Electron and hole trapping in WS2 nanoclusters

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Abstract
Time resolved emission polarizationspectroscopy has been used to study the electron and hole trapping dynamics in room temperature WS 2 nanoclusters. The results indicate that radiative recombination of conduction band electrons and valence band holes results in polarized emission. Hole trapping partially depolarizes the emission, and emission from trapped electrons and holes is unpolarized. The kinetics of electron versus hole trapping can be separated by comparison of the depolarization kinetics in the presence and absence of 2,2′-bipyridine. Bipyridine acts as an acceptor for electrons in the conduction band, but not in traps. The decay of the polarized emission and the rise of the unpolarized emission indicate that electron and hole trapping take place on the 300–500 ps and 30 ps time scales, respectively. Time resolved spectral reconstruction results indicate that hole traps are about 3000 cm−1 deep while electron traps are about 270 cm−1 deep.