Energy transfer between Eu3+ ions in calcium diborate glasses

The evolution of the D-5(0) --> F-7(0) emission of Eu3+ ions in calcium dib orate glasses has been analysed using time resolved fluorescence line narro wing measurements in order to give a complete view of the energy transfer p rocesses between these ions. At low concentration (2.5 mol% of Eu2O3) and e xciting within the high energy side of the inhomogeneous F-7(0) --> D-5(0) absorption band, the luminescence spectrum mainly consists of a narrow reso nant peak that repeats the exciting profile, indicating that the migration processes between Eu3+ ions within the D-5(0) level is not important. Howev er, at higher concentrations (5 to 11.5 mol% of Eu2O3) the luminescence spe ctrum contains not only a narrow emission but also a broad band due to ions excited by energy transfer (background fluorescence), which for long times well reproduces the inhomogeneous profile. The temporal evolution of the n arrow band fluorescence and the shape of the background fluorescence have b een analysed using a previously proposed model. The purpose is to understan d the dynamics involved in the energy transfer processes caused by the inte raction between Eu3+ ions and the implications in their luminescence. A ver y good agreement with the experimental results is found taking into account an energy dependent quadrupole-quadrupole (S = 10) non-radiative energy tr ansfer process assisted by a phonon from Eu3+ ions at high crystal held sit es to ions at low crystal field sites. The temperature dependence of the en ergy transfer processes is analysed in the range from 13 to 60 K.