The spectroscopic fingerprints of blue and green fluorescent resins from La Cumbre mine in the Dominican Republic.

Blue and green fluorescent resins from the La Cumbre deposit in the Dominican Republic represent one of the most distinctive and sought-after varieties of amber, yet the nature of their unusual visible-light-induced luminescence remains insufficiently understood. In this study, we combine Ultraviolet-Visible (UV-Vis) Spectroscopy, Fluorescence Spectroscopy (including EM-EX matrices and lifetime measurements), Fourier-Transform Infrared Spectroscopy (FTIR), and Raman Spectroscopy (RS) - supported by hierarchical cluster analysis (HCA) and principal component analysis (PCA) - to characterize yellow (YC), red (RC), blue (BC), and green (GC) resins from the La Cumbre mine. UV-Vis data confirm that all samples exhibit absorption features consistent with a yellow to red body colour, whereas blue to blue-green fluorescence is observed most prominently under surface excitation and collection conditions. Fluorescence matrices of BC and GC resins reveal excitation-emission pairs consistent with one dominant fluorophore or fluorophore family in blue amber and a more complex set of emitting species in green resin. FTIR and Raman spectra show only subtle chemical differences among resin types; however, selected chemometric analyses highlighted YC/BC and RC/GC affinities, whereas full-range FTIR-HCA reflected broader matrix-level variability. In turn the shift from yellow to blue, or red-to-green is most plausibly explained by localized chemical and microstructural modifications occurring within closely related La Cumbre resin material, which aligns with their strong spectral similarities observed in the fluorescence, UV-Vis, RS and FTIR chemometric datasets. Our results suggest that the characteristic luminescence of La Cumbre amber arises from the combined influence of localized molecular and microstructural modifications developed during diagenesis and polymerization, rather than from the uniform distribution of a single fluorophore. Overall, the integrated multi-method spectroscopic approach, with fluorescence spectroscopy providing the clearest differentiation, offers a framework for characterising the investigated blue-fluorescent Dominican amber and its relationships to the other La Cumbre resin varieties.