Colloidal processing of Gd2O3:Eu3+ red phosphor monospheres of tunable sizes: Solvent effects on precipitation kinetics and photoluminescence properties of the oxides

The synthesis of basic carbonate monospheres was attempted for the Gd/Eu binary system via urea-based homogeneous precipitation, with emphases on particle size and cation distribution control. It was demonstrated that the use of water/organic-solvent mixture as the reaction medium not only allows facile particle size control in the wide range of ∼50–500 nm but also effectively alleviates the detrimental sequential precipitation between the Gd and Eu components. The results are discussed from the mechanism of carbonate precipitation and the dielectric constant and surface tension of the organic co-solvent. Annealing the basic carbonate monosheres at 800 °C for 12 h yields well-dispersed (Gd1−xEux)2O3 phosphor particles that exhibit sharp red emissions at 610 nm under 259 nm charge transfer excitation. The phosphor spheres show a luminescence quenching concentration of 7–9 at.% for Eu3+ and clearly size-dependent luminescent behavior. Both the intensity of the 610 nm emission and the asymmetry factor of luminescence [I(5D0 → 7F2)/I(5D0 → 7F1)] steadily increase with smaller particle size—findings that have been ascribed to decreased grain-boundary density and enhanced surface/volume effects, respectively. With their excellent morphological uniformity and close-packing ability, the (Gd1−xEux)2O3 phosphor spheres synthesized in this work may find potential applications in various lighting and display devices.