Near infrared ray to ultraviolet up-conversion luminescence of Tm³⁺–Yb³⁺ co-doped (CaY)F₂ nanocrystals

Near Infrared Ray (NIR)-ultraviolet (UV) up-conversion luminescence (UCL) materials have potential application in many fields of biological science, including cells and tissue labeling for bio-imaging, bio-detection, therapy or multiplexed analysis. Tm³⁺/Yb³⁺ co-doped (CaY)F₂ nanocrystals have been successfully synthetized through the hydrothermal method, and the effect of different synthesis conditions on the morphology and luminescence property of (CaY)F₂ phosphors have been discussed. When the molar concentration of Tm³⁺ and Yb³⁺ were 0.4 and 20%, respectively, the obtained (CaY)F₂ nanocrystals have excellence density, crystallinity, single particle dispersion, uniform particle size (55.5 nm), and high up-conversion luminescence efficiency with the hydrothermal conditions of 180° C and 12 h and calcined temperature of 500° C. Specifically, the synthesized nanocrystals could be stably excited by a 980 nm pump light, converted to 360 nm UV. In addition, the cytotoxicity of (CaY)F₂ nanocrystals has also be explored, which shows low cytotoxicity examined by the L929 murine fibroblast cells. With this biocompatibility and excellent up-conversion luminescence properties, the obtained (CaY)F₂ nanocrystals have a high potential as biomaterials for photodynamic therapy assisted by TiO₂.