Uniform Colloidal Spheres for (Y_1−xGd_x)₂O₃ (x = 0–1): Formation Mechanism, Compositional Impacts, and Physicochemical Properties of the Oxides

Abstract

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 °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.

Monodisperse colloidal spheres for (Y,Eu)2O3red-emitting phosphors: establishment of processing window and size-dependent luminescence behavior

“…Monodisperse colloidal precursor spheres with a general chemical composition of RE(OH)CO 3 ·nH 2 O (RE = Y and Eu) were produced by the UBHP method, which agrees with our previous results [10][11][12]. In this work, we defined the processing window and found that the urea/RE 3+ molar ratio R and the ion concentration in the reaction system significantly affect the precursor morphologies.…”

“…At the R of 133.3, the decomposition of excess urea generates more OH − ions, which change the medium from acidic to alkaline; thus, carbonate plates appear instead of carbonate spheres [7], as shown in figures 1(g) and 3. In our previous work, the sequential precipitation of Eu 3+ and Y 3+ was observed in the UBHP method, resulting in homogeneous nucleation of Eu(OH)CO 3 in priority [10,11]. When all the Eu 3+ ions were contained in monodisperse carbonate spheres at the initial precipitation stage, a small amount of Y 3+ ions still existed in the reaction solution.…”

“…It relies 3 ) into the reaction system [5][6][7][8][9][10][11][12]. Systems containing one rare-earth element (RE) were systematically studied by Matijević and Hsu [5], Hsu et al [6], Aiken et al [7], Sordelet and Akinc [8] and Sordelet and Akinc [9] through UBHP processing.…”

“…Systems containing one rare-earth element (RE) were systematically studied by Matijević and Hsu [5], Hsu et al [6], Aiken et al [7], Sordelet and Akinc [8] and Sordelet and Akinc [9] through UBHP processing. More recently, Li et al [10][11][12] have extended their compositions to Y/Gd, Y/Eu, Gd/Eu and even Y/Gd/Eu mixed systems. They also proposed using the monodisperse basic carbonate colloid spheres processed via UBHP as the precursors for luminescent oxides, which definitely widens the practical applications of these phosphors.…”

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

“…This is reported in Figures 1-3 for d,d-metals mixed oxides, where the measured optical band gaps as a function of the alloys composition are reported for passive films grown on Ti-Zr and Ta-Nb alloys as well as for physically deposited (Gd x Y (1-x) ) 2 O 3 . [30][31][32][33][34] The amorphous nature of the passive film on Nb-Ta alloys and the absence of any indirectto-direct optical transition crossover in the case of crystalline films grown on Ti-Zr alloys, allowed testing of the suggestion of Zunger and coworkers 25,26 for the regular semiconducting alloys reported above. Figures 1 and 2 show the dependence of experimental E g values of thin anodic passive films vs alloys composition for Ti-Zr and Ta-Nb mixed oxides.…”