Ce3+ and Eu2+ luminescence in calcium and strontium aluminates

Abstract

Compound CaAl4O7 (CA4), SrAl4O7 (SA4), CaAl12O19 (CA12) and SrAl12O19 (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce3+ and Eu2+ ions. The luminescence properties of Ce3+ and Eu2+ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu2+ ions have been accurately predicted from those of Ce3+ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce3+ and Eu2+ at different Ca2+, Sr2+ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce3+ and Eu2+ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.