Influence of antisite defects in yttrium–aluminum garnet on paramagnetic centers of Ce$^{3+}$ and Tb$^{3+}$

In yttrium aluminum garnet (YAG) crystals containing terbium and cerium impurities, along with the main EPR signals of Ce$^{3+}$ and Tb$^{3+}$ ions located in the dodecahedral sites of the YAG lattice in a regular environment, EPR lines with a lower (several percent) intensity were observed. They also belong to the paramagnetic centers of terbium and cerium, but are characterized by slightly altered parameters–the initial level splitting for non-Kramers Tb$^{3+}$ ions and $g$-factors for Ce$^{3+}$ ions. It is shown that the nature of such centers and their number can be explained by the presence of Y$_{\mathrm{Al}}$ antisite defects, i.e. yttrium ions in the octahedral aluminum positions, in the environment of Ce$^{3+}$ and Tb$^{3+}$.