Size-effect on concentration quenching in Yb3+-doped Y3Al5O12 nano-crystals

Ytterbium-doped nano-crystalline powders of yttrium aluminium garnet Y3Al5O12 (Yb3+-doped YAG) have been prepared by a modified Pechini method. The morphology of the annealed materials was observed using SEM images. The structure and the average crystalline grain sizes have been determined by X-ray powder diffraction measurements. An increase in elongated spherical crystalline grain sizes from 20 to 50 nm has been observed with annealing temperature increasing from 800 to 1200 °C. The Yb3+ concentration dependence of both luminescence spectra and lifetimes has been investigated and compared with those reported for the Yb3+-doped YAG bulk single crystals. Decays of Yb3+ 2F5/2 excited state, much longer in nano-crystalline powders than in bulk single crystals, are discussed in terms of refractive index dependence.