Ultrafast Photodoping and Plasmon Dynamics in Fluorine-Indium Codoped Cadmium Oxide Nanocrystals for All-Optical Signal Manipulation at Optical Communication Wavelengths.

We show the ultrafast photodoping and plasmon dynamics of the near-infrared (NIR) localized surface plasmon resonance (LSPR) of fluorine-indium codoped cadmium oxide (FICO) nanocrystals (NCs). The combination of high temporal resolution and broad spectral coverage allowed us to model the transient absorption (TA) spectra in terms of the Drude model, verifying the increase in carrier density upon ultrafast photodoping. Our analysis also suggests that a change in carrier effective mass takes place upon LSPR excitation as a result of the nonparabolic conduction band of the doped semiconductor with a consequently high signal response. Both findings are combined in this new type of plasmonic material. The combination of large transmission modulation with modest pump powers and ultrafast recombination times makes our results interesting for all-optical signal processing at optical communication wavelengths. At the same time, our results also give insights into the physical mechanisms of ultrafast photodoping and LSPR tuning of degenerately doped semiconductor NCs.