Optical properties absorption peak

On the other hand in the exciton description occasionnally adopted by some authors to interpret the main absorption peak in the polydiacetylenes one finds x " negative and its values two orders of magnitude lower than expression 6 since electron correlation (28) is essential in the exciton model, the calculation of even the simplest optical properties becomes prohibitively complicated and the physical insight is obscured. 

Temperature changes do not appreciably affect ultraviolet optical properties of both metals and insulators, although at low temperatures absorption bands associated with excitons and electron band transitions are usually sharper, and frequencies of peak absorption may shift slightly. In the soft x-ray region, transitions of core electrons buried in the interior of atoms hardly notice temperature changes. 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

Octasilacubanes were used as a model in an attempt to understand the optical properties of porous silicon because both porous silicon and octasilacubane show a broad photoluminescence spectra and large Stokes shifts52. 16 for example, shows an absorption edge at ca 3.2 eV and a broad photoluminescence spectrum with a peak at 2.50 eV. 

Most Phase I oxidations are performed by cytochrome P-450. "Cytochrome," derived from Greek, literally means "colored substance in the cell." The color is derived from the properties of the outer electrons of the transition element iron. "P-450" denotes a reddish pigment with the unusual property of having its major optical absorption peak (Soret maximum) at about 450 nm, when it has been reduced and combined with carbon monoxide.330 Although the name "P-450" was intended to be temporary (until more was known about the substance), the terminology has persisted for 18 yr because of the increasing complexity of this enzyme system and because of the lack of agreement on new nomenclature. 

In the LC box, metalloporphyrins can coordinate with 5CB [10,11]. Tetraphenylporphyrinatozinc have special property that the coordination interaction between ZnTPP and 5CB change, in other words, porphyrinatozinc changes from 5-coordinate (or 6-coordinate) to 4-coordinate because the transitions in the fluorescence spectra exhibit the corresponding absorption peaks [9,12]. We attribute this to that the excitation electron transfers from ZnTPP to 5CB and 5CB occurs optical-induced Fr edericksz transition so as to uncoordinate with ZnTPP (as shown in Figure 6). 

The optical properties of NPs with different in-plane size (resulting from different PB diameters) and different evaporated thickness, were examined. The absorption spectra for a range of NP dimensions are shown in Figure 6.3. It is evident that the peak position of plasmon resonance could be tuned by varying the PB diameter. was shifted to the red by increasing the PB diameter. could be... 

The physical and optical properties of the NPs used in this investigation are described in Table 6.1. The optical absorption properties of the ruthenium dye complex are also detailed in the table. It can be seen that there is good overlap between 7 of the pure silver and alloy NPs and the absorption band of the complex, while the gold NPs lie outside the absorption peak and are used as a negative control. The dependence of the excitation spectra of the dye complex on NP-dye distance is shown in Figure 6.14 for the case of the pure silver NPs. Also included in the figure is the excitation spectrum for the complex coated on the PEL layer in the absence of NPs. From Table 6.1, it can be seen that there is very good overlap between 7 of the silver NPs and the dye absorption band which constitutes the optimum plasmonic enhancement condition for the case of excitation enhancement. 

The skeleton-side-chain interaction is reflected in optical properties. The absorption and photoluminescence spectra of poly(methylpropylsilane) and poly(methylphenylsilane) are shown in Figure 14. For poly-(methylpropylsilane), the spectrum profiles are explained by the simple band model just discussed. However, for poly(methylphenylpolysilane), the spectrum profiles are very different. The absorption peak at 3.7 eV corresponds to a a-a transition, and the second peak at 4.5 eV corresponds to a tt-tt transition in phenyl side chains. The sharp photoluminescence peak originates from the a -CT transition. 

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