High crystalline quality of hydrophilic LiYF4: Tm3+/Yb3+ particles prepared by fluorination of layered yttrium hydroxides under assistance of DTPA

Up-conversion emissions can be achieved by doping Tm3+ in hydrophilic LiYF4 crystal particles, with Yb3+ as a sensitizer. They are considered to be excellent up-conversion materials used in bioimaging. However, the crystalline quality of hydrophilic LiYF4 particles prepared by traditional methods is not satisfied and lowers the fluorescent performance. Herein, some additives were employed in preparation of LiYF4 crystals via fluorination transformation from layered yttrium hydroxides (LYHs). The reaction mechanism of additives was discussed in detail. Especially, diethylenetriaminepentaacetic acid (DTPA) can effectively promote the crystallization and Oswald ripening of LiYF4 crystals. The as-prepared LiYF4: Tm3+/Yb3+ up-conversion phosphors have a marvelously intense emission at 793 nm and would be beneficial to the application in bioimaging.