Transitions host matrices

This investigation shows that it is indeed possible to study the flexibility of polymer chains in polymer matrices by means of excimer-forming probes and that the rotational mobility of these probes reflect the glass transition relaxation phenomena of the polymer host matrix, in agreement with the appropriate WLF equation. 

Figures 4.34a,b demonstrate the emission lines of titanite, which according to their spectral positions may be confidently connected with Nd " ". The luminescence spectrum in the 860-940 nm spectral range, corresponding to the transition, contains six peaks at 860, 878, 888, 906, 930 and 942 nm, while around 1,089 nm corresponding to F3/2- fn/2 transition it contains five peaks at 1,047,1,071,1,089,1,115 and 1,131 nm. The decay time of IR luminescence of Nd " equal to approximately 30 ps in titanite is evidently the shortest one in the known systems activated by Nd ". The typical radiative lifetime of this level depends on the properties of the solid matrix and varies from approximately 100 ps to 600 ps (Kaminskii 1996). To explain the fast decay time of Nd " in titanite, the energy level quenching by the host matrix may be considered.

The model PBZT/ABPBI molecular composite system is limited since the rod and the matrix do not possess glass transition temperatures for subsequent post form consolidation. In an effort to improve the processability for molecular composites, thermoplastics were used as the host matrix. Processing from acidic solvents requires the thermoplastic host to be soluble and stable in meth-anesulfonic add. Thermoplastic matrices were investigated including both amorphous and semicrystalline nylons [71,72], polyphenylquinoxaline (PPQ) [73] and polyetheretherketone (PEEK) [74], Table 5 shows the mechanical properties obtained for various processed PBZT thermoplastic molecular composite systems. As an example, the PBZT/Nylon systems showed 50-300% improvement over uniaxially aligned chopped fiber composite of comparable compositions. However, the thermally-induced phase separation during consol-... 

The absorption spectrum of Bk(III) in a lanthanum chloride host matrix at 77 K was first obtained in 1964 (102). A prediction of the energy level structure of Bk(III) was made by others the same year (103). Extensive, low-temperature spectroscopic studies of BkCl3 showed the absence of transitions to excited J = 0 and J = 1 states (104, 105). This provided good evidence for a fi = 0 ground level for Bk(III), consistent with that of Tb(III)-LaCl3 (106). Experimental and theoretical studies of the crystal field parameters of Bk(III) in a LaCl3 host lattice have also been reported (107). 

As an example, we estimate the resonance enhancement of an intraband optical transition in silicon carbide (SiC) nanociystals. The dielectric function of SiC is well modeled by the expressions (7) with = 6.52, Qt = 793.9 cm" (and the wavelength At = 12.6 pm), = 970.1 cm (Al = 10.3 pm), and y = 4.763 cm. Note that the relaxation parameter y is much less than the optical phonon frequencies, y/Qi = 0.006 and y/ L = 0.005. The solution of the resonance condition (6) results in Q w 902cm and the corresponding resonance wavelength A 11 pm. Here and hereafter, in all onr numerical estimates we accept the permittivity of a host matrix Shost = 2.25, because this value is typical for many solvents, glasses, and polymers. Then, the gain factor G(Q) is estimated to be approximately 3.6 x 10. ... 

Fig. 13.1 Relaxation in the X X (ground electronic state) and A n (excite electronic state) vibrational manifolds of the CN radical in Ne host matrix at T = 4 K, following excitation into the third vibrational level ofthe If state. Populations in individual vibrational levels in both electronic states are monitored independently by fluorescence (for the If state) and by laser induced fluorescence (for the X state). The preferred relaxation pathway for energies above the origin of the Tt state is found to be medium assisted internal conversion as indicated by arrows in the left panel. The right panel shows the dynamics of population and subsequent decays of the vibrational levels 6, 5, 4, and 3 of the ground X state. Levels 6 and 5 relax much faster (lifetimes in the order of 1-3 /xs) than levels 4 and 3 (lifetimes in the ms range). For the latter the internal conversion-assisted pathway is closed as seen in the state diagram on the left, so these long lifetimes correspond to pure vibrational transitions. (From V. E. Bondybey and A. Nitzan, Phys. Rev. Lett. 38, 889 (1977).)...

The linear dichroism of nickel(II), palladium(II) and zinc(II) complexes of mesomorphic 4-alkoxydithiobenzoic acids has been investigated in the commercial eutectic mixture of cyanobiphenyls and cyanoterphenyls, E7 (from Merck) for the palladium(II) complexes and in the commercial mixture of cyanobicyclohexanes, ZLI2830 (from Merck) for the nickel(II) and zinc(II) complexes (Figure 2.12).For the nickel(II) and palladium(II) complexes both a ligand-based transition and a charge-transfer band (MLCT) were observed, whereas only a ligand-based transition was present for the zinc(II) complexes. These complexes had a much lower solubility in the liquid crystal host matrix than the dithiolene... 

In directing their study mainly to complexes or molecules (in particular those containing transition metal ions) that can be considered largely in isolation from the host matrix and for which a localized electron approach is appropriate, chemists have paid less attention to the study of many interesting aspects of the study of concentrated systems. In particular the lattice periodicity of such compounds encourages a band theoretical approach to bonding and structure, and experimental and theoretical study by solid-state physicists has been intense, but the spread of knowledge between dis-... 

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