Cr<sup>3+</sup>‐Cr<sup>3+</sup> Ion Pair Induced Fast Energy Migration in Cr<sup>3+</sup> Doped Na‐β‐Al<sub>2</sub>O<sub>3</sub> Ultra‐Wide Near‐Infrared Phosphors for NIR Spectroscopy Application
Qianxi Pang, Yichao Wang, Liqing Yan, Ge Zhu, Sai Xu, Jinsu Zhang, Xizhen Zhang, Yongze Cao, Baojiu Chen
Abstract
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.