ENERGY-LEVELS OF THE LASER ACTIVE ER3+ ION IN EACH OF THE 2 CRYSTALLOGRAPHIC SITES OF YTTRIUM ORTHOSILICATE

There are two non-equivalent sites of yttrium in the lattice of Y2SiO5 . Both of them may be occupied substitutionally by Er3+, resulting in a laser active material. We measured absorption spectra of Y2SiO5:Er3 at several low temperatures and we studied its emission spectrum at 4 .2 K following selective excitation of individual Stark components of the I-4(13/2) --> I-4(15/2) transition by the light of a tunable colou r centre laser. The results of these two experiments allow classificat ion of the absorption and emission lines into two independent systems, thus yielding two energy level schemes 1 and 2. Moreover, simple crys tal field calculations strongly suggest from which Y2SiO5 crystallogra phic site spectrum 1 arises, and from which one spectrum 2.