New investigation of nanosized co-doped Gd-Sm anatase TiO2 structural, magnetic, optical, and first-principles study

Abstract

For the time we investigated the structural, optical and magnetic properties of (Sm, Gd) co-doped TiO2 anatase nanoparticles, in addition to Sm-doped TiO2 anatase nanoparticles using sol–gel method. The X-ray diffraction confirmed the single phase of tetragonal anatase with space group I41/amd, where the crystallite size was found 7.2 nm and 8.8 nm for Ti0.99Sm0.01O2 and Ti0.99Sm0.005Gd0.005O2, respectively. The Fourier-transform infrared spectra showed the basic absorption bands in tetragonal anatase structure with a stretching vibration around 500 cm−1 assigned to Ti–O–M, M = (Gd, Sm). Raman spectroscopy demonstrated the presence of the six active vibrational modes for anatase TiO2. Scanning electron microscopy analysis revealed that the particles are spherical in nature and agglomerated. Energy-dispersive X-ray spectroscopy confirmed the high purity of the as-prepared materials. The UV–VIS analysis showed absorption in visible range, due to the electronic transition, which has been confirmed theoretically, also a slight decrease in the band gap was noticed compared to the pure TiO2 anatase. The magnetic measurements reveal the existence of weak ferro or ferrimagnetic behavior. In this work, it is the first time that experimental and theoretical results prove that rare earth ions are incorporated into the sites of the TiO2 lattice without the formation of separate phases. In addition, the experimental work carried out has revealed the importance of surface area, crystallinity, light absorption, the presence of oxygen vacancies and structural defects on the magnetic and more particularly optical properties with the highlighting of the intermediate energy level between the valence and conduction bands. This study was complemented by first-principles calculations to investigate the effects of doping anatase TiO2 with the rare-earth elements Sm and Gd on its structural, optical and magnetic properties.