A rhodamine-based sensing probe excited by upconversion NaYF4:Yb3+/Er3+ nanoparticles: The realization of simple Cu(II) detection with high sensitivity and unique selectivity

► Upconversion nanoparticles of β-NaYF4:Yb3+/Er3+ have been constructed. ► A rodamine derivative for Cu2+ sensing has been synthesized. ► An effective energy transfer between excitation source and sensor was achieved. ► β-NaYF4:Yb3+/Er3+:Rd-NH2 system showed linear response towards Cu2+. ► Good selectivity and high chemostability have been realized.