In Er3+-doped CaF2 crystals, strong upconversion processes promote higher-lying emissions while limiting the population of the 4I13/2 level, undermining its 1.5 μm laser potential. In this work, we demonstrate that anion engineering through oxygen incorporation into Er:CaF2 allows manipulation of the erbium emission dynamics, significantly suppressing upconversion losses. Specifically, O2− is introduced as a charge-compensator in place of interstitial Fi− and shown to be favorably paired with Er3+ by first-principles calculations, which yields adjacent vacancy defects that serve as energy sinks for mid-infrared transitions. This structural modification provides an inhibitor for interrupting upconversion pathways and redirecting population to the 4I13/2 level. Moreover, robust 1.5 μm emission is preserved due to the suppressed formation of erbium clusters. These findings highlight the role of anion dopants in the modulation of structure–property relationships, thereby enabling effective tuning of the emission properties of optical materials.
Zhang et al. (Mon,) studied this question.