Oxygen vacancies can alter the crystal structure and defect concentration which may change the electronic and chemical properties of transition metal oxide surfaces. Oxygen vacancies can be obtained via thermal annealing or illumination with ultraviolet photons. Thermal annealing is considered to be the most obtained approach to creating oxygen vacancies , narrowing the band gap and enhance the electrical conductivity. Oxygen vacancies can observed by XPS analysis.

Itink that XPS analysis help to you. from O 1s spectra , İf it is broad and it has two binding energy around 531 532 eV, this coomes from surface hydroxl species. In addition, crystallite defect shows this phenomenon.

Actually, the XPS spectra of O 1s (Oxygen vacancy) is observed in different binding energy. It was observed in 530-533 eV range in different articles. So, i am in confusion. Thank you all.

You should take EPR of your sample. If there is oxygen vacancy then you will observe peak at a particular magnetic field. EPR is of two type one being low temperature (100 K) and other being room temperature. It depends on your material which will work best.

With Raman also we can get an idea of oxygen vacancy because the over stoichiometry is broken due to oxygen vacancy, so you might observe a blue shift in Raman Band wrt to your original pristine material.

XPS is also powerful technique which will show a negative peak shift in O1s peak position wrt to pristine material.

These above mentioned characterization techniques if done properly must be enough to prove oxygen vacancy.

Optical techniques like UV vis can show an enhanced absorption in visible region because of mid gap states created in the bandgap, so this might also give an idea of changed bandgap of your material mainly due to oxygen vacancies.

Thank you very much Saurav ji.