Full understanding of KNaSiF6:Mn4+ properties under hydrostatic pressure based on the Tanabe−Sugano energy-level diagram

Highlights: • A discussion is given on the luminescent properties of Mn⁴⁺ ion in KNaSiF₆ host. • A sophistical method is presented for analyzing optical spectra under hydrostatic pressure. • Accurate Racah/crystal-field parameters are determined for Mn⁴⁺ ion in KNaSiF₆ host. • Relations of the ligand-field-related parameters for Mn⁴⁺ ion in KNaSiF₆ under hydrostatic pressure are discussed. The aim of this study is to make clear the photoluminescence (PL) properties of Mn⁴⁺-activated phosphors under the application of hydrostatic pressure (p). A determination of the excited-state zero-phonon line (ZPL) energies in the 3d³-configuration ions is possible from a set of Racah (B and C) and crystal-field splitting parameters (Dq), and vice versa. It has been demonstrated that detailed analyses of PL and PL excitation spectra make possible exact determination of the excited-state ZPL energies, E (²E_g)_ZPL and E (⁴T_2g)_ZPL, as a function of p. Introducing such determined ZPL energies into a newly proposed set of formulae, we obtain reliable Racah-related parameter values for 3d³ (Mn⁴⁺, Cr³⁺, etc.) activator ions in the red-emitting phosphors. Some examples of analyses are given on the Mn⁴⁺-activated KNaSiF₆ fluoride phosphor. The present analysis model can be used to obtain broad perspectives and insight for deeply understanding metal−ligand chemistry and related phenomena in the various 3d³ ion-activated phosphors under the application of hydrostatic pressure.