Eu3 + amidst ionic copper in glass: Enhancement through energy transfer from Cu+, or quenching by Cu2 +?

Abstract

A barium-phosphate glass system doped with europium(III) and containing a high concentration of copper(I) together with a copper(II) remnant has been studied spectroscopically. The main object is to elucidate whether the orange-red emission of Eu3+ ions succeeds through sensitization via luminescent Cu+ ions or else is preferentially quenched by non-radiative transfer to Cu2+. A characterization of the melt-quenched glass was first performed by UV/Vis optical absorption, 31P nuclear magnetic resonance and infrared absorption spectroscopy. A photoluminescence (PL) spectroscopy and emission decay dynamics assessment was subsequently performed. Despite the concentration of Cu+ being estimated to be much higher than that of Cu2+, the data shows that quenching of Eu3+ PL by Cu2+ dominates. The lifetime analysis of emitting centers Cu+ and Eu3+ points to the origin of the manifestation being that the Eu3+→Cu2+ non-radiative transfer rate responsible for the quenching is almost two times higher than that for the Cu+→Eu3+ transfer accountable for the enhancement. Finally, an effort was made for the determination of Cu2+ in the glass containing Cu+, Cu2+ and Eu3+ ions based on the Eu3+ (5D0) emission decay rates. It was found to be in excellent agreement with the UV/Vis spectrophotometric approach, thus supporting the utility of Eu3+ ions for optical sensing of copper(II) in the solid state.