Abnormal Bi3+-Activated NIR Emission in Highly Symmetric XAl12O19 (X = Ba, Sr, Ca) by Selective Sites Occupation

Near-infrared light-emitting diodes (NIR-LEDs) are potential candidates in food composition analysis, temperature and security monitoring, biometrics, and medical applications. To realize the above objectives, the development of NIR-emitting phosphors is urgently required. Herein, a novel NIR emission is successfully achieved in Bi3+-activated XAl12O19 (X = Ba, Sr, Ca) compounds by constructing the selective site occupation of Bi3+ in Al3+ polyhedra with small coordination number. The designed phosphors exhibit broad-band NIR emission of Bi3+ from 600 to 1000 nm. Interestingly, a broad photoluminescence control from blue to red is also achieved by just changing the sintering atmosphere. The blue emission of Bi3+ should be assigned to the prior occupation in X2+ sites and the existence of oxygen vacancy. This work not only provides a novel insight to develop NIR-emitting Bi3+-activated phosphors but also helps to reveal the underlying NIR luminescence mechanism of Bi3+ in inorganic compounds.