The spectroscopic investigation of the highly transparent rare earth (Pr<sup>3+</sup>, Nd<sup>3+</sup>, Ho<sup>3+</sup>, Er<sup>3+</sup>, Tm<sup>3+</sup>, Yb<sup>3+</sup>) doped Sc<sub>2</sub>O<sub>3</sub>
ceramics produced by the solid-state synthesis technique indicate that these materials could substitute the single crystals
in construction of solid-state lasers. These studies indicate also that the rare earth doped transparent ceramics could
extend considerably the variety and performances (new active systems, wavelength ranges or emission schemes) of these
The information on the variety, nature and structure of the centers formed by the rare earths ions doped in the transparent laser ceramics of garnets and cubic sesquioxides, acquired from high-resolution spectroscopy and emission decay is analyzed. The quantum states (energy levels, transition probabilities) of several doping rare earth ions, their distribution at the available lattice sites, the interactions between ions, and energy transfer processes are also presented. It is inferred that from spectroscopic point of view these materials could substitute the melt-grown single crystals in construction of solid-state lasers and extend considerably their capabilities.
The high resolution and polarized spectroscopic investigation of Nd<sup>3+</sup> in Mg-compensated strontium lanthanum aluminate Sr<sub>l-x</sub>La<sub>x-y</sub>Nd<sub>y</sub>Mg<sub>x</sub>Al<sub>12-x</sub>0<sub>19</sub> (Nd: ASL) function on composition makes possible the elucidation of the nature of non- equivalent centers and enables the selection of composition and pumping conditions that grant the efficient quasi-three-level laser emission around 900 nm. Based on a proper selection of these conditions, 900 nm laser emission with slope efficiencies of 0.74 and 0.84 at 792 nm <sup>4</sup>F<sub>5/2</sub> and respectively 865 nm <sup>4</sup>F<sub>3/2</sub> pumping of Nd<sup>3+</sup> is demonstrated.