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

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.