On the role of Gdions in enhancement of UV emission from Yb-Tmup-converting LiYFnanocrystals.

Materials capable of emitting ultraviolet (UV) radiation are sought for applications ranging from theranostics or photodynamic therapy to specific photocatalysis. The nanometer size of these materials, as well as excitation with near-infrared (NIR) light, is essential for many applications. Tetragonal tetrafluoride LiY(Gd)Fnanocrystalline host for up-converting Tm-Ybactivator-sensitizer pair is a promising candidate to achieve UV-vis up-converted radiation under NIR excitation, important for numerous photo-chemical and bio-medical applications. Here, we provide insights into the structure, morphology, size and optical properties of up-converting LiYF:25%Yb0.5%Tmcolloidal nanocrystals, where 1, 5, 10, 20, 30 and 40% of Yions were substituted with Gdions. Low gadolinium dopant concentrations modify the size and up-conversion luminescence, while the Gddoping that is exceeding the structure resistance limit of the tetragonal LiYFresults in appearance of foreign phase and significant decrease of luminescence intensity. The intensity and kinetic behavior of Gdup-converted UV emission are also analyzed for various gadolinium ions concentrations. The obtained results form a background for further optimized materials and applications based on LiYFnanocrystals.