Manipulating trap distribution and density by chemical unit cosubstitution for near-infrared persistent luminescent Zn1−2xLixGa2+xO4:Cr3+ solid solutions
Near-infrared (NIR) emitting phosphors with persistent luminescence have attracted much interest in the past decade, due to their widespread applications in medical diagnostics, night-vision surveillance, multi-level anti-counterfeiting, and security encryption. Although NIR luminescent materials have been extensively investigated, it is challenging to explore novel phosphors or new compositions with tunable NIR persistent luminescence performance. Herein, chemical unit co-substitution is explored in a series of NIR emitting Zn1−2xLixGa2+xO4:Cr3+ solid solutions. Substitution with [Li+–Ga3+] for the [Zn2+–Zn2+] unit results in tunable emission in the deep-red and NIR regions coming from the typical Cr3+ emission of the 2E → 4A2 and 4T2 → 4A2 transition. Upon UV or X-ray irradiation, intense NIR persistent luminescence is realized and composition-related variation of trap distributions and densities are identified. Importantly, a higher trap density of the Cr3+-doped solid solutions (i.e., x = 0.2–0.4) than that of the benchmark NIR persistent phosphor of ZnGa2O4:Cr3+ and LiGa5O8:Cr3+ is achieved. This work proves the feasibility of chemical unit co-substitution in developing new NIR persistent phosphors, which can motivate further exploration of luminescent materials with novel properties.
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