Department of Chemistry, Duke University, Durham, North Carolina, 27708, United States.
Nano Lett. 2011 Oct 12;11(10):4405-10. doi: 10.1021/nl2025745. Epub 2011 Sep 13.
Double-walled carbon nanotubes (DWNTs) have recently been recognized as important members in the carbon nanotube family because they are expected to have certain unique properties. For example, DWNTs are expected to replace single-walled carbon nanotubes (SWNTs) in biomarker applications and optoelectronics if the observed luminescence from DWNTs can be verified. However, due to unavoidable byproducts, such as SWNTs, optical properties of DWNTs still remain controversial. There is an ongoing debate concerning the ability of DWNTs to exhibit photoluminescence (PL). In this report, we aim to clearly resolve this debate through the study of carefully separated DWNTs. DWNTs were successfully separated from SWNTs using density gradient ultracentrifugation. Here we clearly show that light is emitted from the inner wall of DWNTs; however, the intensity of the emission is significantly quenched. Interestingly, it was found that a very narrow range of diameters of the inner walls of DWNTs is required for PL to be observable. All other diameters led to complete PL quenching in DWNTs. In short, we have shown that both sides of the debate are correct under certain situations. The real answer to the question is that some DWNTs do emit light but most DWNTs do not.
双壁碳纳米管（DWNTs）最近被认为是碳纳米管家族中的重要成员，因为它们有望具有某些独特的性质。例如，如果可以证实 DWNTs 的观察到的发光现象，那么 DWNTs 有望在生物标志物应用和光电子学中取代单壁碳纳米管（SWNTs）。然而，由于不可避免的副产物，如 SWNTs，DWNTs 的光学性质仍然存在争议。关于 DWNTs 表现出光致发光（PL）的能力存在持续的争论。在本报告中，我们旨在通过仔细分离的 DWNTs 研究来明确解决这一争论。我们使用密度梯度超速离心法成功地将 DWNTs 从 SWNTs 中分离出来。在这里，我们清楚地表明光从 DWNTs 的内壁发射；然而，发射的强度显著猝灭。有趣的是，发现只有当 DWNTs 的内壁直径处于非常狭窄的范围内时，才可以观察到 PL。所有其他直径都导致 DWNTs 中的完全 PL 猝灭。简而言之，我们已经表明，在某些情况下，争论的双方都是正确的。这个问题的真正答案是，一些 DWNTs 确实会发光，但大多数 DWNTs 不会。
