Fabrication and optical properties of transparent fine-grained Zn_1.1Ga_1.8Ge_0.1O₄ and Ni²⁺ (or Cr³⁺)-doped Zn_1.1Ga_1.8Ge_0.1O₄ spinel ceramics

For the first time, a Zn1.1Ga1.8Ge0.1O4 transparent spinel ceramic has been fully densified by spark plasma sin-tering. XRD measurements show that this ceramic is composed of a pure cubic spinel phase. SEM analysis revealed a homogeneous and dense microstructure with the average grain size being 200 +/- 100 nm. The transmittance of these fine-grained ceramics reached 70 % in the visible range and is very close to 80 % at 2 mu m, thus close to the Tmax value deduced from the measurement of the refractive index. The ceramics exhibit excellent mechanical properties with a Young modulus of 222 GPa, a Vickers hardness of 14.25 GPa and a thermal conductivity of 7.3 W.m(-1). K-1. By doping with Cr3+ ions, transparent Zn1.1Ga1.8Ge0.1O4 ceramics present both a red luminescence and a long-lasting afterglow during several minutes. Moreover, a near infrared broadband emission at 1.3 mu m is also achieved with Ni2+ ions.