Local Structure Distortion Induced Broad Band Emission in the All-Inorganic BaScO₂F:Eu²⁺ Perovskite

Perovskites are a class of materials with applications in photovoltaics, solid-state lighting, and catalysis. Extensive research has gone into modifying the chemical composition of these distortion-prone structures to manipulate and achieve their tremendous physical properties. Here, we report a BaScO2F perovskite that, when doped with Eu2+, produces a highly efficient cyan emission stemming from the structure’s high symmetry and dense connectivity. However, the emission peak is broader than expected and steady-state, temperature-dependent, and time-resolved photoluminescence spectroscopy reveals the presence of two distinct emission peaks despite a single rare-earth substitution site. Ab initio calculations subsequently prove that substituting the smaller Eu2+ induces an unexpected local structure distortion driven by zone-boundary octahedral tilting. This produces two different local coordination environments around Eu2+ that cause the dual emission. This work shows the critical need to analyze local distortions in phosphors upon rare-earth substitution, especially in perovskites on the verge of structural instabilities.