Sub-Doppler resonances formed by scanning the laser frequency in the region of the 4S_1/2→4P_1/2 transition at a wavelength of 770 nm in K atomic vapors placed in a nanocell were studied. For atomic vapor thicknesses of L = λ/2 = 385 nm and L = λ = 770 nm, sub-Doppler resonances are formed in the transmission spectrum, located at the unshifted atomic transitions F_g = 1, 2→F_e = 1, 2. The resonance amplitudes observed in the nanocell are proportional to the probability amplitudes of the corresponding transitions. It is shown that a nanocell with a vapor thickness of L = λ = 770 nm can be used as a convenient frequency reference, tied to the unshifted frequencies of the atomic transitions. The advantages of the proposed frequency reference over a commonly used frequency reference based on saturated absorption techniques are demonstrated.

The solvatochromism of polymethine (cyanine) dyes (PDs) was studied to determine the influence of solvent properties on their spectral characteristics. For this purpose, the absorption and fluorescence spectra of PDs of various classes were measured in solvents of different nature (from highly polar to nonpolar and from proton-donating to aprotic). Based on the experimental results obtained and literature data available, a correlation was established between the wavenumbers of the absorption and fluorescence maxima of PDs (ν_abs and ν_fl, respectively) and the polarity (dielectric constant ε) and polarizability (refractive index n) of the solvent. It has been shown that the ν_abs and ν_fl values poorly correlate with Bayliss function f(n²) = (n² – 1)/(2n² + 1). However, good linear correlations are achieved by combining the Bayliss function with the solvent dielectric constant functions f(ε) or ϕ(ε) in the form f(n²) + αf(ε) or f(n²) + αf(ε) (where f(ε) = (ε – 1)/(2ε + 1) and ϕ(ε) = (ε – 1)/(ε + 2)). Such correlations were found for symmetrical PDs – carbo-, dicarbo-, and, partially, tricarbocyanines and monomethines. No significant effects of the proton-donating ability or nucleophilicity of the solvent on such correlations were found. Therefore, solvent polarizability and polarity are the dominant factors determining the spectral shifts of symmetrical PDs. The results obtained provide a basis for the use of symmetrical PCs as probes and sensors of the polarity/polarizability of the molecular environment in various systems, with potential applications in biochemistry, biophysics and other research fields.

Possible mechanisms of broadband structural luminescence in the transparency band of disordered widegap dielectrics are considered theoretically for the case of electronic transitions at deep-lying levels of intrinsic structural defects such as valence-alternation pairs in v-SiO₂. It is concluded that the main mechanism is the geminate recombination of carriers at deep-lying levels of valence-alternation pairs. It is shown that accompanying mechanisms can be associated with polaron effects on isolated centers and phenomena on delocalized defect states.

Crystalline luminescent complex compounds of europium(III) with hexafluoroacetylacetone, trifluoroacetic acid, and 2,2ʹ-dipyridyl were obtained. Luminescent properties and kinetics of photodecomposition of complex compounds in high-pressure polyethylene were studied. It is shown that europium(III) hexafluoroacetylacetonate with 2,2ʹ-dipyridyl is more photostable. It is established that the photoluminescence spectra are due to f–f transitions of the europium(III) ion.

The photoluminescence (PL) spectra and PL excitation spectra (PLES) of microcrystalline powders of CaGa₂S₄:5%Tm,5%Yb and CaGa₂S₄:5%Tm thiogallates were studied at room temperature. The PLES were measured in the wavelength range from 240 to 850 nm, and the PL spectra were measured in the range of 400–2100 nm with excitation in the UV and violet-blue spectral regions. Microcrystalline gadolinium oxychloride powder GdOCl:5%Tm, in which thulium ions are in the trivalent state (Tm³⁺), was used as a sample for comparison of properties. It was concluded that thiogallates contain thulium ions in both di- and trivalent states (Tm²⁺ and Tm³⁺). In this case, the absorption of excitation energy by the CaGa₂S₄:5%Tm crystal is ensured primarily by the 4_f–5_d transition of the Tm²⁺ ion, while in the CaGa₂S₄:5%Tm,5%Yb compound, it is additionally due to the formation of charge transfer states from CaGa₂S₄ ligand atoms to Yb³⁺ ions. It was shown that in CaGa₂S₄:5%Tm crystals co-activated with Yb³⁺ ions, the photoluminescence efficiency increases many times over compared to non-co-activated crystals, and the effective excitation range extends to 530 nm.

Changes in the luminescence and luminescence excitation spectra of near-cluster radiation-induced color centers in the nanocrystals of sodium, magnesium and lithium fluorides are examined by changing in the sizes of the nanoclusters, near which the centers are localized. Shifts in the luminescence bands of near-cluster centers are investigated with changes in sample storage temperature before or after radiation exposure. Shifts and widths of the luminescence and luminescence excitation bands are determined after thermal annealing of the samples, when nanocluster sizes decrease. A method for increasing nanocluster sizes is developed, and the effect of this increase on the spectra of the nanocrystals is studied.

The optical properties of polycrystalline lutetium were studied at room temperature. The optical constants were measured by the ellipsometric method using a spectral LED ellipsometer SPEL-7LED (Russia) in the spectral range of 277–1000 nm. Based on the measured values of the refractive index and absorption coefficient, the dispersion dependences of optical conductivity σ, reflectance R, and the real and imaginary parts of the dielectric constant ε₁ and ε₂, as well as the electron energy loss function Im(ε)^–1, were calculated. It was found that interband electron transitions have a significant effect on the optical properties of solid lutetium. In the optical conductivity spectra of lutetium, two absorption bands are observed with maxima at photon energies of 1.86 and 3.11 eV, associated with interband transitions.

The disadvantage of existing methods for quantitative determination of graphene content is their limited application for the analysis of multicomponent polymorphic mixtures including solid amorphous, graphite and graphene phases. The aim of the study is the research of the possibility for determination of the amount of graphene in a polymorphic multicomponent carbon mixture using color lightness in the CIELAB system. As the object of the research the samples of chemically exfoliated graphene mixed with amorphous carbon were used. It was found that the amount of graphene is related to color lightness of the mixture in the CIELAB system by a linear relation. The discovered relations were tested on model mixtures and confirmed by statistical data processing. The practical use of the discovered phenomenon in the technology of carbon materials lies in the possibility of estimating the content of graphene in mixtures containing other carbon modifications.

The phase composition, surface condition and nature of paramagnetic centers in the sample of MAX-phase Cr₂TiAlC₂ obtained by sintering pressed powders of Cr, Al, TiC, C in vacuum at 1300°C were studied using X-ray phase analysis, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance. According to X-ray diffraction data, the main phase is MAX-phase 312 (Cr_2/3Ti_1/3)₃AlC₂ with impurities of Cr_1.5Ti_0.5AlC, Cr₂AlC, α-Al₂O₃, carbides and chromium oxides. XPS analysis revealed that aluminum oxide and oxidized states of titanium and chromium predominate on the sample surface, with the Ti⁴⁺/Ti³⁺/Ti²⁺ ratio being 1.58/1.0/1.08, and the Cr³⁺ content exceeding the Cr⁶⁺ content by more than three times. The nature of paramagnetic centers in the (Cr_2/3Ti_1/3)₃AlC₂ sample is established. Electronic defects and various types of O^– and Cr³⁺ hole centers were identified in various oxide matrices of the near-surface layers, which may be important for the electron conductivity and magnetic properties.

The interaction characteristics of accelerated 3.2 MeV/nucleon xenon ions with 100 μm-thick thermoradiation-modified polytetrafluoroethylene (TRM-PTFE) films were determined using computer modeling. It was found that, during radiolysis, the initially homogeneous TRM-PTFE sample was transformed into a layered structure including zones of intense and partial radiolysis, as well as a layer of intact polymer. The spatial distribution characteristics of ionization losses and the absorbed dose field in the region of radiation damage around the latent track of a xenon ion were calculated. The optical properties of 100 μm-thick TRM-PTFE films exposed to 3.2 MeV/nucleon xenon ions to a fluence of 1.08 · 10⁶ cm^–2 were studied. The optical spectra of TRM-PTFE exhibit absorption maxima at 206 and 476 (374, 578) nm, which may be due to isolated double bonds and polyene structures containing 14 conjugated double bonds, respectively. Radiation-induced interference was detected, which may be due to the formation of a 0.34–0.39 μm-thick radiation-damaged layer, which may be located at a distance of up to ~36 μm from the surface of the TRM-PTFE sample. A correlation was concluded between the predicted estimates of radiation-induced changes in the optical properties of TRM-PTFE films and the experimental data obtained.

The formation of inclusion complexes of the (6-FAM)₂ bifluorophore with α-, β-, and γ-cyclodextrins in a phosphate buffer solution (pH 9.0) was studied by spectrophotometry and fluorimetry. The association constants and Gibbs energy changes for 1:1 stoichiometry was determined. The highest association constant was observed for the complex with β-cyclodextrin, which is explained by the optimal spatial match between the guest molecule and the host’s cavity. The effect of the (6-FAM)₂/β-CD inclusion complex on the fluorescent response of the system in the presence of protein (bovine serum albumin) is shown.

Using hyperspectral imaging, the ontogenetic and heat-induced changes in the reflectance spectra of primary leaves of Hordeum vulgare L. seedlings of different ages in the visible and near-infrared (NIR) spectral regions we studied. It was found that, NIR light reflectance decreased and the mesophyll structure became less compact during leaf growing. Chlorophyll pigment absorption increased from 4 to 7 day of growth and then decreased. High temperature (40°C, 3 h, illumination of 120 µmol quanta · m^–2 · s^–1) effected insignificantly the reflectance coefficients of leaves of 4- and 7-day-old seedlings in NIR, but significantly reduced leaf density in 11-day-old plants. At the same time, the absorption of chlorophyll pigments significantly decreased in 4- and 11-day-old seedlings and remained unchanged in 7-day-old leaves after heating. Light absorption by water molecules in the studied seedlings of all age groups did not change significantly after heat exposure. A comparative and correlation analysis of eight commonly used vegetation indexes was carried out. It was found that the heat led to a significant decrease in the “photochemical reflectance index” (PRI) in 4-day-old leaves and the “red-edge normalised difference vegetation index” (NDVI705) and “structure-insensitive pigment index” (SIPI) in 11-day-old seedlings. It is proposed to use these vegetation indexes to assess heat stress in plants.

The potential of Raman spectroscopy (RS) and photoluminescence (PL) for studying energy materials is discussed (phase composition analysis, assessment of crystal structure perfection and stability of a wide range of materials, study of electrodes for metal-ion batteries, photostability testing of photovoltaic devices, etc.). Specifically, the feasibility of assessing material quality based on the spectral linewidth in the RS spectrum and the intensity of the exciton line in the PL spectrum, determining corrosion resistance, establishing the behavior of electrodes for metal-ion batteries during their electrochemical polarization using operando Raman spectroscopy, and identifying ongoing photoinduced processes in solar cells by jointly recording the spectral and photoelectric characteristics and their evolution under illumination.

Machine learning methods (principal component analysis, support vector regression and partial least squares) are used to calibrate the temperature based on the spectra of Ho³⁺ upconversion fluorescence in alumofluoride glasses in the wavelength ranges of 505–560 nm and 605–670 nm for the temperature range from 30 to 105°C along with the traditional ratiometric method. Among the methods considered, the best calibration models were obtained by the partial least squares with searching the combination of moving window partial least squares with the fluorescence spectra of 95MgCaSrBaYAl₂F₁₄-5Ba(PO₃)₂:5%Yb³⁺,0.1%Ho³⁺ glass. The values of absolute sensitivity of 0.021 K^–1 and temperature uncertainty of 0.12 K achieved by machine learning methods significantly exceed the characteristics of the ratiometric method.

The paper presents the results of developing a multiwavelength TEA laser with a selective dispersive resonator, providing multiwavelength generation in the near- and mid-IR ranges (1.1–3.5 and 9.2–10.8 μm). The use of a combined gas mixture containing CO2 molecules and inert gases (Xe, Kr, Ar, and Ne) enables high-quality radiation with narrow spectral lines, which are necessary for applied spectroscopy and remote gas analysis. The developed optical scheme with a diffraction grating and blocking units ensures fast (0.2 s) sequential switching between spectral lines, which allows for the efficient achievement of the so-called “frozen atmosphere” effect during measurements. The proposed approach significantly simplifies the design and improves the reliability of multi-wavelength gas analyzers, expanding their functionality while reducing cost and size. The developed laser could become a promising radiation source for remote sensing of the atmosphere and determining the concentrations of gases such as CO₂ and NH₃.

An in situ Raman spectroscopy study has established a chemical mechanism for the interaction of gadolinium oxide with a molten fluoride mixture, FLiNaK, which holds promise for the use as a medium for the pyrochemical reprocessing of spent uranium-gadolinium oxide nuclear fuel. High-temperature spectral studies along with the use of Х-ray phase analysis have indicated an irreversible heterogeneous reaction Gd₂O_3s + 2LiF_sol→2GdOF_s + Li₂O_sol. The influence of temperature on the kinetics and completeness of the reaction has been established. When the temperature increases, the interaction process accelerates, the equilibrium content of Gd₂O₃ decreases, and one of GdOF increases. The reaction product (gadolinium oxyfluoride GdOF) has been shown to form rhombohedral (R3m) crystal modification. The difference in the reactivity of Gd₂O₃ and La₂O₃ in the fluoride melt FLiNaK was established.

The preparation of LaAlO₃ doped with various concentrations of Dy³⁺ via a solid-state reaction technique is reported. Optimum photoluminescence (PL) emission was observed for 3.0 mol.% dopant. The critical distance between the activators for the optimum PL case was 3.330 Å. PL emission peaks centered at 478 and 494 nm and at 590 and 615 nm were observed and attributed to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺, respectively. The thermoluminescence glow curve shape factors for various cases indicated the existence of second-order kinetics with deeper traps with activation energies in the range of 0.44–0.46 eV.

This work reports on a composite nanostructure for the detection of dipicolinate (DPA), using a luminescent metal-organic framework (MOF) as the supporting lattice and a Rose Bengal-derived organic dye as the sensing probe. This composite structure was characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and photophysical analyses. Two possible sensing paths were identified: colorimetric sensing based on absorption spectra and ratiometric fluorescent sensing based on emission spectra. The sensing mechanism involved a combination of the dye emission turn-on effect induced by DPA and the Eu emission turn-off effect caused by an energy transfer process. Linear sensing responses and good selectivity were observed for both sensing pathways, with a limit of detection of 2.2 μM. The advantage of this composite structure lies in its capability for naked-eye detection and the presence of two sensing pathways with linear responses.

The quantitative nuclear magnetic resonance (qNMR) method of quantifying the content of pharmaceuticals is an important and growing science in the current era. The deuterium-based solvents contribute to the main costs of the NMR-based analysis. In this study, we introduced the use of deuterium-free solvent (i.e., water H₂O) for the quantification of ciprofloxacin (CIP) using the qNMR method. p-Nitrophenol (PNP) was used as an internal standard to solve the absolute integration of signals in NMR spectra. Quantification results were compared with literature-reported high-performance liquid chromatographic (HPLC) methods and analyzed by analysis of variance (ANOVA). The ANOVA results show that the regression model is highly significant (F = 37515.62, p < 0.001), indicating that the actual quantity of the analyte is a powerful predictor of the quantized concentration. An ANOVA study demonstrated that using simple water as a solvent in the qNMR method is as effective as the HPLC method for the quantitative analysis of CIP. The investigated method accurately compensated for the deficiencies of the current HPLC method for quantitative measurement of CIP, and the use of PNP overcame the problem of absolute integration of signals associated with NMR spectra.

We present an analytical technique for quantifying the elemental composition of human teeth using low-energy photon attenuation in the 10–150 keV range. The method leverages the strong atomic number (Z) dependence of the photoelectric effect, facilitating the precise identification and quantification of major constituents (e.g., Ca, P) and trace elements (e.g., Na, Mg). Dental samples, representing demographic groups from children to elderly individuals, were analyzed using a high-purity germanium (HPGe) ϒ-ray spectrometer, configured for high energy resolution at low photon energies. Experimental mass attenuation coefficients were validated against both Geant4 Monte Carlo simulations and the XCOM database, demonstrating strong agreement with deviations consistently below 5%. The technique offers distinct advantages over surface-sensitive methods for obtaining depth-averaged compositional data.

Poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) polymer-based light-emitting diodes (PLEDs) were synthesized using toluene and tetrahydrofuran (THF). The PFO-based PLEDs were deposited onto polyaniline (emeraldine base) (PANI)/ITO using the doctor blade technique, followed by structural, morphological, topographical and electrical properties of the polymer films were examined. The chemical bonds, absorbance and photoluminescence (PL) spectra of the samples were also investigated, and the effect of the precursor solvent on these characteristics of PFO-based PLEDs was studied, revealing that the toluene-PFO film (higher viscosity and surface roughness) displayed a higher PL intensity. Polarity affects the emission wavelength by causing a red shift in the PL spectra to the THF-PFO film, which is attributable to its higher polarity index. Vapor pressure was shown to cause switching of the PL intensity for both PFO-based PLEDs. The results also revealed poor color quality in the green emission at 2.2 to 2.4 eV; thus, viscosity, vapor pressure and polarity of the solvents strongly affect the characteristics of PFO thin films. The precursor solvent for the synthesis of PFO can be considered a tuning factor for the emission of PFO-based PLED.

Trace element analysis of ancient human remains plays an important role in reconstructing dietary habits and living environments. However, conventional analytical methods have critical limitations such as destructive sampling, high costs, and inadequate sensitivity. To address these challenges, a reversible fluorescent probe with specific recognition for Cu^2⁺ was fabricated and characterized in this study for cell detection and bioimaging. Compared with other cations in solution, the probe exhibited exceptional selectivity and sensitivity towards Cu^2⁺. The interaction between the probe and Cu^2⁺ accelerated the ring-opening process, resulting in a new emission band at 525 nm within a specific pH range. A strong linear relationship between the fluorescence intensity and Cu^2⁺ concentration, ranging from 0.0 to 1.0 equivalents, with a detection limit of 4.52 μM, was observed. In addition, Job plots and infrared spectral analysis revealed that B probe complexed Cu²⁺ at a 1:1 ratio. Biological testing revealed that the probe has good biocompatibility and can be effectively used for Cu^2⁺ cell imaging. Cu²⁺-specific reversible fluorescent probes can be designed and fabricated with good fluorescence response characteristics and combined with fluorescence spectroscopy technology to accurately quantify Cu²⁺ in complex ancient human samples.

A perylene-based turn-off fluorescent strategy for tetracycline antibiotics (TCs) detection has been established with gold nanoparticles. TCs directly participate in the reduction of chloroauric acid to generate gold atoms, which subsequently nucleate and assemble into gold nanoparticles (TCs-AuNPs). Because of the overlap between the absorption of TCs-AuNPs and the fluorescence emission of the perylene probe (PDI), the inner filter effect (IFE)-based fluorescence turn-off assay was successfully established. Consequently, the fluorescence peaks of the PDI at 550 and 591 nm were quenched by TC-AuNPs via the IFE process. The assay method shows high sensitivity with a limit of detection of 2.4 mM, and remarkable selectivity against common interfering substances. The turn-off fluorescence sensing method is fairly simple, fast, and inexpensive, and it has also been successfully used for real water sample analysis. Consequently, a highly sensitive and selective method for the detection of TC via a fluorescent turn-off mechanism based on the IFE between the PDI probe and TC-AuNPs in aqueous media was successfully established.

Tin oxide, a distinguished metal oxide suitable for optoelectronic usage, has features that can be easily enhanced through doping. In the current study, films of zinc-doped SnO₂ (Zn/Sn = 0.03) were synthesized via the sol-gel screen-printing strategy and subsequently sintered at 450°C for 10 min. X-ray diffraction findings established the polycrystalline characteristics and single-phase tetragonal configuration of the synthesized films. The occurrence of Sn, O, and Zn ions is evidenced by energy-dispersive X-ray analysis. According to UV-Vis analysis, the band gap energy (direct transition) was found to be 3.62 eV. Hall measurement analysis revealed the n-type conductivity of the films, characterized by a resistivity of 1.03x10^–3 Ω · cm.

This research presents the successful synthesis of copper sulfide (CuS) nanoparticles (NPs) through a controlled hydrothermal synthesis approach. Complete material characterization is performed using multiple analytical techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, UV-visible diffuse reflectance spectroscopy, differential thermal analysis, and photoluminescence measurements. SEM indicated the presence of NPs, and energy-dispersive X-ray spectroscopy data confirmed the existence of sulfur and copper elements as primary constituents of the synthesized materials. Crystallographic investigation through XRD provided detailed structural information, with an average particle size of 18.07 nm. The sample confirms a hexagonal crystal framework with 12-fold coordination geometry. CuS nanostructures displayed characteristic optical absorption behavior in the ultraviolet spectrum, with notable absorption features spanning a 150–500 nm wavelength range, revealing a calculated optical bandgap of 2.19 eV. Photoluminescence analysis shows emission at a 503 nm wavelength, indicating characteristic blue emission in the synthesized materials. Thermal characterization showed a material stability across the 300–400°C temperature range, with exothermic behavior occurring at 342°C, complemented by heat release of 50.5 µV.

Elemental imaging is widely attracting attention from various scientific fields, but it suffers from slow sampling speed using conventional Nd:YAG lasers (<100 Hz) and motorized stages. Moreover, using these higher-quality techniques to accelerate the imaging speed to 1,000 Hz would be costly. To provide an even faster and more cost-effective elemental imaging alternative, this research integrated a high-repetition-rate fiber laser, a galvanometric scanner, an F-Theta lens, and a high-speed spectrometer to build a high-speed laser-induced breakdown spectrometry imaging system. By optimizing the instrumentation and laser/spectrometer parameters, the spectrum signal was significantly improved compared with that produced by the original system. The limit of detection values for Cu, Mg, Mn, Si, and Cr were calculated to be 422.6, 361.3, 256.4, 481.9, and 300.3 μg/g, respectively. After the moving parameters of the galvanometric scanner were thoroughly adjusted, a maximum pixel sampling rate of 2,013 Hz was achieved. A real rock sample was tested using the imaging system, by which the distribution pattern of nine elements – Mg, Al, Si, K, Li, O, Sr, Fe, and Na – was clearly determined to be in accordance with the different regions of color in the corresponding photograph. The results verify the viability of the high-speed imaging system devised in this study.

The aim of this study is to develop and validate UV spectrophotometric and RP-HPLC methods for the simultaneous quantification of empagliflozin and losartan in a synthetic fixed-dose combination. In addition to method validation, a sustainability and complexity assessment was performed to support method selection for routine pharmaceutical analysis. The UV method is based on a Q-absorbance ratio approach using 225 and 239.20 nm, while the HPLC method employed a C18 column with a mobile phase of orthophosphoric acid buffer (pH 3.0) and acetonitrile (50:50, v/v), at a flow rate of 1.0 mL/min with detection at 217 nm. Both methods were validated according to ICH Q2(R2) guidelines. Further evaluation was conducted using the blue applicability grade index (BAGI) and click analytical chemistry index (CACI) to assess greenness and procedural efficiency. Both methods demonstrated excellent linearity (r² > 0.996), precision (%RSD < 2), and recovery within the acceptable range of 98–102%. The UV method achieved good scores in environmental sustainability (BAGI = 82.5) and practical simplicity (CACI = 74) compared to the HPLC method (BAGI = 72.5, CACI = 77). The assay results confirmed the accuracy of both methods for simultaneous estimation of empagliflozin and losartan without interference from excipients. The developed UV spectrophotometry and RP-HPLC methods are found to be accurate, precise, and suitable for routine estimations of empagliflozin and losartan in bulk and laboratory-prepared mixtures. The greenness assessments of developed methods further support the UV method as a more sustainable and efficient choice, while the HPLC method remains preferable where greater sensitivity or automation is required.

This paper presents optical and photoluminescence (PL) properties of liquid crystalline (LC) compound-like p-n-nonyloxy (9OBA) benzoic acid, with the dispersion of zinc oxide (ZnO) nanoparticles (NPs) in different concentrations (0.5–2 wt.%). The optical absorbance reveals an absorption peak for pure 9OBA at 240 nm that is shifted to 238 nm upon dispersion of 1 wt.% ZnO NPs. PL studies show two significant peaks at 362 and 588 nm for pure 9OBA and 389 nm for dispersed ZnO NPs. The peak observed at 389 nm corresponds to the near-band-edge emission of free exactions, while the peak at 588 nm is indicative of deep-level emission, resulting from point defects such as vacancies and interstitials within the bandgap. Refractive indices, birefringence, and dispersive power are measured for the prepared samples. The properties related to refractive index, birefringence, and dispersive powers are enhanced through the dispersion of ZnO NPs in the 9OBA LC compound. The refractive indices measured are fitted with two- and three-coefficient Cauchy models. The outcome of the results suggests an enhancement in material properties that are beneficial for display technologies.

This study aims to measure the concentrations of chemical oxygen demand (COD), nitrate, ammonia nitrogen, total nitrogen (TN), and total phosphorus (TP) in the main treatment stages of an urban wastewater treatment plant (WWTP) using a fused spectral technique integrating three-dimensional fluorescence spectroscopy and UV-Vis absorption spectroscopy, combined with a single-parameter feature selection method. Three-dimensional fluorescence spectra (Excitation-Emission-Matrix Spectra, EEMs) and UV-Vis absorption spectra of water samples were collected at the inlet, anaerobic tank, anoxic tank, aerobic tank, biochemical tank, secondary sedimentation tank, high-efficiency sedimentation tank, deep-bed filter, and effluent of the WWTP. Then, pretreatment methods, including standard normal variate (SNV), total normalization (Total), maximum normalization (Max), and min-max normalization (Max-Min) were applied to the original spectra, including raw three-dimensional fluorescence spectra and raw UV-Vis absorption spectra, to facilitate spectral data fusion. Given the different responses of various water quality parameters to fluorescence and absorption spectra, multiple feature selection methods – including competitive adaptive reweighted sampling (CARS), random frog (RF), uninformative variable elimination (UVE), and successive projections algorithm (SPA) – were employed to extract the characteristic fluorescence and absorption wavelengths for each water quality parameter. The results show that spectral preprocessing based on SNV and a characteristic wavelength extraction method based on CARS had the best prediction results for multi-parameter water quality in the key processes of the WWTP. Among them, the coefficients of determination (R²) between the predicted values and the actual values of COD, nitrate, ammonia nitrogen, TN, and TP all exceed 0.95. This method can provide theoretical guidance for the rapid diagnosis of operational stability in WWTPs.

The algal photosynthetic inhibition method for biological toxicity detection offers advantages such as rapid response and simple measurement. To address the insufficient response sensitivity of existing photosynthetic fluorescence parameters to typical photosystem I (PSI) inhibitors, this study developed a comprehensive parameter index (CPI) for aquatic biological toxicity, which is established based on the segmented inhibition characteristics of the fluorescence kinetic curve. CPI was systematically compared with the commonly used chlorophyll fluorescence parameters: the maximum quantum yield of photosystem II (F_v/F_m) and the performance index on an absorption basis (PI_abs). The comparison focused on three key aspects: toxicity response time, response sensitivity, and stability, and the results indicated that, unlike F_v/F_m, both CPI and PI_abs exhibited shorter toxicity response times and higher response sensitivities when exposed to typical photosystem I(PSI) and photosystem II(PSII) inhibitors. Consequently, subsequent investigations focused exclusively on evaluating the representational efficacy of these two parameters (CPI and PI_abs). For the PSII inhibitor Atrazine, when CPI and PI_abs were employed as response parameters, the limits of detection (LODs) for short-term inhibition (15 min) were 6.65 and 4.49 μg/L, respectively, and for long-term inhibition (4 h) they were 2.22 and 2.44 μg/L, respectively. No significant difference in response sensitivity was observed between CPI and PI_abs against the PSII inhibitor; however, with respect to the PSI inhibitor Paraquat, when using CPI and PI_abs for toxicity characterization the LODs were 0.68 and 1.21 mg/L for short-term inhibition (15 min), and 0.22 and 0.42 mg/L for long-term inhibition (8 h). Specifically, for PSI inhibitors, the LODs of CPI for both short-term and long-term inhibition were approximately reduced by 50% lower than those obtained with PI_abs. In terms of the stability of toxicity response, the relative standard deviations (RSDs) for the PSII inhibitor Atrazine were 5.15% (CPI) and 14.14% (PI_abs) after a short exposure duration of 15 min, and 4.43% (CPI) and 5.38% (PI_abs) after an extended exposure duration of 4 hours. For the PSI inhibitor Paraquat, the RSDs were 10.18% (CPI) and 32.79% (PI_abs) after 15 min, and 3.30% (CPI) and 13.54% (PI_abs) after 8 h. These results confirmed that CPI demonstrated superior performance in ensuring the stability of toxicity characterization for both representative inhibitors. Collectively, these findings demonstrate that the CPI can be effectively applied for the highly sensitive detection of biological toxicity induced by both PSI and PSII inhibitors. This not only resolves the issue of low response sensitivity of the algal photosynthetic inhibition method toward PSI inhibitors, but also provides a critical parameter support for the unification of toxicity response indicators corresponding to PSI and PSII inhibitors.