Impact of hydrostatic pressure on the crystal structure and photoluminescence properties of Mn4+-doped BaTiF6 red phosphor.

High-efficiency red phosphors with non-rare-earth activators are emerging as an alternative for next generation solid-state warm white LEDs. Their optical properties depend strongly on the local site symmetry and the crystal field strength. Herein we present the pressure tuning of structural and photoluminescence (PL) properties of Mn(4+)-doped BaTiF6 up to 40 GPa. In situ high pressure synchrotron X-ray diffraction, Raman and PL spectroscopy studies show that the crystal symmetry changes from trigonal at ambient pressure to monoclinic from 0.5 GPa and triclinic above 14 GPa, attributed to the distortion of (Ti/Mn)F6 octahedra. The red emission peaks shift monotonically to longer wavelengths due to the reinforced crystal field strength within MnF6 octahedra as pressure increases. A detailed comparison of emission shift rate, PL intensity and FWHM between Mn(4+)-doped BaTiF6 and ruby (Cr(3+)-doped Al2O3) was performed using neon pressure transmission medium. This demonstration provides not only an efficient way to artificially tune the emission properties of practically useful phosphors by means of hydrostatic pressure, but also alternative candidates as potential pressure gauges for high pressure techniques.