Enhanced near-infrared luminescence at 1.07 μm of Nd3+ doped PbCl2–Li2B4O7 glasses for solid state laser and optical fiber amplifier applications

Abstract

Nd3+ doped PbCl2–Li2B4O7 glasses have been synthesized using melt quenching technique. XRD spectra reveals the signature of non-crystalline behavior of synthesized glasses. DSC studies reveal glass transition temperature and thermal stability parameter (ΔT) exhibit composition dependent trends and ΔT is as high as 114 °C. UV–Vis spectra contain eleven well-defined absorption peaks with five intense absorption bands centered at 527, 586, 750, 806 and 876 nm which are assigned to transitions from 4I9/2 → 4G7/2, [4G5/2,2G7/2], [4F7/2, 4S3/2], [4F5/2, 2H9/2] and 4F3/2 respectively. The maximum absorption cross section 1.139×10−20 cm2 of 806 nm pump level transition 4I9/2 → [4F5/2, 2H9/2] is comparable with maximum absorption cross section 1.149×10−20 cm2 of 586 nm hypersensitive transition 4I9/2 → [4G5/2, 2G7/2]. Near infrared emission spectra exhibit very high emission intensity at 1070 nm for 4F3/2 → 4I11/2 transition along with two dominant emission bands at 904 and 1340 nm corresponding to 4F3/2 → 4I9/2 and 4F3/2 → 4I13/2 transitions. This high absorption and emission intensities are attributed to high degree of covalent environment of ligands surrounding Nd3+ ions. Bonding parameter, δ increase with Nd2O3 content which suggests dominance of covalency between Nd3+ ion and ligands. 11B MAS NMR studies reveal that, the addition of Nd2O3 to Li2B4O7 converts diborate units into chain-like network structures such as charged trigonal borate units which is further supported by FTIR study. Two photon absorption coefficient shows linear relationship with optical band gap energy. Hence Nd3+ doped PbCl2–Li2B4O7 glasses with superior absorption and emission properties are found to be potential candidates for near-infrared solid state laser and optical fiber amplifier applications.