Cr modified Raman, optical band gap and magnetic properties of SnO₂ nanoparticles

Pure and Cr (1, 3, 5, 7 and 10 at.%) doped SnO₂ nanoparticles were synthesized in aqueous solution by a low cost chemical co-precipitation method without using any stabilizing agent. The effects of Cr doping on Raman, optical band gap and magnetic properties of SnO₂ nanoparticles were investigated. Particle size is found to decrease with Cr doping into the SnO₂ matrix which was confirmed by TEM. Besides of the fundamental mode of vibration, two additional peaks are also observed in Raman spectra which are correlated to Cr. The absorption spectra showed two peaks at 340 and 454 nm. The absorbance peak at 340 nm is assigned to the transition from valence band (VB) to conduction band (CB) and the peak at 454 nm was due to the transition from VB to mid gap energy level introduced by Cr. The optical band gap of undoped SnO₂ nanoparticles is calculated to be 3 eV. With the doping of Cr in SnO₂, band gap increases due to the decrease in particle size. The emission intensity is found to decrease with the increase in Cr doping due to the emission from CB to mid gap energy levels introduced by Cr between CB and VB. Undoped SnO₂ nanoparticles show room temperature ferromagnetism due to the presence of defects and oxygen vacancies. The heavily doped SnO₂ nanoparticles show paramagnetic nature due to the antiferromagnetic coupling between Cr and its nearest neighbour.