Lifetime Values Research Articles

Multi-focal lipid membrane characterization by combination of DAS-deconvolution and anisotropy: Novel insight of fluorescence analysis

Three analogue solvatochromic probes, Laurdan, Prodan, and Acdan, are extensively used in the study of biological sciences. Their locations in lipid membranes vary greatly in depth, and their fluorescence responds to their surrounding environment based on their corresponding locations in the membrane. Utilizing the fluorescence lifetimes (τ) and emission peaks (λ) acquired from time-resolved emission spectrum, one can effectively determine the local lipid environment using the analytical approach refer to as τ and λ plots. Herein, τ and λ plot was created using the aforementioned probes to expand the analytical field according to their location. Furthermore, the solvent modeling method in τ and λ plot was upgraded to artificially emulate the complex environment in lipid membranes by utilizing liquid paraffin and glycerol to assess the contribution of viscosity to each fluorescence distribution. According to the results from a series of solvent mixtures, the effect of solvent viscosity on lifetime values was confirmed in the short lifetime region (∼ 3 ns). However, it was impossible to emulate the long lifetime values (4 ns ∼) observed in lipid membranes containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the range of viscosity applied in this study. From the insight of the limiting anisotropy (r∞), the τ and λ plot was divided into a solvent-like region with isotropic environment (r∞ < 0.15) and a highly ordered region enough to define as anisotropic environment (0.15 <r∞) at τ: 4 ns. Also, the membrane-specific distribution was illustrated as 4 ns <τ and λ < 460 nm from this work. Updated analytical model was created to visualize multiple fluorescence components of each probe in 6 types of lipid bilayers, confirming the different distributions between these probes. Our results well-illustrated the multiplicity of lipid environments modeled with solvent and ordered environments in each lipid bilayer systems.

Thermally stable white light emission and energy transfer analysis of tungstate-tellurite glasses co-activated with Dy3+/Eu3+ for optoelectronic applications

In this study, dual ions (Dy3+/Eu3+) doped tungstate-tellurite (TWKZBi: Dy3+/Eu3+) glass matrices have been formed with the help of the melt quenching approach. The structural, thermal, morphological, and photoluminescent (PL) characteristics, as well as the energy transfer (ET) processes were thoroughly investigated. The structural features of the titled glasses have been explored via X-ray diffraction (XRD) analysis. The morphology and elemental studies of the titled glass matrices were verified with the help of field emission scanning electron microscopy (FE-SEM) along with energy dispersive spectroscopy (EDS). The PL results designate that the TWKZBi doped with Dy3+ ions glass samples exhibit a strong emission peak at 575 nm when excited via n-UV light, whereas Eu3+ doped TWKZBi glass sample demonstrates a conspicuous red emission band at 614 nm when stimulated with the n-UV light. In addition, TWKZBi glasses doped with both Dy3+ and Eu3+ ions demonstrate the emission peaks in the blue (B), yellow (Y) and red (R) zones of the electromagnetic spectrum. The combination of these peaks generates white and orange-red light through properly controlling the activator ion concentrations and selected excitations. Based on Dexter's and Reisfeld's approximation, dipole-dipole (d-d) interaction is responsible for the transfer of energy from donor (Dy3+) to accepter (Eu3+) ions. The decay profiles demonstrate the bi-exponential behavior with a decline in the average lifetime (τavg) values as varying activator (Eu3+) ion concentrations in the titled TWKZBi: Dy3+/Eu3+ glasses. All the results above validate that the titled TWKZBi: Dy3+/Eu3+ glass samples could be fascinating for white LEDs and other optoelectronic applications.

Preparation and Photophysical Properties of Znq2 Metallic Nanomaterials

AbstractBis(8‐hydroxyquinolates) Zinc (Znq2) can be used as a light‐emitting layer material in OLED devices to achieve its efficient electroluminescence effect. In this paper, Znq2 powder has been successfully synthesized and modified by the physical vapor deposition (PVD) method. Precursors and nano‐materials are characterized by XRD, SEM, PL, and so on. The performance of the modified material has been significantly improved. The emission intensity and absorption intensity in the deposited products increased with the increase in PVD temperature. At 453 K, luminous properties such as luminous intensity reach the optimal value including its fluorescence lifetime. Fluorescence lifetime values vary from 13 to 17 ns with the increase in temperature. The luminescence mechanism is also discussed. The energy gap and absorption spectrum of HOM‐LUMO are calculated by the DFT/UB3LYP method. The experimental values agree well with the theoretical values. The nanomaterial crystals modified by PVD technology are more orderly, impurities are reduced, and the luminous stability of the material is improved, which may be one of the reasons for the relatively slow decline in product life. The research combined with theoretical simulation is expected to be helpful to the research and promotion of such materials.

Concentration-Dependent Photoluminescence of Carbon Quantum Dots Useable in LED.

We synthesized carbon quantum dots (CQDs) using a solvothermal method with o-phenylenediamine as the carbon and nitrogen source. The sample was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. When we continued the optical characterization of the CQDs, we were surprised to discover that the colors of the synthesized CQDs changed with the dilution of the original solution. In addition, the photoluminescence (PL) of CQDs under 405 nm continuous wave laser excitation was also investigated. It was found that CQDs with different concentrations exhibited different PL spectra. In order to explain the mechanism of different PL spectra, chemical characterization of the CQDs at different concentrations was performed again, revealing that the color change is independent of particle size and surface functional groups. Systematic optical characterization and theoretical analysis indicate that this color change results from the interparticle distance. Furthermore, we investigated the PL lifetimes of CQDs using time-resolved PL measurements and found that the PL lifetime values change with the concentration of CQDs, which is attributed to nonradiative transitions. Finally, we fabricated warm white-light-emitting diodes with CQDs that are proportionally adjusted in concentrations. The investigation developed a simple and effective method to tune the color of CQDs by adjusting the concentration through dilution of the original solution, which provides a new approach for the preparation and regulation of multicolor CQDs.

Precision measurement of the Ξb− baryon lifetime

A sample of pp collision data, corresponding to an integrated luminosity of 5.5 fb−1 and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Ξb− baryon to that of the Λb0 baryon, rτ≡τΞb−/τΛb0. The value rτ=1.076±0.013±0.006 is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain rτRun 1,2=1.078±0.012±0.007. Multiplying by the world-average value of the Λb0 lifetime yields τΞb−Run 1,2=1.578±0.018±0.010±0.011 ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λb0 lifetime. This measurement improves the precision of the current world average of the Ξb− lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Fully relativistic energies, transition properties, and lifetimes of lithium-like germanium

Abstract Employing two fully relativistic methods, the multi-reference configuration Dirac–Hartree–Fock (MCDHF) method and the relativistic many-body perturbation theory (RMBPT) method, we report energies and lifetime values for the lowest 35 energy levels of the (1s2)nl configurations (where the principal quantum number n = 2–6 and the angular quantum number l = 0, …, n–1) of lithium-like germanium (Ge XXX), as well as complete data on the transition wavelengths, radiative rates, absorption oscillator strengths, and line strengths between the levels. Both the allowed (E1) and forbidden (magnetic dipole M1, magnetic quadrupole M2, and electric quadrupole E2) ones are reported. The results from the two methods are consistent with each other and align well with previous accurate experimental and theoretical findings. We assess the overall accuracies of present RMBPT results to be likely the most precise ones to date. The present fully relativistic results should be helpful for soft x-ray laser research, spectral line identification, plasma modeling and diagnosing. The datasets presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00113.00135.

Light-induced fading effects on TL and OSL signals and feasibility of dose re-assessment with PTTL signals in BeO dosimeters

Abstract This study aims to investigate both light-induced fading effects on thermoluminescence (TL) and optically stimulated luminescence (OSL) signals under three different light sources (fluorescent, UV-254 and daylight) and dose reassessment with phototransferred TL (PTTL) signals in Beryllium oxide dosimeters. TL and OSL signals were deconvoluted for each light source. Accordingly, variations in the maximum peak temperature, activation energy, peak area value for the TL signal, and intensity and lifetime values for the OSL signal were monitored. Each peak, OSL component, and total area value exhibited different behaviors depending on the light source. Considering the total area condition, the TL intensity decreased by ∼90%, ∼80%, and ∼70% in UV-254, daylight, and fluorescent light exposure, respectively, at the end of the 120 min. On the other hand, the OSL total area intensity faded quickly for both UV-254 and daylight, while it decreased by ∼45% for fluorescent light. According to these results, regardless of TL and OSL measurements, the dosimeters should be kept primarily away from daylight and fluorescent light after irradiation, instead of UV-254, which is rarely encountered in daily life. The feasibility of dose reassessment using PTTL signals under UV-254 light was investigated within a wide dose range from 0.1 to 128 Gy. It is feasible to reassess doses between 0.5 and 32 Gy considering the total area intensity of PTTL signals. In conclusion, PTTL signals can be easily used in fields of the order of Gy, such as in reevaluating doses in radiotherapy applications.

Comparative analysis of predose effects on TL and OSL signals in BeO dosimeters

This study investigates in detail the effects of predose on TL and OSL signals for BeO dosimeters. The TL and OSL signals were deconvoluted to each peak and component. As a result of deconvolution, the variations in the kinetic parameters (E, Tmax, b) for the TL signals and the lifetime values of the OSL signals were investigated. In addition, sensitivity changes according to predose were monitored for each peak and component. Finally, dose response curves were studied using the dose linearity index (f(D)) for each peak and component. Accordingly, the peak structures and kinetic parameters did not change according to the predose for the TL signal, whereas variations in the lifetime values for the OSL signal were observed, especially at the initial dose values (0.1 and 0.2 Gy). There was no change in sensitivity according to the predose for the total area condition although each peak and component exhibited independent behavior. Therefore, TL and OSL signals should be evaluated based on the total area in predose applications. The TL and OSL dose response curves exhibited different behaviors according to predose. TL dose response curves were not affected by the predose except for 1000 Gy, while the OSL dose response curves were affected by the predose considering the total area condition. The possible reason for the differences between the TL and OSL dose response curves is the significant transfer effect in the OSL signal at low doses, which results in greater changes at low doses compared to the TL signal. Also, thermal quenching effects may have resulted in lower intensity in the case of the TL signal. In future studies, preheating tests and thermal quenching corrections on TL peaks at high predoses may increase our understanding of deep trap interactions in BeO dosimeters.

Nanoparticle doping and molten-core methods towards highly thulium-doped silica fibers for 0.79 μm-pumped 2 μm fiber lasers – A fluorescence lifetime study

We study the fluorescence lifetime of Thulium-doped silica fibers for efficient laser operation in the 2 μm “eye-safe” wavelength range pumped by 0.79 μm radiation. A large set of optical fibers prepared by Modified Chemical Vapor Deposition combined with solution doping or nanoparticle doping, and Molten-core method is investigated in terms of fluorescence lifetimes of the 3F4 and 3H4 excited levels, which contain information about the Tm3+ ion environment, the rate of unwanted processes, such as concentration quenching or multiphonon relaxation, as well as the inter-ionic energy-transfer processes, including the cross-relaxation. Maximum evaluated lifetime values are 778 μs for the 3F4 level and 56 μs for the 3H4 level. From the lifetime study, we conclude that for Tm3+ concentrations above 10,000 ppm and enhanced aluminum concentrations above 5 mol. % Al2O3, the cross-relaxation efficiency is enhanced and multiphonon relaxation is remarkably reduced due to the lower phonon energy of the resulting alumino-silicate glass.

Solvent effect on the excited state photophysics of Imiquimod: A DFT/TD-DFT and spectroscopic study

Solvation plays an important role in chemistry and biology. The role of the solvent is crucial in any chemical processes such as tautomerization that controls the structure and function of biomolecules. The current study aims to explore how different solvent medium affects the tautomeric forms of an antitumor drug, Imiquimod (IMQ). We have used several spectroscopical methods, including UV–Vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and quantum mechanical (QM) calculations. Our results revealed that solvent, indeed, plays a significant role in the modulation of the photophysics of the drug. IMQ has three emission bands in protic and aprotic solvents and two bands in non-polar medium associated with different forms of the drug. Using time-resolved technique, and comparing with the predicted lifetimes from QM calculations, we succeed to assign these three forms as cation, tautomer and neutral of IMQ with 1.6 ns, 2.0 ns and 4.0 ns lifetime values, respectively. Since IMQ is a nucleobase analogue and one of the most effective medications for skin tumors; these findings about which specie of IMQ is present in a given medium, and beyond, how the medium alters the photophysics of the molecule may provide deeper insights into its structure and function.

Analysis of luminescent properties of 40PbO–35Bi2O3–25Ga2O3 glasses doped with Er2O3

The Er3+ doped lead–bismuth–gallium oxide glasses were prepared by melt quenching technique. The spectral and luminescent properties were analyzed based on experimental and theoretical calculations. Analysis of Er3+ concentration dependences of density and electronic optical polarizability was carried out. The radiative lifetime values for 4S3/2 and 4F9/2 energy states were calculated using Judd-Ofelt theory. In the glassy system under study, the concentration quenching of state 4S3/2 was discovered at content of erbium ions above 0.869 × 1020 cm−3. It was also shown that 4F9/2 energy state was isolated from concentration effects and showed an increase in luminescence intensity with increasing concentration of activator ions. The luminescence quantum efficiency for transition 4S3/2 → 4I15/2 was about 40%, which allows us to consider this system as a glassy matrix effective for activation by rare-earth ions.

Investigation of column purified dye derived carbon nanomaterials for security printing and supercapacitor applications

Literature evidence reveals versatile applications of carbon dots (CDs), but generally mixtures of various types of carbon nanomaterials, molecular intermediates as well as side products are obtained upon hydrothermal treatment of the precursor material. This demands isolation of pure components and their complete characterization before these nano carbonaceous materials are chosen for suitable applications. In the present study, perylenetetracarboxylic dianhydride (PTCDA) is subjected to hydrothermal treatment and the mother liquor obtained is separated using column chromatography technique using dichloromethane-methanol solvent system to isolate fractions of various fluorescent carbonaceous nanostructures. The TEM imaging of nano carbonaceous particles of all five fractions indicated that the first and third fractions were composed of nanoribbons, while the latter two fractions largely contained quasi-spherical nanoparticles of both lesser (carbon quantum dots) and greater (carbon nanodots) than 10 nm dimensions. The XPS results of all the fractions suggested separation based on polarity difference. The ID/IG ratios obtained from Raman spectra implied the presence of several defects on the CDs. The time resolved fluorescence spectra of third, fourth and fifth fractions revealed mono-exponential decay of fluorophores with excitation independent average lifetime values. The fifth fraction exhibited good biocompatibility and the highest absolute fluorescence quantum yield of 58.47 % among all the isolated samples. As these CDs displayed a remarkable rise in the quantum yield to 88.60 % when dispersed in water, a water-based flexo-ink was formulated. The photostable pale yellow flexo print proofs obtained on UV dull paper exhibited a green fluorescence under 365 nm illumination, whereas a yellow glow when shined with blue light, which can serve as an authentication feature for security documents and currency notes. Moreover, as the third fraction constitutes mainly of carbon nanoribbons (CNRs), an optimized polymer electrolyte was prepared along with sodium alginate (SA), and MgCl2 to understand their potential use in energy storage application. A supercapacitor was fabricated and tested for its electrochemical performance such as cyclic voltammtery (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD). An enhanced current window was observed in the CV of SA/CNRs compared to pure SA and SA/CNRs/Mg films, which indicated a structural interaction of CNRs with SA. The conductivity of SA/CNRs/Mg was lesser than SA/CNRs in EIS studies due to the presence of Mg ions, while pure SA showed lesser conductivity. The dual ionic interaction of Na and Mg along with enhanced structural stability due to doped CNRs favors its convenient supercapacitor application. The fabricated eco-friendly supercapacitor showed a specific capacitance of 84 F/g. The GCD of the device displayed pseudocapacitance behaviour and was quite stable for 2000 cycles with coulombic efficiency of 96 %.

Microstructural evolution and luminescence properties of multi-excitable cubic-ZrW2O8:Dy3+ nanorods for white light applications

ZrW2O8 nanorods doped with various concentrations of Dy3+ ions (5 - 15 mol%) showing excellent photoluminescence (PL) properties were synthesized by the facile hydrothermal method for white light applications. The products were comprehensively analyzed using a range of structural, morphological, and optical techniques. The optical studies were conducted by utilizing UV–visible and photoluminescence spectrophotometers. The photoluminescent emission spectra exhibit two prominent peaks at wavelengths of 479 nm and 572 nm, along with a less intense peak at 661 nm when subjected to excitations at wavelengths of 286 nm and 352 nm, and a highly dominating yellow emission with a faint red emission was obtained at 452 nm excitation. The almost constant value Y/B intensity ratios, lifetime values, CIE coordinates, and CCT values suggest that the obtained nanophosphor can be effectively employed in white light-emitting diodes (WLEDs) and various other lighting devices.

New results on the two-body decay of neutrons shed new light on neutron stars

In attempts to resolve the neutron lifetime puzzle, there was suggested a hypothetical decay of neutrons into some unspecified dark matter (DM) particles. Later there were performed studies on how the hypothetical decay of neutrons would affect neutron stars. Recently it was shown that with the allowance for the second solution of Dirac equation for hydrogen atoms, the theoretical branching ratio (BR) for the two-body decay of neutrons (compared to their three-body decay) is amplified by a factor of 3300 from 0.000004. So, the BR becomes about 1.3% in the excellent agreement with the “experimental” BR = (1.15 ± 0.27)% required for reconciling the two distinct experimental values of the neutron lifetime: one from the beam experiments, another from the trap experiments. This meant that the two-body decay of neutrons in the beam experiments (that count only the protons) plays a much more sizable part in the overestimation of the lifetime of neutrons in these experiments than previously thought. Hydrogen atoms corresponding to the second solution of Dirac equations are called the second flavor of hydrogen atoms (SFHA) by the analogy with the flavors of quarks. The existence of the SFHA is evidenced by four different types of atomic/molecular experiments. The primary feature of the SFHA is that due to having only the s-states, they do not emit or absorb the electromagnetic radiation (except for the 21 cm line): they are practically dark. The SFHA became a candidate for a part of DM for the first time after the SFHA-based successful qualitative and quantitative explanation of the perplexing observation by Bowman et al. of the anomalous absorption in the redshifted 21 cm line from the early Universe. In the present paper we analyzed how this neutron decay into the SFHA affects neutron stars. We showed that old neutron stars could very slowly generate the new specific, described in detail baryonic DM in the form of the SFHA. Some old neutron stars would release it into their tiny atmospheres, while some other old neutron stars would release it into the interstellar medium. Besides, mergers of a neutron star with another neutron star or with a black hole, accompanied by the ejection of neutron-rich material, can also lead to the formation of SFHA as the ejecta cools down. This is another interesting aspect of the multi-messenger astronomy focused on studying these mergers through the gravitational waves they generate. These mechanisms of generating new baryonic DM in the universe should have the fundamental importance. We point out the indirect observational evidence of the continuing generation of new baryonic DM. We hope that our results will stimulate a further research in this direction.

Structural, optical and luminescent properties of Tm3+-doped phosphate oxyfluoride glasses for blue emission solid state devices

In this work, the visible luminescence of P2O5-KF-Al2O3 glasses with Tm2O3 was studied. The Tm3+ ion can have a strong blue emission, which allows the development of LEDs in this color region. This study refers to the synthesis of oxyfluorophosphate glasses, 38P2O5+(50-x)KF+12Al2O3+xTm2O3 (PKAl:Tm), with x = 0.25, 0.50, 0.75, and 1.00 mol%, by the melt-quenching method. The prepared materials showed amorphous characteristics verified by XRD data. The absorption spectra shown six main bands characteristic of Tm3+ ions, from ground state 3H6 to excited levels 3F4, 3H4, 3H5, 3F3,2, 1G4 and 1D2, in which the intensities increased with the concentration of Tm2O3. In the FTIR spectra, it was verified that the profiles of the PKAl samples are similar to glasses based on phosphate systems. The Judd-Ofelt parameters were calculated, where for PKAl glasses the trend was Ω2>Ω4>Ω6. The excitation spectra of PKAl:Tm glasses shown an intense band centered at 358 nm (3H6→1D2). The luminescence spectra with excitation at 358 nm shown two bands at 453 nm (1D2→3F4), and 480 nm (1G4→3H6); the highest emission intensity was observed to the sample doped with 0.75 mol% of Tm2O3. The calculated CIE diagram shown that the doped samples have coordinates close to the primary blue color, which favors the application for the development of blue LEDs and wLEDs. The decay curves for the 1D2 level were fitted by single exponential with lifetime values decreasing with increasing concentration of Tm2O3. These results show that the PKAl:Tm glasses are potential candidates for applications in LEDs.

Photoluminescence emission enhancement in the LiSrVO4:Eu3+ vanadate phosphor by partial substitution of M+ ions (M+=Li+/Na+/K+); optical thermometry; and optical transition probabilities using Judd-Ofelt analysis

In solid state lighting (SSL), pcWLEDs gain more attention for various illumination applications. The Eu3+ activated LiSrVO4:xEu3+ (0–15 mol% in steps of 3) phosphors are prepared by the conventional solid state method and their phase formation is confirmed by PXRD. It suggest that the samples are in a monoclinic structure with P2/m space group. SEM results confirmed that the size of the prepared phosphor is in a micrometer range with an irregular spherical shape. The optical diffuse reflectance spectrum (DRS) consisted broad band absorption in the ultraviolet (UV) region (270–350 nm) and also, they are found to absorb strongly the NUV light (396 nm) and the blue light (466 nm). They exhibit the strongest emission at 617 nm for the samples under 326 nm excitation. The PL intensity of the phosphors are improved by co-doping. The optical transition probabilities of the LiSrVO4:9 mol% Eu3+ phosphor are also analyzed using the Judd-Ofelt theory. The optimized phosphor showed a good thermal stability and the lifetime values are in the millisecond range. The absolute and the relative sensitivities are obtained from the temperature dependent lifetime measurements. The LiSrVO4:9 mol%Eu3+ phosphor yielded CIE coordinates (x, y) of (0.5987, 0.4005), a low CCT of 1468K, and a color purity of 96.4 %. These results indicate the potential application of the LiSrVO4 based phosphors in WLEDs.

Characterization and classification of pathogenic bacteria using native fluorescence and spectral deconvolution.

Identification and classification of pathogenic bacterial strains is of current interest for the early treatment of diseases. In this work, protein fluorescence from eight different pathogenic bacterial strains were characterized using steady state and time resolved fluorescence spectroscopy. The spectral deconvolution method was also employed to decompose the emission contribution from different intrinsic fluorophores and extracted various key parameters, such as intensity, emission maxima, emission line width of the fluorophores, and optical redox ratio. The change in average lifetime values across different bacterial strains exhibits good statistical significance (p ≤ 0.01). The variations in the photophysical characteristics of bacterial strains are due to the different conformational states of the proteins. The stepwise multiple linear discriminate analysis of fluorescence emission spectra at 280 nm excitation across eight different bacterial strains classifies the original groups and cross validated group with 100% and 99.5% accuracy, respectively.

The Effect of Conjugated Nitrile Structures as Acceptor Moieties on the Photovoltaic Properties of Dye-Sensitized Solar Cells: DFT and TD-DFT Investigation.

A major challenge in improving the overall efficiency of dye-sensitized solar cells is improving the optoelectronic properties of small molecule acceptors. This work primarily investigated the effects of conjugation in nitriles incorporated as acceptor moieties into a newly designed series of D-A-A dyes. Density functional theory was employed to specifically study how single-double and single-triple conjugation in nitriles alters the optical and electronic properties of these dyes. The Cy-4c dye with a highly conjugated nitrile unit attained the smallest band gap (1.80 eV), even smaller than that of the strong cyanacrylic anchor group (2.07 eV). The dyes lacking conjugation in nitrile groups did not contribute to the LUMO, while LUMOs extended from donors to conjugated nitrile components, facilitating intramolecular charge transfer and causing a strong bind to the film surface. Density of state analysis revealed a considerable impact of conjugated nitrile on the electronic properties of dyes through an effective contribution in the LUMO, exceeding the role of the well-known strong 2,1,3-benzothiadiazole acceptor unit. The excited state properties and the absorption spectra were investigated using time-dependent density functional theory (TD-DFT). Conjugation in the nitrile unit caused the absorption band to broaden, strengthen, and shift toward the near-infrared region. The proposed dyes also showed optimum photovoltaic properties; all dyes possess high light-harvesting efficiency (LHE) values, specifically 96% for the dyes Cy-3b and Cy-4c, which had the most conjugated nitrile moieties. The dyes with higher degrees of conjugation had longer excitation lifetime values, which promote charge transfer by causing steady charge recombination at the interface. These findings may provide new insights into the structure of conjugated nitriles and their function as acceptor moieties in DSSCS, which may lead to the development of extremely effective photosensitizers for solar cells.

Quantifying the short- and long-term effects of promotional incentives in a loyalty program: Evidence from birthday rewards in a large retail company

Nowadays, many retail companies implement their original loyalty programs to stimulate the willingness of their customers to make a purchase. In these programs, promotional incentives are often incorporated to further enhance customer loyalty; however, few previous studies have assessed the effectiveness of such incentives. Therefore, our study examined both short- and long-term effects of promotional incentives in a loyalty program on customer purchase behavior by analyzing a loyalty program using birthday rewards implemented by a major retail company in Japan. For the analysis, we used the Weibull proportional hazards model, generalized linear model, and Pareto/NBD & gamma-gamma framework after implementing propensity score matching. The estimation results indicated that promotional incentives in a loyalty program temporarily weaken the points pressure effect on the purchase frequency. In addition, promotional incentives in a loyalty program had no positive effect of increasing the customer lifetime value. Furthermore, our study revealed that the lifetime values of loyalty program members who do not exhibit their active purchasing behavior for a certain period of time after impulsive actions induced by promotional incentives are particularly low. These findings will help companies to decide how promotional incentives should be incorporated into their loyalty programs.

Investigating the impact of gamma irradiation and temperature on vacancy formation and recombination in ZrB2 ceramics using positron annihilation spectroscopy

In the presented work, the mechanism of evolution of defects in the crystalline structure after irradiation with 1500 kGy and 3000 kGy absorption dose at room temperature in a 60Co gamma source was studied, using 43 nm sized ZrB2 crystals. The crystals were characterized by a purity of 99.9%, a powder density of 0.23 g/cm3, a specific surface area of 80 to 120 m2/g, and a hexagonal P6/mmm spatial structure. The dose rate applied was 6.05 Gy/s, with 1.17 and 1.37 MeV energy lines. The effect of particles resulting from the decay of 22Naradioactive isotope β+ with an activity of 10.5 μCi, as well as gamma quanta with an energy of 1.27 MeV, on the core and valence electrons and vacancies in the crystal structure was studied using Positron Annihilation Lifetime Spectroscopy (PALS) and Doppler broadening analysis methods. Additionally, the changes in the S and W parameters, which characterize the distribution of defects within the volume of the ZrB2 crystal, were studied using the Doppler broadening method. For unannealed material, the positron lifetime τ1 component varied between 174±2 ps and 181±1 ps. After annealing, the positron lifetime component τ2 was decreased from 290±3 ps to 226±3 ps, and the intensity component I2 increased from 17.49% to 40% depending on the radiation dose. The calculated values of the positron lifetime τ for one boron vacancy from ABINIT and MIKA packages were found to be 172 ps and 145 ps, respectively. The material was observed to satisfy the necessary functional conditions at gamma doses not exceeding 3000 kGy.