Thermal, structural and optical properties of un-doped and lanthanide-doped germanate ceramics

In present work, thermal, structural and optical properties of un-doped Li2MgGeO4 and lanthanide - doped Li2MgGeO4:Ln3+ (Ln = Er, Ho) germanate ceramics have been studied. Based on DSC measurements, two reversible phase transitions were verified during heating and cooling process of germanate ceramics. The results obtained from the Rietveld refinement indicate that Li2MgGeO4 ceramics crystallize in monoclinic crystal lattice. Structural aspects were also evidenced by Raman and infrared spectroscopy. Emission investigations indicate that the most intense green bands due to the 4S3/2 → 4I15/2 (Er3+) and 5F4,5S2 → 5I8 (Ho3+) transitions are well overlapped with broad band located near 500 nm. Broad green emission is attributed with the presence of magnesium in ceramic matrix. Based on literature data it can be assigned to F-type centers.