Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

Authors

  • Dr. Bob C. Fitzmorris,

    1. Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)
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  • Jonathan M. Patete,

    1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (USA)
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  • Jacqueline Smith,

    1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (USA)
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  • Xiomara Mascorro,

    1. Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)
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  • Staci Adams,

    1. Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)
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  • Prof. Stanislaus S. Wong,

    Corresponding author
    1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (USA)
    2. Condensed Matter Physics and Materials Sciences Department, Building 480, Brookhaven National Laboratory, Upton, NY 11973 (USA)
    • Stanislaus S. Wong, Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (USA)

      Jin Z. Zhang, Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)

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  • Prof. Jin Z. Zhang

    Corresponding author
    1. Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)
    • Stanislaus S. Wong, Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (USA)

      Jin Z. Zhang, Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California, 95064 (USA)

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Abstract

Much progress has been made in using hematite (α-Fe2O3) as a potentially practical and sustainable material for applications such as solar-energy conversion and photoelectrochemical (PEC) water splitting; however, recent studies have shown that the performance can be limited by a very short charge-carrier diffusion length or exciton lifetime. In this study, we performed ultrafast studies on hematite nanoparticles of different shapes to determine the possible influence of particle shape on the exciton dynamics. Nanorice, multifaceted spheroidal nanoparticles, faceted nanocubes, and faceted nanorhombohedra were synthesized and characterized by using SEM and XRD techniques. Their exciton dynamics were investigated by using femtosecond transient absorption (TA) spectroscopy. Although the TA spectral features differ for the four samples studied, their decay profiles are similar, which can be fitted with time constants of 1–3 ps, approximately 25 ps, and a slow nanosecond component extending beyond the experimental time window that was measured (2 ns). The results indicate that the overall exciton lifetime is weakly dependent on the shape of the hematite nanoparticles, even though the overall optical absorption and scattering are influenced by the particle shape. This study suggests that other strategies need to be developed to increase the exciton lifetime or to lengthen the exciton diffusion length in hematite nanostructures.

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