Luminescence properties and quantum efficiency of the Eu-doped borate glasses

The luminescence and radiative properties of the Eu-doped borate glasses with Li2B4O7, CaB4O7, and LiCaBO3 basic compositions have been investigated and analysed. The borate glasses of high chemical purity and optical quality, doped with Eu2O3 in amounts of 0.5 and 1.0 mol. % were obtained from the corresponding polycrystalline compounds in the air atmosphere using standard glass synthesis technology. The spectroscopic and radiative properties of obtained Eu-doped glasses were studied using electron paramagnetic resonance (EPR), optical absorption, photoluminescence (excitation and emission spectra, decay kinetics) techniques, and modified Judd-Ofelt analysis. The photoluminescence spectra of the Eu-doped borate glasses reveal intense emission bands, which correspond to the 5D0 → 7FJ (J = 0 ÷ 4) transitions of Eu3+ ions. The observed luminescence decay curves are satisfactory described in the framework of single exponential approximation with lifetimes, which lie in the 2.04 ÷ 2.26 ms range. The Judd-Ofelt intensity parameters (Ωλ) for Eu3+ centres in the investigated glasses were calculated from their luminescence emission spectra. Radiative lifetimes and internal quantum efficiencies were estimated for observed emission transitions of the Eu3+ centres in the investigated glasses. External quantum yield of luminescence was measured experimentally via an absolute method. The high calculated internal quantum efficiency (∼50%) and relatively high measured external quantum yield (∼11%) of the Eu3+ luminescence show that the Li2B4O7:Eu, CaB4O7:Eu, and LiCaBO3:Eu glasses belong to perspective luminescent materials.