This paper reviews the spectroscopic properties of octahedral Cr3+ and
tetrahedral Cr4+ active centers in silicate crystals of diopside (CaM
gSi2O6), Sc2SiO5, AB(4)(SiO4)(3)O With A = Ca or Sr and B = Y, Ln, Gd.
These crystals demonstrate unusual spectroscopic features and potenti
al for new laser applications.