A strategy to achieve 808 nm excited single-band red upconversion luminescence of Ho(3+) 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 Nd(3+) (∼10 mol %) in the shell layer and, thus, markedly enhance red upconversion emission from Ho(3+) activators in the core with the assistance of spatially confined doping of Nd(3+) ions and efficient energy transfer of Nd(3+) → Yb(3+)(shell) → Yb(3+)(core) → Ho(3+). Importantly, introducing Ce(3+) into the core was beneficial to the competition of radiation transitions from the two intermediate excited states of Ho(3+): (5)S2,(5)F4 (green-emitting) and Ho(3+): (5)F5 (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.
Keywords: NaYF4; biolable; energy transfer; lanthanide; nanocrystals; upconversion.