Site Occupation Engineering toward Giant Red-Shifted Photoluminescence in (Ba,Sr)<sub>2</sub>LaGaO<sub>5</sub>:Eu<sup>2+</sup> Phosphors
Yu Chen, Zhiyu Yang, Jiance Jin, Jianwei Qiao, Yuzhen Wang, Мaxim S. Моlokeev, H.C. Swart, Zhiguo Xia
Abstract
Exploring oxide-based red-emitting phosphors is essential for improving the color rendering index ( R a ) and reducing the correlated color temperature (CCT) of white-light-emitting diode (LED) lighting sources. Especially, it is challenging to design Eu 2+ red emission in inorganic solids. Here, the Eu 2+ -activated oxide phosphor Sr 2 LaGaO 5:Eu 2+ was synthesized with red emission peaking at 618 nm under 450 nm excitation. The crystal structure and spectral analysis indicate that Eu 2+ tends to occupy [Sr1/LaO 8 ] polyhedrons with a smaller coordination number, resulting in a large crystal field splitting at the 5 d level and realizing the broadband 4 f –5 d red emission. When Sr is substituted by Ba atoms, density functional theory calculations verify that Ba tends to enter [Sr2O 10 ] with a large coordination number, further giving rise to the lattice distortion and a giant spectral redshift (618–800 nm). The white LED device fabricated by mixing red Sr 1.8 Ba 0.2 GaO 5:Eu 2+ and green Lu 3 Al 5 O 12:Ce 3+ phosphors exhibits a high color rendering index ( R a = 92.1) and a low color-dependent temperature (CCT = 4570 K). This study will give guidance for exploring new Eu 2+ activated oxide-based red phosphors as well as achieving tunable emission through cations’ substitution.