Spectro-FLIM for heritage: scanning and analysis of the time resolved luminescence spectra of a fossil shrimp

Abstract We describe the use of a single-photon counting imaging device to scan the surface of a flat fossil specimen. We studied an Early Triassic shrimp identified as Anisaeger longirostrus , from the Paris Biota (Idaho, USA; ca 249.1 Ma). Chemically, the specimen consists of a polycrystalline material composed of relatively monodisperse transparent crystals about 10 µm in size. We collected time-resolved fluorescence spectra at each pixel along 300 µm wide ribbons at a rate of 10 µm per second with a spatial resolution of 1 µm × 10 µm. Fluorescence is excited along a line. We demonstrate the presence of two types of crystals whose luminescence significantly differs. The first type emits at 450 nm with a decay time of 840 ps. The second type contains two independent emission centres emitting at 437 nm and 490 nm. They exhibit multiexponential decays with lifetimes of 1 ns and more than 5 ns, respectively. Although a variable proportion of long emitters was observed, the fluorescence of the fossil appeared to be relatively uniform. Thus, over time, fossilization processes have therefore resulted in a homogeneous distribution of fairly pure crystals.