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Description
Optically Stimulated Luminescence (OSL) of quartz is widely applied for equivalent dose (De) determination for sedimentary geochronology. Blue-light stimulated OSL (BOSL) is a widely accepted technique and dominated by the fast component, which is commonly attributed to electron release from a trap located approximately 2.8–2.9 eV below the conduction band. Although blue photons (~2.6 eV) are typically used for stimulation, even lower-energy photons (green or red) can release electrons from this trap due to phonon-assisted photoionization processes. This trap is characterized by high thermal stability and rapid optical bleaching, indicating a large photoionization cross-section under blue stimulation and efficient recombination via the principal luminescence center.
Violet Stimulated Luminescence (VOSL), employing higher photon energies (> 2.6 eV), has been proposed to access deeper and more thermally stable traps with higher saturation doses. Because the optical detrapping probability depends on both the photoionization cross-section and the overlap between photon energy and trap ionization threshold, violet stimulation is expected to enhance ionization of traps less efficiently excited under blue light, potentially extending the measurable dynamic dose range.
CW-OSL and LM-OSL measurements were performed on quartz extracted from Rio Negro sediments (Amazon, Brazil). Three resolvable decay components were identified under both BOSL and VOSL using general-order kinetic modeling. VOSL intensity is approximately twenty times higher than BOSL. The fast component exhibits a decay constant of ~0.1 s under violet stimulation, compared to ~0.28 s for BOSL, suggesting an increased effective photoionization cross-section and/or greater participation of deeper trap populations. Slower components also show enhanced intensity under VOSL
The saturation dose increases from ~182 Gy (BOSL) to ~390 Gy (VOSL). De values agree with ramp TL results. These findings indicate that VOSL probes a distinct and potentially deeper trap distribution, improving the applicability of quartz OSL for dating older sediments.