Applied Spectroscopy最新文献

Chromium-doped zinc selenide (Cr:ZnSe) crystals are the gain media of choice for mid-infrared lasers operating over a 1.9-3.4 µm spectral range. In this study, we used laser-induced breakdown spectroscopy (LIBS) of Cr:ZnSe polycrystalline materials to improve the sensitivity of detecting chromium concentration in the laser-active materials. The fundamental harmonic of a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was used as an excitation source. After calibration of the LIBS signal, we calculated that chromium's limit of detection (LOD) was 30 parts per million (ppm). Normalization of the Cr(I) intensity peak at 357.9 nm by the square root of the Zn(I) peak at 636.2 nm reduced the LOD to 20 ppm and increased the coefficient of determination to R² ≈ 0.98. These results demonstrate the potential of LIBS for microscale mapping of dopant distributions in laser crystals and for on-site monitoring of material quality during fabrication.

Phthalate-based plasticizers in polyvinyl chloride (PVC) polymer were examined using infrared (IR) spectroscopy and evolved gas analysis-mass spectrometry (EGA-MS), a type of mass spectrometry (MS). IR signals arising from the C=O stretching vibrations of the plasticizers are observed but it is difficult to distinguish individual components due to their structural similarity. In contrast, temperature-dependent mass spectra of the PVC sample revealed a characteristic increase in total ion signals within the 100-220 °C range, indicating that plasticizer desorption occurs predominantly before decomposition of the PVC polymer. The application of two-dimensional correlation spectroscopy (2D-COS) to the mass spectra elucidated the detailed sequence of spectral changes during thermal desorption. The 2D correlation spectra derived from the mass spectra within the 100-220 °C range exhibited distinct correlation peaks associated with bis(2-ethylhexyl) phthalate, bis(2-ethylhexyl) adipate, and bis(2-ethylhexyl) sebacate. These results demonstrate that EGA-MS, combined with 2D-COS, can effectively identify individual additives in polymer systems.

In the first paper in this series, we proposed the use of a set of colored LEGO blocks as "standard" samples for the evaluation of fluorescence avoidance and mitigation schemes in Raman spectroscopy, as well as for use to evaluate the instruments' performance on dark samples. In the second paper we described the spectra obtained on the same blocks from ten different handheld Raman instruments. We found that the combination of a series of colored blocks (white, yellow, red, and blue), and successively darker tone blocks (white, gray, and black) do challenge these instruments and shed light on the ways that their manufacturers have optimized these instruments in specific areas and for different purposes. In this paper we extend the work using an advanced Raman data collection technique: A fast-repetition-rate, short-pulse, laser with a single-photon avalanche photodiode (SPAD) array detector capable of providing a time-sequence output, commonly known as a "time-gating" or "time-resolved" approach. The results are evaluated and compared to those in the first two papers. In addition, X-ray fluorescence (XRF) spectra were also collected to confirm identifications of some of the blocks' inorganic pigments, which were detected via their Raman spectra.

Optical identification of liquid droplets, aerosols, or thin films is critical for many applications. While reference spectra are sometimes available for such measurements, they are not always applicable to the observed spectrum or the given sample morphology. Reference spectra for many forms can be modeled, however, if the n/k vectors (real and imaginary refractive indices) are available. In previous work we have reported protocols to determine the n/k vectors for dozens of liquids, primarily in the mid-infrared (MIR) spectral range from 7500 to 400 cm^-1. In this work we extend the spectral range into the near-infrared (NIR) region, demonstrating a method to measure and merge the data sets to create composite n/k data ranging from 10 000 to 400 cm^-1 (1.0 to 25 µm) with absorbance fidelity spanning over four orders of magnitude, and vastly improved signal-to-noise in the NIR. The precision of the composite data is evaluated for three different liquids, focusing primarily on the steps for converting the raw absorbance spectra to k values. The variability in both MIR and NIR data as well as in the final n/k vectors is also investigated for several liquids. For typical liquids, the overall variability (reported as 2σ) in the final n and k-vectors is determined to be ∼0.4% and 3%, respectively. Finally, the derived n/k data are used to calculate absorbance spectra for aerosol droplets, showing marginal variability due to the typical measurement errors in the final n/k vectors.

Butterfly wings exhibit optical phenomena resulting from pigments as well as from intricate nanostructures of the scales that plays an important role in their ecology mainly, communication, thermoregulation as well as mating. In our study, we examined the optical behavior of butterfly wing scales by analyzing their percent reflectance, absorbance, percent transmittance, and effective refractive index using ultraviolet-visible near-infrared (UVVis-NIR) spectroscopy which is a valuable analytical technique that provide details of the optical properties of materials. In the study conducted with 10 butterflies, the UV, visible, and NIR regions are highlighted to determine the optical properties of butterflies. From the study, it is explored that the UV region exhibit major absorbance, the visible region exhibits major reflectance, and infrared regions exhibit minor reflectance. Optical parameters other than reflectance and absorbance are derived from the spectroscopic data and plotted using Origin software. The percent reflectance, absorbance, percent transmittance, effective refractive index, and their respective wavelength of butterflies studied vary across species. Ariadne merione is observed to have the highest percent reflectance and the lowest is observed in the Eurema hecabe. The overall percentage of reflectance observed in the study ranges between 46%-68%. The absorbance is observed highest for Parantica aglea and lowest for Ypthima huebneri with optimum absorbance ranging between 1.23-0.82. The highest transmittance percentage is observed for Tirumala septentrionis, and the lowest value is observed in Mycalesis mineus and E. hecabe with optimum transmittance ranging between 63% to 47%, respectively. The refractive index was analyzed using the Fresnel equation, followed by an empirical Cauchy dispersion fit to characterize its wavelength dependence. The results revealed unusually high refractive index values for a biological specimen, indicating an effective refractive index behavior influenced by structural, pigmentation and optical complexity rather than representing the intrinsic material refractive index. This study is the first record on comprehensively determining the optical properties of Indian butterflies especially effective refractive index using UVVis-NIR spectroscopy.

Soil reflectance spectroscopy is a powerful tool for rapid, non-destructive assessment of soil properties and the foundation for data-driven soil science applications. However, systematic discrepancies during routine spectral measurement procedures, particularly those arising from contamination or deterioration of white reference (WR) calibration panels, may compromise spectral data stability and hinder harmonization practices across laboratories. This study investigates the impact of using a non-contaminated WR panel as a calibration target to measure soil reflectance across the visible (Vis), near-infrared (NIR), and short-wavelength infrared (SWIR) spectral regions. The study evaluates the effectiveness of an internal soil standard (ISS) Lucky Bay sand to correct discrepancies within a controlled laboratory setting. Twelve soils from the Israeli Legacy Soil Spectral Library were analyzed using a contact-probe setup that was calibrated with both a clean and a contaminated WR. The spectral correction method, based on IEEE P4005 protocols and the ISS calibration, significantly reduced spectral inconsistencies, especially in the Vis region where contamination effects were most pronounced. Results show that the ISS effectively harmonized spectra acquired under different WR conditions, reducing the modified average spectral difference stability (mASDS) measure across all samples. While ISS correction is commonly employed for cross-laboratory harmonization, our findings highlight its critical role in enhancing intra-laboratory consistency under routine operational variability. We recommend that every WR calibration process will be accompanied with ISS measurements. The continuous use of a well-maintained WR and ISS improves the reliability of soil spectral datasets and supports the long-term harmonization of soil spectral libraries.

Laser-induced breakdown spectroscopy (LIBS) offers a promising alternative due to its minimal sample preparation, real-time analysis capabilities, and versatility in analyzing a broad range of materials. However, the challenge lies in determining its ability to effectively distinguish high-iron ore content from mineralogically similar ores with lower iron content. This study focuses on differentiating iron ore from a variety of ores with lower iron content, including calcite, biotite, dolomite, chalcopyrite, rutile, chromite, olivine, limonite, and astrophyllite, using LIBS. By comparing the obtained spectra and applying receiver operating characteristic (ROC) curve analysis, the study assesses the specificity of the technique. The results demonstrate a high specificity (>70%) in distinguishing iron ore from biotite, dolomite, chalcopyrite, rutile, olivine, and astrophyllite, revealing the potential of LIBS for effectively identifying iron ore from some ore types. However, when comparing iron ore to other ore types, such as limonite, chromite, and calcite, the results are not statistically significant. This means that the spectral or compositional similarities between these ores may limit the method's capacity to give clear separation in certain situations. To further validate the results, two common classification models, principal component analysis followed by linear discriminant analysis (PCA + LDA) and k-nearest neighbors (KNN) were applied to the spectral data. The comparison results demonstrate the resilience of LIBS classification and the impact of mineral matrix influences on diagnostic performance.

In this paper, a lanthanide complex-based fluorescent sensor Tb(4-MBA) was developed for the selective recognition of diabetic ketoacidosis (DKA) and the diabetes biomarker β-hydroxybutyric (β-Hb). β-Hb significantly enhanced the fluorescence emission of the Tb(4-MBA) complex at 539  nm. Based on the analysis of the surface electrostatic potential distribution and time-resolved spectra, we speculate that in the reaction system of β-Hb with Tb(4-MBA), β-Hb and Tb(4-MBA) may form a complex through hydrogen bonding interactions, which brings β-Hb closer to Tb³⁺ and thus reduces the non-radiative energy loss of the solvent molecules to Tb³⁺ and significantly enhances the Tb(4-MBA) fluorescence intensity. The linear range of Tb(4-MBA) for β-Hb was 2-55 μM, and the limit of detection (LOD) was 50.6 nM. This sensor has high sensitivity and selectivity and shows great potential in the field of screening and diagnosis of diabetes mellitus and DKA.

Tropical mosquitoes transmit diseases like malaria, yellow fever, and Zika. Classifying mosquitoes by species, sex, age, and gravidity offers vital insights for assessing transmission risk and effective mitigations. Photonic monitoring for mosquito classification can be used in distributed sensors or lidars on longer ranges. However, a reflectance model and its parameters are lacking in the current literature. This study investigates mosquitoes of different species, sexes, age groups, and gravidity states, and reports metric pathlengths of wing chitin, body melanin, and water. We use hyperspectral push-broom imaging and laser multiplexing with a rotation stage to measure near-infrared spectra from different angles and develop simple models for spectral reflectance, including wing thickness and equivalent absorption path lengths for melanin and water. We demonstrate wing thickness of 174 (±1) nm - the thinnest wings reported to our knowledge. Water and melanin pathlengths are determined with ∼10 µm precision, and spectral models achieve adjusted R² values exceeding 95%. While mosquito aspect angle impacts the optical cross-section, it alters shortwave infrared spectra minimally (∼2%). These results demonstrate the potential for remote retrieval of micro- and nanoscopic mosquito features using spectral sensors and lidars irrespective of insect body orientation. Improved specificity of vector monitoring can be foreseen.