Uniform colloidal spheres for (Y1-xGdx)2O3 (x=0-1):: Formation mechanism, compositional impacts, and physicochemical properties of the oxides

Uniform spheres of (Y(1-x)Gd(x))(2)O(3) (x = 0-1) are valuable for applications in phosphors, in optical ceramics fabrication, and in combinatorial synthesis. We made in this work such particles by thermal decomposition of precursors synthesized via homogeneous precipitation. Growth kinetics and composition evolution of the precursor spheres were investigated in detail, and it was identified for the first time that (1) differential nucleation occurs with regard to Y and Gd, and as a result concentration gradients exist within each precursor particle of the mixed Y/Gd system (more Gd and less Y from particle surface to the core), (2) average particle size of the colloidal sphere is inversely proportional to nucleation density and is significantly affected by the Gd content, (3) growth of the colloidal spheres is diffusion controlled and follows the cubic-root law, and (4) the dried precursor spheres directly convert to cubic-structured (Y(1-x)Gd(x))(2)O(3) (x = 0-1) oxides at 1000 degrees C while largely retaining their morphologies. The resultant oxides exhibit linearly increased lattice parameters and linearly decreased bandgaps (from 5.57 eV for Y(2)O(3) to 5.20 eV for Gd(2)O(3)) with increased Gd addition. The findings of this work may have wide implications to other mixed materials systems.