Up-Conversion Fluorescence of Tm³⁺ and Gd³⁺ in Yb³⁺/Tm³⁺ Co-Doped Gd₂O₃ Nanocrystals

Through a co-precipitation method Gd(OH)₃:20%Yb³⁺, 1%Tm³⁺ nanorods were synthesized. After sintered at 900 °C for 1 h in air, the as-prepared Gd(OH)₃:20%Yb³⁺, 1%Tm³⁺ nanorods were converted into Gd₂O₃:20%Yb³⁺, 1% Tm³⁺ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd₂O₃:20%Yb³⁺, 1%Tm³⁺ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm³⁺, but also show UV UC emissions of host Gd³⁺. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm³⁺ to Gd³⁺ is very efficient.