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 (Eu3+) ions in the vicinity of nanometer-sized metal particles in glasses. In this study, gold (An) colloids synthesized in solution were introduced into a borosilicate (B2O3-SiO2) glass matrix together with Eu3+ 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 degreesC led to a great enhancement of Eu3+ 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 degreesC, a conspicuous decrease in the relative intensity of Eu3+ fluorescence was observed, regardless of the presence of Au nanoparticles. Since a group of carbonyl terminations, when coordinated to Eu3+ ions (1>C=O --> Eu3+), can be an energy donor, these observations showed that Eu3+ 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.