Photoinduced Band Gap Shift and Deep Levels in Luminescent Carbon Nanotubes

Abstract

Individual air-suspended single-walled carbon nanotubes are imaged both spatially and spectrally in photoluminescence. At low excitation power, photoluminescence is bright and stable with high quantum efficiency; however, higher power initially causes a gradual red shift and then more severe changes. Blinking, the loss of quantum efficiency, and the appearance of new deep levels are all seen and can be explained by the introduction of defects. We propose that optical excitation induces molecular deposition onto the nanotube by optically induced van der Waals interactions, leading to physisorption and ultimately chemisorption which severely degrades the luminescence.KEYWORDS: single-walled carbon nanotube . photoluminescence . exciton . quantum efficiency . band gap shift . van der Waals interaction ARTICLE FINNIE AND LEFEBVRE

Prolonged spontaneous emission and dephasing of localized excitons in air-bridged carbon nanotubes

“…We note that we have not been able to follow the thermalization behavior for this particular SWCNT up to higher temperatures since it exhibited at 80 K a sudden blue shift event and a strong diminishing of the PL intensity. Similar behavior was observed recently by Finnie and Levebre and attributed to molecular deposition and subsequent deep level formation under optical excitation [10].…”

“…Unlike quantum dots, the photoluminescence (PL) quantum yield in one-dimensional SWCNTs is rather low [3]. It is however increasingly understood that this is caused by extrinsic nonradiative recombination (NR) of highly mobile excitons exploring defects and dopants along the tube [4][5][6][7][8][9][10][11], and to a lesser extend due to intrinsic exciton dark states affecting PL yields only below 50K [12]. There is also increasing evidence that excitons localize randomly along the tube and form quantum dot like states [13], as is indicative from near-field scanning experiments [14] and the observation of photon antibunching at low temperatures [15,16].…”

Strong Acoustic Phonon Localization in Copolymer-Wrapped Carbon Nanotubes

“…The data show no general trend with isotope tuning since one can find examples of both 12 C and 75% 13 C carbon nanotubes that feature spectral linewidths that are either ultra-narrow with values of about 120-200 µeV or significantly broader with values approaching 600 µeV.…”

“…49 The fact that we find no clear trend with isotope tuning in the data of Figure 3 indicates that the exciton emission spectrum is not dominated by pure exciton dephasing with 1D acoustic phonons. These data provide an upper bound for the contribution of 13 To probe for the possibility of impurity-bound exciton emission from excitons localized at unintentional dopant sites or defects, we investigated the E 11 emission spectra of 48 SWCNTs. Figure 4 displays the low pump power spectra of 10 individual SWCNTs for three different chiralities including (6,4), (6,5), and (5,4) SWCNTs.…”

Ultrafast Spectral Exciton Diffusion in Single-Wall Carbon Nanotubes Studied by Time-Resolved Hole Burning

“…[1][2][3][4][5] However, s-SWNT photophysics are strongly affected by interactions with the environment which can lead to inhomogeneous line broadening, blinking and spectral diffusion. [6][7][8][9][10][11] While the specific origin and mechanism of environmental perturbations for the exciton dynamics remains subject to debate, it is important to understand the nature of the corresponding interactions and their implications for key photophysical properties of s-SWNTs such as radiative and non-radiative decay and electronic as well as vibrational 2 dephasing. [12][13][14][15] Moreover, the extraordinary large surface-to-volume ratio of s-SWNTs and the corresponding surface sensitivity of their properties can give rise to large variations of key photophysical properties reported in the literature.…”