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

In this paper, NaYF 4 nanocrystals and NH 4 Y 3 F 10 sub-microcrystals were prepared using a polyol method. After being annealed, NH 4 Y 3 F 10 can convert into YF 3 , which is a very efficient host matrix for upconversion. The structures of obtained NaYF 4 , NH 4 Y 3 F 10 and YF 3 samples are pure cubic phase, a mixture of cubic and hexagonal phase and pure orthorhombic phase, respectively. The size of obtained NaYF 4 nanocrystals is about 20 nm, and those of NH 4 Y 3 F 10 and YF 3 sub-microcrystals are both about 200 nm. When co-doped with Er 3+ and Yb 3+ , NaYF 4 and YF 3 samples can emit bright light under 978 nm excitation. Upconversion mechanisms in Yb 3+ /Er 3+ co-doped NaYF 4 and YF 3 samples were discussed.