawa of Nemoto & Co., Ltd. (Japan) successfully developed a new-generation phosphor, SrAl₂O₄:Eu²⁺,Dy³⁺, opening up a new era of scientific research on persistent luminescence. Three decades later, despite great progress in understanding the phenomenon and in discovering new materials, details of the underlying mechanism for the persistent luminescence observed in rare-earth (RE) doped SrAl₂O₄ and similar materials are still under debate, and the search for new or improved persistent phosphors is still largely trial and error. In this talk, on the 30-year anniversary of the Nemota team’s discovery, we present the first detailed understanding of native point defects and RE (co)dopants in SrAl₂O₄ based on results from hybrid density-functional defect calculations, assign the absorption and emission bands experimentally observed in Eu-doped SrAl₂O₄, including the material's characteristic green and blue emissions, to specific defect configurations and optical transitions, and identify charge carrier trapping centers responsible for the delayed luminescence. Our work will call for a re-assessment of all the mechanisms previously proposed for RE-doped SrAl₂O₄.