Effect of hot isostatic pressing on optical properties of YAG:Cr ceramics with different stoichiometry

In this work, YAG:Cr nanopowders were synthesized by the chemical precipitation method. The nominal compositions of the samples varied in stoichiometry. Within the composition range of 0.6032 ≥ [Y 2 O 3 ]/([Al 2 O 3 ] + [Cr 2 O 3 ]) ≥ 0.5936, the lattice parameter of the YAG:Cr phase ranged from 12.01247 Å to 12.00956 Å, with no secondary phases detected by X‐ray diffraction. The effects of hot isostatic pressing (HIP) at 1700°C and 200 MPa, on the optical properties of YAG:Cr 3 ⁺/YAG:Cr⁴⁺ ceramics were investigated as functions of composition and preliminary vacuum sintering temperature ( T sint ). CaO and MgO were used as sintering additives. It was demonstrated that HIP post‐processing of stoichiometric YAG:Cr 3 ⁺ samples ([Y 2 O 3 ]/([Al 2 O 3 ] + [Cr 2 O 3 ]) = 0.6) reduces the concentration of light‐scattering centers and increases light transmittance, regardless of T sint within the range of 1775°C to 1850°C. Notably, light transmittance at 1100 nm was enhanced up to 84%, approaching the theoretical limit. Furthermore, enrichment of the YAG:Cr 3 ⁺ composition with either aluminum or yttrium oxide was found to narrow the T sint range over which HIP improves the ceramics’ light transmittance. A decrease in transmittance between 200 and 1100 nm after HIP was observed in samples with excess aluminum oxide ([Y 2 O 3 ]/([Al 2 O 3 ] + [Cr 2 O 3 ]) = 0.5936) and in those with excess yttrium oxide ([Y 2 O 3 ]/([Al 2 O 3 ] + [Cr 2 O 3 ]) = 0.6032). After annealing in air at 1500°C, conversion of Cr 3 ⁺ to Cr⁴⁺ ions was detected in all samples, regardless of composition. Moreover, HIP post‐processing of stoichiometric ceramics increased the Cr 3 ⁺ → Cr⁴⁺ conversion by approximately 1.2 times.