Optical thermometry based on thermolabile intrinsic polarons in Tm3+ and Yb3+ co-doped congruent lithium niobate single crystal

Abstract

By contrast with the conventional optical thermometry based on fluorescence intensity ratio (FIR) of thermally coupled levels (TCLs), we propose a novel thermometry strategy based on the diversity in thermal responses of non-TCLs of Tm3+ (3H4→3H6/1G4→3F4). Notably, the exacerbated response-contrast stems from the intrinsic structure variation induced by thermolabile polarons of NbLi3+ and NbNb4+ in congruent Tm3+,Yb3+:LiNbO3(LN) single crystal. The luminescence mechanism incorporated with energy transfer processes associated with polarons levels is revealed by investigating the abnormal temperature dependence of emission spectra under 980 nm excitation. The maximum absolute (SA) and relative (SR) sensitivities reach as high as 3.7% K−1 and 1.25% K−1 at 80 K, much higher than those of the TCLs strategy based on thermally coupled Stark sublevels of Tm3+ (3H4|1→3H6/3H4|3→3H6) in Tm3+,Yb3+:LN. This study demonstrates an effective pathway for developing new FIR strategies with improved sensitivities via taking advantage of host structure variation.