Selective Enhancement of Inner Tube Photoluminescence in Filled Double-Walled Carbon Nanotubes

A highly selective enhancement of the optical response of the inner tubes of double-walled carbon nanotubes has been identified upon transformation of the residual C atoms inside the hollow core to linear carbon chains (LCC). By varying the growth conditions and using standardized suspensions, it has been observed that this optical response depends sensitively on the tube diameter and LCC growth yield. It is reported how the formation of LCC by postsynthesis annealing at 1400 degrees C leads to an increase of the photoluminescence (PL) signal of the inner tubes up to a factor of 6 for tubes with (8,3) chirality. This behavior can be attributed to a local charge transfer from the inner tubes to the carbon chains, counterbalancing quenching mechanisms induced by the outer tubes. These findings provide a viable pathway to enhance the low PL quantum yield of double-walled carbon nanotubes and proof the capability of inner tubes to exhibit photoluminescence.