Anti-Site Defects and Trigonal Center of Holmium in Y3Al5O12:Ho3+ Crystal According to the Results of Wideband EPR Spectroscopy

EPR spectra of Ho3+ impurity ions were recorded in single crystals of yttrium aluminum garnet (Y3Al5O12, YAG) in the frequency range of 114–410 GHz, at a temperature of 4.2 K. Besides the centers due to unusual substitutions by Y3+ for Al3+ ions (anti-site defects), a trigonal center was found, which indicates the replacement of Al3+ ions by Ho3+ ions in octahedral positions with local symmetry C3i. The magnitude of g-factor, the hyperfine structure constant and the energy interval between the main and the first excited sublevel of the main 5I8 muliplet were determined. A comparative analysis of the formation of satellite centers for crystals grown under different conditions is made.