Fluoride-Assisted Synthesis of Plasmonic Colloidal Ta-Doped TiO2 Nanocrystals for Near-Infrared and Visible-Light Selective Electrochromic Modulation

Dual-band electrochromic materials are integral to the development of smart windows where visible and near-infrared (NIR) light transmittance may be individually controlled. We present here colloidal Ta-doped TiO 2 anatase nanocrystals (NCs) as a promising candidate and their preparation by a fluoride-assisted synthesis method. The dual-band electrochromic performance of these NCs may be credited to their strong localized surface plasmon resonance (LSPR) absoption in the NIR region. The Ta doping of the TiO 2 NC host, which has not been attempted before, is made easy in the presence of the fluoride anions. The synthesis produces Ta-doped TiO 2 NCs as a highly uniform colloidal solution. Spectroscopic measurements indicate the generation of free carriers in the TiO 2 conduction band by the Ta 5+ substitution of Ti 4+ cations as the origin of the LSPR. Good dual-band electrochromic performance in terms of a high dynamic range for visible and near-infrared light modulation (86.3% at 550 nm and 81.4% at 1600 nm) and good electrochemical stability (the optical modulation at 550 and 1600 nm decreased by 1.3% and 6.7%, respectively, after 2000 cycles) were demonstrated in three-electrode cells to suggest Ta-doped TiO 2 NCs as a promising new electrode material for the smart windows.