The Upconversion Luminescence of Er(3+)/Yb(3+)/Nd(3+) Triply-Doped β-NaYF(4) Nanocrystals under 808-nm Excitation

In this paper, Nd(3+)–Yb(3+)–Er(3+)-doped β-NaYF(4) nanocrystals with different Nd(3+) concentrations are synthesized, and the luminescence properties of the upconversion nanoparticles (UCNPs) have been studied under 808-nm excitation for sensitive biological applications. The upconversion luminescence spectra of NaYF(4) nanoparticles with different dopants under 808-nm excitation proves that the Nd(3+) ion can absorb the photons effectively, and the Yb(3+) ion can play the role of an energy-transfer bridging ion between the Nd(3+) ion and Er(3+) ion. To investigate the effect of the Nd(3+) ion, the decay curves of the (4)S(3/2) → (4)I(15/2) transition at 540 nm are measured and analyzed. The NaYF(4): 20% Yb(3+), 2% Er(3+), 0.5% Nd(3+) nanocrystals have the highest emission intensity among all samples under 808-nm excitation. The UC (upconversion) mechanism under 808-nm excitation is discussed in terms of the experimental results.