Bidirectional energy transfer induced single-band red upconversion emission of Ho3+ in KZnF3:Mn2+,Yb3+,Ho3+ nanocrystals

Abstract

In contrast to common multiple upconversion (UC) emission characteristic from Ho3+, intense single-band red UC emission is realized in perovskite KZnF3: Mn2+,Yb3+,Ho3+ nanocrystals via controlling the doping concentration ratio of Mn2+ to Ho3+. Based on stokes emission, UC luminescence and energy levels of Mn2+ and Ho3+, a bidirectional energy transfer from the 5S2/5F4 state of Ho3+ to the 4T1(4G) state of Mn2+or |F27/2,T41(G4)〉 state of Yb3+-Mn2+ dimer, then to 5F5 state of Ho3+ (ET2) is provided to explain the unique UC emission behaviors of KZnF3: Mn2+,Yb3+,Ho3+. The effects of dopant concentration on the UC luminescence properties of KZnF3: Mn2+, Yb3+, Ho3+ is investigated in detail. Analysis of the dominant red UC emission of KZnF3: Mn2+, Yb3+, Ho3+ under different laser pulse width excitation indicates the energy transfer process. The special temperature dependent UC luminescence for Mn2+ doped and Mn2+ freely doped KZnF3:Yb3+, Ho3+ further confirm the bidirectional energy transfer mechanism in the UC process. The study of these single-band red UC nanocrystals provides deep insights into the understanding of bidirectional energy transfer in UC mechanism, offering the possibility for applications in biolabels and bioimaging.