title: Giant enhancement of upconversion emission in (NaYF₄:Nd³⁺/Yb³⁺/Ho³⁺)/(NaYF₄:Nd³⁺/Yb³⁺) core/shell nanoparticles excited at 808 nm.
abstract: In this work, colloidal hexagonal-phase (NaYF4:Nd3+/Yb3+/Ho3+)/(NaYF4:Nd3+/Yb3+) core/shell nanoparticles with intense visible upconversion emissions under 808-nm laser excitation were prepared. Compared with the core-only nanoparticles, a maximum 990-fold overall enhancement in the emission intensity of Ho3+ ions was achieved with the help of active-shell coating design, due to the significant increase in the near-infrared absorption and efficient energy transfer from Nd3+ primary-sensitizers to Ho3+ activators via Yb3+ bridging sensitizers. The luminescence-enhancement effect exhibited a strong dependence on the doping concentrations of NaYF4:Nd3+/Yb3+ active-shell. The optimal concentrations of Nd3+ and Yb3+ ions in the active-shell layer were found to be 30 and 5 mol. %, respectively. Moreover, the upconversion emission intensity of NaYF4:Nd3+/Yb3+-coated nanoparticles was about 2.5 times higher than the one coated with a NaYF4:Nd3+ active-shell.
authors.forename: Xiaoyong
authors.initials: X
authors.lastname: Huang
mesh_terms: D005459:Fluorides / Q000737:chemistry*; D006695:Holmium / Q000737:chemistry*; D007834:Lasers; D008163:Luminescent Measurements; D053758:Nanoparticles / Q000737:chemistry*; D009354:Neodymium / Q000737:chemistry*; D015018:Ytterbium / Q000737:chemistry*; D015019:Yttrium / Q000737:chemistry*
chemical_list: C525362:sodium yttriumtetrafluoride; D009354:Neodymium; D015019:Yttrium; D015018:Ytterbium; D005459:Fluorides; D006695:Holmium