Solid-solution Er:(Sc,Y)2O3 transparent ceramics: Optical spectroscopy , inhomogeneous line broadening, C3i sites and mid-infrared laser operation

Rare-earth-doped transparent sesquioxide laser ceramics enable engineering of their gain bandwidths via solid-solution compositions exhibiting a strong inhomogeneous spectral line broadening. We report on a detailed spectroscopic study and the first mid-infrared laser operation of Erbium-doped yttria-scandia, (ScxY1-x)(2)O-3, ceramics fabricated by vacuum sintering at 1750 degrees C from laser-ablated nanoparticles. The effect of the Sc fraction on the spectral and kinetic properties of Er3+ emission around 2.8 mu m owing to the I-4(11/2) -> I-4(13/2) is revealed. The inhomogeneous spectral line broadening leading to merging of individual Stark sub-levels of Er3+ multiplets is evidenced by low-temperature spectroscopy. An original method of quantifying the distribution of dopant Er-3+ ions over C-2 and C-3i symmetry sites in the cubic bixbyite structure is suggested based on the transition probabilities derived by the Judd-Ofelt theory. In the parent Er:Y2O3 ceramic, the Er3+ ions nearly follow the ideal distribution with 3/4 of ions residing in C-2 sites, and Sc addition skews it in favor of C-3i sites. A continuous-wave Er:(Sc,Y)(2)O-3 ceramic laser generated 312 mW at 2716 nm with a slope efficiency of 18.6 % and a laser threshold of 128 mW.