On the role of Gd3+ ions in enhancement of UV emission from Yb3+-Tm3+ up-converting LiYF4 nanocrystals

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)F-4 nanocrystalline host for up-converting Tm3+-Yb3+ activator-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 LiYF4:25%Yb(3+)0.5%Tm3+ colloidal nanocrystals, where 1, 5, 10, 20, 30 and 40% of Y3+ ions were substituted with Gd3+ ions. Low gadolinium dopant concentrations modify the size and up-conversion luminescence, while the Gd3+ doping that is exceeding the structure resistance limit of the tetragonal LiYF4 results in appearance of foreign phase and significant decrease of luminescence intensity. The intensity and kinetic behavior of Gd3+ up-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 LiYF4 nanocrystals.

Automated summary

Materials capable of emitting UV radiation under NIR excitation are highly desirable for various applications. This study investigates the size, structure, and luminescence properties of tetragonal LiY(Gd)F-4 nanocrystals doped with different concentrations of Gd3+ ions. The results demonstrate that low concentrations of Gd3+ ions can modify the size and up-conversion luminescence, while excess doping leads to the appearance of foreign phases and a significant decrease in luminescence intensity. The intensity and kinetics of Gd3+ up-converted UV emission are also analyzed. These findings provide a foundation for the development of optimized materials and applications based on LiYF4 nanocrystals.