Structural and Optical Study of SnO Nanoparticles Synthesized Using Microwave–Assisted Hydrothermal Route

SnO nanoparticles were synthesized using microwave–assisted hydrothermal method. It was noticed that at 300 and 600 watt microwave power, SnO formed and remained in the tetragonal phase. At 900 watt, SnO2 started appearing and a mixture of SnO and SnO2 phases coexisted. The particle size varied from ~2 to ~13 nm at 300 to 900 watt radiation power. The UV-V absorption spectra showed the excitonic peaks of ~288,  ~300 and ~315 nm corresponding to crystal sizes of ~2, ~6 and ~10 nm, respectively. For particles larger than 10 nm, no excitonic peak was observed. The appearance of these excitonic peaks could be attributed to the conversion of indirect band gap in bulk SnO to direct band gap in SnO nanoparticles. To verify this assumption, photoluminescence spectroscopy was carried out. The results showed a strong emission of 677 nm upon excitation at 336 nm wavelength, confirmed the assumption.