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.