LAUSR

Abstract Single-band red upconversion luminescence (UCL) is vital to in vivo bioimaging as well as “see and treat” biomedicines. Herein, starting with the previously reported β-NaErF4:Tm UCNPs, we examined the effects of both Yb3+ doping and inert shell coating on the red-to-green (R/G) ratio for Er3+ based UCL. The doping of Yb3+ into the β-NaErF4:Tm3+ core not only enhances the whole UCL intensity, but also raises the R/G ratio by 1.25 times. In addition, the coating of an inert NaYF4 shell, which is usually adopted for the enhancement of UCL intensity, further boosts the R/G value up to as high as 77.92. This work may benefit the potential bioimaging application of single-band red UCL.