Facile synthesis, growth mechanism and luminescence properties of uniform La(OH)3 : Ho3+/Yb3+ and La2O3 : Ho3+/Yb3+nanorods

Abstract

One-dimensional (1D) La₂O₃ and La₂O₃ : Ln³⁺ (Ln = Ho/Yb) nanorods have been successfully synthesized at a mild condition via a facile homogenous precipitation method followed a heat treatment of their corresponding hydroxides. It can be found that the type of alkali and dosage of urea play crucial roles in the formation of uniform lanthanum hydroxide nanorods. The lanthanum hydroxide nanorods are morphology-formative intermediate for the formation of lanthanum oxides nanorods. The possible formation processes of 1-D lanthanum hydroxide and oxide nanorods were investigated. Under ultraviolet light and low-voltage electron beam excitation, the as-prepared Ho³⁺-doped La₂O₃ nanorods show a strong green emission corresponding to ⁵S₂ → ⁵I₈ transition of Ho³⁺ ions, which possesses sharper transition lines in the green region and higher color purity than that of commercial ZnO : Zn phosphor. At the same time, La₂O₃ : Ho³⁺ nanorods have higher luminescence intensity than its bulk samples under the same excitation condition. Furthermore, green and red up-conversion emissions originating from two-photon ESA and ET are also observed from the La₂O₃ : Yb³⁺, Ho³⁺ nanorod samples.