Properties of chromium ions in the lattice of yttrium aluminium garnet (YAG)

YAG crystals containing chromium ions (Cr3+) were grown using the method of optical zone melting. The absorption and fluorescence spectra of YAG crystals with different amount of trivalent chromium have been measured and the energy levels fitted to a four-parameter crystal-field theory. The values of the Racah parameters derived from the absorption spectra are discussed. It is found that an increase of the concentration of chromium ions leads to a decrease of the Racah parameters B, C, and the magnitude Dq of the crystal field strength. It is established from the data of the fluorescence spectra that even when the concentration of chromium ions in YAG is small, there are two types of centres: monomeric and polymeric ones. The investigations of the YAG (Cr3+, Nd3+) crystals show the great probability of energy transfer from chromium ions in polymeric centres to Nd3+ ions. [Russian Text Ignored.]