Transparent Cr4+-doped YAG ceramics for tunable lasers

Transparent Cr4+:YAG (Y3Al5O12) ceramics doped with Ca and Mg as counterions and SiO2 as a sintering aid were fabricated by a solid-state reaction method using high-purity powders of Al2O3, Y2O3, and Cr2O3. The mixed powder compacts were sintered at 1750 degrees C for 10 h in oxygen, or 1750 degrees C for 10 h under vacuum, and then annealed at 1400 degrees C for 10 h in oxygen, Cr-doped YAG ceramics sintered in oxygen had a brown color and characteristic absorption by Cr4+ ions, whereas these YAG ceramics sintered under different conditions (vacuum + oxygen) had a green color and absorption at similar to 590 and 430 nm by Cr3+ ions. The absorption behavior of YAG ceramics sintered in oxygen was almost equivalent to that of Cr4+:YAG single crystals fabricated by the Czochralski method.