Facile synthesis of mono-disperse sub-20 nm NaY(WO4)2:Er3+,Yb3+ upconversion nanoparticles: a new choice for nanothermometry

Abstract

We report a novel optical nanothermometer based on ultra-small NaY(WO₄)₂:Er³⁺,Yb³⁺ (NYW:Yb,Er) upconversion nanoparticles (UCNPs). The monodisperse, diamond-shaped sub-20 nm NYW:Er,Yb UCNPs with an average size of ∼8.5 × 12.5 nm were prepared via a facile one-step thermolysis protocol. Upon 980 nm laser excitation, the NYW:Er,Yb UCNPs yield bright green UC emission. The maximum relative sensitivity (S_rel) and absolute sensitivity (S_abs) were determined to be ∼1.2% K⁻¹ at 293 K and ∼0.9% K⁻¹ at 503 K, respectively. The excellent repeatability of fluorescence intensity ratio (FIR) and low temperature uncertainty ΔT_min of ∼0.4 K at 293 K make them promising for optical nanothermometry covering a wide temperature range of 293–503 K.