Wet-chemical syntheses for quasi two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising methods for straightforward solution-processing of these materials.However, photoluminescence properties of colloidal TMDs are virtually unexplored due to the typically non-emitting synthesis products. In this work, we demonstrate room temperature microphotoluminescence spectroscopy on delicate ultrathin colloidal WS 2 nanosheets synthesized from WCl 6 and elemental sulfur in oleic acid and oleylamine at 320 °C for the first time. Both, monoand multilayer photoluminescence is observed, revealing comparable characteristics to exfoliated TMD monolayers and underpinning the high quality of colloidal WS 2 nanosheets. In addition, a promising long-term air-stability of colloidal WS 2 nanosheets is observed and the control of their photodegradation under laser excitation is identified as a challenge for further advancing nanosheet monolayers. Our results render colloidal TMDs as easily synthesized and highly promising 2D semiconductors with optical properties fully competitive with conventionally fabricated ultrathin TMDs.

Colloidal two-dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materials for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligible attenuation. In this work, we demonstrate...

2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics....

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Colloidal 2D PbSe nanoplatelets (NPLs) are promising near- and short wave-infrared emitters for optoelectronic applications at telecommunication wavelengths. However, their photoluminescence quantum yield (PLQY) is limited by the ubiquitous presence of surface-related trap states. Here, we apply a treatment of colloidal PbSe NPLs with different metal halides (MX2, M = Zn, Cd, Pb; X = F, Cl, Br, I) to improve their emission brightness. A surface passivation of the NPLs by PbI2 leads to the best results with a strongly increased PLQY (27% for PbSe NPLs emitting at 0.98 eV (1265 nm) and up to 61% for PbSe NPLs emitting at 1.25 eV (989 nm)). Simultaneously, the full width at half-maximum of the NPL photoluminescence decreased by 10% after the treatment. X-ray photoelectron spectroscopy and complementary surface treatment of PbSe NPLs with organic halides reveal the combined passivating role of both X-type binding halides X– and Z-type binding metal halides MX2 in enhancing the optical properties of the PbSe NPLs. Our results emphasize the potential of 2D PbSe NPLs for efficient emission tailored for the application in fiber optics.