Sensitive Luminescence Thermometry through Excitation Intensity Ratio in Eu-Doped BaTiO3

Optical ratiometric thermometry techniques have gained much attention in recent years due to their reliable and noncontact temperature sensing capability for industrial and biorelated applications. Herein, we exploited the temperature dependence of the absorption band of BaTiO3 (BTO) for novel excitation intensity ratio (EIR) thermometry. Photoluminescence and excitation properties of Eu3+-doped BTO powders were studied as a function of Eu3+ doping concentration. The excitation peak intensities at 397 and 468 nm, corresponding to the 7F0 → 5L6 and 5D2 transitions of Eu3+, were used as EIR parameters. The temperature dependence of the EIR can be explained by the competitive absorption between Eu3+ and the BTO host. The EIR properties were studied in relation to the doping concentration, registering a maximum relative sensitivity (S r) of 4.89% K–1 in BTO:Eu3+ (0.5%) at 303 K. An amphoteric Eu3+ occupation mode at both Ba2+ and Ti4+ sites was found to interpret the doping concentration dependence of the S r. The reduced Ba2+ site occupation ratio proved to be responsible for the low S r values at high Eu3+ doping concentrations. Accordingly, an Eu3+/Ti3+ codoping method was further proposed to improve the S r by increasing the Ba2+ site occupation ratio. Our result showed that BTO:Eu3+ (0.5%) demonstrated an enhancement of S r from 4.89 to 6.42% K–1 at 303 K after 2% Ti3+ codoping.