Polarized emission

This equation also limits the set of observable LEED spots by the condition that the expression inside the brackets must be greater than zero. With increasing electron energy the number of LEED spots increases while the polar emission angle relative to the surface normal, 6 = arctan(k /kz), decreases for each spot except for the specular spot (0,0) which does not change. Eig. 2.47 shows examples of common surface unit cells and the corresponding LEED patterns. 

Electron-Deficient Polymers - Luminescent Transport Layers 16 Other Electron-Deficient PPV Derivatives 19 Electron-Deficient Aromatic Systems 19 Full Color Displays - The Search for Blue Emitters 21 Isolated Chromophores - Towards Blue Emission 21 Comb Polymers with Chromophores on the Side-Chain 22 Chiral PPV - Polarized Emission 23 Poly(thienylene vinylene)s —... 

The polarized emission experiments on partially photooxidized aligned PF films indicate that the emission from the keto defects exhibits a somewhat smaller polarization ratio than the blue emission from the defect-free chains [263]. This observation was explained with the support of quantum mechanical calculations, which showed that the polarization of the fluorenone emission is influenced by local disorder [263]. 

In addition to 195-200, many other alkyl substituents and their derivatives have been introduced at position 9 of the fluorene nucleus in order to create a processible stable blue-emitting PF material, e.g., 203a-h [273-275,305], Chiral-substituted PFs 200 and 203g,h have been synthesized to study their chiroptical properties [306], particularly interesting due to polarized emission in such materials (see Chapter 5 in this book) (Chart 2.47). 

Most of the LC polymer systems discussed so far contain the LC moiety incorporated in the polymer main chain. One of the few examples of polarized emission of light using a side-chain LC system was reported by Chang et al. [107]. A polyacrylate was used as the polymer backbone. The nematic LC side-chains consisted of ethyl- and propyl-substituted bis-tolan units. When deposited on a rubbed PEDOT film, polarized EL dichroic ratios were reported to be around 6. 

M Voigt, M Chambers, and M Grell, Circularly polarized emission from a narrow bandwidth dye doped into a chiral nematic liquid crystal, Liq. Cryst., 29 653-656, 2002. 

Y Yoshida, N Tanigaki, K Yase, and S Hotta, Color-tunable highly polarized emissions from uniaxially aligned thin films of thiophene/phenylene co-oligomers, Adv. Mater., 12 1587-1591, 2000. 

KS Whitehead, M Grell, DDC Bradley, M Inbasekaran, and EP Woo, Polarized emission from liquid crystal polymers, Synth. Met., 111 181-185, 2000. 

Fluorescence polarization. Emission anisotropy Brownian diffusion equation for a spherical particle... 

With the exception of the orientation factor, all the parameters in this equation may be obtained within reasonable error by direct experimental measurement or by estimation. The problem of setting reasonable values for k2, which may vary from 0 to 4 for orientations in which the dipole moments are orthogonal or parallel, respectively, is nontrivial. A value of , which is an unweighted average over all orientations, is often used. Dale et al.(53) have examined this problem in great detail and have shown that a k2 value of is never justified for energy transfer in macromolecules because it is impossible for the donors and acceptors to achieve a truly isotropic distribution. They do provide an experimental approach, using polarized emission spectroscopy, to estimate the relative freedom of motion for the donor and acceptor that allows reasonable limits to be set for k2. 

Thus, the electric dipole a polarized emissions departing from the Ai level (in which the electric field of the emitted light is parallel to x or y) are those defined by the direct product Ai x L. An inspection of Table 7.6 shows that Ai X E = E, so that only A E emissions are allowed for a emitted radiation (as shown in Figures 7.7 and 7.8). 

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