Ni2+-Doped Yttrium Aluminum Gallium Garnet Phosphors: Bandgap Engineering for Broad-Band Wavelength-Tunable Shortwave-Infrared Long-Persistent Luminescence and Photochromism

Functional phosphors with shortwave infrared (SWIR) persistent luminescence have attracted an ever-increasing interest from scientists owning to the self-sustainable emission for deeper tissue penetration, real-time monitoring, and nondestructive analysis. In this work, we report for the first time on the broad-band wavelength-tunable SWIR luminescence and photochromism properties of divalent nickel-doped yttrium aluminum gallium garnet solid solutions. The crystal-field-driven wavelength-tunable superbroad band emission within SWIR wavelength region, attributed to the T-3(2)(F-3) -> (3)A(2)(F-3) transitions of the Ni2+ ions, can be controllably adjusted. The observation of SWIR long-persistent luminescence also can be modified by bandgap engineering via the simple adjustment of the Ga/Al ratio. Besides, the accompanied observation of photochromism, i.e., the reversible body color change by alternative UV and visible illumination/heating treatment, shows robust fatigue resistance. The nature of traps, color centers, and trapping and releasing of electrons are studied by electron paramagnetic resonance and thermoluminescence. Finally, an energy level schematic diagram is established to discuss the SWIR persistent luminescence and photochromism mechanisms in detail. This work opens an avenue to motivate researchers to rationally design and purposely explore novel bifunctional phosphors with broad-band wavelength-tunable SWIR persistent luminescence and photochromism.