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

Exploring oxide-based red-emitting phosphors is essential for improving the color rendering index (Ra) 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 Sr1.8Ba0.2GaO5:Eu2+ and green Lu3Al5O12:Ce3+ phosphors exhibits a high color rendering index (Ra = 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.