crystals grown by the Czochralski technique and and crystals grown by the floating-zone technique were investigated using methods of optical spectroscopy. Polarized absorption and emission spectra were recorded at room temperature and at . The crystal-field analysis was performed assuming the site symmetry for ions. In this way the missing crystal-field components of the ground multiplet were located. Room temperature absorption spectra were analyzed in the framework of the Judd-Ofelt theory. Evaluated radiative lifetimes of luminescent levels of follow a general trend diminishing in agreement with the sequence: . Luminescence lifetimes measured for the systems under study are similar except for the lifetime, which appears to be surprisingly short for . Anisotropy of optical spectra is particularly pronounced in . Peak absorption cross section for the band relevant for optical pumping at about is roughly three times higher for polarization. Stimulated emission cross sections for the transition near were evaluated using the reciprocity method. The diode-pumped continuous wave laser operation in with a slope efficiency of up to 40% is demonstrated. In the diode-pumped laser oscillation in a pulsed mode was observed.