Laser-Induced Heating and Modal Interference Limit the Accuracy of Single Upconversion Particle Thermometry on a Chip

Luminescent nanothermometry based on individual upconversion particles has been heralded as a powerful tool for noncontact temperature measurements with nanometer-scale resolution. However, their accuracy within integrated photonic systems remains uncertain despite their essentiality for practical applications. In this work, we investigate a single β-NaYF4:Yb,Er microparticle integrated into a silicon chip with fiber-based excitation and signal collection. We identify two main effects that limit the measurement accuracy. First, the high pump power density (>3500 W/cm2) required for detection induces significant local heating of the particle. This manifests as an anomalous reduction of the energy gap ΔE determined from the LIR between Er3+ levels to 260 cm–1, corresponding to overheating by approximately 110 K relative to the substrate. Second, we observe and characterize periodic intensity oscillations, which we attribute to multimodal interference within the optical fiber. Despite these challenges, we demonstrate that the nonmonotonic trend of the integrated intensity can be described by a photophysical model, confirming the feasibility of a simplified analytical approach without using a spectrometer. Our results reveal critical design factors for hybrid sensing platforms and provide clear directions for their optimization, including the use of highly sensitive detectors to reduce pump power and the implementation of specialized fibers. Thus, our work experimentally demonstrates and quantitatively evaluates these factors within a realistic integrated system. The obtained results suggest design principles for the development of the next generation of precision sensing platforms.