Electron and hole trapping in WS2 nanoclusters

Time resolved emission polarization spectroscopy has been used to study the electron and hole trapping dynamics in room temperature WS2 nanoclusters. The results indicate that radiative recombination of conduction band electr ons and valence band holes results in polarized emission. Hole trapping par tially depolarizes the emission, and emission from trapped electrons and ho les is unpolarized. The kinetics of electron versus hole trapping can be se parated by comparison of the depolarization kinetics in the presence and ab sence of 2,2'-bipyridine. Bipyridine acts as an acceptor for electrons in t he conduction band, but not in traps. The decay of the polarized emission a nd the rise of the unpolarized emission indicate that electron and hole tra pping take place on the 300-500 ps and 30 ps time scales, respectively. Tim e resolved spectral reconstruction results indicate that hole traps are abo ut 3000 cm(-1) deep while electron traps are about 270 cm(-1) deep. (C) 200 0 American Institute of Physics. [S0021-9606(00)70526-5].