Fluorescence of trivalent neodymium in various materials excited by a 785 nm laser

Abstract

The nature of the fluorescence in the frequency-shift range of 1000-2500 cm -1 observed in the Raman spectra of many minerals when excited by a 785 nm laser has been investigated. Among the trivalent rare earths only Nd 3+ has the combination of a good ionic-radius match to substitute for Ca 2+ and an arrangement of energy levels to produce fluorescence in the frequency-shift range of interest. Raman/ fluorescence spectra of six calcium-based minerals, namely fluorite, calcite, powellite, scheelite, apatite, and grossular/tsavorite, have been obtained at both room temperature and liquid-nitrogen temperature and transition assignments made for the majority of fluorescence lines in fluorite, powellite, scheelite, and grossular/tsavorite. The room-temperature results agree closely with results on individual minerals obtained by previous workers for fluorite and scheelite. The liquid-nitrogen-temperature results as well as the transition assignments for powellite and grossular/tsavorite are new. The Nd concentration has been measured by laser-ablation induction-coupled-plasma mass spectrometry (LA-ICP-MS) and correlated with Nd 3+ fluorescence intensity where possible. For fluorite, the fluorescence intensity increases at least linearly with concentration at levels up to a few parts per million and then saturates at higher levels due to concentration quenching. Analysis of room-temperature Raman/fluorescence spectra of a much larger group of minerals available on the RRUFF web site shows that strong or very strong Nd 3+ fluorescence is much more likely in calcium-based minerals than in non-calcium-based ones and is completely absent for minerals containing iron in the chemical formula. Nd 3+ fluorescence is best understood in fluorite and less well understood in the other five minerals. Further study of calcite, apatite, and grossular/tsavorite is necessary to improve the understanding of the charge-compensation mechanisms and increase the number of identified transitions in calcite and apatite. The results of this work indicate that Nd 3+ fluorescence in calcium-based minerals, when excited by a 785 nm laser, has potential uses in three areas: mineral identification, structure characterization and determination of trace-element concentration.

Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X‐ray diffraction study

“…It is probable that similar fluorescence may occur also in natural fluorites, as they are known to easily incorporate various amounts of REE . Chen and Stimets (2014) describe that the transition energy produced by a 785 nm laser is close to particular 4f energy levels of trivalent rare‐earth ions, and as the crystal field of the host fluorite split the 2J + 1 degenerate levels of the ionic multiplet by an amount of up to a few hundred cm −1 , several fluorescence bands may occur in the spectrum. The transition strengths of some of the bands are weak; therefore, not all of them will be observed.…”

“…The most plausible explanation of the bands above 500 cm −1 is that they are fluorescence bands—they are quite broad, which is atypical for normal Raman bands, and they occur only during measurements with certain laser wavelengths. As Aminzadeh (1997) notes, the presence of fluorescence bands is an effect known mainly in the measurements made by FT‐Raman instruments equipped with 1064 nm laser, but Chen and Stimets (2014) showed that the fluorescence bands may be excited also by a 785 nm laser. The presence of rare earth elements (REE) is known to cause fluorescence in several Ca‐minerals, and Chen and Stimets (2014) showed it specifically on Dy 3+ ‐doped fluorites with Nd 3+ ‐related fluorescence.…”

“…As Aminzadeh (1997) notes, the presence of fluorescence bands is an effect known mainly in the measurements made by FT‐Raman instruments equipped with 1064 nm laser, but Chen and Stimets (2014) showed that the fluorescence bands may be excited also by a 785 nm laser. The presence of rare earth elements (REE) is known to cause fluorescence in several Ca‐minerals, and Chen and Stimets (2014) showed it specifically on Dy 3+ ‐doped fluorites with Nd 3+ ‐related fluorescence. It is probable that similar fluorescence may occur also in natural fluorites, as they are known to easily incorporate various amounts of REE .…”

Laser-induced REE3+ photoluminescence of selected accessory minerals — An “advantageous artefact” in Raman spectroscopy

“…We demonstrated that Nd 3+ emissions strongly interfere with Raman bands in spectra of the four accessory minerals studied. Chen and Stimets (2014) found that the PL of Nd 3+ (λ exc = 785 nm) is very common for many other Caminerals as well.…”

Genetic significance of the 867 cm− 1 out-of-plane Raman mode in graphite associated with V-bearing green grossular

“…Given the high REE concentration in the primary fluid inclusions indicated by the REEbearing-or REE-carbonate daughter mineral, currently of unclear composition, the appearance of other REE minerals in the fluid inclusions, and the presence of cerianite-(Ce) and fersmite as a mineral inclusions in green grossular, we speculate that primary REE intercalates in graphite were formed (see for example Shikin et al 2000;Chen and Stimets 2014). This is justified by the experimental result that by grinding graphite together with Lacarbonate or NdF3 (10 : 1) in a motar, the graphite clearly displays the 867 cm -1 band (see Fig.…”