LOCAL-STRUCTURE AROUND RARE-EARTH IONS IN INDIUM-BASED AND LEAD-BASED FLUORIDE GLASSES WITH HIGH UP-CONVERSION EFFICIENCY

Er3+-doped fluoride glasses containing a large amount of In and Pb revealed strong upconversion fluorescences. In order to clarify the correlation between the upconversion fluorescence and the local structure around rare-earth ions, fluorescence and Mossbauer spectroscopy of Eu-151(+3)-doped glasses were investigated. From the measurement of phonon sideband of Eu3+, it was found that the lower phonon energy, h-omegaBAR, generated the stronger upconversion fluorescence, and also this h-omegaBAR was smaller than the IR-active maximum phonon energy of glass matrix. It can be explained that h-omegaBAR corresponds to the local vibration including rare-earth (RE) ions, i.e. Ln-F-M (Ln: RE; M: Zr, Al and In) vibration.