Engineering the upconversion luminescence in fluoride KCdF3:Yb3+,Mn2+,Er3+ nanocrystals under 980, 940 and 915 nm multi-excitations

Yb 3+ -Mn 2+ dimer based upconversion nanocrystals (UCNCs) have great prospects in biological and photonic applications. In this work, the broadband upconversion luminescence (UCL) of Yb 3+ -Mn 2+ dimer in perovskite nanocrystals is systematically engineered under multi-wavelength excitations. Under the excitation of 980, 940 and 915 nm lasers, KCdF 3 :Yb 3+ /Mn 2+ UCNCs generate yellow broadband UCL from Yb 3+ -Mn 2+ dimer at room temperature and achieve maximum intensity as Mn 2+ concentration reaches 7.5 mol%. By introducing Er 3+ ions into the KCdF 3 host matrix, the UCL color can be further tuned to pure red with high spectral purity , and the red-to-green (R/G) UC intensity ratio is promoted dramatically. The bidirectional energy transfer (ET) processes between Yb 3+ -Mn 2+ dimer, Mn 2+ and Er 3+ ions facilitate color modulation, supported by power dependence and lifetime measurements. Especially, the ET efficiency is evaluated under the multi-wavelength excitations, confirming the high efficiency of ET processes from Yb 3+ -Mn 2+ dimer to Er 3+ ions. Moreover, the obtained KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ UCNCs present a maximum magnetization intensity of 2.01 emu/g when Mn 2+ concentration reaches 98.5 mol%. Both the tunable UCL and excellent paramagnetism properties indicate that these KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ UCNCs have the capability of bifunctional biomarkers of nanomaterials and can be a candidate for bio-related applications. • Broadband upconversion of Yb 3+ -Mn 2+ dimer was observed in KCdF 3 nanocrystals under 980, 940 and 915 nm excitations. • Upconversion luminescence properties of KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ were investigated under multi-wavelength excitations. • Pure red upconversion of Er 3+ was obtained based on the bidirectional energy transfer under multi-wavelength excitations. • An excellent magnetization intensity of 2.01 emu/g was achieved in paramagnetic KCdF 3 :Yb 3+ /Mn 2+ /Er 3+ nanocrystals.