Optical absorption doping effects

Figure 3.70 Room temperature optical absorption spectra of a 45(X)A-lhick film of neutral polypyrrole doped with at0.03 torr. (a) before exposure to I2, conductivity <10 6fl 1cm"1 (b) after 2 minutes I2 exposure, conductivity 4.8 ft em 1 (c) after 7 minutes exposure, conductivity 6,7 ft em 1 (d) after 22 minutes I2 exposure, conductivity 32ft cm The three structures seen on the low-energy side of (a) (c) arc possibly artifacts due to interference effects in the films. From Pfluger et at. (1983).

Optical absorption spectra of as-grown and laser-annealed areas are shown in Fig. 11 for an undoped and a B-doped a-Si H film (Staebler, 1979). Phosphorus-doped films have an absorption characteristic straddling between the undoped and the boron-doped films but showed additional illumination effects. These curves revealed that all films darken on exposure... 

Our first steps toward the single-molecule regime arose from work at IBM Research in the early 1980s on persistent spectral hole-burning effects in the optical transitions of impurities in solids (for a review, see [20]). Briefly, if a molecule with a strong zero-phonon transition and minimal Franck-Condon distortion is doped into a solid and cooled to liquid helium temperatures, the optical absorption becomes inhomogeneously broadened (Fig. 2.2A). The width of the lowest electronic transition for any one molecule (homogeneous width, Yjj) becomes very small because few phonons are present, while at the... 

Hall and Williams [96] doped thin films of lead azide with T1 and Bi. There was no marked effect on the photodecomposition efficiency at 330 nm as compared to undoped films. However, both the spectral dependence of the rate and the optical absorption were altered by thallium. The incorporation of T1 (10 mole fractions) removed the 375 nm peak from the optical absorption spectra while the incorporation of Bi left the peak unaltered. Partial decomposition of films (0.1%) also removed the 375 nm peak (dotted curve. Figure 32). The results are consistent with the fact that the Tl " impurities require anion vacancies for charge compensation. This is equivalent to partial decomposition. They concluded that the peaks in the optical absorption curve and spectral photodecomposition curves are probably a result of charge-transfer excitons. Furthermore, peak separations may arise because of differences in the interaction energies of inequivalent lead and azide ions in the unit cell. The selective removal with decomposition of the 375 nm peak may indicate selective decomposition of the azide site having the highest valence band energy. The selective decomposition would reduce the density of states and thus the extinction coefficient for electronic transitions from that particular azide band. 

A semiconductor can be doped with donor atoms to provide electrons to the conduction band. Semiconducting materials can also be doped with acceptor atoms that take electrons from their valence band and leave behind some positive charges (holes). The most effective properties of semiconducting nanoparticles are noticeable changes in their optical properties which differ from their bulk counterpart materials. There is a significant shift in the optical absorption spectra toward the blue region (shorter wavelengths) as the particle size is reduced [360]. 

POLARONS AND SOLITONS IN HALOGEN-BRIDGED PLATINUM COMPLEXES EFFECTS OF PHOTOEXCITATION AND HALOGEN-DOPING ON OPTICAL ABSORPTION AND ESR SPECTRA... 

Frequency upconversion of 800 nm ultrashort 175 fs optical pulses by two-photon absorption in a stilbenoid compound-doped polymer (PMMA) optical fiber was reported [28]. By the intensity-dependent transmission method, the two-photon absorption cross section was deduced. The combination of a well-designed organic chromophore incorporated into a fiber geometry is appealing for the development of an upconversion blue polymer laser. Upconversion fluorescence and optical power limiting effects based on the two- and three-photon absorption process of a frans-4,4 bis(pyrrolidinyl)stilbene were investigated [29]. The molecular TPA cross section three-photon absorption (3PA) cross section g3 at 720-1000 nm were measured. The 3PA-induced optical power-limiting properties were also illustrated at 980 nm. 

A review of the progress in the understanding and applications of the TL of R-doped (and Mn-doped) Cap2 phosphors was given by Jain (1990). It also discusses effects of the radiation doses and of the LET on the GCs. Optical absorption ESR and TL emission spectra which lead to the identification of traps and luminescence centers are also given. 

Solitons in PoijAacetylene Effects of Dilute Doping on Optical Absorption Spectra" Phys. Rev. Lett. 45, 1209-1213. 

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