Fabrication of REVO4 films via sacrificial conversion from layered rare-earth hydroxide (LRH) films: the investigation of the transition mechanism and their photoluminescence

Abstract

Rare-earth orthovanadate REVO₄ (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y) films were directly synthesized within 2 hours by sacrificial conversion from electrodeposited layered rare-earth hydroxide (RE₂(OH)₅NO₃·nH₂O) films at pH ∼ 10, without subsequent heat treatment. Detailed characterization of the products was achieved by combined X-ray diffraction, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence excitation and photoluminescence. The mechanisms of phase and morphology evolution from Y₂(OH)₅NO₃·nH₂O to YVO₄ were unveiled through systematic investigations into the influences of the concentration of the anion sources (Na₃VO₄) and the reaction temperature. The effects of lanthanide contraction on the phase structure and particle morphology of the REVO₄ films were also clarified. Additionally, the photoluminescence of RE³⁺ activators (RE = Eu, Dy, and Eu and Dy) was elaborated with YVO₄ as a representative host lattice, and the color-tunable emission and energy transfer from Dy³⁺ to Eu³⁺ were also investigated. Electrodeposition combined with a hydrothermal anion exchange technique established in this study led to the rapid synthesis of REVO₄ films, and it might have wide implications for the generation of other types of inorganic functional films.