Monodispersed Colloidal Spheres for Uniform Y₂O₃:Eu³⁺ Red-Phosphor Particles and Greatly Enhanced Luminescence by Simultaneous Gd³⁺ Doping

Uniform red-phosphor spheres (∼60−300 nm in diameter) of Y2O3:Eu3+ binary and (Y,Gd)2O3:Eu3+ ternary systems exhibiting excellent emission at 610 nm have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The precursor spheres (approximate composition: [(Y1-xGdx)1-yEuy](OH)CO3·1.3H2O, x = 0−0.5 and y = 0−0.11) are directly solid solutions, but arising from sequential nucleation each of the spheres has more Gd and especially Eu while having less Y going from the particle surface to the core. Eu3+ is more effective than Gd3+ in raising nucleation density, leading to rapidly decreased average size of the precursor particles at a higher Eu3+ addition. Diminishing the concentration gradients through adequate annealing is identified to be crucial to high luminous intensity of the oxide particles. At the optimal annealing temperature of 1000 °C, cation homogenization is achieved and the oxide particles largely retain their precursor morphologies, yielding dispersed uniform spheres of excellent luminescence. The (Y1-xEux)O1.5 phosphor particles exhibit typical red emissions at 610 nm upon UV excitation into the charge transfer band at ∼255 nm, and the quenching concentration of Eu3+ is found to be ∼5 at. %. Partially replacing Y3+ with Gd3+ (up to 50 at. %) while keeping Eu3+ at the optimal content of 5 at. % linearly improves the 610 nm emission, and the phosphor particles of [(Y0.5Gd0.5)0.95Eu0.05]O1.5 exhibit an luminous intensity ∼103% of that of a commercially available Y2O3:Eu red phosphor. The uniform phosphor spheres obtained in this work are expected to have wide applications in high-resolution display technologies of contemporary interest.