Absorption cross-sections of carbon nanotubes revealed by energy
transfer in nanotube/porphyrin compounds
F. Vialla1, C. Roquelet2 , B. Langlois1 , G. Delport2 , C. Voisin1 , J.S. Lauret2
1
Laboratoire Pierre Aigrain, École Normale Supérieure, CNRS (UMR 8551), Université Pierre
et Marie Curie, Université Paris Diderot, 24 rue Lhomond, 75005 Paris, FRANCE
2
Laboratoire Aimé Cotton, École Normale Supérieure de Cachan, CNRS (UPR 3321), Université
Paris Sud, 91405 Orsay, FRANCE
Presenting author's contact : [email protected]
The optical absorption cross-section is a fundamental parameter in photo-physical
studies. Yet its quantitative evaluation in the case of carbon nanotubes remains a long-standing
question at the heart of both metrological and applicative issues. Usual absorbance
measurements on solutions fails to extract the individual nanotube species cross-sections owing
to the non-selectivity of regular synthesis methods and therefore to the lack of knowledge of the
species abundances. On the other hand, absorption measurements at the single nanotube scale
remain quite challenging and have to date brought information mainly on large diameter
nanotubes [1,2].
Here, we present an original method to carry out a systematic experimental study of the
absorption cross-sections for a broad range of small diameter semiconducting nanotubes [3],
corresponding to those prevalently found in commercial samples (namely HiPCO and
CoMoCAT). Using non-covalent functionalization of the wall of carbon nanotubes with dye
molecules (porphyrins), we achieve uniform photo-excitation of the whole set of chiral species
present in a sample using an ultra-efficient energy transfer from the dye to the nanotube [4]. By
comparing the photoluminescence signals induced whether by energy transfer or by intrinsic
nanotube excitation, the well-known dye absorption cross-section can used to quantitatively
evaluate nanotubes absorption properties.
Figure 1 : (left) Artistic view of the energy transfer mechanism in dye functionalized nanotubes.
(right) Experimental photoluminescence excitation map of such compounds in solution
showing the uniform energy transfer luminescence with excitation at 2.8 eV.
We reveal a strong variation of the absorption cross-sections at the optical resonance S 22
with the nanotube geometry, already pointed out by several theoretical studies. We show that the
absorption is larger for type I nanotubes and that it varies up to a factor 2.5 with the chiral angle
[3]. In contrast, the absorption out of the resonances and the luminescence quantum yield remain
almost constant for all the species. Building on this knowledge, optical spectroscopy can be used
as a simple, fast and quantitative tool for the assessment of the chiral species abundance of
samples, leading to a major breakthrough in systematic analysis and optimization of synthesis
methods.
Figure 2 : (black and green) Experimentally evaluated absorption cross-sections of 13 chiral species
as a function of the geometrical parameter q.cos(3θ) (θ being the chiral angle and q = n-m (mod 3)
for a given chiral species (n,m)), following well the theoretical trend in purple triangles from [5].
[1] Blancon et al. Nat. Com. 4, 2542 (2013).
[2] Oudjedi et al. JPCL 4(9), 1460 (2013).
[3] Vialla et al. PRL 111, 137402 (2013).
[4] Roquelet et al. APL 97(14), 141918 (2010).
[5] Oyama et al. Carbon 44, 873 (2006).