Multi-wavelength excitable europium-doped borosilicate glasses for orange-red emission: composition-induced structure and valence variation

Europium-doped borosilicate glasses were prepared by melt-quenching procedure in the air. The mixed valence of Eu2+ and Eu3+ was identified by photo luminescence spectrum and electron paramagnetic resonance (EPR). The existence of mixed valence was observed owing to the unequivalent substitution and de-polymerization network of the as-prepared borosilicate glasses. The variation of the glass composition in B2O3/BaO ratios changed the stability of the Eu3+ ions distinctly. In particular, as-prepared borosilicate glasses exhibited a tri-wavelength light excitable spectra centered at 397, 466 and 534 nm to give the broadened orange-red emission at around 592 and 617 nm, due to supersensitive transitions of Eu3+ ions. This simultaneous tri-wavelength excitation happened to correspond with the emitting wavelength from near ultraviolet, blue AlInGaN chips and that from YAG:Ce3+. The total quantum yield (QY) of the Eu-doped glasses under 466 nm excitation was evaluated to be 10%, potentially providing a versatile combination with the europium-doped borosilicate glasses for red component addition to improve the quality of white light.