Fabrication, Patterning, and Optical Properties of Nanocrystalline YVO₄:A (A = Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) Phosphor Films via Sol−Gel Soft Lithography

Nanocrystalline YVO 4:A (A = Eu 3+, Dy 3+, Sm 3+, Er 3+ ) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline YVO 4 phosphor films because of an efficient energy transfer from vanadate groups to them. The Sm 3+ and Er 3+ ions also showed upconversion luminescence in a YVO 4 film host. Both the lifetimes and PL intensity of the rare earth ions increased with increasing annealing temperature from 400 to 800 °C, and the optimum concentration for Eu 3+ was determined to be 7 mol % and those for Dy 3+, Sm 3+, and Er 3+ were 2 mol % of Y 3+ in YVO 4 films, respectively.