Pressure effect on the zero-phonon line emission of Mn⁴⁺ in K₂SiF₆

In this work, effects of pressure and temperature on the luminescent properties of the K2SiF6:Mn4+ system have been presented. At ambient pressure, the luminescent spectrum of Mn4+ consists of several lines at 610-650 nm attributed to phonon repetitions of the 2Eg → 4A2g transition and does not contain the zero phonon line (ZPL). At pressure above 9 kbar, an additional line at about 624 nm occurs, which can be attributed to the ZPL of the 2Eg → 4A2g transition in the Mn4+ ions. This change in the emission spectra is accompanied by shortening of the luminescence decay time. Further increasing pressure up to 220 kbar causes the red shift of all emission lines. Upon releasing pressure, all observed lines are going back to their previous positions. The ZPL remains visible even at ambient pressure. Taking into account XRD and Raman spectra at ambient pressure before and after compression-decompression, we have attributed these changes to pressure-induced local structure change of MnF62- octahedron.