Extraordinary Room-Temperature Photoluminescence in Triangular WS₂ Monolayers

TLDR

"Raman and PL measurements show that PL intensity decreases with layer number due to a direct‑to‑indirect bandgap transition, while the edges of triangular WS₂ monolayers emit ~25× stronger PL than the center, indicating edge structure and composition are key to the enhancement." That is one sentence. Ensure each ends with period. No extra punctuation that might be interpreted as separate sentences. Use single period at end.

Abstract

Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from those of their bulk counterparts. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). The Raman response as well as the luminescence as a function of the number of S–W–S layers is also reported. The PL weakens with increasing number of layers due to a transition from direct band gap in a monolayer to indirect gap in multilayers. The edges of WS2 monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than that at the platelet's center. The structure and chemical composition of the platelet edges appear to be critical for PL enhancement.