Bulk and surface chemical compositions and microstructure properties of CaF2:Y3+ material

The structural and chemical compositions of Y3+ ion-doped CaF2 were investigated as a possible lanthanide hosting material. A series of CaF2 nanomaterials doped with various concentrations of Y3+ ions under the chelating agent ethylene diamine tetraacetic acid (EDTA) were synthesized using the hydrothermal method. The x-ray diffraction results demonstrated that a mixture of cubic CaF2 and [CaY]F2 phases gradually formed with an increasing Y3+ ion concentration. A single [CaY]F2 cubic phase was formed when EDTA was added as the chelating agent. Scanning electron microscopy results demonstrated that the particle size and the morphology of the material depended on the Y3+ concentration and that EDTA (0.5 g) produced a spherical morphology. The surface and bulk chemical compositions were determined using a combined system of soft x-ray photoemission spectroscopy (XPS) (Al-Kα 1486.7 eV) and hard x-ray photoemission spectroscopy (HAXPES) (Cr-Kα 5414.7 eV). The relative changes in the chemical composition of the surface and subsurface/bulk were investigated. The combined XPS-HAXPES analysis demonstrated that the surface impurities in the accessible peaks (Ca 2p, Y 3d, and F 1s) completely diminished in the subsurface region. However, XPS-HAXPES analysis confirmed that the composition of the [CaY]F2 nanomaterial on the surface differs from that in the subsurface region.