Trivalent rare-earth activated hexagonal lanthanum fluoride (LaF3 :RE3+ , where RE = Tb, Sm, Dy and Tm) nanocrystals: Synthesis and optical properties.

The LaF3 nanocrystals through a facile hydrothermal route with hexagonal structures have been synthesized via doping of trivalent rare earth (RE3+ ) ions - RE = Tb, Sm, Dy and Tm - with rod-like and perforated morphologies using NH4 F as fluorine precursor. Hexagonal phase formation was confirmed by powder X-ray diffraction. The crystalline sizes were calculated by the Scherrer equation where found to have an average crystalline size of 12 to 35 nm. The morphological studies of the nanocrystals were carried out by means of transmission electron microscopy (TEM). The LaF3 :Tm3+ ,Sm3+ ions show the characteristic emission of Tb3+ and Tm3+ respectively. In Sm3+ -doped LaF3 , three prominent emission peaks at 561, 597 and 641 nm were found, which belong to 4 G5/2  → 6 H5/2 , 4 G5/2  → 6 H7/2 (magnetic dipole) and 4 G5/2  → 6 H9/2 (electric dipole) transitions, respectively. The Dy3+ activated LaF3 shows blue and yellow emission and the corresponding CIE color coordinate show white light emission (CCT value 10650 K).