EFFECTS OF CA2+ZR4+ION-PAIRS ON SPECTROSCOPIC PROPERTIES OF CR3+MULTISITES IN CR3+-DOPED GD3GA5O12 GARNETS

Some disorder exists in Gd3Ga5O12 (GGG) garnets because of a partial occupation of the octahedral sites by the Gd3+ ions. The luminescence of the Cr3+ ions introduced as dopant in the material is then affected. The situation is worse in (Ca,Zr)-substituted GGG due to a great deal of Ca-Zr defects introduced in large quantity in order to have a congruent composition. A simple model based on the local dilatation of the lattice around each defect is presented in order to describe the Cr3+ luminescence at any temperature. The influence of Ca-Zr ion pairs on the average Cr3+-->Tm3+ energy transfer is also studied.