Infrared Emission Properties of Ni²⁺ Ions Doped MgCr₂O₄ Materials

It is important to develop high emissivity infrared radiation materials for energy saving in high-temperature furnaces. In this work, Ni²⁺-doped MgCr₂O₄ materials were prepared by a high-temperature solid-phase reaction process. The effect of Ni²⁺ doping content on the infrared radiation properties of MgCr₂O₄ materials was investigated, and the mechanism of emissivity enhancement of MgCr₂O₄ materials was explored. The results show that Ni²⁺ ions can be doped into the lattice of MgCr₂O₄ materials, and the prepared Mg_1–xNi_xCr₂O₄ (0.1≤x≤0.5) materials produce the lattice distortion and a small amount of Ni²⁺ valence state transformation. Also, the concentration of oxygen vacancies increases,the forbidden band width decreases with the increase of Ni²⁺ doping, thus improving the emissivity of the prepared materials in the near–mid-infrared band. The material with x of 0.5 (Mg_0.5Ni_0.5Cr₂O₄) has an average emissivity of 0.88 in the near infrared ref bands (i.e.,0.8–2.5 μm), which is 167% greater than that of the undoped specimens. Ni²⁺ ions doping enhances the lattice vibration absorption, free carrier absorption and impurity energy level absorption, and improves the infrared emissivity of MgCr₂O₄ materials in the near–mid-infrared band.