Semiconducting photoluminescence

The introduction of bulky side chains that contain adamantyl groups to poly(p-phenylenevinylene) (PPV), a semiconducting conjugated polymer, decreases the number of interchain interactions. This action will reduce the aggregation quenching and polymer photoluminescence properties would be improved [93]. 

Photoluminescence spectroscopy is used to analyze the electronic properties of semiconducting CNTs [64]. The emission wavelength is particularly sensitive to the tube diameter [65] and chemical defects [66], However, a more dedicated sample preparation is required in order to eliminate van der Waals and charge transfer interactions between bundled CNTs. This can be done via ultrasonication or treatment of the bundles with surfactants that separate individual CNTs and suppress interactions between them [67]. 

Currently silicon is still one of the most important semiconductors as it is the basis of any computer chip. It exhibits an indirect band gap of 1.1 eV at room temperature in the microcrystalline phase. Similar to Ge, silicon nanoparticles show a size-dependent photoluminescence. It was reported by Katayama el al. that a thin Si layer can be electrodeposited in l-ethyl-3-methylimidazolium hexafluorosilicate at 90 °C [44], However, upon exposure to air the deposit reacted completely to SiC>2, which makes it difficult to decide whether the deposit was semiconducting or not. Recently, we showed for the first time that silicon can be well electrodeposited from SiCU in the air and water stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([BMPJTfiN) [45, 46]. This ionic liquid can be... 

It has been observed that the SWNTs suspended in a micellar solution exhibit a well-defined optical spectrum and show a bright photoluminescence in the near infrared region (Figme 22). The individual SWNT suspended in air at room temperature also shows a bright photoluminescence. The emission spectrum of the semiconducting SWNTs correlates well with the absorption spectrum in a micellar solution. The intensity of emission decreases dramatically when the isolated nanotubes start aggregating in a destabilized micellar solution. The decrease in the emission is attributed to the quenching of electrons by the metallic nanotubes when... 

Concentration quenching is not a major problem in semiconducting polymers. Typically, the quantum efficiency for photoluminescence from thin films is comparable to that from dilute solutions. The absence of strong concentration quenching is the result of the spatial delocalization of the excited states. Because the weakly bound excitons are spread over many repeat units, the Davidov splitting that results from interchain interactions is small. As a result, the disorder that is present in films cast from solution is sufficiently large to mix the dark and emissive Davidov-split states. Thus, quantum efficiencies in excess of 60-70% can be obtained from thin solid films of luminescent semiconducting polymers. 

Photoluminescence results from the radiative emission of photon absorptiongenerated excited states. In principle, both intramolecular and intermolecular excited states can be generated with singlet and triplet configurations by photon absorption in organic semiconducting materials (Scheme 4.2). 

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