Exploring the excitation spectrum behavior of Dy in CaWO4 for a new excited-state-based ratiometric thermometry

Exploring excited-state transition behavior is of great importance for understanding the optical characteristics of lanthanide ions, which may potentially develop new optical thermometry by the thermally affected excitation processes. In this work, we explore the detailed excitation transition behaviors of Dy3+ and propose a new thermometry strategy based on excited-state absorption intensity ratio (EIR) in Dy3+ doped CaWO4 phosphors. The optimal Dy3+ doping concentration in CaWO4:Dy phosphors was determined and its fine excitation transition lines from low-lying levels of 6HJ (J = 15/2, 13/2, 11/2, and 9/2) to the respective high-lying levels of Dy3+ ions were identified by well-resolving the photoluminescence excitation (PLE) spectra. By taking advantage of the opposite trends of temperature-dependent PLE intensities of Dy3+, a new ratiometric thermometry based on the EIR of Dy3+ was proposed to be independent of the excitation wavelength and only excitation peak intensities required, with the merit of high absolute and relative sensitivities, excellent repeatability and reusability, good excitation wavelength selectivity. These findings demonstrated an effective strategy for developing a Dy3+-based EIR luminescent thermometer, as well as the enormous potential of Dy3+ doped CaWO4 phosphors in temperature sensing.