Deconstructing excitation transitions in Dy3+-doped CaWO4 to develop a new ratiometric luminescent thermometry for achieving ultra-high sensing sensitivity

Investigating excitation transition behavior is crucial for elucidating the photoluminescence (PL) characteristics of lanthanide ion-doped phosphors. This investigation provides a basis for developing new ratiometric luminescent thermometry methods based on thermally influenced excitation processes. In this study, the excitation transition lines of trivalent dysprosium (Dy3+) and charger-transfer band (CTB) in Dy3+-doped CaWO4 (CaWO4:Dy) phosphors were effectively deconstructed using the Dy3+ concentration- and temperature-dependent PL excitation (PLE) spectra in the ultraviolet range of 280–340 nm. The phosphors exhibited a thermal-quenched PLE intensity for Dy3+ and a thermal-enhanced PLE intensity for CTB owing to energy transfer between the CaWO4 host and Dy3+. A new ratiometric thermometry strategy was introduced using the opposite thermal-dependent PLE intensity of CTB as the temperature probe and Dy3+ as the reference signal. This method was based on the excited-state absorption intensity ratio between CTB and Dy3+. This new thermometry method exhibited ultra-high performance, reaching maximum absolute and relative sensitivities of 1.72 K−1 at 575 K and 4.66% K−1 at 300 K, respectively. This study presents a novel approach for developing highly sensitive and stable optical thermometric Dy3+-based materials and provides guidance for constructing an effective ratiometric thermometry strategy based on the deconstructed PLE properties.