Low-energy visible light excitable Bi2+-activated near-infrared persistent phosphors for information encryption application

Near-infrared (NIR, 700–900 nm) emissive persistent phosphors have been given substantial attention in the past decade due to their bright future for many advanced applications from night vision surveillance to biomedical imaging. Here, we report the intense NIR persistent luminescence from a series of Bi2+-activated persistent luminescence materials achieved by the cation disorder strategy in CaSnO3 host. Taking Ca0.95(Na,Gd)0.025SnO3:Bi2+ as an example, it exhibits long-lasting NIR afterglow with a peak maximum at 805 nm assigned to the 2P3/2(1)→2P1/2 transition of Bi2+ and a long persistence time of more than 24 h after the ceasing of external excitation. More importantly, NIR self-sustained luminescence can be triggered by wideband irradiation with ultraviolet to visible light over 230–550 nm. As expected, 365 nm UV lamp, natural sunlight and LED flash can all effectively charge these NIR persistent phosphors and induce commendable NIR persistent luminescence performance. Considering the invisibility of NIR emission to the naked eye, very broad persistent luminescence excitation band, and long-lasting NIR luminescence after excitation, these Bi2+-activated NIR persistent phosphors are expected to find important applications in optical information storage and anti-counterfeiting fields.