optical properties
... that carotene can be used to alter the optical properties of carbon nanotubes?
... that <a href="./Carotene" id="mwC6Y" rel="mw:WikiLink" title="Carotene">carotene</a> can be used to alter the <b id="mwC6c"><a href="./Optical_properties_of_carbon_nanotubes" id="mwC6g" rel="mw:WikiLink" title="Optical properties of carbon nanotubes">optical properties</a></b> of <a href="./Carbon_nanotube" id="mwC6k" rel="mw:WikiLink" title="Carbon nanotube">carbon nanotubes</a>?