Polyol-mediated syntheses and characterizations of NaYF4, NH4Y3F10 and YF3 nanocrystals/sub-microcrystals

In this paper, NaYF4 nanocrystals and NH4Y3F10 sub-microcrystals were prepared using a polyol method. After being annealed, NH4Y3F10 can convert into YF3, which is a very efficient host matrix for upconversion. The structures of obtained NaYF4, NH4Y3F10 and YF3 samples are pure cubic phase, a mixture of cubic and hexagonal phase and pure orthorhombic phase, respectively. The size of obtained NaYF4 nanocrystals is about 20 nm, and those of NH4Y3F10 and YF3 sub-microcrystals are both about 200 nm. When co-doped with Er3+ and Yb3+, NaYF4 and YF3 samples can emit bright light under 978 nm excitation. Upconversion mechanisms in Yb3+/Er3+ co-doped NaYF4 and YF3 samples were discussed.