Boosting the sensitivity of Er3+-based luminescent ratiometric thermometry

Abstract Non-contact optical thermometry, based on the luminescence intensity ratio (LIR) of two thermally-coupled levels (TCLs), has received increasing attentions nowadays. Designing novel TCLs-based temperature sensor becomes one of the most significant things in the field of optical thermometry. In this work, a novel strategy for temperature measurement is proposed. It is based on the 4F7/2 and 4S3/2 TCLs, rather than the widely studied 2H11/2 and 4S3/2 TCLs of Er3+. Both the two pairs of TCLs have been confirmed to be under the control of the Boltzmann distribution and thus can be used for luminescence ratiometric thermometry. The former TCLs have a larger energy gap (1808 cm−1) than the latter ones (711 cm−1). Based on this fact, it is shown here that using the 4F7/2-4I15/2 and 4S3/2-4I15/2 transitions can achieve a more sensitive temperature measurement than that depending on the 2H11/2-4I15/2 and 4S3/2-4I15/2 transitions at the operating temperatures from 333 to 773 K. At 333 K, the relative sensitivity (SR) of the former two transitions is calculated to be ~2.3% K−1. By comparison, using the latter two transitions only has a SR of 0.9% K−1 at the same temperature.