The optical absorbance from 6000 to 29 000 cm -1 of vapor deposited thin films and dilute solutions of Na + (C222)Na -, as well as the reflectance from 4000 to 25 000 cm -1 of oriented single crystals, were measured. The major common feature is a broad band centered at approximately 15 600 cm -1 (1.94 eV). The film spectra also have a shoulder at 18 900 cm -1 (2.34 eV) and a smaller, broad peak at 24 400 cm -1 (3.03 eV) that are not present in the solution spectra. While the solution peak broadened somewhat and shifted dramatically to lower energy with an increase in temperature, the film peak shifted only slightly because of broadening on the low-energy side, indicative of phonon-assisted excitation. As expected from the anisotropic structure, the features of the reflection spectra at near-normal incidence show major differences for light polarized parallel and perpendicular to the c-axis of single crystals. A Kramers-Kronig analysis of the reflection spectra yields the frequency-dependent optical constants of Na + (C222)Na -: the real and imaginary parts of the dielectric function, the energy loss function, the extinction coefficient, and the absorption coefficient. Comparisons between the calculated and observed absorption spectra indicate that the polycrystalline thin films prepared by codeposition of sodium and cryptand[2.2.2] are partially ordered, with the c-axis perpendicular to the substrate surface.
The optical properties of the alkalide Na + (cryptand[2.2.2])Naare sensitive to the presence of defect electrons and can be dramatically altered by irradiation with light. Fluorescence intensities decrease markedly at excitation power densities above about 1 mW cm -2 , even though this power level is some 10 7 times lower than that required to affect the absorbance. Partial recovery occurs in powder samples over a period of several minutes at 30-100 K. The enhanced quenching of fluorescence is attributed to the presence of photoproduced trapped electrons. Pronounced changes occur in the optical absorbance spectra of vapordeposited thin films of Na + (cryptand[2.2.2])Nafollowing irradiation by high intensity doubled-and tripled-YAG laser pulses. The effects are attributed to the intermediate formation of a "p-band metal" in which half of the electrons in the ground s 2 state of Naare promoted to the p-level, resulting in a high concentration of electrons trapped at some distance from the parent anion site.
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