High sensitive optical thermometry based on redshift of charge transfer band in Ba₂CaWO₆:Eu³⁺ phosphors

Optical thermometry has emerged as a promising technology to overcome the limitations of traditional thermometry techniques. Herein, we report an Eu3+-activated tungstate Ba2CaWO6 phosphors for luminescent thermometry with a maximum relative sensitivity of 4.84% based on a single-band ratiometric technique. By monitoring the D-5(0) -> F-7(1) (595 nm) emission of Eu3+, excitation spectrum of the as-prepared sample was measured, showing a dominant broad band ranging from 240 to 345 nm corresponding to the O2--W6+ charge transfer band (CTB). The intensity of CTB gradually decreases and the CTB edge shows an appreciable red shift when the temperature increases due to thermal population of the [WO6](6-) moiety at higher vibrational levels. The opposite temperature dependences of the two specific excitations, one at the peak of CTB and the other from the edge of CTB, were employed to design a luminescence intensity ratio thermometry scheme in the tungstate. When compared to other related schemes, our scheme showed a higher relative sensitivity.