Optical and spectroscopic properties of Eu2+/Eu3+-doped Calcium Boroaluminate glasses

In this work, europium rare-earth doped Calcium Boroaluminate (CaBAl) glasses were synthesized by conventional melt-quenching method, and carbon was used to control the ratio of Eu3+ and Eu2+ during the melting process. Optical and spectroscopic properties were studied and discussed in terms of the carbon content. X-ray absorption near edge structure (XANES) measurements show the correlation of the luminescence behavior of the material with the Eu2+/Eu3+ concentration ratio. Absorption spectra exhibited five Eu3+ characteristic bands and one band attributed to Eu2+ for the samples with carbon. The excitation spectra showed a maximum intensity at 398 nm for Eu3+ and a band at 250–400 nm for Eu2+. The luminescence spectra presented expressive increase in the emission intensity of Eu2+ (blue) and decrease of Eu3+ (red-orange) with carbon content. CIE chromaticity coordinates were calculated to evaluate the white light emission as a function of the increase of Eu2+ concentration to obtain ideal white light (0.33, 0.33). The luminescence as a function of the temperature presented an increase of 12% on the luminescence intensity for the Eu3+ ion and a decrease of 59% for the Eu2+ ion, up to 480 K. The CRI value for the sample was synthesized with 5% carbon was 81, higher than the values found in the literature for RGB white LEDs and neodymium incandescent lamps. The results show that those glasses have potential for applications in White Light Emitting Diodes.