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Carrier-Specific Femtosecond XUV Transient Absorption of PbI2 Reveals Ultrafast Nonradiative Recombination C

Lin, Ming-Fu, Verkamp, Max A., Leveillee, Joshua, Ryland, Elizabeth S., Benke, Kristin, Zhang, Kaili, Weninger, Clemens, Shen, Xiaozhe, Li, Renkai, Fritz, David, Bergmann, Uwe, Wang, Xijie, Schleife, André, Vura-Weis, Josh
Journal of physical chemistry 2017 v.121 no.50 pp. 27886-27893
absorption, electrons, energy, iodine, models, photochemical reactions, semiconductors, spectral analysis, spectroscopy, temperature
Femtosecond carrier recombination in PbI₂ is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 to 62 eV measures transitions from the iodine 4d core level to the conduction-band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band, and therefore the XUV absorption spectrum, is temperature-dependent, and nonradiative recombination converts the initial electronic excitation into thermal excitation within picoseconds. Ultrafast electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. The XUV and UED results support a second-order recombination model with a rate constant of 2.5 × 10–⁹ cm³/s.