Optical spectroscopy of Li2B4O7, CaB4O7 and LiCaBO3 borate glasses doped with europium

Abstract

We have investigated the optical properties (optical absorption, photoluminescence emission and excitation spectra, and luminescence kinetics) of a series of Eu-doped glasses with the compositions Li2B4O7, CaB4O7 and LiCaBO3. Li2B4O7:Eu, CaB4O7:Eu and LiCaBO3:Eu glasses of high chemical purity and optical quality have been obtained from the corresponding polycrystalline compounds in the air atmosphere, using a standard glass technology. The Eu impurity has been introduced into the borate compounds in the form of Eu2O3 oxide in the amounts of 0.5 and 1.0 mol. %. On the basis of electron paramagnetic resonance and optical spectroscopy data we have shown that the impurity is incorporated into the glass network exclusively as Eu3+ (4f6, 7F0) ions. We have identified all 4f-4f transitions of the Eu3+ centres observed in the optical absorption and luminescence spectra. The most intense emission band of Eu3+ peaked about at 611 nm (the 5D0 → 7F2 transition) is characterized by a single exponential decay, with typical lifetimes that depend on the basic glass composition and the local structure of the luminescence centres Eu3+. The peculiarities of the electron and local structures of the Eu centres in the Li2B4O7, CaB4O7 and LiCaBO3 glasses have been discussed and compared with the reference data for Eu-doped borate single crystals and polycrystalline compounds with the similar chemical compositions, as well as with other borate glasses.