Blue emission-dominated NaYbF₄@NaYF₄:2%Ho@NaYF₄ upconversion nanoparticles for detecting ascorbic acid

The blue emission-dominated NaYbF₄@NaYF₄:2%Ho@NaYF₄ (CSS) upconversion nanoparticles (UCNPs) were designed to detect ascorbic acid (AA). The blue emission of CSS was increased, ∼34 and ∼8 times higher than that of NaYF₄:2%Ho@NaYbF₄@NaYF₄ (CSS (I)) and NaYbF₄@NaYF₄:20%Yb,2%Ho@ NaYF₄ (CSS (II)), respectively. The dominant blue emission of CSS might be attributed to three aspects: (1) the protected NaYbF₄ core for high near-infrared absorption, (2) the spatial separation of Yb³⁺ and Ho³⁺ preventing back energy transfer, and (3) their inert shell inhibiting surface quenching. It is worth noting that the fluorescence resonance energy transfer (FRET) of the CSS (donor) to MnO₂ nanosheets (acceptor) was developed to trace AA. The detection limit is 0.75 μM and the detection range is 0.5-100 μM. In summary, our work not only explored the blue emission mechanism of Ho³⁺, but also constructed a CSS/MnO₂-based nanosensing platform for the rapid and sensitive detection of AA. The blue emission of Ho³⁺ has promising applications in the field of sensing and detection.