Resonance Energy Transfer from Monolayer WS₂ to Organic Dye Molecules: Conversion of Faint Visible‐Red into Bright Near‐Infrared Luminescence

Abstract The synergetic combination of transition metal dichalcogenides (TMDCs) with organic dye molecules in functional heterostructures is promising for various optoelectronic applications. Here resonance energy transfer (RET) from a red‐emitting WS₂ monolayer (1L‐WS₂) to a layer of near‐infrared (NIR) emitting organic dye molecules is demonstrated. It is found that the total photoluminescence (PL) yield of the heterostructures is up to a factor of eight higher as compared to the PL yield of pristine 1L‐WS₂. This is attributed to the efficient conversion of the mostly non‐radiative excitons in 1L‐WS₂ into radiative excitons in the dye layer. A type‐I energy level alignment of the 1L‐WS₂/dye interface assures the emission of bright PL. From excitation density‐dependent PL experiments, it is concluded that RET prevails against defect‐assisted non‐radiative recombination as well as Auger‐type exciton‐exciton annihilation in 1L‐WS₂. The work paves the way for employing organic dye molecules in heterostructures with TMDCs in nanoscale light‐emitting devices with improved efficiency and tunable color.