Impact of the addition of silicon, calcium and magnesium ions on the microstructure and optical properties of chromium-doped polycrystalline aluminium-chromium garnet

The study examined polycrystalline chromium-doped yttrium-aluminium garnet (Cr: YAG), produced by vacuum reaction sintering of aluminium, yttrium and chromium oxides. Magnesium oxide and calcium oxide were used as additives stabilizing Cr4+ ions. It was confirmed that Mg2+ and Ca2+ can serve as charge-compensating ions as well as sintering additives. The effect of content of Ca2+ and Mg2+ ions and the post sintering annealing in air on the microstructure and spectroscopic properties of the materials produced were investigated. The effect of silicon addition on Cr: YAG spectroscopic properties was also determined. The Cr:YAG emission spectra obtained by stimulation with 450 nm radiation varied with annealing conditions. Increasing the temperature or time of air annealing resulted in a gradual increase in the emission level in the range of about 1400 nm, which can be attributed to the change in the degree of oxidation of chromium ions from Cr3+ to Cr4+. These changes were less pronounced in the case of materials obtained with the addition of silicon ions, which indicates the undesirable stabilization of chromium in the third degree of oxidation by silicon.