After controlled thermal degradation of acetylacetonato (AA) complexes, mixtures of monodisperse similar to 5 nm large isometric particles of Y2-xYbxO3 (x = 0.06, 0.10, 0.20, 0.40) were synthesized. Detailed information on nanoparticles' microstructure and core crystal structure is reported. The Yb3+ ions occupy preferently C-3i sites for low Yb3+ concentrations, while for 20 at.% Yb3+, a random distribution was found. It was shown that the particle/crystallite size and strain as well as Raman modes positions and widths are influenced by Yb3+ concentration. Crystallographic and Raman spectroscopy results indicate that the particles are core/shell structured with cubic crystalline core and monoclinic-like disordered shell. Most probable particle's shell/core volume ratio decreased with annealing at 500 degrees C and the shell disappeared when annealed at 1000 degrees C. (C) 2010 Elsevier B.V. All rights reserved.