Abstract
A new method that simultaneously alters multicolor upconversion luminescence (UCL) and improves overall UCL intensity, predominantly in red-emission bands, is presented here. Remarkedly enhanced temperature sensitivity at ultralow temperatures was also observed in Yb/Cu co-doped NaErF4 through transition metal Cu2+-doping. Varying the dopant (Cu2+) concentration in NaErF4:Yb effectively controlled the structure, allowing for blue, green, and red UCL output. Large enhancement across the entire UCL spectrum was observed for Cu2+-doped upconversion nanoparticles (UCNPs) compared to UCNPs not doped with Cu2+, resulting from non-radiative energy transfer between Cu2+ and Er3+. The rapid response of the NaErF4:Yb/Cu complex allowed for bioimaging of heart tissue within 1 h. Moreover, the relative sensitivity of UCNPs increased from 0.91% K−1 to 1.48% K−1 with metal Cu2+ doping at an ultralow temperature, which significantly impacts biomarker dependence on UCNPs.
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