RESUMEN
Research on lithium compounds has attracted much attention nowadays. However, to elucidate the precise structure of lithium compounds is a challenge, especially when considering the small ions that may be transferred between the interstitial voids. Here, the discovery of reduced local symmetry (symmetry breaking) in small domains of Li2SrSiO4 is reported by employing Eu3+ as a spectroscopic probe, for which X-ray, neutron, and electron diffraction have confirmed the average long-range structure with the space group P3121. However, luminescence shows a lower local symmetry, as confirmed by the extended X-ray absorption fine structure. By considering the reduced symmetry of the local structure, this work opens the door to a new class of understanding of the properties of materials.
RESUMEN
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.
RESUMEN
The site-selective spectra and decay curves at 20 K of Eu3+ ions doped KGd2F7 were measured to study the local environment of the Eu3+ sites. The experimental results show that Eu3+ ions occupy three types of sites in the KGd2F7 host. And Eu3+ ions in different types of sites exhibit quite distinct emission spectra and have remarkably different 5D0 level decay lifetimes. Based on the intensity ratio of 5D0--> 7F2,1 transitions of Eu3+ and the 5D0 decay lifetimes in different types of sites, the correlation between the luminescent properties and the site symmetry is discussed.