Simultaneous enhancement of fluorescence intensity, thermometric sensitivity and SNR of upconversion thermometers via optical field localization

Abstract

Lanthanide-doped upconversion nanoparticles (UCNPs) can be used as nanoscale thermometers and have recently attracted great attention. However, due to their intrinsically low quantum yield and remarkable intensity attenuation with increasing temperature, simultaneous improvement of their fluorescence intensity, thermometric sensitivity and signal to noise ratio (SNR) is still a challenge. In this work, we have proposed a 2D photonic crystal (PC)/Au/UCNPs upconverted platform and investigated its optical properties and thermal response. The excitation field can be highly localized by the all-dielectric optical concentration and plasmonic hot carrier, which can not only enhance the detecting signal intensity and the SNR but also increase the thermometric sensitivity by creating extra amplified interfacial thermal fields around the UCNPs, which is also known as the thermal self-amplification effect. Compared with traditional UCNPs, the fluorescence intensity, thermometric sensitivity and SNR of the proposed upconverted platform are enhanced by over 1500%, 30% and 3000%, respectively. This study presents a route for enhancing the comprehensive performance of upconversion thermometers via optical field localization.