We report a localized surface plasmon enhanced upconversion luminescence in Au/SiO₂/Y₂O₃:Yb³⁺,Er³⁺ nanoparticles when excited at 980 nm. By adjusting the silica spacer's thickness, a maximum 9.59-fold enhancement of the green emission was obtained. Effect of the spacer distance on the Au-Y₂O₃:Yb³⁺, Er³⁺ green upconversion mechanism was numerically simulated and experimentally demonstrated. In theory for radiative decay and excitation rates, they can be largely enhanced at the spacer thicknesses of less than 70 and 75 nm, respectively, and the quenching can be caused by the non-radiative energy transferring at the distance of less than 55 nm.

As potential single-phase multiferroic materials, Aurivillius compounds have attracted much interest in recent years. In this paper, Bi₅Fe_0.9Co_0.1Ti₃O₁₅ (BFCTO) nanosheets were first synthesized by a hydrothermal method; lateral length and thickness of them are ∼600 nm and ∼100 nm, respectively. The BFCTO nanosheets were assumed to form by a co-effect of the aggregate process, the oriented attachment of neighboring nanorods, and Ostwald ripening. Besides, an obvious hysteresis loop with 2M_r = ∼0.55 emu g⁻¹ and 2H_c = ∼2600 Oe at 300 K was observed in the final products. Both dielectric permittivity and dielectric loss decrease with the increase of the frequency at room temperature. Our results could serve as guidance to realize a controllable synthesis of Aurivillius nanoparticles and will shed light on designing new nanodevices.

Lanthanide-doped upconversion nanoparticles have attracted extensive research interest due to their promising applications in various fields.