The Si 3N 4 and Ge 3N 4 are important structural ceramics with many applications because of their attractive high temperature and oxidation resistant properties. The high-pressure and high-temperature spinel phases of these two materials were noticed to have wide, direct electronic band gaps. Other single and double spinel nitrides formed from IVA and IVB group elements have also attracted much attention. Present research focuses on selecting a special substance with promising optical properties and stability besides the attractive electronic properties. The formation energies of spinel nitrides are calculated and stabilities of a group of spinel nitrides are discussed, the structural and electronic properties of them are investigated in detail. By random phase approximation (RPA), the optical properties of spinel nitrides are researched. We obtain that γ-SiGe 2N 4 has some promising properties with potential technological applications from various aspects. The band transitions which contribute most to the peak of ε 2 have been identified. An assumption is proposed to raise the peak of ε 2.