Monodispersed Colloidal Spheres for Uniform Y2O3:Eu~(3+) Red-Phosphor Particles and Greatly Enhanced Luminescence by Simultaneous Gd~(3+) Doping

摘要

Uniform red-phosphor spheres (～60—300 nm in diameter) of Y2O3:Eu~(3+) binary and (Y,Gd)2O3:Eu~(3+) 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: [(Y_(1-x)Gd_x)_(1-y)-Eu_y](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. Eu~(3+) is more effective than Gd~(3+) in raising nucleation density, leading to rapidly decreased average size of the precursor particles at a higher Eu~(3+) 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 (Y_(1-x)-Eu_x)O_(1.5) 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 Eu~(3+) is found to be ～5 at. %. Partially replacing Y~(3+) with Gd~(3+) (up to 50 at. %) while keeping Eu~(3+) at the optimal content of 5 at. % linearly improves the 610 nm emission, and the phosphor particles of [(Y_(0.5)Gd_(0.5))_(0.95)Eu_(0.05)]O_(1.5) 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.