Multi-site incorporation of Cr3+ in CaAl12O19

In this study, a series of Cr3+-doped CaAl12O19 exhibiting multi-site luminescence was prepared by the solid-state reaction in air. Time-resolved spectroscopy revealed that luminescence spectra consist of three spectral components: narrowband emission at 689 nm, wideband emission at 785 nm and previously unreported narrowband emission at 700 nm with unusually long photoluminescence lifetime. Electron paramagnetic resonance (EPR) spectroscopy confirmed that Cr3+ forms three centres with different site symmetries. Based on the results, the assignment of Cr3+ luminescence centres, EPR signals and Al crystallographic sites in CaAl12O19 was performed, expanding the knowledge base on the relationship between optical properties of Cr3+ ions and the host structure.