The synthesis and characterization of substitutional Fe 3+ in sub-10 nm colloidal SrTiO 3 and BaTiO 3 nanocrystals (NCs) are reported. Significant and reversible changes to the electronic structure of the Fe dopants in the NCs with excess n-type defects are observed by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. These n-type defects are identified as paramagnetic Ti 3+ trap states that are created by anaerobic photodoping of colloidal suspensions with UV light in the presence of a hole scavenger. The appearance of the Ti 3+ defects is correlated with the disappearance of the Fe 3+ EPR signal that we attribute to the reduction of Fe 3+ dopants to the EPR-silent Fe 2+ . This reduction of the Fe dopant is totally reversible upon reoxidation of the nanocrystals with air. The stabilization of Fe 2+ in these lattices has been observed in SrTiO 3 and BaTiO 3 thin films and bulk powders after reducing the samples under extreme conditions that convert only a fraction of the Fe 3+ dopants. In contrast, the controlled reduction of apparently every Fe 3+ dopant to Fe 2+ in these colloidal NCs can be achieved with just UV photons at room temperature. This work expands upon the types of reversible interactions that can exist between aliovalent magnetic dopants and charge carriers in d 0 -based metal oxide semiconductors.
We report facile and reversible electron storage in colloidal SrTiO3 nanocrystals using photochemical and redox titration methods. A very high electron storage capacity (~180 e– per 7 nm nanocrystal) is...
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