Nd³⁺:Ga-Ge-Sb-S glasses and fibers for luminescence in mid-IR: synthesis, structural characterization and rare earth spectroscopy

With high refractive indices, appropriate solubility of rare earth, low phonon \nenergy and transparency from the visible to 10 µm, a Ga-Ge-Sb-S system allows emission \nfrom Nd3+ ions in the near- and mid-IR spectral ranges. The glass transition temperature, \ndensity, expansion coefficient, and near and mid-IR refractive indexes were measured on bulk \nsamples. Their glass network structures were analyzed by Raman scattering spectrometry, \nNMR of 71Ga and extended X-ray absorption fine structure (EXAFS, K-edge of Ga, Ge, Sb, S \nand Nd). The absorption and emission spectra of neodymium doped sulfide glasses were \nrecorded from the visible to the mid-IR. Excited state lifetimes were measured for several \ntransitions. The lifetimes decrease with the concentration of Nd3+, especially for the 4 \nI13/2 and 4 \nI11/2 levels. The spectroscopic parameters were determined by the Judd-Ofelt method, \nallowing the calculation of cross-section emissions and the evaluation of quantum yields. \nOptical attenuation and emission measurements of fiber were also performed with a broad \n4.7-5.7 µm emission band in the mid-IR.