Carbon nanodots (CNDs) are surface-passivated fluorescent nanomaterials which can be potentially applied for, e.g., full-color lighting and displays. Here, we present a pioneering study on magneto-optical properties of nitrogen-doped CNDs (N-CNDs) using terahertz (THz) time-domain spectroscopy in the presence of the magnetic fields from 0 to 8 T at a fixed temperature of 80 K. In the Faraday geometry and applying the optical polarization tests, we can measure the real and imaginary parts of the left- and right-handed circularly polarized magneto-optical conductances for a thin N-CND layer on a sapphire substrate, which can fit well with the magneto-optical Drude-Smith formula we previously generalized. By fitting the experimental data with the theoretical model, we can determine magneto-optically the key electronic parameters of N-CND layer, such as the electron density related coefficient $\gamma$, the electronic relaxation time $\tau$, the photon-induced electronic localization factor $\alpha$, and particularly, the effective electron mass $m^{*}$ obtained under noncyclotron resonance condition. The impact of the magnetic field on these parameters is investigated. We find that the presence of the magnetic field can result in smaller $\gamma$ and $\alpha$, heavier $m^{*}$, and longer $\tau$ in the N-CND layer. The outcomes of this work are valuable in providing us with a deeper understanding of the basic electronic properties of N-CNDs.

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• Magneto-optics
• Optoelectronics
• Quantum dots
• Terahertz time-domain spectroscopy