Site Occupation Engineering toward Giant Red-Shifted Photoluminescence in (Ba,Sr)2LaGaO5:Eu2+ Phosphors

https://doi.org/10.1021/acs.chemmater.3c01980

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 Eu²⁺ red emission in inorganic solids. Here, the Eu²⁺-activated oxide phosphor Sr₂LaGaO₅:Eu²⁺ was synthesized with red emission peaking at 618 nm under 450 nm excitation. The crystal structure and spectral analysis indicate that Eu²⁺ tends to occupy [Sr1/LaO₈] polyhedrons with a smaller coordination number, resulting in a large crystal field splitting at the 5d level and realizing the broadband 4f–5d red emission. When Sr is substituted by Ba atoms, density functional theory calculations verify that Ba tends to enter [Sr2O₁₀] 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_1.8Ba_0.2GaO₅:Eu²⁺ and green Lu₃Al₅O₁₂:Ce³⁺ 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 Eu²⁺ activated oxide-based red phosphors as well as achieving tunable emission through cations’ substitution.