Concentration-dependent studies of Nd³⁺ -doped zinc phosphate glasses for NIR photoluminescence at 1.05 μm

Nd³⁺ -doped lead-free zinc phosphate glasses with the chemical compositions (60-x) NH₄ H₂ PO₄  + 20ZnO + 10BaF₂  + 10NaF + xNd₂ O₃ (where x = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) were prepared using a melt quenching technique. Vibrational bands were assigned and clearly elucidated by Raman spectral profiles for all the glass samples. Judd-Ofelt (J-O) intensity parameters (Ω_λ : λ = 2, 4, 6) were obtained from the spectral intensities of different absorption bands of Nd³⁺ ions. Radiative properties such as radiative transition probabilities (A_R ), radiative lifetimes (τ_R ) and branching ratios (β_R ) for different excited states were calculated using J-O parameters. The near infrared (NIR) photoluminescence spectra exhibited three emission bands (⁴ F_3/2 level to ⁴ I_13/2 , ⁴ I_11/2 and ⁴ I_9/2 states) for all the concentrations of Nd³⁺ ions. Various luminescence properties were studied by varying the Nd³⁺ concentration for the three spectral profiles. Fluorescence decay curves of the ⁴ F_3/2 level were recorded. The energy transfer mechanism that leads to quenching of the ⁴ F_3/2 state lifetimes was discussed at higher concentration of Nd³⁺ ions. These glasses are suggested as suitable hosts to produce efficient lasing action in NIR region at 1.05 μm.