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 TiO2 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 TiO2 NC host, which has not been attempted before, is made easy in the presence of the fluoride anions. The synthesis produces Ta-doped TiO2 NCs as a highly uniform colloidal solution. Spectroscopic measurements indicate the generation of free carriers in the TiO2 conduction band by the Ta5+ substitution of Ti4+ 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 TiO2 NCs as a promising new electrode material for the smart windows.