Relaxation and electron transfer dynamics in bare and DTDCI sensitized MoS2 nanoclusters

The trapping dynamics of photogenerated electrons and holes in MoS2 nanoclusters has been studied using time resolved emission polarization and absorption spectroscopies. These results are compared to absorption kinetics obtained on MoS2 nanoclusters with adsorbed DTDCI (DTDCI=diethylthiodicarbocyanine iodide) dye. The results indicate that emission from the MoS2 band edge state is polarized, while emission from trapped electrons and holes is unpolarized. This polarization difference is used to obtain the electron and hole trapping times and values of 275 ps and 42 ps, respectively, are obtained. Decays having the same time constants are observed in the transient absorption results. The results obtained on the MoS2/DTDCI system show that electron injection occurs with a time constant of 12 ps. These kinetics also show a 225 ps decay component which is assigned to electron trapping and reverse electron transfer. The 225 ps decay time along with the 275 ps trapping time indicates that reverse electron transfer from the conduction band has a time constant of about 1.2 ns. Following trapping, reverse electron transfer from deep traps is slow. (C) 2000 American Institute of Physics. [S0021- 9606(00)70337-0].