Femtosecond Carrier Dynamics in Solid C60 Films

Energy Relaxation Dynamics of Photoexcited C60 Solid

“…Under extremely high laser fluence condition, the inelastic collisional processes with multiple particle interactions can occur in such diverse ways as singlet exciton-singlet exciton, singlet exciton-triplet exciton, and singlet exciton-charge carrier collisions. These processes would dominate the overall decay behavior, especially in the excited state dynamics investigated by pump/probe experiments (transient absorption or transmittance), [4][5][6][7][8][9][10] which gives much faster relaxation than that monitored by PL decay such as in the present study using a much lower laser fluence condition. It should be pointed out that a photon density higher than 10 19 cm -3 was employed in most of pump/probe experiments, which corresponds approximately to one photoexcitation per C 60 molecule.…”

“…The laser fluence dependence of the relaxation process can be explained as follows. The exciton model has often been employed 6,7,10,12,16 to explain the laser fluence dependent relaxation behavior of photoexcited C 60 solid. In C 60 solid, exciton annihilation is a nonradiative process that results in a net depopulation of the excited state.…”

“…The relaxation dynamics of photoexcited C 60 in solid has been much studied under various conditions, [4][5][6][7][8][9][10][11][12][13][14][15][16] which revealed complex nonexponential relaxation dynamics. This unusual nonexponential behavior has led to a great deal of speculation as to the physical origin of the relaxation process, and a wide range of mechanisms have been proposed to explain the decay dynamics.…”

“…Cheville and Halas 4 monitored the change in timeresolved optical transmission following the 633 nm photoexcitation and found that the relaxation behavior is nonexponential and independent of temperature between 150 and 400 K. But Juhasz et al 5 observed that as the sample was cooled from room temperature to 5 K, the nonexponential decay of time-resolved optical transmission becomes an exponential decay and shows dependence on excitation laser fluence. Both Brorson et al 6 and Thomas et al 7 observed the dependence of time-resolved photoinduced absorption on laser fluence. On the other hand, Ebbeson et al 8 reported no laser fluence dependence of their transient absorption spectra.…”

Comparative Study of Exciton Relaxation Dynamics in C60 and C70 Solid

“…The relaxation dynamics of photoexcited C 60 solid has been extensively investigated under various conditions, and a wide range of mechanisms have been proposed to explain the decay dynamics. [2][3][4][5][6][7][8][9][10][11] The exciton model [2][3][4][5][6][7] has often been employed to explain the laser fluence dependent relaxation dynamics of photoexcited C 60 solid. Models based on Frenkel-type excitons were used because weak intermolecular forces induce little change in the electronic structure of the molecule upon formation of the solid phase, thereby allowing the exciton states to almost retain their molecularity.…”