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

Upconversion materials have attractedmuch attentionbecause oftheir broad application prospects in biomedicine and energy. Althoughvarious 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 transitionmetal chalcogenides (2D-TMDs) are a class of excellent luminescentsemiconductors, offering a promising platform due to their chemicalaccessibility and physical sensitivity. However, multi-lanthanidedoping, typically boosting the upconversion efficiency, has not beenaccomplished in monolayer TMD nanosheets. In this work, an optimizedliquid precursor-assisted technique is designed to synthesize monolayerMoS(2) nanosheets embedded with Er/Yb and Er/Ho by surmountingthe precipitation of Ln(3+)-doped precursors, which is confirmedby structural characterization. The monolayer MoS2 cansplit the 4f configuration remarkably to produce diverse energy levelsdue 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 rangeswas obtained on these codoped MoS2 nanosheets. This workprovides an effective way to tune the luminescence performance andwavelength of 2D-TMD nanosheets as well as a strategy for the designof UCL nanomaterials for light applications as nanophotonic devices.