Effects of synthesis method on cation distribution and optical properties of Co/Cr co-doped MgGa2O4 nanoparticles

• Co2+/Cr3+ co-doped MgGa2O4 nanoparticles were prepared by three different methods.
• The effect of synthesis method on the distribution of the cations was studied by XPS.
• The samples prepared by sol–gel method have the largest inversion degree.
• The synthesis method has also effect on the optical absorption and emission properties.
• Optical properties of the nanoparticles are discussed on the basis of the structural results.

Co2+/Cr3+ co-doped MgGa2O4 nanoparticles were prepared by three different methods (sol–gel, co-precipitation and solid state reaction). The effect of synthesis method on distribution of cations (Ga3+, Mg2+ and Cr3+ ions) was studied using X-ray photoelectron spectroscopy (XPS). These cations occupied octahedral sites as well as tetrahedral sites of the spinel structure in all samples. However, the inversion degree of these samples is greatly influenced by the synthesis method. The Co2+/Cr3+ co-doped MgGa2O4 nanoparticles prepared by the sol–gel method a larger inversion degree than those prepared by other methods. The effect of the synthesis method on absorption spectra and emission spectra was also studied. Samples obtained by sol–gel and co-precipitation methods exhibit broad absorption bands in two wavelength ranges: 300–500 nm and 500–700 nm, while the sample synthesized by solid state reaction only has an absorption peak at 430 nm in the range 300–500 nm. The difference in absorption spectra can be related to the distribution of Co2+ and Cr3+ ions. Emission spectra for samples prepared by sol–gel and co-precipitation methods show a broad emission band peaking at 700 and 680 nm, combining the emission characteristic of octahedral Cr3+ and tetrahedral Co2+ ions.