Nd3+-Sensitized Ho3+ Single-Band Red Upconversion Luminescence in Core Shell Nanoarchitecture

A strategy to achieve 808 nm excited single-band red upconversion luminescence of Ho3+ via the core-shell nanoarchitecture design was provided. Specifically, the synthesized Yb/Ho/Ce: NaGdF4@Yb/Nd: NaYF4 active-core@active-shell nanoparticles were evidenced to enable high-content doping of Nd3+ (-40 mol %) in the shell layer and, thus, markedly enhance red upconversion emission from Ho3+ activators in the core with the assistance of spatially confined doping of Nd3+ ions and efficient energy transfer of Nd3+ -> Yb3+(shell) -> Yb3+(core) -> Ho3+. Importantly, introducing Ce3+ into the core was beneficial to the competition of radiation transitions from the two intermediate excited states of Ho3+: S-5(2), F-5(4) (green-emitting) and Ho3+: F-5(5) (red-emitting), which induced great enhancement in the red to green intensity ratio and ultimately intense single-band red upconversion emission. We believe that this preliminary study will provide an important advance in developing luminescent markers suitable for biolabeling applications.