Eu^3 + amidst ionic copper in glass: Enhancement through energy transfer from Cu⁺, or quenching by Cu^2 +?

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 Eu^3 + ions succeeds through sensitization via luminescent Cu⁺ ions or else is preferentially quenched by non-radiative transfer to Cu^2 +. 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 Cu^2 +, the data shows that quenching of Eu^3 + PL by Cu^2 + dominates. The lifetime analysis of emitting centers Cu⁺ and Eu^3 + points to the origin of the manifestation being that the Eu^3 + → Cu^2 + non-radiative transfer rate responsible for the quenching is almost two times higher than that for the Cu⁺ → Eu^3 + transfer accountable for the enhancement. Finally, an effort was made for the determination of Cu^2 + in the glass containing Cu⁺, Cu^2 + and Eu^3 + ions based on the Eu^3 + (⁵D₀) emission decay rates. It was found to be in excellent agreement with the UV/Vis spectrophotometric approach, thus supporting the utility of Eu^3 + ions for optical sensing of copper(II) in the solid state.