10.1021/nn403682r.s001 Liangxu Lin Liangxu Lin Yaoxian Xu Yaoxian Xu Shaowei Zhang Shaowei Zhang Ian M. Ross Ian M. Ross Albert C. M. Ong Albert C. M. Ong Dan A. Allwood Dan A. Allwood Fabrication of Luminescent Monolayered Tungsten Dichalcogenides Quantum Dots with Giant Spin-Valley Coupling American Chemical Society 2016 quantum information technology monolayered tungsten dichalcogenide contrast bioimaging application conduction band split valence band energy levels flake precursors 570 meV PL monolayered WS 2 sheets WS 2 flakes UV Luminescent Monolayered Tungsten Dichalcogenides Quantum Dots luminescence peaks defect level monolayered WS 2 QDs optoelectronic devices room temperature 2016-02-18 20:27:06 Journal contribution https://acs.figshare.com/articles/journal_contribution/Fabrication_of_Luminescent_Monolayered_Tungsten_Dichalcogenides_Quantum_Dots_with_Giant_Spin_Valley_Coupling/2374159 A high yield (>36 wt %) method has been developed of preparing monolayered tungsten dichalcogenide (WS<sub>2</sub>) quantum dots (QDs) with lateral size ∼8–15 nm from multilayered WS<sub>2</sub> flakes. The monolayered WS<sub>2</sub> QDs are, like monolayered WS<sub>2</sub> sheets, direct semiconductors despite the flake precursors being an indirect semiconductor. However, the QDs have a significantly larger direct transition energy (3.16 eV) compared to the sheets (2.1 eV) and enhanced photoluminescence (PL; quantum yield ∼4%) in the blue-green spectral region at room temperature. UV/vis measurements reveal a giant spin-valley coupling of the monolayered WS<sub>2</sub> QDs at around 570 meV, which is larger than that of monolayered WS<sub>2</sub> sheets (∼400 meV). This spin-valley coupling was further confirmed by PL as direct transitions from the conduction band minimum to split valence band energy levels, leading to multiple luminescence peaks centered at around 369 (3.36 eV) and 461 nm (2.69 eV, also contributed by a new defect level). The discovery of giant spin-valley coupling and the strong luminescence of the monolayered WS<sub>2</sub> QDs make them potentially of interests for the applications in semiconductor-based spintronics, conceptual valley-based electronics, quantum information technology and optoelectronic devices. However, we also demonstrate that the fabricated monolayered WS<sub>2</sub> QDs can be a nontoxic fluorescent label for high contrast bioimaging application.