Excited state properties of ferrate (VI) doped crystals of K 2SO 4 and K 2CrO 4

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The 15 K polarized single-crystal absorption spectra of Fe 6+ doped K 2SO 4 consist of two sharp bands below 10 000 cm −1 assigned to the spin-flip transitions 3A 2 → 1E, 1A 1 and a series of broad bands in the near-infrared (NIR) and visible region assigned to 3A 2 → 3T 2, 3T 1 d → d transitions and O → Fe charge transfer transitions. From the excited state absorption (ESA) spectrum we derive that the 1T 2 state lies 19 300 cm −1 above the 3A 2 ground state. This allows a clear assignment of all the ligand field states below 33 000 cm −1, which is in good agreement with an angular overlap model (AOM) calculation. Differences in the temperature dependence of the 1E → 3A 2 luminescence intensity upon broadband and 3A 2→ 1a 1 excitation are shown to be due to direct nonradiative relaxation processes from 3T 2 to the 3A 2 ground state.