for photocatalytic appliaction of metal oxide , we need to avoid recombination of electron and holes after creation of these by radiation. So, we can create electron trap by using doping.
How oxidation state play this role in creation of these defects?
Recall that different oxides exhibit differing compensation mechanisms in response to external charge effects; typically, via the formation of compensating, charge-trapping, lattice defects that can accommodate the excess charge introduced by dopant(s). Electron donor-type impurities are conducive to the formation of cationic vacancies that can act as electron trap sites. Oxygen-vacancies analogously can serve as an electron trap for low-valency dopants. By introducing a dopant with a higher oxidation state than the lattice is analogous to the oxygen-vacancy case. Hope this helps somewhat.
Yes because when you introduce a metal with higher oxidation state to maintain the electrical neutrality of lattice it will leave oxygen vacancies or electron traps which behave as negative charges in tn number which would nullify the extra positive charges added by metal ions with higher oxidation states.
Dear Deepak, I agree with Shrikaant sir. In a metal oxide, doping of metal with higher oxidation state results in the formation of oxygen vacancies for charge compensation.
In my opion, the introduction of a impurity ion with higher oxidation state would lead to the formation of electron-trapping center, similar like oxygen vacancy defect. The reality is that the stacking of atoms is generated by neutral atoms and the charge states are due to the chemical bonding. Thus, the real introduction of a dopant ion with higher oxidation state is a neutral atom with more valence electrons. The more excess electrons trapped around the impurity center can play a role as electron-donor.
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