Enhanced red upconversion luminescence induced by Yb-Fe dimer for bifunctional biological applications in optical thermometry and photothermics

The enhancement of the intensity of red upconversion (UC) emission has significant implications for biological applications. In KZnF₃:Yb³⁺, Er³⁺ which inherently produces high-purity red emission, the introduction of Fe³⁺ markedly improves the UC intensity by a factor of 13. The mechanism behind the enhanced UC red luminescence is deduced to originate from the Yb³⁺-Fe³⁺ dimer, as determined by first principle calculation and analysis of UC luminescence properties. The thermometry performance, based on splitting peaks of red emission, demonstrated enhanced temperature sensitivity at lower ranges. Exploring the photothermal properties, it was observed that temperature exhibited a linear correlation with pump power under a 980 nm laser, achieving levels up to 48 °C. This temperature range is ideal for applications in mild photothermal therapy (MPTT). This work elucidates the material’s potential in advanced biological applications, merging optical thermometry and photothermics, indicating its multifunctional utility.