Extinction peak shifts

Calculations for a range of particle sizes are shown in Fig. 11.13. Note that the scales have not been shifted for the different sizes extinction increases with size because of scattering. The extinction band for the 0.1-jam particle faithfully reflects the characteristics of the intrinsic absorption band. But asymmetries develop for particles larger than about 0.2 jam indeed, at a radius of 0.3 jam the absorption band looks like an emission band relative to the continuum. The explanation for this strange extinction behavior near an absorption band lies in the preceding section extinction is not a steadily increasing function of bulk absorption. A narrow absorption band is similar to a small absorption edge that falls just as rapidly as it rises, which can thus cause extinction peaks, dips, or both. 

Fig. 23 Alkanethiol chain length dependence on the LSPR spectral peak shift. All extinction measurements were collected in a N2 environment. Linear regression was used to fit the data to a line described by the following equation y = 3.3(x) — 9.3. Reproduced with permission from [42]. Copyright 2001 American Chemical Society...

Polymer adsorption on gold nanoparticles results in two effects (1) it increases the extinction and scattering maxima and (2) it shifts the resonance to the red part of spectrum. Detailed calculations for the gold-core diameters <7 = 10-160 nm, the shell thickness 5=0-10 nm, and the shell refractive indices = 1.4 and = 1.5 can be fotmd elsewhere [12], Here we provide only two examples that illustrate the effect of polymer adsorption on the value of the extinction maximum (Fig. la) and on the extinction peak position (Fig. lb). 

The decrease in the value of was also observed for the fluorescent probe 1-anilino-8-naphthalene sulfonate (ANS) in presence of apomyoglobin. In fact, the absorption peak shift from 265 mu when free in solution to 271 mu in presence of apomyoglobin while the extinction coefficient decreases from 19200 to 13000 cm / mmole L, (Fig. 1.15). 

Figure 3. Calculated extinction (black), absoiption (dark grey), and scattering (Ggbt grey) cross section as a Auction of wavelength for a 20,40,80, and 120 nm diameter gold particle in water. As the particle diameter is increased, the plasmon resonance scattering peak shifts to loiiger wavelengths and beconre broader.

Figure 5. Calculated spectra from a 120 nm diameter silica particle coated with gold shell thickness that ranges from 5 nm to 20 nm. As the thickness of the shell is decreased, the peak extinction location shifts from 730 nm out to 1030 nm. Reproduced from [18] with permission from the author.

Experimentally, the sensor optical response (R), defined as the change in extinction or shift in peak resonance wavelength as a function of the refractive index of the surroimding medium can be represented by Eq. (S), as follows "... 

An encouraging result from our recent study of the N3 dye molecule bound to a Ti02-coated oxidized silver sphere is that an IPCE enhancement factor of 9.9 was obtained for a Ti02 thickness of 2.0 nm, in excellent agreement with the experimental value of 6.0. Furthermore, the observed red shift of the primary extinction peaks of the PDSSC relative to the plasmon maximum was also found in our simulations. By comparing the location of the experimental extinction peaks, we are able to estimate theoretically the thickness of an intermediate Ag20 layer that is not experimentally measurable yet and is found to be essential in limiting the photovoltaic efficiency of the PDSSC. 

The microenvironment in water-containing AOT-reversed micelles has a marked effect on the spectral properties of flnorescein. The absorption peaks are red-shifted by about 10 nm from the corresponding positions in aqueous solution, the absorption extinction coefficient increases with R, and the fluorescence is more effectively quenched in AOT-reversed micelles than in aqueous solution [149],... 

The excitation maximum for the molecule occurs at 535 nm and its emission at 552 nm. Its Stoke s shift is slightly greater than some of the other BODIPY fluorophores, producing a 17nm separation between excitation and emission peaks. BODIPY 530/550 C3 has an extinction coefficient in methanol of about 62,000 M 1 cm-1 at 535 nm. 

Bolis et al (43) reported volumetric data characterizing NH3 adsorption on TS-1 that demonstrate that the number of NH3 molecules adsorbed per Ti atom under saturation conditions was close to two, suggesting that virtually all Ti atoms are involved in the adsorption and have completed a 6-fold coordination Ti(NH3)204. The reduction of the tetrahedral symmetry of Ti4+ ions in the silicalite framework upon adsorption of NH3 or H20 is also documented by a blue shift of the Ti-sensitive stretching band at 960 cm-1 (43,45,134), by a decrease of the intensity of the XANES pre-edge peak at 4967 eV (41,43,134), and by the extinction of the resonance Raman enhancement of the 1125 cm-1 band in UV-Raman spectra (39,41). As an example, spectra in Figs. 15 and 16 show the effect of adsorbed water on the UV-visible (Fig. 15), XANES (Fig. 16a), and UV-Raman (Fig. 16b) spectra of TS-1. 

Ionization of the phenol hydroxyl group in tyrosine shifts the 277-nm absorption peak to 294 nm and the 223-nm peak to 240 nm. The molar extinction coefficient for the peak of the lower energy band increases from about 1350 M l cm-1 to about 2350 M em-1 and for the higher energy band from about 8200 M cm-1 to about. 1,000 M l cm-1.113 141 In addition, the lower energy absorption band of tyrosine shows vibrational structure that is lost upon ionization of the phenol side chain. 

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