<p>The influence of the content and ratio of MgO and CaO sintering additives on the optical properties of YAG:Cr³⁺ and YAG:Cr⁴⁺ ceramic materials was investigated. All samples showed high transparency at 1100 nm (more than 80%). However, in the approx. 340 nm region, the light transmittance values of the samples decreased with increasing amounts of Ca²⁺ or Mg²⁺ ions. The most intense absorption in the range of 750 – 1100 nm after annealing in air was observed in the samples containing the highest value of sintering additives. The absorption of Cr⁴⁺ cations increased with the increase of Ca/Mg content. The optimum CaO content among the investigated samples was 0.12 wt.%. Above this value, additional absorption was observed due to the formation of microdefects. The data obtained by scanning electron microscopy showed that the ceramic samples had a granular structure with grain size ranging from 1 to 10 μm. There were no significant differences in the microstructure depending on the content and type of sintering additives.</p>