Replacing traditional incandescent bulbs with energy-efficient LED lighting is one of the simplest methods to reduce electricity consumption. Current commercial LED light bulbs work by converting a nearly monochromatic LED emission using a luminescent inorganic phosphor, which in combination covers nearly the entire visible spectrum to produce white light. The phosphors used in this application must be highly efficient, have a thermally robust emission, and possess a narrow emission peak. Current design rules for developing phosphors with these properties suggest pursuing host structures that are highly symmetric and contain a single site for rare-earth substitution. One class of materials that seemingly meet these requirements but have not been extensively explored is perovskites. This talk focuses on the BaScO2F perovskite that, when substituted with Eu2+, produces a brilliant cyan emission stemming from the structure’s high symmetry and dense connectivity. However, the emission peak is broader than expected. Steady-state, temperature-dependent, and time-resolved photoluminescence spectroscopy reveal the presence of two distinct emission peaks stemming from two crystallographically independent Eu2+ ions despite the fact there is only a single rare-earth substitution site in the host. Ab initio calculations subsequently show that substituting the smaller Eu2+ induces an unexpected local structure distortion driven by zone-boundary octahedral tilting. As a result, the structure has two different local coordination environments around Eu2+ that cause the observed dual emission. Our work shows the critical need to analyze local distortions in phosphors upon rare-earth substitution, especially in perovskites on the verge of structural instabilities.

Local structure induced broad band emission in the BaScO2F:Eu2+ perovskite

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.