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HL: Fachverband Halbleiterphysik
HL 48: Poster 2
HL 48.19: Poster
Donnerstag, 26. März 2009, 15:00–17:30, P2
Defect Induced Photoluminescence from Dark Excitonic States in Individual Single-Walled Carbon Nanotubes — •Tobias Gokus1, Hayk Harutyunyan2, Alexander A. Green3, Mark C. Hersam3, Maria Allegrini2, and Achim Hartschuh1 — 1Department Chemie und Biochemie, Ludwig-Maximilians-Universität München and CeNS, 81377 München, Germany — 2Dipartimento die Fisica "E. Fermi", Universitá di Pisa and CNISM, Largo Pontecorvo 3, 56127 Pisa, Italy — 3Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3108, USA
We show that new low-energy photoluminescence (PL) bands (ΔE∼30-190 meV) can be created in the spectra of individual semiconducting single-walled carbon nanotubes (SWNT) by intense pulsed laser irradiation at room temperature. These new bands are attributed to emission from different nominally dark excitons that are "brightened" due to defect-induced mixing of states with different parity and/or spin. Time-resolved PL studies on single nanotubes reveal a significant reduction of the bright exciton lifetime (1-40 ps) upon brightening of the dark excitons. The lowest energy dark state (ΔE∼190 meV) has longer lifetimes up to 177 ps and is not in thermal equilibrium with the bright state. In addition we show that the same satellite bands can be observed by exposure of the SWNTs to a gold solution, and using low power CW laser excitation, indicating that the lowest energy emission is due to triplet exciton recombination facilitated by magnetic defects or impurities.