Crystallinity-sensitive absorption bands

The role of cerium in these lighting phosphors is not as the emitting atom but rather as the sensitizer. The initial step in the lighting process is the efficient absorption of the 254 nm emission Ce ", with broad absorption bands in the uv, is very suitable. This absorbed energy is then transferred to the sublattice within the crystalline phosphor eventually the activator ion is fed and emission results. Cerium, as a sensitizer ion, is compatible in crystal lattices with other lanthanide ions, such as Eu and Tb, the usual activator atoms. 

Tetrakis(acetato)di- U-amido-diborane is a white crystalline compound which is not too sensitive to moisture. It can be stored in a nitrogen atmosphere in a refrigerator for long periods without decomposition. It is sparingly soluble in most organic solvents and slowly dissolves in glacial acetic acid and acetic anhydride. Monoclinic and triclinic crystalline forms were obtained by recrystallization from acetic anhydride and glacial acetic acid, respectively.1 The infrared spectrum recorded (Beckman i.r.-12) by the KBr pellet technique contains major absorption bands (at frequencies cm.-1) 3280(s), 3230(s), 3100(s), 1740(w,sh),... 

Nickel cyanides seem to behave differently from the isomorphous complexes of Pd and Pt. Already in the free state the spectrum indicates the presence of very weak bands due to d—d transitions, giving rise to the orange coloration of concentrated solutions. The passage to the crystalline state results in an absorption spectrum which is not very sensitive to the nature of the cation, except perhaps for BaNi(CN)4, 4 H2O, and is structured in the same way as the spectrum of the free ion except for the relative intensity of the absorption bands. 

The infrared band at 875 cm of the syndiotactic polypropylene is used to estimate crystallinity. These three crystallinity sensitive bands (1167, 998, and 875 cm ) do not appear in the IR spectrum of atactic polypropylene. If a sample of polypropylene is drawn to one direction—that is, it is uniaxially oriented—some of the absorption band intensities become dependent on the angle between the drawn axis and the angle of polarization of the infrared radiation. 

Figure 12.15 shows typical FTIR-ATR spectra between 700 and 1500cm wavenumbers for quenched PH BV films annealed at room temperature for different periods of time. The shapes and intensities of some IR absorption bands are sensitive to the degree of crystallinity. In these spectra, the relative intensity of the absorption band at 1182 cm displays the largest difference between the crystalline and amorphous states. The band decreases with increase in the degree of crystallinity. 

Most high quality spectral collections have been obtained with moderate spectral resolution - 2 cm-1 to 5 cm-1 with a peak-to-peak noise level of less than 1% T. If data are recorded with less resolution then there is a risk of loss of fine detail even for condensed phase spectra. It is this fine detail that helps in the discrimination of chemically or structurally similar compounds. Furthermore, crystalline compounds and also certain liquids, such as indene, can have narrow absorption bands that are resolution sensitive. A high noise level, as indicated in Figure 2d is undesirable but not necessarily unavoidable. Techniques such as signal... 

---