Enhancement of ⁵D₀-⁷FJ Emissions of Eu³⁺ Ions in the Vicinity of Polymer-Protected Au Nanoparticles in Sol−Gel-Derived B₂O₃−SiO₂ Glass

The paper reports the enhanced photoluminescence of trivalent europium (Eu 3+ ) ions in the vicinity of nanometer-sized metal particles in glasses. In this study, gold (Au) colloids synthesized in solution were introduced into a borosilicate (B 2 O 3 −SiO 2 ) glass matrix together with Eu 3+ ions via a sol−gel route. To control in size and protect Au colloids two types of polymers poly(vinylpyrrolidone) (PVP) and polyacryronitorile (PAN) were used. As a result, PVP provided excellent homogeneity of Au nanoparticles in the hybrid gel. A novel finding on its photoluminescence properties is that a heat treatment of the gel at 400 °C led to a great enhancement of Eu 3+ fluorescence under a long ultraviolet excitation, six times higher than without Au nanoparticles, accompanied with a broad fluorescence around 400 nm due to carbonyl moieties of PVP. On the contrary, when the carbonyl groups were removed by heat treatment at temperatures higher than 400 °C, a conspicuous decrease in the relative intensity of Eu 3+ fluorescence was observed, regardless of the presence of Au nanoparticles. Since a group of carbonyl terminations, when coordinated to Eu 3+ ions (>C O → Eu 3+ ), can be an energy donor, these observations showed that Eu 3+ ions were strongly excited by the energy transfer from C O groups, which were placed in enhanced local fields near Au nanoparticles due to higher orders of surface plasmon resonances.