Investigation on the site occupation of rare-earth ions in CaInO with the fluorescence probe of Eu.

Rare-earth doped CaInO phosphors have been widely investigated due to their excellent luminescent property, but the site occupation of rare-earth ions in CaInO is not very clear and needs to be clarified. Using Eu as a fluorescence probe, such a clarification has been made in this work. 1% and 2% Eu doped CaInO 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 CaInO. 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 Eu embedded in In sites; the other three are attributed to Eu substitution on Ca sites, which show slight distortion. Energy transfers from the B site to the A and C1 sites were observed in the 2% Eu doped CaInO sample. The transitions of Eu ions in the Ca sites make the main contribution to the emission spectra excited at room temperature. These results may provide a guide for optimizing rare-earth doped CaInO phosphors for their application in the solid state lighting field.