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 BaTiO 3 (BTO) for novel excitation intensity ratio (EIR) thermometry. Photoluminescence and excitation properties of Eu 3+ -doped BTO powders were studied as a function of Eu 3+ doping concentration. The excitation peak intensities at 397 and 468 nm, corresponding to the 7 F 0 → 5 L 6 and 5 D 2 transitions of Eu 3+, were used as EIR parameters. The temperature dependence of the EIR can be explained by the competitive absorption between Eu 3+ 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:Eu 3+ (0.5%) at 303 K. An amphoteric Eu 3+ occupation mode at both Ba 2+ and Ti 4+ sites was found to interpret the doping concentration dependence of the S r . The reduced Ba 2+ site occupation ratio proved to be responsible for the low S r values at high Eu 3+ doping concentrations. Accordingly, an Eu 3+ /Ti 3+ codoping method was further proposed to improve the S r by increasing the Ba 2+ site occupation ratio. Our result showed that BTO:Eu 3+ (0.5%) demonstrated an enhancement of S r from 4.89 to 6.42% K –1 at 303 K after 2% Ti 3+ codoping.