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

Abstract

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 ≥ [Y2O3]/([Al2O3] + [Cr2O3]) ≥ 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:Cr3⁺/YAG:Cr⁴⁺ ceramics were investigated as functions of composition and preliminary vacuum sintering temperature (Tsint). CaO and MgO were used as sintering additives. It was demonstrated that HIP post-processing of stoichiometric YAG:Cr3⁺ samples ([Y2O3]/([Al2O3] + [Cr2O3]) = 0.6) reduces the concentration of light-scattering centers and increases light transmittance, regardless of Tsint 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:Cr3⁺ composition with either aluminum or yttrium oxide was found to narrow the Tsint 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 ([Y2O3]/([Al2O3] + [Cr2O3]) = 0.5936) and in those with excess yttrium oxide ([Y2O3]/([Al2O3] + [Cr2O3]) = 0.6032). After annealing in air at 1500°C, conversion of Cr3⁺ to Cr⁴⁺ ions was detected in all samples, regardless of composition. Moreover, HIP post-processing of stoichiometric ceramics increased the Cr3⁺ → Cr⁴⁺ conversion by approximately 1.2 times.