Uniform colloidal spheres for RE 3 BO 6 (RE = Eu‐Yb, Y) and excitation‐dependent luminescence of Y 3 BO 6 :Eu 3+ red phosphor

Phosphor particles of spherical shape and uniform size are desired for high‐definition displays to improve the resolution and the overall luminescent performance. However, the synthesis of RE 3 BO 6 spherical particles is a considerable challenge in materials science. Here, uniform spheres of RE 3 BO 6 (RE = Eu–Yb, Y) have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The amorphous precursor spheres are solid particles with decreased boron going from the surfaces to the cores. Smaller particles were observed at decreased ionic radius from Eu 3+ to Ho 3+ (including Y 3+ ), but particles with nearly unvaried sizes were observed by further decreasing the ionic radius from Ho 3+ to Yb 3+ . They crystallized in monoclinic RE 3 BO 6 at 900°C, with maintaining the spherical shape of precursors. However, the crystal growth and the densification toward the particle surfaces resulted in the formation of hollow spheres for smaller particles and core‐shell structured spheres for larger particles. The parameters, a , b , and c , increase nearly monotonically with increasing the radius of rare earth ions. The uniform spheres of Y 3 BO 6 :Eu 3+ exhibited a typical red emission at ~613 nm ( 5 D 0 → 7 F 2 electric dipole transition of Eu 3+ ), with an intensity ratio I ( 5 D 0 → 7 F 2 )/ I ( 5 D 0 → 7 F 1 ) of ~3.5. The luminescence behavior of Y 3 BO 6 :Eu 3+ phosphor is dependent on the excitation wavelength, which is closely related to the Eu 3+ ions at different coordination sites. Driven by a 460‐nm blue‐LED chip, the Y 3 BO 6 :Eu 3+ spheres exhibited a red emission with the CIE coordinates of (~0.65, ~0.35), indicating that they are an excellent red‐emitting phosphor candidate for application in white‐LEDs.