Photophysics and light-matter interaction in two-dimensional (2D) van der Waals (vdW) materials

Cavity-engineering of 2D vdW semiconducting magnets. I investigated the exciton-polaritons in a 2D vdW semiconducting magnet, CrSBr, coupled with an anisotropic photonic crystal cavity, where the spin, exciton, and photon are strongly correlated with new properties emerging from strongly coupled atomic- and photonic-anisotropies. This work impacts fundamental studies of quantum materials and provide a new system for on-chip lasing and emitting devices with tunable polarization.
Q. Li et al. Phys. Rev. Lett. 2024, Accepted. (arXiv:2306.11265)
A new method for fabricating high-quality large-area transition metal dichalcogenide (TMD) monolayers. I developed a simple and reliable molecular encapsulation method for creating TMD monolayers (MoSe2 and WS2) with uniformly high optical quality over millimeter-scale and enhanced light-matter coupling strength. This innovative method hugely improves 2D materials’ fabrication for experimental studies and devices. The high quality over a large area can be utilized for on-chip photonic and electronic circuits.
Q. Li et al. Nature Communications 2023, 14, 1837.
Long-lived spin-polarization in TMD hetero-bilayers. I studied the spin-polarized charge separation in TMD hetero-bilayers (MoSe2/WSe2) using time-resolved Faraday rotation spectroscopy. The one order of magnitude longer-lived spin-polarization in TMD hetero-bilayer compared to TMD monolayer provides an excellent semiconductor model substrate for spin-polarized interfacial chemical reactions.
Q. Li et al. J. Phys. Chem. C 2022, 126, 15795-15800.
Strong polaronic effect in 2D vdW superatomic material. I discovered the strong polaronic effect in a superatomic semiconductor, Re6Se8Cl2. The small polaron was directly evidenced by the temperature-dependent band structure of Re6Se8Cl2 probed by angle-resolved photoemission spectroscopy (ARPES) with a tabletop femtosecond extreme ultra-violet (EUV) pulse (photon energy 21.7 eV). This discovery highlights the potential of this 2D vdW superatomic semiconductor for future optoelectronic applications.
Q. Li et al. J. Chem. Phys. 2020, 152, 171101.

Excitons and ultrafast dynamics in colloidal nanocrystals

Physical properties and dynamics of excitons in colloidal 2D nanoplatelets (NPLs). I comprehensively studied the physical properties of excitons (2D coherent area, in-plane transport, multi-exciton annihilation, phase-space filling) in colloidal 2D CdSe and CsPbBr3 perovskite NPLs using femtosecond transient absorption spectroscopy, providing insights of 2D excitons in nanocrystals.
Q. Li et al. Nano Lett. 2020, 20, 6162–6169.
Q. Li et al. J. Phys. Chem. Lett. 2019, 10, 1624–1632.
Q. Li et al. Nano Lett. 2019, 19, 5620–5627.
Q. Li et al. Nano Lett. 2017, 17, 3152-3158.
Q. Li et al. ACS Energy Letters 2017, 2, 174-181.
Q. Li et al. ACS Nano 2016, 10, 3843-3851.
Optical gain mechanims and lasing threshold in 2D nanoplatelets. I unveiled the mechanisms of the optical gain and the key factors that determine the lasing threshold of CdSe NPLs and CdSe/CdTe core/crown heterostructures, providing opportunities for lasing and emitting devices.
Q. Li et al. Acc. Chem. Res. 2019, 52, 2684–2693.
Q. Li et al. Chem. Sci. 2018, 9, 728–734.
Q. Li et al. ACS Nano 2017, 11, 2545–2553.
Charge carrier dynamics and solar-to-H2 conversion performance of nanocrystal-metal heterostructures. I studied the charge transfer in colloidal cadmium chalcogenides and perovskite nanocrystals, optimized the solar-to-H2 conversion efficiency using nanocrystal-metal heterostructures, and controlled their charge carrier dynamics with nanocrystal dimensions, providing a new strategy for photosynthesis.
Q. Li et al. Chem. Rev. 2024, 124, 9, 5695–5763.
Q. Li et al. Springer Handbook of Inorganic Photochemistry, 2022, Ch. 33, 985-1012.
Q. Li et al. J. Phys. Chem. Lett. 2019, 10, 566−573.
Q. Li et al. J. Am. Chem. Soc. 2018, 140, 11726−11734.
Q. Li et al. Nano Research 2018, 11, 3031-3049.