Blue and red upconverted emission from fluoride crystal nanoparticles

Yb,Tm:BaY₂F₈ nanocrystals have been prepared and a complete spectroscopic characterization is given. After infrared pumping at 970nm we observed strong upconverted emission in the blue and red spectral regions together with infrared emissions. The lifetimes of the observed levels are in agreement with similar results in bulk crystal and no evidence of additional loss processes in the nanocrystals with respect to the bulk material is found.