Multiband Monochromatic Upconversion Emissions of Lanthanide Codoped Monolayer MoS₂ Nanosheets for Lighting Applications

Upconversion materials have attracted much attention because of their broad application prospects in biomedicine and energy. Although various methods have been tried in nanoparticles and nanocrystals, it is still a challenge to realize monochromatic upconversion luminescence (UCL) in traditional lanthanide-doped materials. Two-dimensional transition metal chalcogenides (2D-TMDs) are a class of excellent luminescent semiconductors, offering a promising platform due to their chemical accessibility and physical sensitivity. However, multi-lanthanide doping, typically boosting the upconversion efficiency, has not been accomplished in monolayer TMD nanosheets. In this work, an optimized liquid precursor-assisted technique is designed to synthesize monolayer MoS 2 nanosheets embedded with Er/Yb and Er/Ho by surmounting the precipitation of Ln 3+ -doped precursors, which is confirmed by structural characterization. The monolayer MoS 2 can split the 4f configuration remarkably to produce diverse energy levels due to its strong Coulomb binding and spin–orbit coupling, as well as the unique asymmetric crystal field along the [001] direction. Hence, multiband monochromatic UCL from violet to near-infrared ranges was obtained on these codoped MoS 2 nanosheets. This work provides an effective way to tune the luminescence performance and wavelength of 2D-TMD nanosheets as well as a strategy for the design of UCL nanomaterials for light applications as nanophotonic devices.