Enhanced Higher‐Energy Afterglow Enabled by Visible‐Light Excitation of Ln 2+ in Eu 2+ ‐Ln 3+ Persistent Phosphor

ABSTRACT An unusual phenomenon in Eu 2+ ‐Sm 3+ codoped SrAl 2 O 4 was observed, i.e., low‐energy visible photons (470–650 nm) exciting Sm enhance the high‐energy afterglow of Eu 2+ , unlike the conventional donor‐acceptor (D‐A) resonant energy transfer. Wavelength‐dependent optically stimulated luminescence and in situ optical/ x‐ray absorption spectroscopy confirmed reversible electron transfer phenomena: under 365 nm irradiation, excited Eu 2 + was photo oxidized to Eu 3+ , while simultaneously triggering charge accumulation on Sm 3+ , resulting in Sm 2+ . Conversely, rapid detrapping occurs at the characteristic excitation wavelength corresponding to Sm 2+ , i.e., 532 nm, resulting in strong afterglow or optically stimulated luminescence. Continuous glow curves at 77 K and rate equations provided both experimental and theoretical evidence that visible photons govern the fading of Sm 2+ , specifically enhancing the visible light‐induced absorption cross‐section. Based on wavelength‐specific response characteristics, advanced concepts and verifications for low‐illuminance dosimetry and dynamic anti‐counterfeiting were proposed and designed. This study elucidates the physical nature of lanthanide trap carriers, holding significant theoretical and practical implications for underlying mechanisms and sunlight harvesting.