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The configuration of the ionic state with filled shells will be Na+ : 1S2 2S2 3S, and for Cl− it will be Cl− : 1S2 2S2 3S2 3P6 . The electrical charge distribution around the ions in the ionic crystal is approximately spherically symmetric, but is slightly distorted at short distances, close to the contact point. For ions with a charge ±q, separated by an interionic distance r, the electrostatic field is given by ±q/r 2 , where the forces are attractive for charges of opposite signs and repulsive for charges of the same signs.

A. Riseberg and M. J. Weber, “Relaxation phenomena in rare-earth luminescence,” in Progress in Optics XIV, 89–159, North-Holland (1976). 14. R. Reisfeld, “Potential uses of chromium (III) doped transparent glass ceramics in luminescent solar concentrators,” Electronic Structure of New Materials Part I, Report No. 40, 7–34, The Swedish Academy of Engineering Sciences in Finland (1985). 15. E. V. Zharikov, N. N. Il’ichev, V. V. , “Spectral luminescence and lasing properties of gadolinium scandium gallium garnet crystals activated with neodymium and chromium ions,” Sov.

2 Ionic bonding In the case of ionic crystals, bonding between the crystal ions is of a coulombic nature which results from electrostatic interaction between the charged ions. The electronic configurations of ionic crystals are closed electronic shells, like inert atoms. However, unlike inert gases, the formation of a closed-shell configuration leads to a charged atom. If we take sodium chloride as an example, the electronic configuration of neutral Na is 1S2 2S2 3S1 while that of the neutral Cl atom is 1S2 2S2 3S2 3P5 .