1532 nm-driven multimode optical thermometry within biological window enabled by Er3+ self-sensitized upconversion luminescence

Abstract

The development of optical thermometers operating within the biological windows is crucial for safe and precise deep-tissue temperature sensing. This work reports a self-sensitized Er3+-doped LaScO3 phosphor for upconversion (UC) luminescence and thermometry under 1532 nm excitation just locating in the longer wavelength region of the second biological window. The UC mechanisms of the samples involving multi-photon processes are systematically investigated. Multiple optical thermometry is developed through the fluorescence intensity ratio (FIR) technique using transitions from Er3+: 4F9/2, 4I9/2 and 4I11/2 level, respectively. While the thermometers based on thermally coupled Stark sublevels show reliable performance, a significantly improved sensitivity of 5.22% K-1 is achieved by employing a non-thermally coupled energy pair 4F9/2 and 4I9/2. The accuracy of the thermometric readings is validated against a standard infrared thermometer. Furthermore, ex vivo penetration experiment demonstrates the superior potential of 4I11/2 → 4I15/2 transition for temperature probing in deep tissues. These findings demonstrate LaScO3: Er3+ is a high-performance candidate for deep-tissue optical thermometry.