Matrix-Imposed Stress-Induced Shifts in the Photoluminescence of Single-Walled Carbon Nanotubes at Low Temperatures

Photoluminescence spectra of water−surfactant dispersions of semiconducting single-walled carbon nanotubes (SWNTs) show large shifts of interband transition energies upon freezing and cooling the dispersions to 16 K. This is accompanied by an increase of the emission intensities up to ∼10 times in the presence of poly(vinylpyrrolidone). The shifts develop mainly in the temperature interval of ∼100−240 K and are reversible by cycling the temperature. Two groups of nanotubes classified by the value of ( n - m ) mod 3, where n,m are structure indices, demonstrate opposite shifts, the largest ones from nanotubes with small chiral angles. The experimental data agree well with calculations of Yang et al. [ Phys. Rev. B 1999, 60, 13874] for SWNTs under axial compression and indicate that large stresses of up to ∼5 GPa are generated in individual nanotubes by thermal contraction of the ice matrix.