Fantastic valence impacts of Pr on microstructures and Faraday magneto-optical effects of transparent (Ho,Pr)2O3 ceramics

Abstract Polycrystalline magneto-optical (Ho1-xPrx)2O3 (x = 0.05‒0.2) ceramics were fabricated by vacuum sintering using layered rare-earth hydroxides as the precursors, among which the 5 at.% Pr doped specimen exhibits the highest in-line transmittance of ∼76.1 % at 700 nm (∼94.5 % of the theoretical value of defect-free Ho2O3 single crystal) and the largest Verdet constant of −82 ± 6 rad∙T−1 m−1 at 1064 nm (∼2.3 times that of the commercial Tb3Ga5O12 crystal and ∼1.8 times that of the pure Ho2O3 ceramic). More Pr addition not only leads to a higher thermal decomposition temperature for the precursor but also a decreasing particle size for the oxide. A 5 at.% Pr dopant in Ho2O3 matrix generally exists in the oxidation state of +3, while an increasing Pr concentration up to 10 at.% induces coexisting valences of +3 and +4. The grain growth was suppressed by the present Pr4+ based on interstitial mechanism. The substitution of Pr3+ for Ho3+ is helpful for the rising Verdet constant of the binary ceramic, but Pr4+ has little positive contribution to it.