You can use X-ray absorption methods, Electron energy loss spectroscopy or X-ray Photoelectron spectroscopy to determine the oxidation states of atoms present in your sample. In the case of XPS it is a surface sensitive method, the other two are more of a bulk method. Each comes with its own perks and limitations, so read about those further.
Whenever the dopants like silver atom is added into a crystal then the product material will change its physical as well as chemical properties thus the impurity atom goes into crystal lattice sites. You can identify both qualitatively and quantitatively. Physical properties like thermal behavior, optical properties can be studies by DSC, UV-vis, FTIR spectroscopy. For chemical bonding you can study X-ray Photoelectron spectroscopy (XPS) and also to determine the oxidation states of atoms present in your sample, atomic absorption spectroscopy, IC-PMS, etc.
If it is low concentration, You can use XPS ( X-ray Photoelectron spectroscopy ) give the good result to identify the oxidation states of the sample. I have prepared 0.025 mol% Au2O3 doped samples and using XPS studies i can find the oxidation states of Gold.
Article Structural and physical characteristics of Au2O3 doped sodiu...