A spectral library for laser-induced fluorescence analysis as a tool for rare earth element identification

Abstract

Abstract. With the recurring interest in rare earth elements (REEs), laser-induced fluorescence (LiF) may provide a powerful tool for their rapid and accurate identification at different stages along their value chain. Applications to natural materials such as minerals and rocks could complement the spectroscopy-based toolkit for innovative, non-invasive exploration technologies. However, the diagnostic assignment of detected emission lines to individual REEs remains challenging because of the complex composition of natural rocks in which they can be found. The resulting mixed spectra and the large amount of data generated demand automated approaches of data evaluation, especially in mapping applications such as drill core scanning. LiF reference data provide the solution for robust REE identification, yet they usually remain in the form of tables of published emission lines. We show that a complete reference spectra library could open manifold options for innovative automated analysis. We present a library of high-resolution LiF reference spectra using the Smithsonian rare earth phosphate standards for electron microprobe analysis. We employ three standard laser wavelengths (325, 442, 532 nm) to record representative spectra in the UV-visible to near-infrared spectral range (340–1080 nm). Excitation at all three laser wavelengths yielded characteristic spectra with distinct REE-related emission lines for EuPO4, TbPO4, DyPO4 and YbPO4. In the other samples, the high-energy excitation at 325 nm caused unspecific, broad-band defect emissions. Here, lower-energy laser excitation is shown to be successful for suppressing non-REE-related emission. At 442 nm excitation, REE reference spectra depict the diagnostic emission lines of PrPO4, SmPO4 and ErPO4. For NdPO4 and HoPO4 the most efficient excitation was achieved with 532 nm. Our results emphasise the possibility of selective REE excitation by changing the excitation wavelength according to the suitable conditions for individual REEs. Our reference spectra provide a database for the transparent and reproducible evaluation of REE-bearing rocks. The LiF spectral library is available at zenodo.org and the registered DOI https://doi.org/10.5281/zenodo.4054606 (Fuchs et al., 2020). Primarily addressing the raw material exploration sector, it aids particularly the development of advanced data processing routines for LiF analysis but can also support further research on the REE luminescence in natural rocks or artificial compounds. It gives access to traceable data for the comparison of emission line positions, emission line intensity ratios and splitting into emission line sub-levels or can be used as reference or training data for automated approaches of component assignment.

Indicator Minerals, Pathfinder Elements, and Portable Analytical Instruments in Mineral Exploration Studies

“…Despite these facts, portable techniques are getting established and producing data with comparable accuracy to those of well-established laboratory-based analytical techniques [155]. Fuchs et al [156] developed a data library consisting of high-resolution spectral information in the visible to near-infrared range (350-1080 nm), which will deal with spectral overlap effects and be useful for the identification of some elements, such as REE.…”

Recognition of multi-component compounds based on occurrence time of secondary crest in the fluorescence lifetime attenuation curve

“…Laser-induced fluorescence (LIF) is a type of detection technology, in which a laser is used to excite the emission of fluorescence of a substance; it is based on the discrimination of the fluorescence signal generated by the interaction between the laser pulse and the medium. Owing to its high sensitivity and good selectivity; it has been widely implemented in the monitoring of industrial waste [1], marine pollution [2][3][4], medical and health industry [5,6], and atmospheric environment [7,8]. With the rapid development technologies of laser, electronics and computer, and the emergence of high-power and shortpulse lasers, Marine laser fluorescence radar monitoring system has been rapidly developed in various countries to detect the distribution of oil and gas in the seabed and oil pollution on the sea surface [9][10][11].…”

Multiphoton Phosphorescence of Simple Ketones by Visible-light Excitation and Its Consideration for Active Sensing in Space

“…Another way in which chemicals and resources have been proposed to be sensed in space is through fluorescent imaging [ 18 – 20 ]. Fluorescence or phosphorescence, where it exists, can be bright and highly indicative of a particular target [ 21 , 22 ], enabling both qualitative and quantitative analysis to be done remotely [ 23 – 25 ].…”