Ionic liquid-based synthesis of luminescent YVO4:Eu and YVO4:Eu@YF3 nanocrystals

Luminescent YVO4:Eu nanocrystals were prepared via an ionic liquid-based synthesis. According to electron microscopy, dynamic light scattering, and X-ray diffraction, the presence of uniform and highly crystalline particles, 12-15 in diameter is validated. As-prepared particles turn out to be nonagglomerated and redispersible. Photoluminescence exhibits characteristic red emission related to Eu3+. Quantum yield of as-prepared YVO4:Eu (15 mol%) is determined to 17-19%. The quantum yield of as-prepared material increases to 44-46% by establishing an YVO4:Eu@YF3 core-shell structure. Since the lattice planes (001) of YVO4 and (100) of YF3 match very well, a crystalline YF3 shell, 1-2 nm in thickness protects the YVO4 core very efficiently. Besides the significantly increased quantum yield, the presence of a core-shell structure is further evidenced by electron energy loss spectroscopy. Element mapping revealed high intensities of Eu in the inner parts, associated with low peripheral fluorine intensities.