Spherical engineering and space-group dependent luminescence behavior of YBO3:Eu3+ red phosphors

Abstract

Spherical particles of (Y1-xEux)BO3 (x = 0–0.20, ∼0.8–1.5 μm in diameter) have been converted from (Y1-xEux)(B(OH)4)CO3 precursors synthesized via homogenous precipitation processing. Detailed characterizations of the samples were achieved by combined techniques of XRD, Raman, FE-SEM, HR-TEM, PLE/PL, and fluorescence decay analysis. Through homogenous precipitation processing in the absence of EG, orthorhombic (Y,Eu)(B(OH)4)CO3 cubic particles were obtained owing to their crystal habit. Proper EG addition leads to the formation of spherical particles, but nano-sized amorphous particles were resulted from the excessive EG content. Longing reaction time or elevating the reaction temperature induced the appearance of cubic ones. Calcining (Y,Eu)(B(OH)4)CO3 at 700 °C yielded hexagonal structured (Y,Eu)BO3 phase with the space group of P63/m, but another hexagonal structured (Y,Eu)BO3 phase (space group: P63/mmc) was obtained with the calcination temperatures of 800–1000 °C. The spherical shape and excellent dispersion of the original particles can be well retained up to 800 °C. Upon UV excitation, the (Y1-xEux)BO3 (x = 0–0.20) spheres exhibited a typical Eu3+ emission with the orange emission at 592 nm from the 5D0-7F1 magnetic dipole transitions of Eu3+ ions taking the dominant role. Space-group vibrations between in 700 °C-phase and 800–1000 °C phase resulted in the blue shift of CTB center, but they did not significantly affect the lifetimes. A higher Eu content (x = 0.01–0.10) leaded more Eu3+ ions occupying the non-centrosymmetric site instead of S6 one, thus inducing enhanced emission of 5D0→7F2 transition, larger asymmetry factor, and red shift of the CIE chromaticity coordinates. However, the asymmetry factor remains nearly constant with the x value up to 0.20. The fluorescence lifetime is similar (5.3 ± 0.3 ms) up to 8 at% of Eu3+, followed by decreases at higher Eu3+ contents.