Optical Investigation of Eu3+ Doped Bi12GeO20 (BGO) Crystals

The spectroscopic properties of Eu3+ doped Bi12GeO20 (BGO) sillenite bulk crystals that were grown by the low-thermal-gradient Czochralski technique (LTG Cz) were investigated. The absorption spectra and the emission properties have been measured at room temperature (300 K) and at 10 K. Luminescence was observed both due to the direct Eu3+ ion excitation, as well as under UV excitation due to the energy transfer between Bi3+ and Eu3+ ions. Bi3+ -> Eu3+ energy transfer mechanisms in Eu3+:BGO doped host were investigated. The Omega(lambda) parameters, as well as radiative lifetimes, were calculated based upon the Judd-Ofelt formalism. The branching ratios and electric dipole transition probabilities were also determined, based upon the obtained experimental results. Luminescence has been observed from the D-5(0,1,2) levels of Eu3+, with emissions from the D-5(0) level being the strongest. The strongest observed luminescence band corresponds to the D-5(0) -> F-7(0) transition at 578.7 nm. Reasons for the strong presence of the theoretically forbidden D-5(0) -> F-7(0) emission were investigated.