Cr3+‐Cr3+ Ion Pair Induced Fast Energy Migration in Cr3+ Doped Na‐β‐Al2O3 Ultra‐Wide Near‐Infrared Phosphors for NIR Spectroscopy Application

Abstract Technological progress has promoted the development of ultra‐wide near‐infrared (NIR) luminescent materials as a new NIR light source. The ultra‐wide near‐infrared (NIR) emission in Na(Al,Ga) 11 O 17 :xCr 3+ (NAGO:xCr 3+ ) phosphors is achieved by constructing unique Cr 3+ ‐Cr 3+ ion pair confined structure. The Cr 3+ ‐Cr 3+ ion pairs can be observed at a low concentration of Cr 3+ ions(x = 0.04), the increase of Ga 3+ ion would promote the formation of Cr 3+ ‐Cr 3+ ion pairs, thereby effectively enhancing the energy migration process from high‐energy Cr 3+ ions to low‐energy Cr 3+ ones. Herein, the full width at half maximum can be finely adjusted in a wide range from 17 to 223 nm, while the emission peaks can shift from 704 to 860 nm. NAGO:xCr 3+ exhibits the longest‐wavelength emission in the known Cr 3+ ‐doped galliates and aluminates phosphors. The study further reveals the inherent mechanism of affect on the photoluminescence properties for Cr 3+ ‐Cr 3+ ion pairs. The quantum efficiency of optimal NaAl 11 O 17 :0.004Cr 3+ (sharp emission) and NaGa 11 O 17 :0.02Cr 3+ (ultra‐wide emission) samples reaches 87.6% and 46.6% with high thermal stability (84.47% and 67.52%@150 °C), respectively. The comprehensive properties are excellent among known phosphors with similar property. Multifunctional applications of NAGO:xCr 3+ in agricultural production, quality inspection, and imaging fields are also demonstrated.