Directional radiation and photothermal effect enhanced control of 2D excitonic emission based on germanium...

Dielectric nanostructures with Mie resonances have shown promising applications for building nanoantennas and metasurfaces. Coupling between Mie resonators and transition metal dichalcogenide (TMDC) monolayers is of great significance, because the existence of Mie resonances can modulate phases and radiation directions effectively. Recently, monolayer binary and ternary TDMCs have drawn more attention owing to the intriguing and tunable excitonic states from visible to near infrared. However, the coupling mechanism between monolayer TMDCs and Mie resonators has not been well studied. Moreover, it is still a great challenge to realize the control of excitonic emission wavelength and intensity simultaneously. Here, for the first time, we demonstrate that germanium nanoparticles (Ge NPs), a typical high refractive index dielectric Mie resonator, are capable of controlling both the intensity and direction of PL emissions in the near-infrared from monolayer WSe_2(1-x)Te_2x. Through putting Ge NPs below or above monolayers, we observed the obvious emission directivity because of the higher refractive index and higher loss of Ge than silicon. Besides, higher absorption in Ge NPs brings photothermal effects during the interaction with TMDCs. These findings indicate that Ge-based Mie resonators may guide the design of new type nanophotonics devices in the future.