Red light generation through the lead boro−telluro−phosphate glasses activated by Eu3+ ions

• Bonding parameter and nephelauxetic ratio reveals predominant covalent nature.
• Higher magnitude of Ω2 indicates the lower symmetry around the Eu3+ ions.
• LBTPE glass with 1 wt% of Eu yields higher σPE and βR values for 5D0 → 7F2 emission.
• CIE colour coordinates support red emission of the XLBTPE glasses.

Lead boro−telluro−phosphate glasses containing 0.05 to 2.0 wt% of Eu3+ ions were prepared through melt quenching technique. Structural characteristics of title glasses were identified through XRD, FTIR and Raman studies. The optical properties of the prepared glasses were studied using UV–Vis–NIR absorption and photoluminescence spectra. From the resultant spectra, we have obtained the bonding parameters (δ), nephelauxetic ratio (β), direct and indirect band gaps and Urbach energy (ΔE) values. A deep red luminescence due to 5D0 → 7F2 transition of Eu3+ ions could be observed for the title glasses. The local site symmetry around the Eu3+ ions and the degree of Eu3+−O2− covalence were assessed from the luminescence intensity ratio of 5D0 → 7F2/5D0 → 7F1 transitions. Judd−Ofelt intensity parameters, calculated from the luminescence spectra, were used to estimate the radiative parameters like transition probability (A), branching ratio (βexp, βcal) and stimulated emission cross-section (σPE) concerning the 5D0 → 7FJ (J = 0, 1, 2, 3 and 4) transitions. The important laser parameters, gain bandwidth and optical gain are also estimated. The decay curves associated with the transition from 5D0 state was found to be single-exponential at all Eu3+ ion concentrations. CIE colour coordinates and colour purity of the prepared glasses were estimated from the CIE chromaticity diagram.

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