Optical Spectroscopy and Excited-State Dynamics of Eu3+ -Doped Bismuth Borate Glasses Containing CuO.

Abstract

Bismuth borate glasses containing phosphors and luminescent rare-earths are of interest for applications in light-emitting devices. Herein, the influence of CuO impurities on red-emitting Eu3+ -doped bismuth borate glasses of the 25Bi2 O3 -15BaO-10Li2 O-50B2 O3 type was investigated by various spectroscopic methods. The glasses were prepared by the melt-quench technique and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV/Vis optical absorption (OA), and photoluminescence (PL) spectroscopy including decay kinetics assessment. The XRD data confirmed the amorphous nature of the glasses whereas FT-IR spectra indicated the basic structural features of trigonal BO3 units and BO4 tetrahedra. The OA analysis showed that addition of CuO up to 0.5 mol% results in significant growth of the visible Cu2+ absorption band around 715 nm, with slight decrease in the optical band gap energies assessed through Tauc plots. A drastic PL quenching of Eu3+ ions emission was evidenced concurring with the detrimental effect of Cu2+ . The assessment of the Eu3+ emission decay curves revealed significant lifetime decrease of the 5 D0 emitting state with increasing CuO concentration. An analysis of quenching constants was finally performed comparing results from integrated PL data with the emission decay rates. It is argued that the bismuth borate glass system supports an effective Eu3+ →Cu2+ energy transfer (more so than phosphates) in connection with a strong spectral overlap between Eu3+ emission and Cu2+ absorption.