Near infra-red luminescence of BaTiO3: Cr

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Abstract
It was found that Cr in BaTiO3 crystals reveals a characteristic luminescence with four sharp emission lines at 781.6 (A 1), 776.4 (A 2), 768.8 (A 2), 766.8 (A 3) and 766.8 nm (A 4) for 74 K. Considering EPR data, temperature- and lifetime behaviour, the A 3 and A 4 lines are interpreted to be R 1,2-lines originating from zero-phonon 2 E → 4 A 2 transitions of octahedral Cr3+ replacing Ti4+. The A 1,2 emission lines may originate from Cr3+ exchange coupled with an unknown compensating defect. It is remarkable that the inhomogeniously broadened A-lines are well described by Lorentz curves at low temperatures, with half-width (FWHM about 10 cm−1) depending hardly on the temperature.