Influence of Al declustering on the photoluminescent properties of Pr ^{3 +} ions in PbO-SiO₂ glasses

Pr^{3 +} doped lead alumino silicate glasses with varying concentrations of Al₂O₃ (from 5 to 10 mol%) have been synthesized. The IR and Raman spectral studies of these glasses have indicated that there is a gradual increase in the depolymerization of the glass network with an increase in the concentration of Al₂O₃. The optical absorption, luminescence spectra and fluorescence decay curves of these glasses were recorded at room temperature. The luminescence spectra of these glasses have exhibited the bands due to ³P₀ → ³F₂, ³F₃, ³H₆, ³H_4, ³H₅ transitions. From these spectra, the radiative parameters viz., spontaneous emission probability A, the total emission probability A_T, the radiative lifetime τ, the fluorescent branching ratio β of different transitions that originated from the ³P₀ level of Pr^{3 +} ions have been evaluated. A considerable enhancement in the luminescence emission, especially in the red region corresponding to ³P₀ → ³H₆, ³F₂ transitions has been observed. The increase has been attributed to the possible admixing of wavefunctions of opposite parities and due to the declusterization of Pr ^{3 +} ions by Al^{3 +} ions in the glass network. The branching ratio β has been observed to be the highest for the transition ³P₀ → ³F₂ and it is found to be ∼ 50% for the glass mixed with 10 mol% of Al₂O₃. The CIE color coordinates for three glasses have been evaluated and found to be in the bright red region.