Adjustable photoluminescence of Bi3+ and Eu3+ in solid solution constructed by isostructural end components through composition and excitation-driven strategy

Most lanthanide doped phosphors need to be prepared in a reducing atmosphere, such as phosphors doped by Eu2+ and Ce3+ ions with d-f transition. In contrast, the doping ion Bi3+ selected in this paper has more advantages. Moreover, the 6S electrons of bare bismuth are very sensitive to the surrounding coordination field environment, which makes it highly tunable. A new type of solid solution Sr3-xGdxAlO4+xF1-x designed by the isostructural end components Sr3AlO4F and GdSr2AlO5 well promotes the luminescence of Bi3+ ion. By adjusting the concentration of Bi3+/Eu3+, the phosphor can be tuned from blue to red, which is due to the energy transfer caused by dipole-dipole interaction between Bi3+ and Eu2+. Surprisingly, by means of excitation-driven, the emission peak position of Bi3+ ions can also be moved from similar to 425 nm to similar to 437 nm, and red shift occurs, so as to realize the tuning of the fluorescence from orange red to blue. We speculate that this is induced by the presence of multiple emission centers of Bi3+, and different absorption strength of Bi3+ and Eu2+. In addition, the thermal response of Bi3+ and Eu2+ ions to temperature is different. They are thermally quenched by energy level cross relaxation (ELCR) and multi-phonon deexcitation (MPD), respectively. The maximum relative sensitivity of optical thermometry based on fluorescence intensity ratio (FIR) is approximately 1.17 %K-1 at 323 K, which is higher than that of previously reported Bi3+ and Eu2+ co-doped phosphors. At 523 K, we also obtained a high absolute sensitivity of 0.0064 K-1. Consequently, the solid solution phosphor prepared by us has a far-reaching application prospect in the field of temperature monitoring.

Automated summary

This study uses Bi3+ ions instead of traditional Eu2+ and Ce3+ ions, and through controlling their concentration and coordination structure, achieves the tuning of the luminescent properties of phosphors, while also increasing the sensitivity of temperature monitoring.