Green defect emission

Enhancement of the Green Defect Emission in the Solid State... 

Green Defect Emission Emerging Under Device Operation. 286... 

We are of the opinion that our single molecule results on PFs copolymerised with lluorenone units represent compelling proof for the monomolec-ular nature of the green defect emission. The development of new synthetic strategies for reaching a blue stable emission in PF-based OLEDs should therefore concentrate on formulating protective groups, rather than on spacers to control intermolecular interactions, which inevitably lower the transport performances. 

Photoluminescence of the films varies greatly, both in intensity and in spectral shape, from one report to another. This is not surprising, since this property is very dependent on the state of the surface of the individual crystals. A red (ca. 1.8 eV) defect emission is usually seen, but green, yellow, and infrared peaks have also been reported. The various wavelengths are related to different defects in/on the crystals even the green emission is probably due to a shallow defect emission. 

More recently, it was shown by List et al. [293-296] and later by Moses et al. [246] that the green emission of the PFs is due to fluoren-9-one defects in the polymer chain. This was confirmed by comparison of PL films annealed in an inert atmosphere and in air a progressive additional band in the green region was observed on annealing in air (Figure 2.12) [246],... 

L. Romaner, A. Pogantsch, P.S. de Freitas, U. Scherf, M. Gaal, E. Zojer, and E.J.W. List, The origin of green emission in polyfluorene-based conjugated polymers on-chain defect fluorescence,... 

Enhanced luminescence of SiC>2 Eu3+ by energy transfer from ZnO nanocrystals (3 nm) was recently reported (Bang et al., 2005). The defect-related green emission from ZnO nanocrystals was completely quenched when they were embedded in Si02 doped with Eu3+, indicating a very efficient energy transfer from the embedded ZnO to Eu3+. As a result, the f-f emissions fromEu3"1" were enhanced 5-10 times. 

The CL spectrum of the ZnO film consisted of intense, near-band-edge ultraviolet emission with a wavelength maximum at 387 nm and a full width at half maximum of 21 nm. This emission is of excitonic nature and is a result of the radiative annihilation of free and bound excitons. A broad defect-related green band with much lower intensity near 510 nm, typical for ZnO, was also observed (Fig. 1). The CL spectrum of the p-Alo. i2Gao 8sN(Mg) film consisted of a very weak near-band-edge emission with at 356 nm, and of a more intense broad band with a maximum at 410 nm. 

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