Optical Properties of Rare-Earth Doped TiO2 Nanocomposites and Coatings; A Sol-Gel Strategy towards Multi–functionality

Abstract

A novel facile sol-gel method was used to synthesize visible-light responsive and photoluminescent rare-earth modified titania nanocomposites and coatings. Titania-silica-lanthanum phosphate nanocomposite doped with terbium ions (Tb3+) was prepared by an aqueous sol-gel process and the films fabricated on glass substrates by dip coating are investigated in the present work. Followed by heat treatment at 400 degree Celsius, Tb doped nanocomposite exhibits green luminescence under visible light excitation (484 nm) and PL spectra show intense peaks at 545 nm (5D4-7F5), characteristic of Tb3+ ion with a life time of ∼0.34 ms. The band gap energy of the nanocomposite was red shifted with Tb doping indicating its visible light response. 0.5 mol% Tb doped nanocomposite coated glass shows ∼66 % methylene blue dye degradation under visible light exposure for two hours while pure titania coating showed the visible light activity of ∼25 % only. 0.5 mol% Tb doped nanocomposite is thus proposed for the development of visible light active, transparent and luminescent coatings on glass substrates. Moreover, the feasibility of a codoping approach (0.25 mol% Tb and 0.25 mol% Eu doped nanocomposite) for getting multiple emission (red and green) by a single excitation wavelength (484 nm) is also demonstrated. A higher decay time of ∼0.48 ms obtained for codoped system shows the possibility of an aqueous sol-gel approach useful for applications in the area of multi-color light emissive displays.