Narrow Results

This paper gives a survey of physical phenomena manifesting themselves in electron and photon collisions with atomic clusters. The emphasis is made on electron scattering, photoabsorption and photoionization of fullerenes and metal clusters, however some results are applicable to other types of clusters as well. It is demonstrated that the diffraction and interference phenomena play an important role in the processes of clusters interaction with photons and electrons. The essential role of the multipole surface and volume plasmon excitations is elucidated in the formation of electron energy loss spectra on clusters as well as in the total inelastic scattering cross sections and in multiphoton absorption regime. Attention is paid to the elucidation of the role of the polarization interaction in low energy electron-cluster collisions. This problem is considered for the electron attachment to metallic clusters and the plasmon enhanced photon emission. The mechanisms of electron excitation widths formation and the relaxation of electron excitations in metal clusters and fullerenes are discussed.

This review focuses on the interrelation between the influences of polymeric structure on the optical properties of polythiophene — a versatile polymer for opto-electronic applications. From the application's point of view, the polymer should either be melt- or solution-processible. Functionalization of polythiophenes really helps for the above. On the other hand, the functionalization at the 3 and/or 4 position of the thiophene ring modifies the band gap of the polymer, which in turn, modifies photo absorption, photo- and electro-emission characteristics of polythiophenes. The present work reviews the influence of the optical properties of polythiophene on the different functional groups present in the thiophene ring.

Fe-doped TiO₂ crystals were successfully prepared using a sol–gel technique in reducing and oxidizing atmospheres. The effects of sintering atmosphere on phase transformation, oxygen vacancy concentration and photoabsorption behaviors were investigated. The results indicate that upon sintering in reducing atmosphere, Ti and Fe ion valences were decreased and highly Fe ions (12 mol%) were entirely dissolved into titania crystals, increasing oxygen vacancy concentration and leading to increased photoabsorption capability. In contrast, sintering in oxidizing atmosphere causes precipitation of the Fe₂O₃ phase, which is detrimental to the photoabsorption capability. The best photoabsorption performance is obtained by sintering 12 mol% Fe-doped TiO₂ in reducing atmosphere, resulting in an absorption edge of approximately 435 nm, which is much higher than that of undoped TiO₂ in the oxidizing atmospheres with the absorption edge 352 nm.

A novel macrocyclic $\pi$-skeleton 1 containing thiazole and thiophene rings was synthesized via MacDonald [3+1]-type condensation, and its optical properties were investigated. Two sulfur atoms were effective for the bathochromic shift of the ultraviolet-visible absorption bands in comparison with the traditional porphyrin and chlorin compounds. The characteristics of the absorption spectrum and the nucleus-independent chemical shift calculations show that the $\pi$-skeleton 1 is the chlorin-type compound.

We have performed systematic large-scale all-electron correlated calculations on boron clusters B_n(n = 2 - 5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the optimized ground-state geometries, the excited states of different clusters were computed using the multi-reference singles-doubles configuration–interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wave functions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion were carefully examined. The contribution of configurations to many body wave-function of various excited states suggests that the excitations involved are collective, plasmonic type.

This is an investigation of the dynamical screening of an atom confined within a fullerene of finite width. The two surfaces of the fullerene lead to the presence of two surface plasmon eigenmodes. In the vicinity of these two frequencies, there is a large enhancement of the confined atom's photoabsorption rate. The dynamical screening factor is given for two cases. In the first case, the atom is fixed at the center of the fullerene. The effect of the interaction between the dipole moments of the shell and the atom on the dynamical screening factor is investigated. In the second case, it is calculated for the atom placed at an arbitrary position inside the fullerene. A method for obtaining the spatially averaged screening factor is outlined.