Incorporation of Eu 3+ in ZnGa 2 O 4 :Ni 2+ for improved NIR persistent luminescence located in second transparency window

Abstract It is well known that near‐infrared (NIR) persistent phosphors have rather low absorption coefficients of biological tissues for NIR light. However, recent research shows that the phosphors emitting NIR lights in second NIR (NIR‐II, 1000–1350 nm) and third (NIR‐III, 1500–1800 nm) biological window have advantages over that in NIR‐I (650–900 nm). Although ZnGa 2 O 4 :Ni 2+ outputs NIR emission and afterglow locatedin NIR‐II, the weak signal significant limits its application. In this work, persistent luminescent phosphors of ZnGa 2 O 4 : x Ni 2+ , y Eu 3+ ( x = 0–0.013, y = 0.01–0.06) (termed as ZEGN) were synthesized via a traditional high‐temperature solid‐state reaction, which feature a broad emission band in the NIR‐II window. The phosphors exhibit a broad NIR emission at about 1300 nm after ultraviolet (UV) or orange–red lights excitation, arising from the 3 T 2 ( 3 F) → 3 A 2 ( 3 F) transition of Ni 2+ . However, incorporation of Eu 3+ ions, the NIR emission intensity significantly increases with the increase of Ni 2+ ion concentration, reaching the maximum by 18 times at x = 0.005. Removing the light source, the sample still outputs intense NIR afterglow and red afterglow that can last over 500 s. It is noteworthy that the red afterglow of Eu 3+ shows a dramatically decrease but the NIR afterglow increases with increasing the Ni 2+ ion concentration, because of energy transfer. Under the excitation of 282‐nm UV light, the ZGEN sample exhibits a good thermal stability. The phosphor offers a promising application in biological imaging due to broadband NIR‐II light and afterglow.