Abnormal Self-Reduction Phenomenon of Europium-Doped Borate and Its Luminescence Properties

In this work, mixed-valence Eu-doped Ba2AlB4O9Cl (BABOC) was successfully synthesized in an air atmosphere for the first time. The samples were determined to possess a good single phase by Rietveld structure refinement and X-ray powder diffraction (XRD). The luminescence spectra of the samples showed that the characteristic emission and excitation peaks of Eu2+ and Eu3+ were both present in the sample, and their emitting color could be adjusted by changing the Eu doping concentration. The band gap of BABOC, calculated by density functional theory (DFT), was found to be 4.70 eV and was confirmed by diffuse reflection spectroscopy (DRS). The relationship between the self-reduction efficiency of the sample and the doping concentration of Eu ions was studied by measuring the decay lifetimes of Eu2+ and Eu3+. The thermal quenching and thermoluminescence spectroscopy of the samples were also studied in detail. All of the results indicated that BABOC:Eu has special self-reduction properties, and the abnormal self-reduction phenomenon was explained by a charge compensation model. Our investigation of BABOC:Eu provides practical evidence and a theoretical basis for the self-reduction phenomenon and a new method to further modify the luminescence properties of phosphors.