Improving the luminescent properties of Fe3+ in CaAl4O7 by co-doping with Bi3+ ions

In the framework of luminescent transition metal ions-doped phosphors for near-infrared (NIR) lighting, Fe3+-activated phosphors have been recently demonstrated to be a potential alternative to the most common Cr3+ and Ni2+-based NIR materials. However, this family of phosphors still suffer from low absorption efficiency and severe thermal quenching. This study investigates the effect of Bi3+ ion concentration on the spectroscopic features of Fe3+ ions in CaAl4O7:Fe3+, Bi3+ system. The presence of the 1S0→1P1 transition band in Fe3+ PLE spectra indicates the Bi3+→Fe3+ energy transfer leading to a corresponding increase in luminescence intensity of Fe3+ ions by over 30-fold compared to Fe3+-singly doped sample. High Bi3+ concentrations also quench Bi3+ ion luminescence, improving NIR emission purity. Additionally, the presence of Bi3+ ions enhances Fe3+ ion luminescence stability by delaying the thermal depopulation, as evidenced by a T50 shift from 323 K to 393 K. Overall, co-doping CaAl4O7:Fe3+ with Bi3+ ions expands excitation spectra, boosts luminescence intensity, and enhances the thermal stability.