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

Abstract

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 °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.

Photoluminescence from an individual double-walled carbon nanotube

“…Regarding the second effect, the observation of a rather strong electronic Raman scattering signal and broad component in the G band in the (14,1)@(15,12) DWNT [36] indicates that the doping level of this tube is, at most, of the order of 0.001 charge/atom [49,50]. Even if we cannot evaluate more precisely this doping, a recent study on DWNTs filled by linear carbon chains [27] has shown that balancing the intrinsic charge transfer between the outer tube and ISCT leads to a maximum increase of one order of magnitude of the PL signal. We thus infer that the main source of quenching would be the decay of the exciton through the lower-energy states of the outer tube compared to S i 11 [25].…”

“…[20]. This weak QY can be understood in terms of (i) ultrafast exciton transfer from the inner to outer tube as suggested by femtosecond time-resolved luminescence measurements [21] and time-domain ab initio simulations [25] and (ii) charge transfer from outer to inner tubes [26,27]. Regarding the second effect, the observation of a rather strong electronic Raman scattering signal and broad component in the G band in the (14,1)@(15,12) DWNT [36] indicates that the doping level of this tube is, at most, of the order of 0.001 charge/atom [49,50].…”

“…Supporting the latter hypothesis, the PL enhancement from the (8,3) ISCT filled with linear carbon chains has recently been demonstrated and understood in terms of charge transfer from the ISCT to the carbon chains, which counterbalances the quenching mechanism of PL induced by the outer tube [27].…”

Raman resonance profile of an individual confined long linear carbon chain

“…It has enabled the study of pressure, charge transfer, and screening e↵ects on the chains and their nanotubes hosts, and revealed that the chirality of the encasing nanotube determines the BLA and hence the band gap and the C-mode frequency of the encapsulated LLCC [10,11,12,6]. The importance of Raman spectroscopy in characterising confined LLCCs is highlighted by the fact that the carbon nanotube hosts prohibit alternative direct optical methods such as absorption or photoluminescence spectroscopy by spectral overlap or quenching, respectively [13].…”

Extraction of Linear Carbon Chains Unravels the Role of the Carbon Nanotube Host

“…29,30 Note that we cannot recognize the contributions of the LCCs from the SWCNTs in this spectrum, since the weak absorption of LCCs overlapps and completely covered by the strong absorption of the SWCNTs. 31,32 The chirality assignment from the absorption shows that most of extracted tubes in the top layer are very small SWCNTs with diameters between 0.6 and 0.8 nm, 33 which are originally extracted from the inner tubes of DWCNTs. Furthermore, the Raman spectra shown in Fig.1c illustrate the difference between the two separated parts and confirm the successful extraction again.…”