A highly sensitive multiple-mode optical thermometer designed in Eu2+/3+ and Li+ co-doped polymorphism compound LaSc3(BO3)4

Abstract

Noncontact optical thermometers have attracted widespread attention, but existing problems such as single-mode and low-sensitivity thermometers still urgently need to be solved. Herein, a novel multiple-mode thermometer was designed for the polymorphism LaSc3(BO3)4:Eu2+/3+,Li+. X-ray diffraction (XRD) patterns revealed a slight transition between α- and β-phases with the concentrations of the dopants, which is further proved by structure refinements and first-principles calculations. The coexistence of Eu2+ and Eu3+ in the phosphors and their relative percentages were confirmed by X-ray absorption near-edge structure (XANES) spectra. Benefiting from appropriate emissions from Eu2+ and Eu3+ without obvious energy transfer and their opposite changing trends with temperatures under 307 nm excitation, a triple-mode optical thermometer is obtained for this material within the temperature range of 150–450 K. The highest sensitivities of 27.65, 14.05, and 7.68 %·K−1 are achieved based on two fluorescence intensity ratio (FIR) modes of Eu2+ and Eu3+ (5d–4f/5D0–7F2,4) and the fluorescence lifetime (FL) mode of Eu2+, respectively. To the best of our knowledge, the former is almost the highest in Eu2+ and Eu3+ co-doped thermometers. These results indicate that this material may be used as an excellent multiple-mode optical thermometer.

Keywords

• europium (eu) ions
• phase transition
• multiple-mode optical thermometer
• thermal quenching properties
• fluorescence intensity ratio (fir)
• fluorescence lifetime (fl)