Polarization of the emission

Polarization of the Emission. We have sought support for the weakly interacting chain segment model from measurements of room temperature fluorescence polarization (19) on dilute solutions of 1 in 3-methylpentane. An independent preliminary report of similar measurements on a dilute glassy solution at 77K and on a neat polymer has also appeared (21). In the latter case, the analysis is complicated by inter-chain energy transfer. 

Maskasky found that the long axis of the fluorescence image of the J-aggregate of the same dye on the 111 surface was parallel to both the <110> direction on the surface and polarization of the emission [18], On the 111 surface of the AgBr octahedron there are three equivalent <110> directions of the molecular arrangement with an angle of 60°. The transition from one excitation of a J-aggregate... 

Chen et al. reported on a general approach by which the polarization of the emission from semiconductor nanorods can be manipulated by an external bias. In their device, the composite of a nematic liquid crystal mixture (E7, Merck) and nanorods (CdS) filled into an ITO-coated cell with an optimized concentration of one CdS nanorod per 1010 LC molecules was used to achieve the highest polarization ratio of the suspended nanorods [447, 448]. The nematic liquid crystal in this system acts as a solvent and media whose direction of alignment can be tuned by an applied electric field. Hence, the orientation of the CdS nanorods can be fine-tuned by an external bias because of the anchoring force between the liquid crystal... 

The spacial symmetry of the emitting state can be uniquely determined for symmetric molecules from a knowledge of the zf origin of the 0,0 band of the phosphorescence emission and its spin-orbit origin as determined from the polarization of the emission (78). 

Doubling of the spectrum could be caused by two different promoting modes whose energy difference is 165cm . This interpretation could also explain the polarization of the emission spectrum which shows that the two progressions have different polarizations [2]. Another possibility is that the... 

In our model, the emission originates from the T2 level at all temperatures, and no polarization of the emission is expected. It is, however, unlikely that non-cubic crystal field components are totally absent. Such a crystal-field component would lift the degeneracy of the T2 level and cause polarized emission at very low temperatures. 

In most studies of this section the influence of the polarization of the emission has been neglected. If polarization is present, the anisotropy in the emission must be taken into account when calculating an emission cross section.1 However, it has been shown21 that due to the hyperfine structure of the alkali atoms the polarization of the sodium and potassium resonance lines is less than 20 %. In these cases the influence of the polarization on the angular distribution of the emitted photons can be neglected. 

Most studies reported below have been made with insufficient resolution in order to measure a true emission cross section. The influence of polarization of the emission on the cross section has been neglected entirely on the other hand it has been shown that the emission from collisionally excited rare gas atoms can be highly polarized.1... 

Among nonisotopic techniques, fluorescence (both intrinsic and extrinsic) offers a convenient mode of detection, and the sensitivity of some fluorescent labels is comparable to that of radiolabeled iodine. Recent innovations include the use of polarized light for excitation, such that the degree of polarization of the emission as well as its intensity can provide information about the concentration and size-related behavior (e.g., rotational diffusion) of the fluorescent-labeled molecule. One disadvantage of steady-state fluorescence techniques is that many analytical samples either autofluoresce or quench the fluorescence of the substance of interest. A recent development that circumvents this problem utilizes long-lived fluorophores such as the lanthanide metal ions as labels. Detection is time resolved and data are collected after the decay of spurious or otherwise unwanted fluorescence, i.e., after 100-200 psec. 

Thus after a period of tf the intensity has dropped to 37% of h, that is 63% of the molecules return to the ground state before tf. In many cases the above expression needs to be modified into more complex expressions. First of all it is assumed that the instrument yields an infinite (or very) short light pulse at time zero. In cases where tf is small Ig must be replaced by a function, which describes the lamp profile of the instrument. Also, more than one lifetime parameter is often needed to describe the decay profile, which is l(t) must be expressed as a sum of exponentials. Finally the concept of anisotropy should be mentioned. Anisotropy is based on selectively exciting molecules with their absorption transition moments aligned parallel to the electric vector of polarized light. By looking at the polarization of the emission the orientation of the fluorophore can be measured. The anisotropy of the system is defined as (Equation 6) (Rendell, 1987 Lakowicz, 2006) ... 

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