Non-contact optical thermometry via non-thermally coupled levels in upconverting glass

This research article reports the non-contact optical thermometric study using the UC emission intensity ratio of thermally and non-thermally coupled levels. Tm3+/Er3+/Yb3+ codoped TeO2-WO3-Bi2O3 (TWBi) glass have been synthesized using melt-quenching technique. After analyzing the optical absorption and UC emission spectra at room temperature, the temperature-dependent study of UC emission spectra has been performed in the 303–523 K range. First, the optical temperature sensing using the luminescence intensity ratio of thermally coupled levels of Er3+ ion has been studied. The maximum value of absolute and relative sensitivities has been found to be ∼0.0088 K−1 at 483 K and ∼0.0120 K−1 at 303 K, respectively. Furthermore, the luminescence intensity ratio approach has been employed to study non-contact temperature sensing in non-thermally coupled levels. While employing the ratiometric approach involving non-thermally coupled levels, a simultaneous improvement in absolute and relative sensitivities has been witnessed. There, the maximum value of absolute and relative sensitivities has been found as high as ∼0.7143 K−1 at 523 K and ∼0.0249 K−1 at 483 K, respectively. It has been found that the relative sensitivity in the case of non-thermally coupled levels (NTCLs) clearly dominates the relative sensitivity of TCLs.