Surface and optical properties of Gd-doped ZrO₂ nano films

Nanosized coatings of ZrO₂ were deposited on silicon substrates using sol-gel and spin-coating techniques. The precursor solutions were prepared from ZrOCl₂.8H₂O with the addition of different percentage (0.5-5%) of rare earth Gd³⁺ ions as dopant. The thin films were homogeneous, with average thickness of 115 nm and refractive index (n) of 1.83. The X-ray diffraction analysis (XRD) revealed the presence of a varying mixture of monoclinic and tetragonal ZrO₂ polycrystalline phases, depending on the dopant concentration, all of which with nanosized crystallites. Scanning electron microscopy (SEM) as well as atomic force microscopy (AFM) methods were deployed to investigate the surface morphology and roughness of the thin films, respectively. They revealed a smooth, well uniform and crack-free surface with average roughness of 0.5 nm. It was established that the dopant concentration affects the photoluminescence (PL) properties of the samples. The undoped films exhibited broad violet PL emission, while the addition of Gd³⁺ ions resulted in new narrow bands in both UV and visible light regions, characteristic of the rare earth metal. These exact emissions can find useful applications in medical lamps or as red phosphors.

Acknowledgement

Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science under contract D01-284/17.12.2019 was used in this investigation.