A highly sensitive ratiometric optical cryothermometer using a new broadband emitting trivalent bismuth singly...

Motivated by the growing demand for noncontact temperature sensing in cryogenic environments, the development of a high performance low temperature optical thermometer has become more and more urgent. Herein, we demonstrate a new broadband emitting bismuth singly activated Ba₂ZnSc(BO₃)₃ optical thermometric material that exhibits a remarkable temperature-dependent emission color variation and a good low temperature sensing performance. First, Bi³⁺ doped Ba₂ZnSc(BO₃)₃ phosphors were successfully synthesized by a high-temperature solid-state reaction. Upon excitation at 320 nm, the emission spectra of Ba₂ZnSc(BO₃)₃:Bi³⁺ cover almost the entire visible region from 350 to 720 nm because of the multiple crystallographic sites occupied by Bi³⁺ ions, which have been verified by structure analysis and time-resolved emission spectroscopy. Interestingly, the temperature dependent emission characteristics indicated that the thermal quenching phenomena of Bi³⁺ at different lattice sites were different, resulting in a very sensitive emission color variation from orange to cyan. Further analysis indicated that these Bi³⁺ doped luminescent materials showed a good performance in temperature sensing over a wide temperature range from 10 to 374 K, with a maximum relative sensitivity of 3.076% K^-1 at 210 K. Finally, this study provides a new perspective for the design of superior thermosensitive phosphors, aimed toward non-rare earth ion doped thermosensitive phosphors for optical cryothermometry applications.