Hydrothermal synthesis of hexagonal lanthanide-doped LaF3 nanoplates with bright upconversion luminescence

Hexagonal Yb/Er or Yb/Ho co-doped LaF3 nanoplates with uniform morphology have been synthesized with an average diameter of similar to 15 nm. It was found that the coating reagent, hydrothermal temperature and time play critical roles in the control of the shape of the final products. A possible growth mechanism including ion exchange, 'burst-nucleation', and 'heat-up' growth is proposed. H-1 NMR spectra and Fourier transform infrared (FTIR) spectra indicate that the surface of the nanoplates is coated with oleic acid ligands. Those hexagonal nanoplates display the capability of forming self-assembled two-dimensional nanoarrays. Moreover, under continuous-wave excitation at 980 nm, the LaF3:12% Yb, 3% Er nanoplates exhibited bright orange emission (a combination of green between 515 and 556 nm and red between 640 and 675 nm) and the LaF3:20% Yb, 1% Ho nanoplates had nearly pure green upconversion luminescence between 530 and 554 nm. The intensity of upconversion luminescence increased with time and increase of the hydrothermal temperature. For the bright upconversion luminescence, the as-prepared samples show potential applications in color displays, the building of nanodevices and as biolabels.