Er^<3+>ドープアルミネートガラスのアップコンバージョンと局所構造

概要

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Optical properties and structure of Er^<3+> doped 66.7CaO・33.3Al_2O_3 glasses were investigated. Among three Judd-Ofelt intensity parameters Ω_2 and Ω_4 showed large values compared with those of Er^<3+> ions in other oxide glasses, indicating a large transition probability of 650 nm absorption. From the Mossbauer measurement, the coordination number of rare earth ions in this glass was found to be about 7 with low symmetry. The phonon energy was about 800 cm^<-1>, which corresponds to the stretching vibration of AlO_4 groups coupled with the rare earth ion in the glass. The multiphonon decay rate and its energy gap dependence were obtained from the fluorescence lifetime and radiative transition probability calculated for ^4S_<3/2> and ^4F_<9/2> levels. The rate was lower than that in silicate glasses and almost corresponded to the value for the phonon energy of 800 cm^<-1>. The upconversion fluorescence at 550 nm was observed by 650 nm pumping and its excitation spectra were monitored by a tunable DCM dye laser. It was concluded that the observation of green upconversion was possible due to a large transition probability of ^4F_<9/2>←^4I_<15/2> and also to an excited state absorption mechanism from ^4I_<13/2> to ^4F_<5/2> level.
1993-01-01