Temperature dependence of afterglow in zirconia and its optically-stimulated luminescence by bone-through irradiation for biological temperature probe

Repetitive afterglow in zirconia by pulsed near-infrared irradiation toward biological temperature sensing

Photoluminescence provides information about the surrounding environment. In this study, aiming to develop a non-invasive deep body-temperature sensing method, we investigated photoluminescence properties of afterglow zirconia (ZrO2) by pulsed near-infrared (NIR) light irradiation based on the biological temperature. Pulsed light irradiation produced optically stimulated luminescence, followed by afterglow, with the property of repeating 100 times or more. Furthermore, the basic principle of temperature measurement was demonstrated through afterglow decay curve measurements. The use of harmless ZrO2 as a sensing probe and NIR light, which is relatively permeable to living tissues, is expected to realize temperature measurements in the brain and may also facilitate optogenetic treatment.

Afterglow Properties and Trap-Depth Control in ZrO2:Ti, M (M = Ca2+, Y3+, Nb5+, W6+)

Ti-doped ZrO₂ is a chemically stable and persistent luminescence material. Doping and co-doping is an effective approach for improving the afterglow properties of phosphors, but few studies have investigated the co-doping of ZrO₂:Ti systems. This study aimed to synthesize ZrO₂:Ti, M (M = Ca²⁺, Y³⁺, Ti single-doped, Nb⁵⁺, W⁶⁺) and evaluate the luminescent properties of the resulting materials, with a specific focus on the relationship between trap depth and the valence state of the co-doped cation. The ratio of the luminescent center to co-doped ion was optimized using the combinatorial approach, where 0.09 mol % Ti led to the best afterglow duration. The emission decay curves of each co-doped sample differed significantly, where a change in curvature was observed in the Ti single-doped and W⁶⁺ co-doped samples due to the presence of multiple traps. From the thermoluminescence glow curves, the trap originating in an oxygen vacancy with a peak at around 270 K was observed. The trap depth was dependent on electrostatic interactions between the trapped electrons and their surrounding cations, and thus related to the valence of the co-dopant. Overall, co-doping with high-valent cations led to improved afterglow duration.