Monodisperse Gd2O3:Ln (Ln = Eu3+, Tb3+, Dy3+, Sm3+, Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) nanocrystals with tunable size and multicolor luminescent properties

Abstract

Multicolor and monodisperse Gd₂O₃:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺, Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, and Yb³⁺/Ho³⁺) nanocrystals (NCs) with narrow size distribution were prepared by a homogeneous precipitation method followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and kinetic decays were employed to characterize the samples. The results show that the Gd₂O₃:Ln NCs can be directly indexed to cubic Gd₂O₃ phase with high purity. And the possible formation mechanism and the chemical reaction of each step to form spherical Gd₂O₃:Ln NCs are proposed according to the concerned analysis. Upon ultraviolet and low-voltage electron beams excitation, Gd₂O₃:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺, and Sm³⁺) NCs exhibit respective bright red (Eu³⁺, ⁵D₀ → ⁷F₂), green (Tb³⁺, ⁵D₄ → ⁷F₅), blue (Dy³⁺, ⁴F_9/2 → ⁶H_13/2) and yellow (Sm³⁺, ⁴G_5/2 → ⁶H_7/2) down-conversion (DC) emissions. Under 980 nm NIR irradiation, Gd₂O₃:Ln (Ln = Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, and Yb³⁺/Ho³⁺) exhibit characteristic up-conversion (UC) emissions of Er³⁺, Tm³⁺, and Ho³⁺, respectively.