Investigations on vacuum sintered ytterbium-doped YAG ceramic: a laser–host material

Abstract

Laser–host ceramics are a new class of materials and have proved to be a good alternative to the single-crystals. They can be produced in large size with higher concentration of activator ions having more homogeneity which is difficult to achieve with the conventional single-crystal growth technology. Ytterbium (Yb)-doped yttrium aluminium garnet (YAG) is a very attractive laser–host material because of its broad emission band, low quantum defect, no excited state absorption or up-conversion loss and wide range of tunability. In the present work, 10 atm% Yb-doped YAG transparent ceramic was fabricated using nano-powder technology and vacuum sintering. Single-phase nano-powders of Yb:YAG were synthesized by a co-precipitation method and thereafter sintered under vacuum at \(1750^{\circ }\hbox {C}\) for 5 h. The as-sintered ceramic samples are of dark greenish colour which is attributed to the reduction of \(\hbox {Yb}^{3+}\) to \(\hbox {Yb}^{2+}\) during vacuum sintering. However, after annealing in air at \(1350^{\circ }\hbox {C}\) for 8 h they retain their natural colour attributed to the transformations from \(\hbox {Yb}^{2+}\) to \(\hbox {Yb}^{3+}\). The transmission spectra of the as-sintered polished ceramics show the presence of broad absorption bands near 250, 380, 480 and 630 nm due to the electronic transitions in the \(\hbox {Yb}^{2+}\) ion. These bands disappear after annealing in air. The well-established bands due to transitions in \(\hbox {Yb}^{3+}\) were observed between 900 and 1000 nm.