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 Ho 3+ , intense single-band red UC emission is realized in perovskite KZnF 3 : Mn 2+ ,Yb 3+ ,Ho 3+ nanocrystals via controlling the doping concentration ratio of Mn 2+ to Ho 3+ . Based on stokes emission, UC luminescence and energy levels of Mn 2+ and Ho 3+ , a bidirectional energy transfer from the 5 S 2 / 5 F 4 state of Ho 3+ to the 4 T 1 ( 4 G) state of Mn 2+ or | F 2 7 / 2 , T 4 1 ( G 4 ) 〉 state of Yb 3+ -Mn 2+ dimer, then to 5 F 5 state of Ho 3+ (ET2) is provided to explain the unique UC emission behaviors of KZnF 3 : Mn 2+ ,Yb 3+ ,Ho 3+ . The effects of dopant concentration on the UC luminescence properties of KZnF 3 : Mn 2+ , Yb 3+ , Ho 3+ is investigated in detail. Analysis of the dominant red UC emission of KZnF 3 : Mn 2+ , Yb 3+ , Ho 3+ under different laser pulse width excitation indicates the energy transfer process . The special temperature dependent UC luminescence for Mn 2+ doped and Mn 2+ freely doped KZnF 3 :Yb 3+ , Ho 3+ 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.