Correlated fluorescence blinking in two-dimensional semiconductor heterostructures

• Published in: Nature (London) 2017-01, Vol.541 (7635), p.62-67
• Main Authors: Xu, Weigao, Liu, Weiwei, Schmidt, Jan F., Zhao, Weijie, Lu, Xin, Raab, Timo, Diederichs, Carole, Gao, Weibo, Seletskiy, Denis V., Xiong, Qihua
• Format: Article
• Language: English
• Subjects: 639/624/400/3925; 639/766/400/3925; Fluorescence; Humanities and Social Sciences; letter; multidisciplinary; Observations; Properties; Quantum dots; Science; Semiconductors (Materials)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature20601

A correlated blinking phenomenon is discovered in two-dimensional bilayer semiconductor heterostructures, whereby a bright emission state occurs in one monolayer while a dark state occurs in the other, and vice versa. Blinking in two-dimensional semiconductors Fluorescence blinking is a fundamental effect in quantum materials that reveals rich dynamic mechanisms, but is usually unwanted in applications. In recent years, two-dimensional semiconductor crystals, which usually show strong and stable light emission, have emerged as promising systems for optoelectronic devices. Qihua Xiong et al . now report an unusual blinking phenomenon that occurs when two different semiconductor monolayers are stacked on top of each other: emission in the two layers is dynamically correlated, with bright states in one monolayer appearing together with dark states in the other—and vice versa. The authors discuss possible mechanisms of charge transfer between the two layers to explain the observations, and suggest that they could be of interest in new quantum photonic applications exploiting the correlated emission. ‘Blinking’, or ‘fluorescence intermittency’, refers to a random switching between ‘ON’ (bright) and ‘OFF’ (dark) states of an emitter; it has been studied widely in zero-dimensional quantum dots 1 and molecules 2 , 3 , and scarcely in one-dimensional systems 4 , 5 . A generally accepted mechanism for blinking in quantum dots involves random switching between neutral and charged states 6 , 7 (or is accompanied by fluctuations in charge-carrier traps 8 ), which substantially alters the dynamics of radiative and non-radiative decay. Here, we uncover a new type of blinking effect in vertically stacked, two-dimensional semiconductor heterostructures 9 , which consist of two distinct monolayers of transition metal dichalcogenides (TMDs) that are weakly coupled by van der Waals forces. Unlike zero-dimensional or one-dimensional systems, two-dimensional TMD heterostructures show a correlated blinking effect, comprising randomly switching bright, neutral and dark states. Fluorescence cross-correlation spectroscopy analyses show that a bright state occurring in one monolayer will simultaneously lead to a dark state in the other monolayer, owing to an intermittent interlayer carrier-transfer process. Our findings suggest that bilayer van der Waals heterostructures provide unique platforms for the study of charge-transfer dynamics and non-equilibrium-state physics, and could s