Enhancing upconversion luminescence via intermediate state in double perovskite phosphor: three-mode optical thermometry with python-assisted validation

High luminescence intensity, multiple modes, and high sensitivity are critical to achieving high measurement accuracy for optical thermometry in microelectronic devices and biological systems. The double perovskite phosphor, Ca2Sc0.63Mg0.07SbO6:Yb3+,Er3+, proves to be promising in overcoming these challenges. A simple high-temperature solid-phase method was used to prepare this sample which was found to exhibit red anti-Stokes luminescence under 980 nm excitation. Heterovalent substitution of Mg2+ for Sc3+ leads to lattice shrinkage and oxygen vacancy content enhancement. The induced generation of the intermediate state by the oxygen vacancy is significantly increased. This consequently enhances the upconversion luminescence intensity. The Ca2Sc0.63Mg0.07SbO6:Yb3+,Er3+ phosphor is capable of three-mode optical thermometry by thermally coupled energy states (TCES), non-thermally coupled energy states (NTCES), and CIE chromaticity shift. The NTCES-based mode has a notable relative sensitivity of Sr-max = 4.8% K-1 and superior signal resolution δT = 0.016 K. Furthermore, the NTCES-based model was tested for practical applications, and the difference between the predicted theoretical temperature and the actual test temperature was kept within 6 K after about 100,000 evaluations via Python assistance.