Ab initio site occupancy and far-red emission of Mn⁴⁺ in cubic-phase La(MgTi)_1/2O₃ for plant cultivation

Mn⁴⁺-activated oxide phosphors La(MgTi)_1/2O₃ (LMT) with far-red emitting were prepared via a sol-gel route. The structures of samples were determined by X-ray diffraction (XRD) and Reitveld refinement. The occupied sites of Mn⁴⁺ (d³ electronic configuration) in host La(MgTi)_1/2O₃ were confirmed by ab initio calculations in which the system has the lower formation energy, stable lattice structure, and strong bonding state as Mn⁴⁺ enters into Ti site. The luminescent properties of Mn⁴⁺-doped samples were investigated; the samples emit far-red light centered at 708 nm with ultraviolet light (345 nm) or blue light (487 nm) excitation. According to the photoluminescence (PL) and excitation (PLE) spectra, the crystal field strength of the Mn⁴⁺-occupied environment was estimated. The thermal stability of phosphor was also evaluated through temperature-dependent PL intensity in a heating and cooling cycle process. The emission band is well-matched with the absorption band of phytochrome P_FR under the excitation of light in near-ultraviolet to blue, which suggests that the LMT: Mn⁴⁺ phosphor has great potential applications in light-emitting diodes (LEDs) for modulating plant growth.