Dual-mode temperature sensitive fluorescence phenomenon based on reconstruction of multi-level system in BaCaLu2F10 micro-nanocrystals

Abstract In this work, we mainly focus on the design of dual-mode temperature (T) sensitive fluorescence phenomenon in single fluoride materials. The compound BaCaLu2F10 with low phonon energy is used as the host to expectantly construct the programmable energy system based on Yb3+-Er3+-Tm3+ rare earth ions, thereby achieving dual-mode fluorescence features of the thermal coupling phenomenon of Er3+ between 2H11/2 and 4S3/2 energy levels, and energy transfer between 4F7/2 energy level of Er3+ and 3F2 energy level of Tm3+. Whereas the T-dependent spectrum indicates that the Yb3+-Er3+-Tm3+ system exhibits excellent thermal stability under the excitation of 980 nm, which is not conducive to the application in T sensors. The V5+/Mo6+ to have rich charge transitions between their d0 electronic structure and ligand orbits could be effective choice to bridge the different energy levels. Consequently, we attempt to reconstruct the Yb3+-Er3+-Tm3+-V5+/Mo6+ energy level system and successful change the fluorescence intensity ratios of 521nm/540 nm and 700nm/654 nm as the T rises. Meanwhile, the UC emission intensities of BaCaLu2F10:Yb3+, Er3+, Tm3+ UCPs are sharply enhanced up to 104 and 4.14 times by doping 3mol% V5+ or 3mol% Mo6+, respectively, which is beneficial to improve the sensitivity of T sensors.