Photoluminescence properties and energy transfer in γ-irradiated Dy3+, Eu3+-codoped fluoroaluminoborate glasses

The photoluminescence (PL) properties of singly doped (Dy3+) and codoped (Dy3+, Eu3+) fluoroaluminoborate glasses, with an emphasis on the white light generation, are studied. The gamma-irradiation led to the formation of defects in Dy3+-doped glasses and photoreduction of Eu3+ to Eu2+ in codoped (Dy3+, Eu3+) glasses. The electron paramagnetic resonance spectra confirm the presence of divalent europium ions and defects in Dy3+, Dy3+-Eu3+-doped glasses. The FTIR spectra mainly establish the compaction of glass network due to gamma-irradiation. From the PL spectra, the intensity ratio of Dy3+ emission bands yellow to blue (F-4(9/2)-H-6(13/2)/F-4(9/2)-H-6(15/2)) defines the site symmetry, covalency, and feasibility of extracting white light. The existence of an energy transfer (ET) from Dy3+ to Eu3+ ions are established due to the decrease in intensity of Dy3+ peaks with an increase of Eu2O3 content. Moreover, the non-exponential nature of decay curves was well fitted with the generalization of Yokota-Tanimoto model for electric dipole-quadrupole (S = 8) interaction that is responsible for ET process from sensitizer (Dy3+) to activator (Eu3+).