Optical Absorption in Compounds of Metals of the First and Second Groups of the Periodic Table and the Crystal Lattice Energy
Abstract Generated abstract
This paper examines how optical absorption in ionic crystals relates to crystal lattice energy for compounds of first- and second-group metals, especially rock-salt-type alkali halides and second-group metal oxides. By comparing experimental absorption data across infrared, visible, and ultraviolet regions, it argues that the intrinsic absorption edge, the F-band absorption maximum, and the infrared vibrational absorption edge vary systematically with lattice energy. The reported trend is that increasing lattice energy shifts absorption onsets, edges, and maxima toward shorter wavelengths, linking optical behavior to periodic chemical variation and suggesting connections with other crystal properties such as the dielectric constant.
Full Text
OPTICAL ABSORPTION IN COMPOUNDS OF METALS OF THE FIRST AND SECOND GROUPS OF THE MENDELEEV TABLE AND THE ENERGY OF THE CRYSTAL LATTICE
A. A. VOROB'EV
Optical absorption in ionic crystals in the visible and ultraviolet parts of the spectrum is observed upon excitation of electrons and their transition to higher energy levels. The short-wavelength edge of the absorption band in the infrared part of the spectrum is associated with excitation of the natural vibrations of the lattice ions. In ionic crystals, optical absorption is accompanied by the transition of electrons into the conduction band and causes photoconductivity.
Thus, the position of a band in the absorption spectrum determines the binding energy of electrons and ions in the lattice and must be related to the magnitude of the energy of the crystal lattice.
Fig. 1. Dependence of the quantum energy, I, corresponding to the edge of intrinsic absorption, and II, the energy quantum of natural vibrations of ions, on the lattice energy for crystals of oxides of metals of the second group.
In the works of L. M. Shamovskii [1], a connection was established between the long-wavelength edge of intrinsic absorption of alkali-halide crystals and the lattice energy. E. K. Zavadovskaya [2], for alkali-halide crystals, established a dependence between the absorption maximum corresponding to the \(F\)-band and the lattice energy.
A comparison of experimental data shows that for compounds of metals of the first and second groups (Figs. 1, 2) of the Mendeleev table,
Fig. 2. I—Dependence of the quantum energy corresponding to the edge of intrinsic absorption. II—Absorption maximum corresponding to the F band. III—Short-wavelength edge in the infrared part of the spectrum, and lattice energy for alkali-halide compounds.
crystallizing in a lattice of the rock-salt type, the absorption of light in the infrared, visible, and ultraviolet parts of the spectrum is regularly related to the crystal-lattice energy. With increasing lattice energy, the onset, edge, and maxima of absorption shift into the short-wavelength region.
These regularities are a consequence of the periodic variation of the properties of the elements in Mendeleev’s table and of the variation in the properties of the compounds formed by these elements. As a result of the relation between light absorption in crystals and lattice energy, there will exist a dependence between light absorption and other properties of crystals.
Earlier [3], for alkali-halide crystals, a relation was shown between light absorption and the dielectric constant.
REFERENCES
- Shamovskii L. M. Absorption spectra of heteropolar crystals and crystal-lattice energy. Moscow, 1938.
- Zavadovskaya E. K. Doklady Akademii Nauk SSSR, 88, 573, 1954.
- Vorob’ev A. A. Doklady Akademii Nauk SSSR, 90, 157, 1953.