f → f transition luminescence of Eu2+ in barium–aluminum–borate oxyfluoride glass ceramics

Abstract

Novel transparent luminescent glass ceramics with the ability to generate the line emission of Eu²⁺ ions were successfully prepared. First, Eu²⁺-doped barium–aluminum–borate oxyfluoride glasses were prepared by high-temperature melting in a reducing atmosphere, and then transparent glass ceramics were obtained by crystallization heat treatment. Fluorescence spectroscopy showed that Eu²⁺ exhibited only broadband luminescence (FWHM ≈ 136 nm) of the 4f⁶5d¹ → 4f⁷ transition in the glasses. However, after heat treatment, a 359 nm line emission (FWHM ≈ 2.8 nm) from the 4f⁷ → 4f⁷ transition of Eu²⁺ appeared in the glass ceramics. To explore the mechanism of transformation of the optical transition of Eu²⁺ from 4f⁶5d¹ → 4f⁷ to 4f⁷ → 4f⁷, the glasses and glass ceramics were analyzed by fluorescence spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy measurements. The results showed that the alteration in the optical transition of Eu²⁺ was a result of the Eu²⁺ ions entering the Ba²⁺ sites with weak crystal field strength in BaAlBO₃F₂ (BABF) crystals from the strong crystal field strength glass phase.