Investigation on the site occupation of rare-earth ions in CaIn2O4 with the fluorescence probe of Eu3+
Rare-earths 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 need to be clarified. Using Eu3+ as a fluorescence probe, the 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, A and B sites belong to Eu3+ embedded in In3+ sites, the other three are attributed to the Eu3+ substitution on the Ca2+ sites which have slight distortion. And the Eu3+ is apt to occupy the Ca2+ site first at low doing concentration. The energy transfers from B to A and C1 sites has been observed in the 2 % Eu3+ doped CaIn2O4 sample. The transitions of Eu3+ ions in Ca2+ site have main contribution to the emission spectra excited at room temperature. These results may provide a guide for optimizing rare-earths doped CaIn2O4 phosphors for their application in the solid state lighting field.