Morphology control, luminescence and energy transfer properties of NaCeF4 and NaCeF4:Tb3+/Yb3+ nanocrystals.

Oil-dispersible monodispersed NaCeF4, NaCeF4:Tb(3+) and NaCeF4:Yb(3+) nanoparticles were prepared through a thermal decomposition method. Phase purity, morphology and luminescence properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), and photoluminescence (PL) spectra, respectively. The starting amount of NaF is crucial for phase purity, and the reaction time had an effect on the morphology of the products. Products with rectangles, rods, and their mixtures could be obtained at different reaction times. Under UV excitation, energy transfer from Ce(3+) to lanthanide ions Tb(3+) and Yb(3+) could be observed in both NaCeF4:Tb(3+) and NaCeF4:Yb(3+). Energy transfer from Ce(3+) to Tb(3+) was proposed to be of a resonant type (ET) by luminescent dynamic studies with a theoretically calculated efficiency of up to 93%. Energy transfer from Ce(3+) to Yb(3+) was demonstrated to be a cooperative (CET) process, and the CET efficiency and total theoretical quantum efficiency were found to be 79% and 158%, respectively.