Investigations on the physical, structural, optical and photoluminescence behavior of Er ³⁺ ions in lithium zinc fluoroborate glass system

Family of lithium zinc fluoroborate glasses with 15ZnF ₂ -10BaO-8Al ₂ O ₃ –12Li ₂ O-(55-x) B ₂ O ₃ -xEr ₂ O ₃ (x = 0.5, 0.7, 1.1, 1.3 and 1.5 mol%) composition were prepared by conventional melt-quench method. The glasses were characterized to study their structural, physical, optical and radiative properties. The amorphous characteristic of glass was noticed in X-Ray Diffraction pattern. A modification in structure was observed as density values increased with Er ₂ O ₃ content. UV–Vis–NIR transitions of Er ³⁺ in the host matrix were identified through absorption spectra. Covalent nature of bonding between Er ³⁺ ions and their surrounding ligands was observed through bonding parameter and Judd-Ofelt parameters. Red shift of the fundamental absorption edge in the absorption spectra and decreasing indirect and direct band gaps with increasing Er ³⁺ concentration jointly confirmed the role of Er ³⁺ ions as network modifier. Hypersensitive transitions of Er ³⁺ ion namely ⁴ I _15/2 → ² H _11/2 & ⁴ I _15/2 → ⁴ G _11/2 were interpreted through their higher oscillator strengths when compared to other transitions. Emission spectra recorded at 980 nm excitation showed a peak corresponding to ⁴ I _13/2 → ⁴ I _15/2 NIR transition of erbium ion. Stimulated emission cross section of Er0.5 sample, gain bandwidth and Figure of Merit were found to be 16.79 × 10 ⁻²¹ cm ² , 1225.83 × 10 ⁻²⁸ cm ³ and 37.36 × 10 ⁻²⁴ cm ² s respectively. Photoluminescence decay curve of Er0.5 sample was well-fitted to single exponential first order function. The experimental decay lifetime τ _exp for the ⁴ I _13/2 level was measured to be 0.34 ms. The wide frequency range of FWHM (1.02–1.67 × 10 ¹³ Hz) and high values of radiative parameters make the glass a suitable candidate as optical amplifier and NIR laser material.