Upconversion enhancement in Yb3+,Tm3+:BaY2F8 quasi-nanoparticles

Yb3+Tm3+:BaY2F8 single crystals have been milled to quasi-nanometric size. A complete characterization of the quasi-nanoparticles has been compared with that of a bulk crystal with the same composition. The emission spectra did not show any difference as for the shape and relative intensity of the various peaks within each band, but the infrared lifetime of the quasi-nanoparticles is significantly longer than that of the bulk crystal. In agreement with other literature results we observed a strong increase of the upconverted luminescence intensity in the quasi-nanoparticles. An explanation is given as the effect of radiation trapping of the pumping radiation that increases the effective pump intensity in the volume of the quasi-nanoparticles with respect to the bulk crystal.