Amplification of green emission of Ho³⁺ions in lead silicate glasses by sensitizing with Bi³⁺ions

This investigation is mainly devoted to the studies on enrichment of green emission of Ho³⁺ions in₂glasses containing 1.0 mol% of Ho₂O₃by co-doping with different concentrations of Bi₂O₃(0–9.0 mol%). The optical absorption spectra, photoluminescence spectra, photoluminescence decay, IR and Raman spectral studies on the above mentioned glasses have been performed as a function of Bi₂O₃concentration. The emission spectra of Bi₂O₃free glasses exhibited green and red emissions due to⁵S₂ + ⁵F₄ → ⁵I₈and⁵F₅ → ⁵I₈transitions of Ho³⁺ions, respectively, when excited at 450 nm. The spectra also exhibited NIR emission due to the⁵I₇ → ⁵I₈transition at 2.0 μm. The intensity of green emission is found to be significantly enhanced (nearly three times) when the glasses are mixed with 5.0 mol% of Bi₂O₃. The reason for this enhancement has been identified as being due to the energy transfer from Bi³⁺to Ho³⁺ions. The predominant participation of Bi³⁺ions in modifying positions and due to the de-clustering of Ho³⁺ions are found to be the other reasons. The overall enhancement of emission has further been explained with the help of rate equations. The quenching of luminescence emission observed in the glasses containing more than 5.0 mol% of Bi₂O₃is attributed to the reason that in these glasses the Bi³⁺ions largely participate in the network forming positions and increase the phonon losses. These arguments have been quantitatively explained with the help of IR and Raman spectral studies.