EPR study on paramagnetic species in nitrogen-doped ZnO powders prepared by a mechanochemical method

Paramagnetic species in nitrogen-doped ZnO (N-ZnO) powders, visible light sensitive photocatalysts exhibiting antibacterial activity, have been investigated using EPR spectroscopy. The N-ZnO photocatalysts showed two kinds of EPR signals due to a singly ionized nitrogen ( N 2 - ) and a shallow donor. Visible light irradiation to the N-ZnO particles shows reversible response of reduction of EPR signal of the N 2 - radical site and increase of that due to shallow donor. The results indicate that the N 2 - is converted to a diamagnetic neutral molecular nitrogen acceptor ( N 2 0 ) by visible light and photoinduced electrons are trapped to the shallow donor sites.