Effects of x and R3+ on the luminescent properties of Eu3+ in nanocrystalline YVxP1-xO4:Eu3+ and RVO4:Eu3+ thin-film phosphors

Using inorganic oxides and salts instead of alkoxides as the main starting materials, we prepared nanocrystalline YV_xP_1-xO₄:Eu³⁺ and RVO₄:Eu³⁺ (0x1; R=Y,La,Gd) thin-film phosphors by the Pechini sol–gel dip-coating process. The resulting films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and photoluminescence excitation and emission spectra as well as luminescence decay. The results of XRD showed that a solid solution formed in the YV_xP_1-xO₄:Eu³⁺ film series from x=0 to x=1 with zircon structure. The same structure also held for the GdVO₄:Eu³⁺ film, but the LaVO₄:Eu³⁺ film crystallized with a different structure, monazite. AFM and SEM studies revealed that the phosphor films consisted of spherical particles ranging from 90 to 400 nm depending on the film compositions. With the increase of x values in YV_xP_1-xO₄:Eu³⁺ films, the integrated emission intensity and the red (⁵D₀–⁷F₂)-to-orange (⁵D₀–⁷F₁) intensity ratio of Eu³⁺ increase due to the increased energy-transfer probability from VO₄^3- to Eu³⁺ and the increased polarizability of the surrounding oxygen ions, respectively. The x values also have an influence on the decay behavior of Eu³⁺. The YVO₄:Eu³⁺ and GdVO₄:Eu³⁺ films showed very similar luminescence properties due to their same crystal structures. However, the LaVO₄:Eu³⁺ film exhibited a much different emission property from those of the YVO₄:Eu³⁺ and GdVO₄:Eu³⁺ films due to the structural effects. PACS 73.63.Bd; 78.55.Hx; 78.66.Nk; 81.15.Lm; 81.20.Fw