Deep eutectic solvents
are a new class of green solvents that are
being explored as an alternative for used nuclear fuel and critical
material recycling. However, there is a paucity of knowledge regarding
metal behavior in them. This paper explores the underlying chemistry
of rare-earth elements in choline chloride-based deep eutectic solvents
by using a multi-technique spectroscopic methodology. Results show
that speciation is highly dependent on the choice of the hydrogen-bond
donor. Collected EXAFS data showed Ln
3+
coordination with
ethylene glycol and urea in their respective solvents and coordination
with chloride in the lactic acid system. Generalized coordination
environments were determined to be [LnL
4–5
], [LnL
7–10
], and [LnL
5–6
] in the ethylene
glycol, urea, and lactic acid systems, respectively. Collected UV/vis
spectra for Nd
3+
and Er
3+
showed variations
with changing solvents, showing that Ln–Cl interactions do
not dominate in these systems. Luminescence studies were consistent,
showing varying emission spectra with varying solvent systems. The
shortest luminescent lifetimes were observed in the choline chloride–ethylene
glycol deep eutectic solvent, suggesting coordination through O–H
groups. Combining all collected data allowed Eu
3+
coordination
geometries to be assigned.
Increased absorption of optical materials arising from exposure to ionizing radiation must be accounted for to accurately analyze laser-induced breakdown spectroscopy (LIBS) data retrieved from high-radiation environments. We evaluate this effect on two examples that mimic the diagnostics placed within novel nuclear reactor designs. The analysis is performed on LIBS data measured with 1% Xe gas in an ambient He environment and 1% Eu in a molten LiCl-KCl matrix, along with the measured optical absorption from the gamma- and neutron-irradiated low-OH fused silica and sapphire glasses. Significant changes in the number of laser shots required to reach a 3σ detection level are observed for the Eu data, increasing by two orders of magnitude after exposure to a 1.7 × 1017 n/cm2 neutron fluence. For all cases examined, the spectral dependence of absorption results in the introduction of systematic errors. Moreover, if lines from different spectral regions are used to create Boltzmann plots, this attenuation leads to statistically significant changes in the temperatures calculated from the Xe II lines and Eu II lines, lowering them from 8000 ± 610 K to 6900 ± 810 K and from 15,800 ± 400 K to 7200 ± 800 K, respectively, for exposure to the 1.7 × 1017 n/cm2 fluence. The temperature range required for a 95% confidence interval for the calculated temperature is also broadened. In the case of measuring the Xe spectrum, these effects may be mitigated using only the longer-wavelength spectral region, where radiation attenuation is relatively small, or through analysis using the iterative Saha–Boltzmann method.
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