Assessment of conversion efficiency of Cr 4+ ions by aliovalent cation additives in Cr: YAG ceramic for edge cladding

Abstract 0.25at.% Cr: YAG ceramics were successfully fabricated as the edge cladding of Yb: YAG transparent ceramic slabs through vacuum sintering of co‐precipitated powders, using oxide additives to introduce different cations. The effects of various cation additives (Si 4+ , Ca 2+ , and Si 4+ + Ca 2+ ) on the conversion efficiency of Cr 4+ ions and optical characteristics of the Cr: YAG edge cladding were investigated. Measurements of the absorption spectra of the Cr: YAG ceramics without any additives revealed 2 absorption bands centered at 430 nm and 600 nm, which imparted the sample with a green color. The introduction of only Si 4+ ‐bearing additive did not promote the transition of Cr ions from the 3+ to 4+ state. Theoretical analysis and experimentation revealed that the addition of CaO not only enhanced the microstructure and improved the transmittance of the Cr: YAG ceramic, but also introduced vacancies that assisted in the formation of Cr 4+ ions. It was determined that CaO has the same effect on the conversion efficiency of Cr 4+ ions whether it is added as a single additive or in combination with SiO 2 . The underlying mechanisms by which these aliovalent cation additives influence the formation of Cr 4+ ions and affect optical properties are discussed in detail. High quality composite ceramics with Yb: YAG transparent ceramic slabs and dark brown‐colored Cr 4+ : YAG ceramic edge cladding were achieved through the addition of 0.05 wt.% CaO to the edge cladding, with no interfacial effects between the 2 regions being observed.