RESUMO
Thus far, Yb3+ has usually served as a sensitizer to improve energy harvesting in lanthanide ion based luminescent materials. Herein, besides the well accepted character as a sensitizer, we revealed a new role of Yb3+, namely an energy reservoir, to improve the upconversion efficiency of several lanthanide activators. The energy cycling between lanthanide activator A3+ and energy reservoir Yb3+ is mainly responsible for the improvement. This energy cycling can facilitate energy utilization by A3+ for the generated upconversion luminescence. Specifically, this energy cycling not only alleviates the dissipation of energy produced at the intermediate level, needed to promote electrons to a higher energy level, but also provides an additional excited-state absorption route for A3+. The benefits of the proposed Yb3+ energy reservoir as well as the energy cycling mechanisms were verified using three representative activators, Nd3+, Tm3+, and Er3+. This study can open new possible avenues to exploit Yb3+ and enrich the available upconversion luminescence pathways of lanthanide ions.
