Synthesis of thermally stable Ag@TiO2 core–shell nanoprisms and plasmon–enhanced optical properties for a P3HT thin film

Abstract

We develop a facile method to synthesize Ag@TiO₂ core–shell nanoprisms (NPs) with a tunable shell thickness through a simple sol–gel route. The thickness of the TiO₂ shell can be precisely tuned from 1 to 15 nm via changing the reaction time and amount of TiO₂ sol–gel precursor. The localized surface plasmon resonance (LSPR) absorption band shows a red-shift of over a hundred nanometers with the increasing TiO₂ shell thickness. The thermal stability of the Ag NPs is significantly improved due to the introduction of the TiO₂ shell. We investigate the enhanced absorption and fluorescence of poly(3-hexylthiophene) (P3HT) via coating bare Ag and Ag@TiO₂ core–shell NPs with P3HT. A similar absorption enhancement indicates that the LSPR absorption enhancement is not affected by the ultra-thin TiO₂ shell. Weak and significant fluorescence enhancements are observed for the P3HT hybrid film with bare Ag NPs and Ag@TiO₂ core–shell NPs, respectively. The bare Ag NPs work as both an enhancement element and a recombination center, which quench the P3HT fluorescence to some degree. The recombination of the charge carriers is effectively depressed by introducing the ultra-thin TiO₂ shell, which blocks the hole transfer to the Ag NPs.