Luminescence of Cr3+ ions in ZnAl2O4 and MgAl2O4 spinels: correlation between experimental spectroscopic studies and crystal field calculations

Details of preparation, spectroscopic and structural studies along with crystal field calculations for two Cr3+ doped spinels MgAl2O4 and ZnAl2O4 are given in the present paper. Both compounds show efficient red emission at about 685 nm, which is due to the 2Eg → 4A2g spin-forbidden transition of Cr3+ ions located at the sites with D3d local symmetry. Analysis of structure of the CrO6 clusters was performed; comparison of the crystal field effects in both compounds revealed that the low-symmetry splitting of the orbital triplet states is more pronounced in ZnAl2O4. Both compounds show potential for applications as red-emitting phosphors.