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 YVxP1-xO4:Eu3+ and RVO4:Eu3+ (0≤x≤1; 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 YVxP1-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 YVxP1-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 VO43- 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.