Room-temperature photoluminescence in MnF2 under high pressure

A novel two-color photoluminescence (PL) is found in MnF2 at room temperature (RT) under high pressure. In contrast to the low-temperature PL, the observation of room-temperature PL is unusual in transition-metal concentrated materials like MnF2 since the de-excitation process at RT is fully governed by energy transfer to non-radiative centers. We show that room-temperature MnF2 emissions originate in the pressure-induced cotunnite phase. Both the nine-fold Mn2+ coordination and the Mn–F–Mn exchange pathway inhibit exciton migration among Mn2+, favoring two-band PL at RT. The electronic structure and the excited-state dynamics are investigated by time-resolved emission and excitation spectroscopies under pressure. The two PL bands at 2.34 and 1.87 eV above 15 GPa are assigned to Mn2+ emissions arising from two distinct Mn2+ centers formed in the MnF2 high-pressure phase. The microscopic origin of the two-color PL is analyzed in terms of exciton dynamics in the MnF2 cotunnite structure.