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

Spherical particles of (Y 1- x Eu x )BO 3 ( x = 0–0.20, ∼0.8–1.5 μm in diameter) have been converted from (Y 1- x Eu x )(B(OH) 4 )CO 3 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 )CO 3 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 )CO 3 at 700 °C yielded hexagonal structured (Y,Eu)BO 3 phase with the space group of P 6 3 / m , but another hexagonal structured (Y,Eu)BO 3 phase (space group: P 6 3 / 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 (Y 1- x Eu x )BO 3 ( x = 0–0.20) spheres exhibited a typical Eu 3+ emission with the orange emission at 592 nm from the 5 D 0 - 7 F 1 magnetic dipole transitions of Eu 3+ 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 Eu 3+ ions occupying the non-centrosymmetric site instead of S 6 one, thus inducing enhanced emission of 5 D 0 → 7 F 2 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 Eu 3+ , followed by decreases at higher Eu 3+ contents. [ABSTRACT FROM AUTHOR]