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

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 S-5(2)/F-5(4) state of Ho3+ to the T-4(1)((4)G) state of Mn2+ or vertical bar F-2(7/2),T-4(1) ((4)G)> state of Yb3+-Mn2+ dimer, then to F-5(5) 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. (c) 2016 Elsevier B.V. All rights reserved.