Photoluminescence changes of C₇₀ nanotubes induced by laser irradiation

(a) SEM image with insert showing XRD pattern of as-grown C₇₀ nanotubes and (b) Raman spectrum with 830-nm laser used as excitation line of as-grown C₇₀ nanotubes.

PL spectrum of as-grown C₇₀ nanotubes irradiated by 514.5-nm laser with power 0.2 mW, with insert showing UV-Vis absorption spectrum of as-grown C₇₀ nanotubes, and red and blue dashed lines denoting two fitted peaks of the PL band of C₇₀ nanotubes.

PL spectra of pristine C₇₀ nanotubes irradiated by 514.5-nm laser with 0.2 mW, 1 mW, 2 mW, 5 mW, and 10 mW, respectively.

(a) Laser power-dependent center positions of PL peak and (b) laser-power-dependent intensity ratio of peak B to peak A of C₇₀ nanocrystals.

Raman spectra of C₇₀ nanotubes irradiated by (a) 514.5-nm laser and (b) 830-nm laser, respectively. Lasers with various powers are employed for comparison, and characterized ${\mathrm{E}}_2^{{}^{\mathrm{\prime }}}$ Raman peak for samples irradiated with different values of laser power are shown in inserts.

(a) PL spectra of C₇₀ nanotubes irradiated by 514.5-nm laser with power of 10 mW (black) and C₇₀ nanotubes treated under 2.0 GPa, 700 K (red). PL spectrum of the laser irradiated sample is fitted to two peaks: Peak A (red dashed curve) and peak B (green dashed curve). (b) Raman spectra of C₇₀ nanotubes irradiated by laser with 10-mW power and HPHT treated under 2.0 GPa, 700 K.