Sensitive Luminescence Research Articles

Supramolecular Luminescent Hydrogel Based on Glycine/Terbium Complex and Fluorescent Dyes for Visual Temperature Monitoring

AbstractThe development of smart synthetic materials that are sensitive, accurate, and visually responsive to changes in temperature is vital. Herein, a supramolecular luminescent hydrogel based on a glycine/terbium (Gly/Tb) complex, rhodamine B (RB), and gelatin is reported. The hydrogel exhibits responsive luminescence and undergoes a temperature‐induced phase transformation from hydrogel to sol. The electrospray ionization time‐of‐flight mass spectra, Fourier‐transform infrared spectra, and simulation results verifiy the coordination mode of the Gly/Tb complex. The Gly/Tb complex and RB emit green and orange luminescence, respectively. When the Gly/Tb complex and RB are co‐doped into the gel network of gelatin, the obtained Gly/Tb/RB hydrogel displays steady yellow luminescence by virtue of luminescence resonance energy transfer. Subsequently, a luminescent switch is constructed owing to the sensitive and reversible luminescence responsiveness of the Gly/Tb/RB hydrogel to temperature stimuli. Remarkably, the Gly/Tb/RB hydrogel undergoes a visual phase transformation from hydrogel to sol above 35 °C, allowing the ambient temperature variation to be monitored. This study establishes a novel and effective route for the construction of smart optical materials and visual temperature monitors.

Ligand-to-Metal Energy Transfer in terbium and europium oxalate heptahydrate crystals: Understanding the influence of oxalate ligand on the photoluminescent properties

The intense green and red emission of terbium and europium oxalates are attributed to the cross-relaxation process between lanthanide ions. However, the role of the organic ligand as a sensitizing agent for the emission has not been fully elucidated, leaving the photoluminescent (PL) properties relatively unexplored. This work presents a comprehensive study of the Ligand-to-Metal Energy Transfer (LMET) in terbium and europium oxalates heptahydrate. Single crystals were grown using the hydro-silica gel technique, and a novel improvement of the synthesis procedure which allowed growing substantially larger europium oxalate crystals than in previous studies in the field is also reported. X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), and thermogravimetric analysis confirmed the chemical composition RE2(C2O4)3⋅7H2O. PL studies provided reliable evidence of a sensitized emission via the antenna effect, indicating that the LMET contributes to the population of the 5Dj emissive levels of Ln3+ ions, assisting the cross-relaxation process. These findings enhance our understanding of the PL properties of terbium and europium oxalates and demonstrate that the oxalate ligand is a more effective luminescent sensitizer for Tb3+ ions than for Eu3+ ions. Additionally, PL excitation studies on terbium and europium oxalate decahydrate crystals were conducted to contrast the emission properties between both forms of hydrate oxalates. Notably, terbium oxalate heptahydrate crystals exhibit a significant improvement in the Charge Transfer (CT) due to higher intramolecular charge transfer.

Ultra-sensitive low-temperature luminescent thermometry based on Boltzmann behavior of the Stark sub-levels of Pr3+

The cryogenic sensor is critical for numerous applications such as cryobiology, aerospace space probes, and solid-state superconducting quantum technology. However, it is still a challenge to operate at temperatures below 100 K using luminescent intensity ratio (LIR) thermometers with typical thermal coupling levels based on the Boltzmann mechanism. In this work, a sensitive low-temperature luminescence thermometry approach has been developed utilizing Boltzmann behavior of the Stark sub-levels of Pr3+. Spectral Stark-splitting feature of the 1D2 multiplet of Pr3+ was observed in CaNb2O6: Pr3+ phosphor, and the luminescence intensity ratio (LIR) of high state (Stark sub-level (2)) and low state (Stark sub-level (0)) of 1D2 was employed for temperature sensing, resulting in a notable relative sensitivity (Sr) of 11.3 % K−1 at 60 K. In addition, the intervalence charge transfer (IVCT)-based strategy improves the temperature sensitivity above room temperature with maximum Sr up to 1.54 % K−1 at 420 K. This work consistently demonstrate high sensitivity at low temperature, indicating potential applications in cryogenic temperature sensor. These results provide a route to the development of luminescent thermometers with a high sensitivity at low temperatures and a wide range of operating temperatures.

Enhance optically stimulated luminescence sensitivity and improve fading of newly developed LiMgPO4:Er phosphor

To avoid fading, the readout time of the old LiMgPO4:Er in the previous study had to be taken to be at least 20 s. The readout time is up to 20 s, which not only contradicts the fast OSL readout, but also eliminates too many OSL signals per readout and is not favourable to the requirement that the OSL can be read multiple times. The primary objective of this study is to reduce readout time under conditions where the OSL signal of LiMgPO4:Er phosphor stabilizes after irradiation. The OSL properties were investigated. To achieve OSL fading of about 5% within 30 d after irradiation, the shortest integration time for new LiMgPO4:Er in this study was 1 s, whereas old LiMgPO4:Er required 20 s. When the integration time was 1 s, the OSL sensitivity of the new LiMgPO4:Er samples in this study was about 2.4 times that of the old LiMgPO4:Er samples. A new LiMgPO4:Er phosphor with an OSL signal loss of about 5% for the shortest integration time of 1 s within 30 days after irradiation, a sensitivity comparable to that of TLD-500k, and an MMD as low as 38 μGy was successfully prepared, which will meet the fast read out and the multiple readings requirements.

Eu-MOF-based highly sensitive and selective luminescence probe for trace, in situ and visual detection of flunitrazepam

Flunitrazepam, as an emerging new psychoactive substance classified as a third-generation drug that is more harmful and camouflaged, is gradually proliferating globally. Maliciously used as a criminal tool in homicide and rape cases, it has already caused serious harm to public safety and social stability. Owing to its special molecular structure, low concentration level and rapid metabolic process in the human body, accurate detection of flunitrazepam remains a major challenge, especially for real sample and on-site detection. In this paper, a lanthanide MOF (Eu-MOF) based on bi-ligand was constructed as a luminescence probe and used for the first time to detect trace amounts of flunitrazepam. The ’antenna effect’ promotes strong luminescence of Eu-MOF, while the lower LUMO orbital energy level of flunitrazepam allows it to accept electrons from the electron donor leading to quenching of Eu-MOF luminescence. The probe has a high sensitivity and can detect flunitrazepam in the range of 0–800 μM with a detection limit as low as 73 nM. Moreover, flunitrazepam was detected in urine from real samples as well as in a variety of beverages to further validate its accuracy and practicality. The reported Eu-MOF represents one of the pioneering luminescence probes for the detection of flunitrazepam, which offers great promise for the on-site or on-line analysis of flunitrazepam.

Study of thermoluminescence characteristics of quartz for high radiation doses (>1kGy): Implications for extending the luminescence dating range

Quartz is an omnipresent abundant natural mineral, used for luminescence dating. Lately, quartz optically stimulated luminescence (OSL) technique is widely used to estimate the equivalent doses (De) for dating geological events (up to 250 Gy, limited by saturation). Some works report thermoluminescence (TL) saturation around ∼ (10–40) kGy. Still dose estimates for such high radiation dose (HRD) range are not achieved. Significant research exists about luminescence response for low dose ranges (<250 Gy) but limited studies are done for HRDs (>1 kGy). This work characterizes the luminescence response of quartz for HRDs (1–21 kGy) to improve existing understanding of luminescence mechanism. Results show that the characteristics of the trap (<200 °C) differ significantly at HRDs than low doses. TL in multi-spectral detection (UV–Visible) band suggest an increase in 340–380 °C peak intensity up to 11 kGy dose. The measurements of saturation dose suggest that it depends on the trapping centres but is independent of recombination centres for the samples used for study. The traps are found bleachable by sunlight, reducing TL signal to residual levels in 1 h. Further, the bleachability is found to be anti-correlated with luminescence emission wavelength. At HRDs luminescence sensitivity is influenced by dose given in previous cycle which is difficult to correct by routine normalization procedures. The work also explores the various normalization methods to find appropriate method for HRD estimation and recommends the use of mass normalization as other normalization methods do not correct the sensitivity changes at HRDs adequately.

Downstream change of luminescence sensitivity in sedimentary quartz and the rearrangement of optically stimulated luminescence (OSL) components along two large rivers

Recently, it has been proposed that the luminescence sensitivity of quartz grains, i.e. their luminescence response to unit dose, might be used for sediment fingerprinting. Sensitivity is determined both by the origin of quartz grains and the sedimentary processes they underwent. However, a more detailed understanding of the factors influencing sensitivity is essential in order to expand and specify the applicability of the parameter in sediment sourcing and geomorphological studies alike. In the present research, we examined the spatial changes of sensitivity parameters of coarse grain quartz in modern sediments of the largest rivers of the Carpathian Basin, Central Europe, to determine the role of source areas and transportation distance.Based on the luminescence analysis of 39 samples, quartz extracts with a Carpathian origin (catchment of the Tisza River have a significantly higher sensitivity, except the LM-OSL medium component, than those originating from the Alpine domain (catchment of the Danube River). No clear relationship could be identified between natural sensitisation and transportation distance. In terms of the Tisza the observed downstream increase of quartz sensitivity is due to high sensitivity quartz grains supplied by its tributaries. In the meantime, a recurring change was observed along the Danube, which can be attributed mostly to local erosional processes. Consequently, tributaries and erosion can overprint the potential downstream sensitisation of quartz grains in large rivers.Meanwhile, in terms of the Danube on sections where a significant downstream increase was detected in LM-OSL fast component sensitivity, LM-OSL medium component sensitivity systematically decreased. Additionally, during laboratory sensitization, the CW-OSL sensitivity of Danube samples increased considerably, whereas changes were more moderate in the case of Tisza samples. Moreover, in the case of Tisza-related quartz extracts, the 110°C TL sensitivity and the LM-OSL fast and medium components showed a strong correlation, indicating the stability of luminescence processes (trapping and recombination). Whereas, in the case of the Danube both LM-OSL components show a weak correlation with the 110°C TL intensity. All these indicate that Alpine-origin quartz grains are more susceptible to the rearrangement of electron traps and/or recombination centres, which can also be an indicator of sediment sources in Quaternary studies in the region.

Maximizing Nanoscale Downshifting Energy Transfer in a Metallosupramolecular Cr(III)-Er(III) Assembly.

Pseudo-octahedral CrIIIN6 chromophores hold a unique appeal for low-energy sensitization of NIR lanthanide luminescence due to their exceptionally long-lived spin-flip excited states. This allure persists despite the obstacles and complexities involved in integrating both elements into a metallosupramolecular assembly. In this work, we have designed a structurally optimized heteroleptic CrIII building block capable of binding rare earths. Following a complex-as-ligand synthetic strategy, two heterometallic supramolecular assemblies, in which three peripherical CrIII sensitizers coordinated through a molecular wire to a central ErIII or YIII, have been prepared. Upon excitation of the CrIII spin-flip states, the downshifted Er(4I13/2 → 4I15/2) emission at 1550 nm was induced through intramolecular energy transfer. Time-resolved experiments at room temperature reveal a CrIII → ErIII energy transfer of 62-73% efficiencies with rate constants of about 8.5 × 105 s-1 despite the long donor-acceptor distance (circa 14 Å). This efficient directional intermetallic energy transfer can be rationalized using the Dexter formalism, which is promoted by a rigid linear electron-rich alkyne bridge that acts as a molecular wire connecting the CrIII and ErIII ions.

Three fluorescent probes based on Cd-MOFs for highly selective, sensitive and stable detection of antibiotics, anions and cations in water

It is essential to explore methods for detecting environmental pollutants to address the issue of pollution. Three novel Cd-based MOFs fluorescent sensors, namely [Cd1.5(TPT)0.5(BTC)H2O·DMF] (CUST-541), [Cd(TPT)(5-NTPA)·H2O] (CUST-542), and [Cd1.5(TPTZ)1.5(BTC)H2O·H2O] (CUST-543) (TPTZ = 2,4,6-Tris(2-pyridyl)-1,3,5-triazine; H3BTC = Trimesic acid; 5-NTPA = 5-Nitroisophthalic acid; TPT = 2,4,6-tri-4-pyridyl-1,3,5-triazine) were successfully compounded under solvent thermal conditions. Single-crystal X-ray diffraction analyses revealed that the crystal structures of CUST-541 and CUST-542 were found to have similar C2/c space group, while CUST-543 was in the monoclinic system with the P2/c space group. We have tested different types of antibiotics, cations, and anions, and found that the MOFs have very low LOD for NFT, Cu2+, and CrO42-. The LODs of NFT, Cu2+, and CrO42- for crystals are 0.53 μM, 0.38 μM, and 2.36 μM, respectively. Furthermore, this method is characterized by its low detection limit, rapid response time, wide linear range, and reproducible luminescence sensitivity.

Quartz luminescence sensitivity enhanced by residence time in the critical zone

The emerging use of quartz luminescence properties to characterize Earth-surface processes shows promise, with optically stimulated luminescence (OSL) sensitivity proposed as a valuable tool for provenance or sediment history tracing. However, the geologic processes that lead to quartz sensitization remain unclear. Here we study the impact of source rock and surface processes on the luminescence properties of quartz sand from bedrock and modern and Late Pleistocene alluvium generated from a mountainous catchment in northern Utah, USA. Continuous wave and linear modulated OSL are used to characterize the luminescence sensitivity and intensity of the fast-decay component. We compare the OSL sensitivity with sand-grain provenance and with proxies for surface processes such as topographic metrics, cosmogenic 10Be-derived erosion rates, chemical weathering indices, and magnetic susceptibility. Late Pleistocene sediment has low OSL sensitivity and a weak fast-decay component, similar to bedrock samples from the source area. In contrast, modern alluvium is dominated by the fast-decay component and has higher and more variable OSL sensitivity, with no clear relationship to upstream bedrock source. There is, however, an inverse relationship between OSL sensitivity and catchment-averaged erosion rates and a positive relationship with chemical weathering indices and magnetic susceptibility. These metrics suggest that the modern alluvium has experienced increased residence time in the shallow critical zone compared to the Late Pleistocene sediments. We suggest that changes in hillslope processes between the effectively wetter, cooler Pleistocene and the dryer, warmer conditions of the Holocene enhanced the luminescence properties. The results suggest that climatic controls on rates and processes of chemical and mechanical weathering and sediment transport and residence within the critical zone are encoded in the luminescence properties of quartz sand.

Rapid and sensitive detection of SARS-CoV-2 based on a phage-displayed scFv antibody fusion with alkaline phosphatase and NanoLuc luciferase

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the subsequent pandemic have led to devastating public health and economic losses. The development of highly sensitive, rapid and inexpensive methods to detect and monitor coronaviruses is essential for family diagnosis, preventing infections, choosing treatments and programs and laying the technical groundwork for viral diagnosis. This study established one-step immunoassays for rapid and sensitive detection of SARS-CoV-2 by using a single-chain variable fragment (scFv) fused to alkaline phosphatase (AP) or NanoLuc (NLuc) luciferase. First, a high-affinity scFv antibody specific to the SARS-CoV-2 nucleocapsid (N) protein was screened from hybridoma cells-derived and phage-displayed library. Next, prokaryotic expression of the scFv-AP and scFv-NLuc fusion proteins were induced, leading to excellent antibody binding properties and enzyme catalytic activities. The scFv-AP fusion had a detection limit of 3 pmol per assay and was used to produce eye-readable biosensor readouts. Moreover, the scFv-NLuc protein was applied in a highly sensitive luminescence immunoassay, achieving a detection limit lower than 0.1 pmol per assay. Therefore, the scFv-AP and scFv-NLuc fusion proteins can be applied for the rapid and simple diagnosis of SARS-CoV-2 to safeguard human health and provide guidance for the detection of other pathogenic viruses.

Sensitive and High-Throughput Time-Resolved Luminescence Detection of Tetracycline in Milk for Eliminating Background Fluorescence on a Miniaturized Apparatus.

Fluorescence detection has always suffered from high background fluorescence from real samples such as milk. Therefore, cumbersome pretreatments of samples were necessary to remove the fluorescent substances but led to long processing times and low efficiency. Time-resolved luminescence detection is a powerful technique for eliminating short-lived background fluorescence without additional pretreatments. However, the related instruments are usually equipped with high-speed excitation sources and detectors, which are always bulky and expensive. Herein, we developed a low-cost and miniaturized imaging system for high-throughput time-gated luminescence detection. An UV LED array was used to excite multiple samples, the luminescence of which could be detected by a smartphone simultaneously. An analog circuit was designed to synchronize the LED to the mechanical chopper to eliminate the background signals resulting from scattering and short-lived autofluorescence. Compared to other synchronous circuits based on FPGAs and microcontrollers, this analog circuit required no programming and memory. For the first time, high-throughput time-resolved luminescence detection of tetracycline in milk without any separation or enrichment was achieved by utilizing a smartphone as a camera, and the scattered signals and the background fluorescence were eliminated efficiently. The limit of detection reached as low as 53 nM (∼0.024 ppm), lower than the residue limit set by the European Union. This high-throughput time-gated luminescence detection method can be used for quantitative analysis of many real samples with high background fluorescence.

Tracing uplift and erosion in orogenic settings using quartz luminescence sensitivity: Insights from the Northern Andes uplift

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range.

Using quartz OSL signals from SAR cycles for sediment provenance studies

Quartz optically stimulated luminescence (OSL) sensitivity is varied and related to Earth surface processes and, thus, it has been shown to be a useful tool for appraising sediment recycling and provenance investigations. These investigations are mainly based on OSL data purposely measured for sensitivity calculations. However, it has been recently shown that the relative sensitivity of the quartz OSL fast component (%BOSLF) from the first test dose (Tn) signal from an OSL dating measurement using the Single Aliquot Regenerative-dose (SAR) protocol can be used to discriminate sediment sources. Here, we investigate the possibility of characterizing %BOSLF for provenance purposes using not only Tn signals but all other OSL signals obtained over SAR protocol cycles from OSL dating measurements. We address the %BOSLF behaviour over SAR cycles (if conservative or not), the %BOSLF dependency on dose-size, differences between %BOSLF values given by natural/regenerative and test dose signals, and %BOSLF application for provenance studies. Quartz sand grains data from twenty Late Quaternary sediment samples, representing orogenic and cratonic sources and diverse depositional contexts from South America, Africa, and Asia, are included in the analysis. All calculations were performed using data that have been previously obtained for equivalent dose estimation. The key finding is that the averaged %BOSLF of all SAR signals was representative of the samples' characteristic sensitivity and could satisfactorily discriminate samples from known sources, mainly in the case of high-sensitivity samples. We could distinguish sediment source areas by averaging the %BOSLF of OSL signals from SAR natural/regenerative and test doses together. Likewise, laboratories worldwide could produce regional/global sediment provenance fingerprinting reference data using their dating measurements accumulated throughout the last decade.

Novel pyrrolidine-alkylamino-substituted dicyanoisophorone derivatives as near-infrared fluorescence probe for imaging β-amyloid in vitro and in vivo

BackgroundThe formation of amyloid-β (Aβ) plaques is one of the key neuropathological hallmarks of Alzheimer's disease (AD). Near-infrared (NIR) probes show great potential for imaging of Aβ plaques in vivo and in vitro. Dicyanoisophorone (DCIP) based Aβ probes have attracted considerable attention due to their exceptional properties. However, DCIP probes still has some drawbacks, such as short emission wavelength (<650 nm) and low fluorescence intensity after binding to Aβ. It is clear that further modification is needed to improve their luminescence efficiency and sensitivity. ResultsWe designed and synthesize four novel pyrrolidine-alkylamino-substituted DCIP derivatives (6a-d) as imaging agents for β-amyloid (Aβ) aggregates. Compound 6c responds better to Aβ aggregates than the other three compounds (6a, 6b and 6d) and its precursor DCIP. The calculated detection limit is to be as low as 0.23 μM. Compound 6c shows no cytotoxicity in the tested concentration for SH-SY5Y and HL-7702 cells. Additionally, compound 6c is successfully applied to monitor Aβ aggregates in live SH-SY5Y cells and APP/PS1 transgenic mice. The retention time in the transgenic mice brain is much longer than that of age-matched wild-type mice. SignificanceThe results indicates that compound 6c had an excellent ability to penetrate the blood-brain barrier and it could effectively distinguish APP/PS1 transgenic mice and wide-type mice. This represents its promising applications for Aβ detection in basic and biomedical research.

Lanthanide-Sensitized Upconversion Iridium Complex via Triplet Energy Transfer.

Cyclometalated iridium (Ir) complexes demonstrate impressive capabilities across a range of fields, including biology and photocatalysis, due to their tunable optical characteristics and structure flexibility. However, generating upconversion luminescence of Ir complexes under near-infrared light excitation is challenging. Herein, by employing lanthanide-doped upconversion nanoparticles (UCNPs) as the sensitizer, a new strategy is demonstrated to gain upconversion luminescence of Ir complexes via triplet energy transfer. This design relies on a rationally designed hybrid of core-shell structured NaYbF4:Tb@NaTbF4 UCNPs and new Ir phosphonate complexes, in which UCNPs can migrate upconverted energy to the surface of nanoparticles through Tb3+-mediated energy migration and then sensitize the upconversion luminescence of Ir complexes upon 980nm excitation. Both experimental and theoretical investigations highlight the significance of triplet energy transfer from excited Tb3+ ions to the triplet state of Ir complexes in the sensitization of upconversion luminescence of Ir complexes. These findings may open exciting avenues for fabricating hybrid Ir materials with new functions and driving the development of UCNP-based nanomaterials.

Ultrasensitive Piezochromic Molecular Crystals: Mechanical Pressure‐Induced Controlled Regulation of TADF and RTP

AbstractConsidering that regulation of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is necessary for a fluorophore to survive and properly show its characteristic features, it is successfully shown herein that a carefully designed novel pyrene derivative can exhibit remarkable aggregation‐induced emission (AIE) overcoming the characteristic fast excitonic decay of pyrene compounds. Moreover, it is established that J‐aggregation in the red‐emitting molecular crystals of the compound reduces the singlet‐triplet energy gap (∆EST), allowing TADF with a very high photoluminescence quantum yield (PLQY) of 72%. Whereas, anisotropic grinding of the same crystals generates well‐defined microcrystals that show RTP as the nature of aggregation changes. Impressively, under isotropic hydrostatic pressure, the crystals show near‐infra‐red (NIR) emission with a very high piezochromic luminescence sensitivity of 46.2 nm GPa−1. The results have established that formation of stable H‐aggregates in the microcrystals is responsible for the ultra‐long RTP. A highly sophisticated full‐spectrum Mueller‐matrix analysis is used for the first time in such systems to demonstrate the details of the effect of perturbation (pressure) on molecular conformation.

Probing sediment burial age, provenance and geomorphic processes in dryland dunes and lake shorelines using portable luminescence data

Luminescence signals from portable optically-stimulated luminescence readers (POSL or port-OSL) can provide expedient insights into sample relative age, and under certain conditions can be simplistically calibrated against existing luminescence chronologies to provide first-order estimates of burial age. This is most straightforward in simple sedimentary systems where samples share a common provenance and geomorphic process history. The spatially extensive southern African dune and palaeolake shoreline luminescence database, for which hundreds of non-light exposed bulk sediments are available, offers a valuable test case to examine the conditions under which POSL-bulk sediment calibration approaches are feasible. To do this we combine measurements of inherent luminescence sensitivity of bulk sediment (BSS) with analysis of sedimentary composition (petrology and presence of calcium carbonate) and texture. We show that BSS, along with POSL IRSL:BSL ratios and petrological data, account for region-to-region variations, whilst internal variability (scatter) within the lake shorelines dataset relates to variations in BSS and sediment texture. At the scale of southern African subcontinent drylands, we see that provenance and geomorphological process history influence sample mineralogical composition and POSL signal characteristic, including BSS.

Investigations on single and multi-grain optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals in quartz derived from sandstones: Insights on provenance of quartz in ancient depositional systems

Trapped charge techniques of luminescence and electron spin resonance (ESR) are classic tools for dating Quaternary deposits. Over the past decade, these techniques have been routinely applied to investigate provenance and/or the sedimentary history of quartz grains based on their different luminescence and ESR characteristics. Of these, optically stimulated luminescence (OSL) sensitivity is one of the most widely investigated parameter for luminescence-based provenance approach. A majority of studies on this parameter are based on evaluation of multi-grain quartz OSL sensitivity of the samples. This is particularly concerning because single-grain quartz luminescence studies have shown that the luminescence signal of a multi-grain aliquot is contributed by less than ∼1–10% of the total grains. Since the sole criteria for discrimination of sources based on luminescence sensitivity relies on its intensity, therefore the results based on multi-grain analysis will most likely be skewed depending on the ‘proportion’ and ‘brightness’ of a few grains. This demands a need to evaluate the potential of single-grain quartz OSL sensitivity in provenance studies. In this study, we investigate single and multi-grain quartz OSL sensitivity from compositionally different sandstones with well-characterised sources based on U–Pb zircon ages. We further complement this analysis with characterisation of ESR centres commonly used in quartz provenance, namely E′1 and [AlO4]0 centres. Our study shows that single-grain quartz OSL sensitivity can help distinguish between sediments that have a predominant input from a single source as compared to those with contribution from multiple sources, which otherwise cannot be inferred from multi-grain studies. Moreover, our results on characterisation of quartz-based ESR intensity of E′1 and saturated [AlO4]0 centres successfully differentiates between sandstones and further complements the luminescence-based characterisation.

Tuning lanthanide luminescence from bipyridine-bis(oxazoline/thiazoline) tetradentate ligands

Organic ligands play a pivotal role in lanthanide luminescence by acting as sensitizers for energy absorption and transfer, a phenomenon known as the fluorescence antenna effect. Herein, we introduce two tetradentate nitrogen ligands renowned for their efficient sensitization of lanthanide luminescence, with their luminous efficacy finely adjustable through subtle modifications to their structure. Through the synthesis of four Eu(III)/Tb(III) mononuclear complexes via the complexation of ligands 6,6′-bis(4,5-dihydrooxazol-2-yl)-2,2′-bipyridine (bpybox, L1) and 6,6′-bis(4,5-dihydrothiazol-2-yl)-2,2′-bipyridine (thio-bpybox, L2) with europium/terbium trifluorosulfonate, structural analysis reveals that the lanthanide ion coordinates with eight nitrogen atoms from two ligands and one oxygen atom from trifluorosulfonate. Among them, two Eu(III) complexes ([Eu(L1)2(SO3CF3)](SO3CF3)2EuL1 and [Eu(L2)2(SO3CF3)](SO3CF3)2EuL2) and one Tb(III) complex ([Tb(L1)2(SO3CF3)](SO3CF3)2 TbL1) exhibit luminosity, displaying characteristic lanthanide metal ion luminescence characterized by high fluorescence quantum yields and prolonged excited state lifetimes. In contrast, TbL2 ([Tb(L2)2(SO3CF3)](SO3CF3)2) is non-luminous, with the sole structural distinction being the substitution of oxygen atoms with sulfur atoms within the ligand. This minor alteration significantly impacts the triplet (3T) state energy level of the ligands, thereby influencing their sensitizing effect on Tb(III) luminescence. These findings underscore the remarkable efficiency of bpybox-type ligands as sensitizers for Ln(III) luminescence, with their structural versatility enabling effective modulation of luminous capacities and efficiency.