The effect of photodoping on relaxation dynamics of undoped SrTiO3 and Cr:SrTiO3 colloidal nanocrystals were studied as a function of temperature. Absorption and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopies were employed to monitor changes in the electronic structure of extrinsic defects (Cr3+) and intrinsic defects (oxygen-related surface defects and Ti3+) at varying photo-irradiation times and temperatures. As the photo-irradiation time increases, the Ti3+ to Ti4+ metal-to-metal charge transfer transition intensity increases with no change in the mid IR region. The EPR data of Cr:SrTiO3 shows the Cr3+ signal disappears when photodoped at room temperature and a very weak signal that appears at long irradiation times and is assigned to Ti3+. The Cr3+ signal returns concurrently with the Ti3+ signal, when the sample is cooled down to cryogenic temperatures. EPR power saturation studies demonstrate strong cross-relaxation imposed upon the Cr3+ dopants by the presence of Ti3+ localized defects in the photodoped SrTiO3 nanocrystals. This result illustrates a new property of nanocrystals that is enabled by the spatial confinement of charge carriers and dopant ions. These results will be compared to other recent reports of dopant-carrier interactions in ZnO nanocrystals.

Investigation of spin dynamics in photodoped Cr:SrTiO3 colloidal nanocrystals

256th National Meeting (2018)

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