Synthesis, characterization, and photoluminescent properties of (La0.95Eu0.05)2O2SO4 red phosphors with layered hydroxyl sulfate as precursor

The sulfate-type layered rare-earth hydroxides of (La0.95Eu0.05)2(OH)4SO4⋅2H2O were synthesized via hydrothermal reaction, which were then converted into (La0.95Eu0.05)2O2SO4 red phosphors through annealing in the air at a minimum temperature of 400 °C. Detailed characterizations of the materials were attained by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry/differential scanning calorimetry (TG/DSC), field-emission scanning electron microscopy (FE-SEM), and optical spectroscopies. The results showed that the hydroxide precursors and their calcination products are direct solid solutions of excellent crystallinity. SEM observations clearly revealed that morphology of the precursor particles is controllable by regulating hydrothermal pH and the precursors present preferable homogeneity and dispersion. TG/DSC analysis found that the precursor decomposes via dehydration and dehydroxylation upon heating in the air. Photoluminescence analysis showed that the (La0.95Eu0.05)2O2SO4 phosphors have their strongest red emissions at 620 nm under 280 nm ultraviolet light excitation that correspond to the 5D0 → 7F2 transition of Eu3+. Luminescence properties of the phosphors exhibit obvious dependence upon particle morphology and calcination temperature. The factors that affect luminescent properties, including phase evolution, annealing temperature, and particle morphology, were also investigated in detail.