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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 EuPO 4 , TbPO 4 , DyPO 4 and YbPO 4. 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 PrPO 4 , SmPO 4 and ErPO 4. For NdPO 4 and HoPO 4 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 10.5281/zenodo.4054606. 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. [ABSTRACT FROM AUTHOR]

With the recurring interest on rare-earth elements (REE), 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 rocks could complement the spectroscopy-based toolkit for innovative, non-invasive exploration technologies. However, the diagnostic assignment of detected emission lines to individual REE 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 for 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 nm, 442 nm, 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, broadband defect emissions. Here, lower energy laser excitation showed 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 most efficient excitation was achieved with 532 nm. Our results emphasise on 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 transparent and reproducible evaluation of REE-bearing rocks. The LiF spectral library is available at https://zenodo.org/ and the registered DOI: http://doi.org/10.5281/zenodo.4054606 (Fuchs et al., 2020). It gives access to traceable data for manifold further studies on 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. [ABSTRACT FROM AUTHOR]

We present Laser-induced Fluorescence (LIF) spectroscopy of Rare Earth Elements (REEs) in minerals as a noninvasive analysis method that can be applied for drill core scanning in order to acquire valuable information about the REE content in rocks omitting extensive chemical analysis. Due to the REE's exclusive f-orbital electronic transitions sharp lines in emission spectra provide distinct features for REE detection. Those features are characteristic for each individual REE and therefore provide an excellent opportunity for identification. Besides the emission of REEs the optical excitation is characteristic as well. The latter enables selective optical excitation of specific REEs leaving others untouched. Considering both, emission and excitation properties, we are able to develop LIF setups aiming to detect and distinguish REEs in natural samples.According to optical excitation properties of REEs we investigate the respective appropriate excitation energy, sufficient light intensity as well as beam geometry with respect to the surrounding matrix. As light sources we use Lasers, LEDs and Laser diodes of monochromatic light in the UV/VIS region. These are a 325/442 nm HeCd Laser, a 405 nm Laser diode, a 365 nm as well as a 470 nm LED and a 532 nm Nd:YAG Laser. In order to provide a reasonable detection speed we develop linear-light excitation concepts enabling to operate in continuous line scan mode, which can cover the surface of drill cores in one operation. Beam shaping is essentially arranged using spherical and cylindrical lenses. With our LIF setup we primarily investigate apatite containing rock samples from Siilinjärvi-Finland and Namibia as well as artificial Smithsonian REE-phosphate standards for data validation. We detect REE emission in the VIS/IR region using CCD as well as sCMOS cameras. As initial results we can show line scan emission spectra covering a sample surface width of 4 - 6 cm depending on the respective light source. Scanning the same rock sample under different excitation conditions delivers diverse emission features that can be assigned to specific REEs. [ABSTRACT FROM AUTHOR]

With the recently intensified development in key technologies for renewable energy, electric mobility as well as computer and telecommunication systems, the robust detection and characterization of rare earth elements (REE) simultaneously gained in importance. REE identification is essential not only for securing a continuous supply from new or re-evaluated mineral deposits, but also for the future recycling of today's high-tech products and plants. Up to now, hyperspectral absorption as well as laser-induced fluorescence (LIF) spectroscopy have proven to be capable of REE detection in different materials [1, 2]. While absorption spectroscopy has been successfully used for identification of REE-bearing mineral phases in complex natural samples, but still show some ambiguities. In contrast, existing studies in LIF spectroscopy often focus on synthetic crystals and single REE standards. Recently, we could prove the benefit of combining both techniques in the case of REE identification in various minerals [3].Within this contribution, we employ both methods for the qualitative and quantitative characterization of REEs in complex rocks, and discuss their suitability for applications in the mining industry. We present detailed 2D-LIF maps of REE-bearing rock pieces and compare them to hyperspectral absorption images. Validation of these results involves the use of mineral liberation analysis (MLA). By the combination of the aforementioned techniques we are able to identify and locate several REEs (e. g. Nd, Eu, Dy, Sm, Er) precisely within the host rock matrix. Furthermore, we could prove similar pattern between 2D LIF REE emissions, REE absorption and host mineralogy as inferred by MLA mineral distribution. This approach sets the basis for LIF-based mapping as a new technique for non-invasive REE detection. [ABSTRACT FROM AUTHOR]

Innovation in raw material exploration relies on efficient and non-invasive technologies. Spectroscopy based methods have proven great potential to deliver instant and spatially continuous information on the composition of an investigated surface. Several studies successfully applied laser-induced fluorescence (LIF) for rare-earth element (REE) identification in natural rocks. However, the diagnostic assignment of detected emission lines remains a complex task, because of the highly variable composition of natural rocks. It needs a transfer of the profound knowledge from the field of applied physics and synthetic materials to the natural rock material under investigation. The evaluation of measured spectra and robust assignment of REEs requires reference data, yet usually based on tables of published emission lines, while data of complete reference spectra are not available.We present a library of reference spectra for all luminescent rare-earth elements using the Smithsonian rare-earth phosphate standards for electron microprobe analysis. We employ laser-induced fluorescence at three commonly used laser wavelengths (325 nm, 442 nm, 532 nm) to acquire reference spectra for REE phosphate minerals in the visible to near-infrared spectral range (350 – 1080 nm). Excitation at all three laser wavelengths yielded spectra with distinct REE-related emission lines for EuPO4, TbPO4, DyPO4 and YbPO4. Lower energy laser excitation at 442 nm showed successful especially for suppressing non-REE-related broadband defect emission. Resulting REE-reference spectra include those from PrPO4, SmPO4 and ErPO4. For NdPO4 and HoPO4 most efficient excitation was achieved with 532 nm. The diagnostic emission lines of GdPO4 lie outside the detection range and none of the three laser wavelengths was appropriate for TmPO4 excitation.Our results demonstrate the suitability of LIF for REE detection and especially the possibility of selective element excitation. Our reference spectra provide the full spectral information at high resolution (0.13nm) as a basis for an improved evaluation of REE-bearing natural rocks allowing for data analysis of emission line positions, emission line intensity ratios and splitting into emission line sub-levels. The spectral library data support the use of LIF for REE analysis in natural samples and its application in raw material exploration. [ABSTRACT FROM AUTHOR]