Boron is diamagnetic in B-doped anatase TiO2 nanoparticles which exhibit photocatalytic activities in the visible light range. Using N as a paramagnetic probe for the formal oxidation state of boron in N/B-codoped TiO2, with more than 90% unpaired spin density in the N2p orbital, we infer that boron enters the oxygen vacancy substitutionally in the form of B1-. Combination of spin-Hamiltonian analysis and interpretation of light dependent EPR spectra in terms of a charge compensating mechanism supports a model of [N2-B1-]+1 for the new EPR active center which acts as a trap for electrons liberated from [N1-] centers under blue light irradiation. Definite assignment of the boron oxidation state will contribute to the preparation, characterization, and understanding of B-TiO2 photoactivity under visible light which has been the subject of extensive work in the past few years.
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Gopal et al. (2008) studied this question.
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