Low temperature luminescence of KMgF3:Eu2+ crystal

Paper presents luminescence spectra and time resolved spectra of KMgF3:Eu2+ system obtained at different temperatures and pressures, under excitation with 325 nm. At temperatures between 200 K and 292 K the spectra consist of sharp line peaked at 27,830 cm−1 related to 6P7/2 → 8S7/2 transition in Eu2+ accompanied by the phonon sideband. Under pressure the red spectral shift with the rate equal to −0.6 cm−1/kbar is observed. Luminescence decay is single-exponential with the lifetime equal to 5.2 ms independent of pressure and temperature. The emission spectra obtained at temperatures lower than 125 K consist of 5 sharp lines peaked at 27,590 cm−1, and 27,670 cm−1, 27,722 cm−1, 27,766 cm−1 and 27,809 cm−1, that relative intensity depends on temperature. Pressure shift of these lines was found to be equal to −0.6 cm−1/kbar; the same as 6P7/2 → 8S7/2 transition in Eu2+, whereas their lifetime is shorter and is equal to 0.7 ms at 100 K. These new lines disappear at temperature greater than 200 K. We tentatively related them to the luminescence of Eu2+–F center (fluorine vacancy with electron) complex.

Research highlights
► Luminescence of KMgF3:Eu2+ strongly depends on excitation wavelength and temperature.
► For excitation below 320 nm the luminescence was in full coincidence with earlier published data.
► Under excitation above 325 nm at temperatures below 170 K novel emission was observed.
► This novel emission was tentatively attributed to the :Eu2+ - F center complex.