Observations of phonon anharmonicity and microstructure changes by the laser power dependent Raman spectra in Co doped SnO2 nanoparticles

Abstract SnO2 nanoparticles are of critical importance owing to their necessity for fundamental studies and highly attractive applications in optoelectronic devices and photocatalytic activities. In this study Raman spectroscopy was rigorously employed to investigate the effect of low concentrations of cobalt doping in rutile SnO2 nanoparticles. The effect of annealing temperature and laser power dependent molecular vibrations was used to directly realize the localized microstructural changes and phonons interaction within the lattice. A large broadening and shifting towards the lower wavenumber side in the Raman spectra for A1g and B2g modes of vibration were observed. This was mainly attributed to microstructural changes, maximum possible quasiharmonic shift and a large proportion from pure anharmonic shifts as a function of increasing laser power. Two approaches were adopted to calculate the localized temperature that has increased due to laser heating during the Raman measurements in the samples. In a more feasible and reliable approach the full with at half maxima (FWHM) broadening and frequency shifting as a function of laser power were directly compared with the previously reported experimental results. In another approach the well-known Klement model based on the kinematics of three-phonon processes was also used to determine the localized temperature.