Control of luminescence by tuning of crystal symmetry and local structure in Mn⁴⁺-activated narrow band fluoride phosphors

Mn⁴⁺-doped fluoride phosphors have been widely used in wide-gamut backlighting devices because of their extremely narrow emission band. In this study, solid solutions of Na₂(Si_xGe_1-x)F₆:Mn⁴⁺ and Na₂(Ge_yTi_gros)F₆:Mn⁴⁺ have been successfully synthesized to elucidate the behavior of zero-phonon line (ZPL) in different structures because of the sensitivity of ZPL intensity to the local coordinated environment. The structures of the products are examined by X-ray diffraction and Rietveld refinement. The ratio between ZPL and the highest emission intensity υ6 phonon sideband exhibits a strong relationship with luminescent decay rate. First-principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. The calculated results are consistent with the experimentally determined structural parameters. To compensate for the limitations of Rietveld refinement, electron paramagnetic resonance and high-resolution steady-state emission spectra are used to prove the diverse local environment for Mn⁴⁺ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical application.