One of the most important applications of the oxide crystals doped with Co²⁺ is passive Q-switching of solid-state lasers operating in the near-infrared region of 1.3-1.6 µm. Passive Q-switches generate high power laser pulses without the use of electro-optic Q-switches, which results in reducing the package size and eliminating high-voltage powder supply. Co²⁺-doped magnesium aluminate (Co²⁺: MgAl₂O₄)  crystal is used as a media for Q-switch of e.g. 1.32 µm and 1.44 µm Nd:YAG lasers, 1.32 µm iodine lasers and  1.54 µm erbium glass lasers. Due to relatively lower costs, faster and easier preparation by ceramic technology it would be interesting to use transparent polycrystalline Co²⁺: MgAl₂O₄ instead of  single crystals.

In this work a series of Co-doped MgAl₂O₄ powders (0.1at.% to 4at.%) and undoped MgAl₂O₄ powders were prepared by co-precipitation and calcination. Precursors obtained after precipitation and calcined powders were examined by XRD and SEM. The powders were sintered by vacuum sintering and hot pressing (HP).  In the second case LiF was used as sintering aid. Both ceramics were of density close to theoretical, but only HP-made were transparent. As found, the main reason of light scattering, as proved by XRD and SEM, were presence of residual porosity and nanograins of cobalt oxide (in the case of higher cobalt content) on spinel grain boundaries. 

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