Near-Infrared Optical Characteristics of Chalcogenide-Bound Nd³⁺ Molecules and Clusters

Abstract

The optical properties of the nanoscale neodymium ceramic cluster (THF)8Nd8O2Se2(SePh)16 (Nd8) and molecular (DME)2Nd(SC6F5)3 (Nd1) were studied by optical absorption, photoluminescence, and time-resolved spectroscopy. Both complexes exhibited emission characteristic of solid-state materials with bands centered at 927, 1078, 1360, and 1843 nm for Nd8 and 897, 1071, 1347, and 1824 nm for Nd1. The observed red-shift in the absorption and emission bands of Nd8 is attributed to the increased covalency and nephelauxetic effect. Using the calculated radiative decay time, the quantum efficiency of the 4F3/2 → 4I11/2 transition is calculated to be 16% in Nd8 and 9% in Nd1 with corresponding stimulated emission cross sections of 3.04 × 10-20 cm2 in Nd8 and 1.61 × 10-20 cm2 in Nd1 that are comparable to those of solid-state inorganic systems. This efficiency is the highest reported value for “molecular” neodymium compounds. This finding, along with the novel 1.8 μm emission, is attributed to the absence of direct Nd3+ coordination with fluorescence quenching vibrational groups such as hydrocarbon or hydroxide groups. The direct coordination of S, Se, and F accounts for the improved fluorescence spectral properties, because these heavy anions facilitate a low phonon energy host environment for neodymium. Monte Carlo simulation permitted analysis of energy transfer processes to show the primary source of fluorescence quenching. Cross relaxation is responsible for the quenching of the 4F3/2 → 4I15/2 emission whereas excitation migration quenches the 4F3/2 → 4I9/2 emission. These processes are mediated by a dipole−dipole interaction for Nd8 and a quadrupole−quadrupole interaction for Nd1.

Hyperspectral REE (Rare Earth Element) Mapping of Outcrops—Applications for Neodymium Detection

“…The main differences between the chemical bonds of the Nd 3+ in monazite and in the bastnaesite solid solution series is the presence of a fluorine atom in the bastnaesites series. It is broadly assumed that the absorption features for REEs can be explained by electronic field transitions [5,21,22] in the 4f-orbitals. The 4f-orbitals are shielded by the 5s² and 5p 6 orbitals.…”

“…In both example spectra, the absorption bands at ~580 nm, ~740 nm, ~800 nm, and ~870 are resolved. These bands are attributed to neodymium based on the publications of [5,16,17,[20][21][22]. Figure 1.…”

“…Two reference spectra for monazite (a neodymium-bearing mineral) and a monazite-rich rock sample (a calcitic carbonatite from the Fen complex). The key spectral characteristic absorption bands in the VNIR range that are associated with neodymium [5,16,17,[20][21][22]. The graph is modified after Boesche et al 2014 [23].…”

2.1 μm emission of Tm3+/Ho3+ - doped antimony-silicate glasses for active optical fibre

“…The total probability of energy transfer in each case is directly dependent on the overlap integral of the spectra, and it is inversely proportional to the average distance between the interacting ions [19].…”

Optical Amplifiers from Rare-Earth Co-Doped Glass Waveguides

“…Also, Ω 2 is strongly dependent on the hypersensitive transitions. Hypersensitivity is related to the covalency through nephelauxetic effect and affects the polarizability of the ligands around the rare earth ions (Kumar et al, 2007). Higher ligand polarizability results in a larger overlap between rare earth ions and ligands orbital, i.e., higher degree of covalency between rare earth ions and the ligands.…”