Evolution of the full energy structure of Mn in fluoride phosphors under high pressure conditions.

This paper analyzes the photoluminescence excitation and emission spectra of fluoride phosphors doped with Mn: KNaSiF:Mn, RbGeF:Mn, and NaHTiF:Mn under high pressure conditions. From the optical spectra, the pressure-dependent energies of optically active T, T, and E crystal field subterms of Mn have been determined in the 0-30 GPa pressure range. A strong blueshift of the T and T subterms was found, as expected from the Tanabe-Sugano diagram for Mn (d). At the same time, the E emitting state exhibited a redshift under pressure - an effect opposite to the prediction of the Tanabe-Sugano diagram. This is a manifestation of the pressure-driven nephelauxetic effect, governed by pressure induced changes of Racah parameters, which demonstrates the necessity of taking into account the Racah parameters for a correct description of Mn emission under pressure. The high pressure experimental data allowed to determine the pressure dependence of crystal field strength parameter and Racah parameters and . Finally, obtaining the pressure dependence of and Racah parameters allowed to calculate the full energy structure of the d configuration of Mn in KNaSiF, RbGeF, and NaHTiF in the pressure range of 0-30 GPa. The calculations reproduced the redshift of the E emitting state under pressure, as well as gave the pressure shift direction and magnitude for all crystal field subterms of Mn up to 50 000 cm ( the equivalent of the Tanabe-Sugano diagram for high-pressure experiments). The approach presented in this paper can be easily extended for calculating the energy structure of materials doped with isoelectronic Cr as well as other transition metal ions.