Luminescence Thermometry Using Dy3+-Activated Na0.25K0.25Bi0.5TiO3 Powders

When activated by Dy3+, Na0.25K0.25Bi0.50TiO3 (NKBT), piezoelectric powders show strong luminescence in the blue and yellow spectral range. Emissions of this material can be effectively utilized for both luminescence intensity ratio and lifetime-based readouts of temperature. Photoluminescence measurements over a temperature range of 293-483 K show that the luminescence intensity ratio temperature readout has maximal relative sensitivity of 1.93% K-1 at 380 K, while the relative sensitivity of the lifetime temperature readout reaches 1.1% K-1 at 480 K. For this study, materials were synthesized by a solid-state reaction using TiO2, Bi2O3, Na2CO3, K2CO3 and Dy2O3 as precursors. X-ray diffraction measurements showed that the NKBT sample crystallized in the A-site substituted distorted perovskite rhombohedral structure (R3c symmetry). The photoluminescence spectra showed characteristic emission bands of Dy3+ ions centered at 457 nm (I-4(15/2) -> H-6(15/2)), 478 nm (F-4(9/2) -> H-6(15/2)), 574 nm (F-4(9/2) -> H-6(13/2)) and 663 nm (F-4(9/2) -> H-6(11/2)). The ratio of emissions from F-4(9/2) and I-4(15/2) excited states to the H-6(15/2) ground state was used as a luminescence intensity ratio indicator of temperature, while the decay of emission from F-4(9/2) -> H-6(13/2) transition was used as a lifetime indicator of temperature. CIE coordinates x = 0.326 and y = 0.361 calculated from room temperature emission spectra show the perspective of this material for use in white light emission devices.