Optical temperature sensing based on upconversion nanoparticles with enhanced sensitivity via dielectric superlensing modulation

Recently, the temperature sensing using the fluorescence intensity ratio (FIR) of two thermally coupled emission bands of upconversion nanoparticles (UCNPs) has attracted more and more attention. Here, we report optical temperature sensing based on UCNPs with enhanced sensitivity via dielectric superlensing modulation. UCNPs are first deposed on an aluminium flake and then coated with a monolayer of polystyrene microspheres (PS spheres) to form a composite film. Under the excitation of near-infrared 980 nm laser, FIR of the transitions 1 I 6 → 3 H 6 (310 nm) and 1 D 2 → 3 H 6 (360 nm) of Tm 3+ ions in UCNPs is highly sensitive to temperature variation. The thermal sensitivity of the composite film is enhanced by more than 70% at the temperature of 350 K relative to that without PS sphere superlens, which is ascribed to the modulation of the dielectric superlensing effect on the wave front of upconversion ultraviolet fluorescence.