Visible light-activated ultra-long orange afterglow phosphor Sr1−x Ga2O4:xCu2+

• The strategic calcination under a reducing atmosphere via carbon burial sintering significantly enhances oxygen vacancy concentration, which not only optimizes trap distribution for visible-light excitation but also tailors the energy transfer pathways between the SrGa 2 O 4 host and Cu 2+ dopants . • This defect engineering enables dual-color emission (green at 530 nm and orange at 610 nm) under UV excitation, while selectively activating orange emission (610 nm) under visible light . • The dynamic color tunability arises from the interplay of host-to-dopant energy transfer and trap-mediated recombination, where oxygen vacancies stabilize Cu 2+ -related deep traps for persistent orange luminescence. • This synergy between defect modulation and excitation-wavelength selectivity provides a versatile platform for advanced anti-counterfeiting and multi-level optical encryption technologies. Because of both their independence from external light sources and their energy-saving properties, efficient visible light-activated long persistent luminescence (LPL) phosphors are in high demand. Designing and developing such materials, however, remains a significant challenge. This report describes new LPL phosphors doped with transition metal ions (Sr 1−x Ga 2 O 4 :xCu 2+ ), which address the challenge of excitation of red light-emitting LPL phosphors by visible light. Visible light excitation is achieved by adjusting the calcination atmosphere during preparation of the phosphor. When the Cu 2+ ion doping level is 2 %, the phosphor can be excited by both UV and visible light. Upon excitation by visible light, the main emission peak occurs at approximately 610 nm; this is observed as orange light, with an afterglow duration of over 11 h. Investigation of the emission spectra after different delay times, together with the photoluminescence and thermoluminescence spectra, revealed a mechanism that involves trapping and de-trapping of electrons. The unique long afterglow and excitation properties, together with the emission characteristics of SrGa 2 O 4 :0.02Cu 2+ , are particularly suited for applications such as night time signage and dynamic anti-counterfeiting. This research provides new directions for the design of visible light-activated LPL phosphors.