Optical properties of europium ions in SrB2O4crystal

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Abstract
We investigate absorption, emission and excitation properties of an SrB2O4:Eu crystal grown from the melt using the Czochralski method. Eu2+ absorption and Eu3+ emission spectra are obtained. The five broad absorption bands peaking at 344, 288, 259, 235 and 212 nm correspond to the transitions from the 4f7(8S7/2) ground state to the excited states of the 4f65d configuration of Eu2+. Several zero-phonon lines for the different 4f6(7FJ) levels of the lowest 4f65d excited state are observed in the absorption spectrum measured at 10 K. The deep-orange luminescence in the 578-640 nm region is due to the transition from the 5D0 excited state to the 7FJ (J = 0, 1 and 2) states of Eu3+.Eu2+ does not give rise to luminescence, even at 10 K, because of the photoionization in the excited state, followed by a nonradiative return to the ground state of Eu2+. The strong emission due to the 5D0 7F0 transition and the existence of different sites of Eu3+ for Sr2+ are explained by the charge compensation and structural characteristic of SrB2O4.