A novel Ho3+ → Yb3+ → Ho3+ multi-step energy transfer caused quantum cutting under 455 nm excitation is observed in Ho3+/Yb3+ co-doped BaZr0.8Y0.2O3-δ phosphor. During the quantum cutting process, Yb3+ ions efficiently increase the particle population of 5I6 level of HO3+, resulting in 10 and 8 times of enhancement of Ho3+ emission at 1216 nm (5I6 → 5I8) and 1926 nm (5I7 → 5I8), respectively. It is interesting that the 2F5/2 → 2F7/2 emission of Yb3+ ions themselves is very weak although the quantum cutting is performed by the Ho3+/Yb3+ ion-pairs. The result indicates that the Yb3+ → Ho3+ back energy transfer in the BaZr0.8Y0.2O3-δ phosphor is quite efficient and helpful for the enhancement of Ho3+ emission in near infrared region. A new valid method based on luminescence intensity ratio is developed to estimate the quantum cutting efficiency. It is found that the energy transfer form Ho3+ to Yb3+ is 52.8% in the phosphor with optimum Ho3+/Yb3+ doping concentration and 90% of near infrared emission of Ho3+ is performed by the multi-step energy transfer induced quantum cutting.
Chen, T., Yang, X., Xia, W., Gao, X., Li, W., & Xiao, S. (2016). Near-infrared quantum cutting in Ho3+/Yb3+ co-doped BaZr0.8Y0.2O3-δ. Materials Science and Engineering B: Solid-State Materials for Advanced Technology, 211, 20–25. https://doi.org/10.1016/j.mseb.2016.05.016