Effects of the Sr/Ba and Dy Content on the Structure, Powder Morphology and Luminescent Emission of Uncoated and Silica Coated (Sr/ba)0.90eu0.1-Xdyxzr4(po4)6 (0≤X≤0.1) Nanophosphors

The preparation and study of new pure uncoated and silica coated M 0.90 Eu 0.1-x Dy x Zr 4 (PO 4 ) 6 samples with M = Sr or Ba and x = 0, 0.025, 0.050 and 0.075 was described in detail. Samples of materials of this type are currently under research because they have tunable luminescence depending on the type and content of ions in the host lattice, which could be applied in different optoelectronic devices. The effect of M and dysprosium content on the structure, shape and size of particles and luminescent emission intensity was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic measurements and photoluminescence (PL) spectroscopy. X-ray diffraction patterns confirm the crystalline phases formation with a NASICON-type structure indexed to a rhombohedral symmetry of R-3 space group with Z = 6. FTIR spectra of uncoated and silica coated samples show a broad band assignable to the vibrational modes of the PO 4 3- group and several bands corresponding to vibrations of the Si-O bonds. The experimental FTIR study was complemented with a theoretical vibrational study based on the SrZr 4 (PO 4 ) 6 structure using different DFT methods and basis sets. Highly agglomerated spherical nanoparticles with an average particle size of 20 nm in the strontium powders and 18 nm in the barium powders, respectively, were found in TEM images. An amorphous silica shell was also observed in silica coated samples. Broad emission bands were observed in the PL spectra of obtained samples, related to both the substitution of strontium by barium and the different dysprosium content. Magnetic susceptibility curves as a function of temperature confirm the presence of Eu 2+ ions in undoped samples and of Eu 3+ and Dy 3+ ions in co-doped samples.