Defect regulation and photodarkening suppression in Yb:Y ₂ O ₃ laser ceramics through charge-compensated Zr–Ca co-doping strategy

Sesquioxide ceramics are promising candidates for high-power laser applications, yet achieving high optical quality remains challenging. This is primarily due to rapid grain-boundary mobility during the final stage of sintering and pump-induced photodarkening under high-power excitation, particularly when traditional tetravalent sintering additives (<em>e.g</em>., ZrO₂) are used. Here, about 1:1 (molar) Zr⁴⁺-Ca²⁺ co-doping is introduced to regulate the sintering behaviors of Yb:Y₂O₃ ceramics, yielding dense microstructures with uniform elemental distributions. The charge-compensation enabled by Zr-Ca co-doping suppresses the formation of point defects, thereby significantly mitigating photodarkening. As a result, the optimized 0.02 at.% Zr-Ca co-doped sample delivers a maximum continuous-wave (CW) output power of 20.5 W at 1076 nm with a slope efficiency of 65.4%. These results demonstrate that Zr-Ca co-doping is an effective strategy for fabricating high-performance sesquioxide laser ceramics with improved optical quality and enhanced resistance to pump-induced photodarkening.