Fine-Line Spectra of Chromium Ions in Crystals

Abstract

The sharp lines of the optical spectrum of trivalent chromium in oxides can be used to determine the position and splitting of the 2E state. They can be calibrated by stress experiments on an ion which is initially in a purely cubic field, and can then be used to study the surroundings of ions in noncubic fields. Further information can be obtained from ground-state splittings, which depend in a different way on the symmetry of the surroundings. The method is used to investigate deformed cubic sites in magnesium oxide and aluminum oxide. In aluminum oxide, chromium lines as narrow as 0.10 cm−1 have been observed at low temperatures, and show a fine structure attributed to the chromium isotopes. Some progress has been made in understanding the chromium pair spectra observed at higher concentrations.