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

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.