Investigation on the site occupation of rare-earth ions in CaIn2O4 with the fluorescence probe of Eu3+

Abstract

Rare-earth doped CaIn₂O₄ phosphors have been widely investigated due to their excellent luminescent property, but the site occupation of rare-earth ions in CaIn₂O₄ is not very clear and needs to be clarified. Using Eu³⁺ as a fluorescence probe, such a clarification has been made in this work. 1% and 2% Eu³⁺ doped CaIn₂O₄ powder samples have been prepared by the sol–gel method. The X-ray diffraction results indicate that the lanthanide doping does not influence the structure of CaIn₂O₄. Site selective excitation at low temperature disclosed five different luminescent centers marked as A, B, C1, C2 and C3. The spectral analysis revealed that the A and B sites belong to Eu³⁺ embedded in In³⁺ sites; the other three are attributed to Eu³⁺ substitution on Ca²⁺ sites, which show slight distortion. Energy transfers from the B site to the A and C1 sites were observed in the 2% Eu³⁺ doped CaIn₂O₄ sample. The transitions of Eu³⁺ ions in the Ca²⁺ sites make the main contribution to the emission spectra excited at room temperature. These results may provide a guide for optimizing rare-earth doped CaIn₂O₄ phosphors for their application in the solid state lighting field.