Synthesis and optical properties of calcium halide-based aluminoborate glasses codoped with Eu2+ and Eu3+ ions

Oxy-halide glasses in systems of CaX2 - Al2 O3 - B2 O3 (X = F, Cl, and Br) doped with Eu2 O3 were prepared by a melt quenching method and their optical properties were characterized by measurements of UV-visible luminescence, hole burning, and electron spin resonance (ESR) spectra. For the CaCl2 - and CaBr2 -based samples, Eu3+ ions were partially reduced during the heating process in ambient atmosphere, so that room temperature persistent spectral hole burning was observed on them. Meanwhile, no obvious band emission or characteristic ESR signal of Eu2+ ion was recorded on the CaF2 -based samples also prepared in ambient atmosphere, and consequently any hole peak was hardly detected even at 10 K. However, hole peaks were produced and persisted at room temperature on the CaF2 -based samples remelted in a reducing atmosphere. The self-reduction mechanism for Eu3+ ion in the CaCl2 - and CaBr2 -based samples is discussed as well as the hole formation in all samples.