Mechanistic insights for regulating the site occupancy, valence states and optical transitions of Mn ions in yttrium-aluminum garnets via codoping

Abstract

The site-dependent photoluminescence of activators can be regulated by the sintering atmosphere, coexistence conditions, and especially cation codoping, which have been intensively studied for design and optimization of optical functional materials. Here, first-principles calculations are performed to determine the regulation of the site occupancy, valence states and optical transitions of Mn activators via codoping in yttrium aluminum garnets (YAGs), which contain three different cation sites. Without any codopants, Mn_oct³⁺ dominates in defect concentration and photoluminescence, which can hardly be tuned by the sintering atmosphere or coexistence conditions of YAGs with other competing compounds. With the low formation energy of Ca²⁺, Be²⁺, Mg²⁺, and Sr²⁺ codopants and in an oxidation sintering atmosphere, the Fermi energy is lowered and the concentration and luminescence of Mn_oct⁴⁺ are enhanced. Na⁺ and Li⁺ codopants with relatively high formation energy have little influence on tuning the Fermi energy. Then with the low formation energy of Ti⁴⁺, Si⁴⁺ codopants and in a reducing sintering atmosphere, the Fermi energy is lifted and the luminescence of Mn_dod²⁺ and Mn_oct²⁺ is enhanced as a result of increased concentrations. The proposed first-principles scheme, with general applicability and encouraging predictive power, provides an effective approach for elucidating the effects of codoping impurities on the design and optimization of optical materials.