Monodisperse colloidal spheres for (Y,Eu)₂O₃ red-emitting phosphors: establishment of processing window and...

The urea-based homogeneous precipitation method was introduced in the preparation of monodisperse colloidal spheres for (Y_0.95Eu_0.05)₂O₃ red-emitting phosphors, and the processing window was defined. Particle size and shape are significantly affected by the ion concentration and the urea/RE³⁺ molar ratio R (RE³⁺=Y³⁺+Eu³⁺). A low ion concentration is beneficial in forming monodisperse spheres and extending their formation domain. Increasing R results in a gradual change in the composition of spherical particles from the core-shell Eu(OH)CO₃@Y(OH)CO₃ structure to a homogeneous solid solution, thereby significantly lowering the calcination temperature at which precursors convert to oxides. Upon UV excitation into the charge-transfer band at 254 nm, the uniform phosphor spheres of (Y_0.95Eu_0.05)₂O₃ exhibit typical red emissions at 613 nm; the emission is stronger from larger particles mainly because of their smaller surface area. Both the luminescence intensity and quantum efficiency of the oxide phosphors increase with elevated calcination temperatures. The spherical shape and excellent dispersion of the precursor particles (∼450 nm in diameter) have been well retained after calcination at 1000 ^○C for 4 h, and the resultant oxide phosphors exhibit external and internal quantum efficiencies of 50 and 82%, respectively.