Uncovering Different Responses and Energy Mechanisms of Sensitizer and Activator in Host Manipulation for Upconversion Nanoparticles
Ye Kuang, Dan Yang, Shili Gai, Fei He, Baichao An, Piaoping Yang
Abstract
Agile and efficient upconversion luminescence (UCL) fine-tuning strategies are the most demanded for in the frontier applications of highly doped upconversion nanoparticles (UCNPs). By doping Zn 2+ ions into NaHoF 4 and NaGdF 4:Yb 3+ shells using the oleate method, the separate influences of Zn 2+ on Ho 3+ and Yb 3+ ions in UCL-related processes were analyzed in detail, revealing relevant UCL changes and underlying energy mechanisms from a novel but explicit perspective. Different behaviors of green and red UCL before and after Zn 2+ -ion doping were attributed to the disparities in the energy pathways and features of the sample structures. Herein, the populations of 5 S 2 / 5 F 4 and 5 F 5 states, not the usually mentioned decay time, decided the UCL intensities of the NaHoF 4 @NaYbF 4 -structured highly doped UCNPs. The advantageous small sizes and intense single-band red UCL of these UCNPs were further developed by combining our previous strategies with introducing Zn 2+ ions into the NaHoF 4 matrix. Overcoming energy loss by surface quenchers and Zn 2+ -triggered inner defects is the key factor in maximizing 4f–4f transitions. To the best of our knowledge, the current study is the first attempt to date to experimentally reveal separate impacts of the heteroions on activators and sensitizers in UCL-related processes and can deepen the theoretical investigation of Ho-based UCL for the broadened applications of NaHoF 4 UCNPs.