All-Optical Reversible Manipulation of Exciton and Trion Emissions in Monolayer WS2

Abstract

Monolayer transition metal dichalcogenides (TMDs) are direct gap semiconductors emerging promising applications in diverse optoelectronic devices. To improve performance, recent investigations have been systematically focused on the tuning of their optical properties. However, an all-optical approach with the reversible feature is still a challenge. Here we demonstrate the tunability of the photoluminescence (PL)properties of monolayer WS2 via laser irradiation. The modulation of PL intensity, as well as the conversion between neutral exciton and charged trion have been readily and reversibly achieved by using different laser power densities. We attribute the reversible manipulation to the laser-assisted adsorption and desorption of gas molecules, which will deplete or release free electrons from the surface of WS2 and thus modify its PL properties. This all-optical manipulation, with advantages of reversibility, quantitative control, and high spatial resolution, suggests promising applications of TMDs monolayers in optoelectronic and nanophotonic applications, such as optical data storage, micropatterning, and display.

Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets

“…We assign the nearly constant offset in this energy range to multilayer PL and the transition X 2 to the neutral exciton. The dominating narrow PL peak at ∼1.97 eV ( X 1 ) might be induced by localized excitons or by trions formed by an electron surplus due to sulfur vacancies in colloidal WS 2 nanosheets. − …”

“…The dominating narrow PL peak at ~1.97 eV (X 1 ) might be induced by localized excitons 44 or by trions obtained by an electron surplus due to the sulfur vacancies in colloidal WS 2 nanosheets. [45][46][47][48][49] When comparing the normalized spectra of the colloidal WS 2 monolayer PL at position 3 with the PL of a state-of-the-art hBN-encapsulated exfoliated WS 2 monolayer (sample 3, see Figure 2D), both samples exhibit similar properties in general with colloidal WS 2 nanosheets showing only a fourfold lower PL intensity as the compared exfoliated sample. Surprisingly, the PL features of colloidal WS 2 nanosheets are much stronger pronounced than the exfoliated monolayer.…”

Giant enhancement of photoluminescence emission in monolayer WS2 by femtosecond laser irradiation

“…We calculated the enhancement factor for the area of full engineered spots (EF1, assuming the diameter of the largest spot to be 3 μm, as the solid line shown in the inset of Figure 1C) and the center area (EF2, as the solid line shown in the inset), the results are shown in Figure 1C. The maximum enhancement factor under these conditions reaches a value up to 60 times, significantly higher than the engineered results under CW laser irradiation [21,28].…”

“…However, the harsh nature of chemical treatment or plasmonic coupling necessitates additional fabrication steps [13]. Furthermore, contaminants and impurities are always inevitably introduced during the fabrications, which may significantly reduce the performance of optoelectronic devices based on these 2D materials [21]. Therefore, achieving high and stable PL intensity of monolayer WS2, through an all-optical scheme without any chemical treatments and additional fabrication steps, is still an exploratory of fundamental research.…”

Enhanced Dielectric Screening and Photoluminescence from Nanopillar-Strained MoS2 Nanosheets: Implications for Strain Funneling in Optoelectronic Applications

“…We discuss possible origins of the PL enhancement below, concluding that the most likely reason is the dissociation of excitons into free electron–hole pairs due to charge and exciton screening. The control of such light–matter interaction with local deformation of nanoscale materials has great implications for strain-engineered optoelectronics such as light-emitting diodes, , solar cells, , lasers, and excitonic switches. − …”