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. (c) 2007 Elsevier B.V. All rights reserved.