Wavelength‐Tunability and Multiband Emission from Single‐Site Mn²⁺ Doped CaO Through Antiferromagnetic Coupling and Tailored Superexchange Reactions

In modern phosphor materials, in contrast to single‐band emission, simultaneous photoluminescence through two or more emission bands enables broad and tailorable emission color, but requires fine control of activator precipitation on specific crystallographic sites. This presents a major obstacle in the design of tunable emitters, since dedicated control of site occupancy is rarely possible. Here, a new paradigm of tunability is considered, which overcomes this limitation. It is demonstrated in CaO:Mn²⁺ that single‐ and dual‐band emission can be generated by involving only a single type of crystallographic sites. This enables tailoring of the emission color alone through dopant concentration. The two emission bands exhibit different spectral, dynamic, and thermal characteristics, but very similar excitation spectra. While the variations in thermal quenching provide a tool for tunability, the variations in decay behavior suggest interesting potential for lifetime‐multiplexing and coding. Energy transfer is observed between the two emission bands, using time‐resolved emission spectra. From the analysis of crystal structure, spectral data, electron paramagnetic resonance analyses, and density functional theory calculations analyses, it is found that the emission bands at ≈600 and 660 nm originate from isolated Mn²⁺ ions and superexchange reactions in Mn²⁺ Mn²⁺ dimers, respectively.