CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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Sample τ 1 (ps) τ 2 (ps) τ 3 (ps) + τ 4 (ps)
GO 0.9 ± 0.2(33.3%) 9 ± 2 (38.5%) >300 (28.2%)
RGO-1 0.7 ± 0.2 (37%) 10 ± 2 (36.5%) >300(26.5%)
RGO-2 0.26 ± 0.1 (65%) 2.5 ± 0.5 (24.5%) 30 ±5 (6.5%) + >300 (4%)
Table 6.2: Life times of the transient absorption signal of graphene oxide (GO), reduced (1 hour) graphene oxide
(RGO-1) and reduced (for 24 hours) graphene oxide (RGO-2) and at 670 nm after exciting at 400 nm laser light.
It is clear that the transient signal decay significantly faster as compared to that of GO. The
faster two lifetimes components (0.26ps and 2.5ps) contribute almost 90% to the relaxation
process, which indicates a significant percolation in GO from sp 3 to sp 2 carbon.
The first two components matches with excited dynamics of photo-excited graphene as
measured in earlier reports. These fast components have been assigned to the relaxation by
electron-phonon interactions. It is reported in the literature [6.31] that carrier relaxation
process in graphite are hindered by accumulation of hot phonons at higher carrier density
which is called hot phonon bottleneck effect as a result one can see slower component in the
relaxation dynamics. Kamfrath et al. [6.32] measured 2.5 ps component of carrier relaxation
dynamics in photo-excited graphite phonon mediated relaxation. In the present studies the
slower 0.26ps and 2.5 ps can be attributed interactions with optical and acoustic phonons
respectively. However in the decay kinetics of RGO-2, we can still observe ~ 4%
contribution >400ps component. In case of transient decay analysis of GO we have explained
that >400 ps component arises due to deep trap states. We can see clearly see that on
reduction of GO to RGO-2 the contribution of 30ps and >400 ps component. These