Strong tunability of cooperative energy transfer in Mn²⁺-doped (Yb³⁺, Er³⁺)/NaYF₄ nanocrystals by coupling with silver nanorod array

Fluorescent rare-earth ions are useful for efficient energy transfer via multichannels with different properties. Tuning these transfer processes in functional rare-earth materials has attracted considerable attention to satisfy the various demands of diverse practical applications. In this study, strong tunabilities of cooperative energy transfer and nonlinear upconversion emissions are realized using (Yb³⁺, Er³⁺)/NaYF₄ nanocrystals with and without doped Mn²⁺ ions by adopting a plasmonic nanocavity composed of a silver nanorod array. The plasmon nanocavity can not only increase the energy transfer between Mn²⁺ and (Yb³⁺, Er³⁺) but also significantly enhance the radiative emission. This reveals a prominent nonlinear gain in the nanocavity nanosystems. These observations suggest the prospective applications in the design and preparation of rare-earth nanocrystals with excellent tunabilities of multiple functionalities.