Nb-Dopant-Induced Tuning of Optical and Electrical Property of Anatase TiO₂ Nanocrystals

For increasing demand of electrochromic smart window, flat panel display synthesis of high quality aliovalent doped wide bandgap semiconductor nanocrystals are gaining interest. In our manuscript we synthesized pure and Nb⁵⁺ doped anatase TiO₂ nanocrystals by colloidal process. On increasing doping percentage size of TiO₂ nanoparticle was found to be decreased. Although pure TiO₂ nanocrystals are terminated with thermodynamically stable {101} facets but Nb⁵⁺ doped TiO₂ was found to be terminated with high energy {103} facet by lowering the surface energy. Successful doping in anatase TiO₂ has been characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) analysis. Aliovalent dopant Nb⁵⁺ generated free carriers in conduction band of TiO₂. These free electrons results distinct plasmon absorption peak which appeared at wavelength of 1900 nm to 2700 nm. Plasmon peak found to be blue shifted with increase of dopant amount. Broad emission bands correspond to distinct transitions related to intermediate energy levels induced by oxygen vacancy. High colloidaly stable nanocrystals was deposited as crack free transparent conducting oxide thin film where we obtained very low sheet resistance with high optical transparency that leads to good figure of merit of thin film. Temperature driven metal-insulator transition for the lowest resistance film is explained by electron localization origination from random substitution of Nb into TiO₂ nanocrystals.