| Abstract
| - A growth mechanism was proposed for YF3 nanocrystals forming in the quaternary reverse microemulsion system with water/cetyltrimethylammonium bromide/cyclohexane/1-pentanol. In the proposed mechanism, primary particles are formed by constant collision, fusion, and fission of micelles. These primary particles can further self-organize to one-dimensional nanostructure at room temperature. Results of X-ray diffraction and transmission electron microscopy reveal that each nanobundle consists of numerous nanowhiskers with a mean length of ∼700 nm and a mean diameter of ∼2 nm. Under 980 nm excitation, blue (1G4 → 3H6 and 1D2 → 3F4) and ultraviolet (1D2 → 3H6 and 1I6 → 3F4/3H6) upconversion fluorescence emitted from the YF3−Yb3+/Tm3+ nanobundles. The relative intensity of the ultraviolet to the blue emission increases with decreasing the size of nanowhiskers. Spectral analysis indicates that the enhancement is attributed to the decrease of Judd−Ofelt parameter Ω2, which precludes the transition from 3F2 to 3F4 and enhances the cross relaxation of 3F2 + 3H4 → 3H6 + 1D2.
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