Abstract
Hollow C70 nano/submicro-crystals with a fcc lattice structure were treated under various high pressure and high temperature conditions. The energy band structure was visibly changed by the high pressure and high temperature treatment, and the luminescence of the treated C70 nano/submicro-crystals were tuned from the visible to the near infrared range. In-situ high pressure experiments at room temperature indicate that pressure plays a key role in the tuning of the band gap and PL properties in C70 nanocrystals, and temperature plays an important role in the formation of stable intermolecular bonds and thus to define the final red-shift of the PL peaks. The polymeric phases of C70 nanocrystals treated at high pressure and high temperature were identified from their Raman spectra, which showed a change from monomers to a dimer-rich phase and finally to a phase containing larger, disordered C70 oligomers.
Highlights
Hollow C70 nano/submicro-crystals with a fcc lattice structure were treated under various high pressure and high temperature conditions
In an earlier in-situ high pressure investigation on C70 nanocrystals we found that when the size of the C70 crystals were in the nano/submicrometer range many novel properties were observed, including higher phase transition pressures and a higher bulk modulus[12], but no irreversible intermolecular bonding was found up to 43 GPa at room temperature
As the fcc structure of C70 nanocrystals was obtained after desolvation, the XRD curve is slightly different from that of bulk C70 crystals[14]
Summary
Hollow C70 nano/submicro-crystals with the fcc structure were produced by a solution method described earlier[12]. The C70 nanocrystals produced were treated under different hydrostatic pressure conditions using a piston-cylinder device. Several additional experiments were carried out to study the evolution of C70 under HPHT conditions and to investigate the mechanism for the change in PL of C70. Raman spectroscopy was used to investigate the lattice structure and the evolution of intermolecular bonding, and PL spectra were used to analyze the optical properties of all the HPHT treated samples. Both Raman and PL spectra were measured with a Renishaw inVia Raman spectrometer at room temperature, using the excitation line wavelengths of 514 nm. The samples obtained were characterized by transmission electron microscopy (TEM, JEM-2010, Japan)
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