Luminescence Measurements Research Articles

Surface flow and aerodynamic drag of Ahmed body with deflectors

This study investigated the surface flow and the aerodynamic characteristics of a 7/10 scale Ahmed model equipped with deflectors at several angles. The experiments were conducted at Reynolds number of 2.45 × 105 based on the model height. A global luminescent oil film skin-friction measurement technique was applied for the flow fields on the slant and base surfaces. The aerodynamic forces of the model were measured to understand the effect of the deflection angle on the aerodynamic characteristics. The pressure was measured and pressure drags acting on the slant and base surfaces were also calculated. The results showed that the drag and lift of the model suddenly dropped at the deflection angle above −5°. The pressure distribution on the slant and base surfaces became flat with a maximum drag reduction of 8% for the model with a deflection angle of 0°. The skin-friction measurement indicated that the drag reduction was connected to the breakdown of the separation bubble and longitudinal vortices on the slant. At the fully separated flow state, the skin-friction results illustrated two small vortices and a counter-clockwise vortex on the slant. Additionally, the wake vortices shifted from horizontal to vertical structures. The relation among the flow fields on the slant surface, flow on the symmetric plan, pressure distribution, and drag was illustrated for the model with different deflection angles.

Sulfonamide drugs: Low-cost spectrofluorometric determination using a computer monitor calibrator for detection

A possibility of the use of a common monitor calibrator as a portable and inexpensive tool for the fluorometric determination of sulfonamide drugs after their reaction with fluorescamine was examined. The luminescence measurements with a calibrator are based on irradiation of a test sample by the device lamp with a broadband spectrum in the visible and near UV regions and simultaneous registration of the secondary radiation by the device detector. Two types of cuvettes with black light absorbing sides eliminating the reflected self-radiation were tested. The commercially available Eppendorf-type black plastic microtubes (“LightSafe”) were suggested as a good option for such measurements. It was shown that a monitor calibrator can be applied for optimization of the determination conditions. By the example of sulfanilamide and sulfamethazine, it was shown that the procedure should be carried out at pH 4–6 and fluorescamine concentration of 200 μmol L−1, and 40 min of the interaction. The limit of detection of sulfanilamide and sulfamethazine using a monitor calibrator is 0.9 μmol L−1 and 0.8 μmol L−1, respectively, which is comparable with their spectrophotometric determination.

Understanding and Hindering Ion Migration in Er,Yb:LiLuF4 Core–Shell Nanoparticles for Nanothermometers with Enhanced Photoluminescence

Developing core–shell nanoparticles is a common approach to improve the luminescence performance of nanomaterials, as an inert shell shields the core, which is doped with luminescent ions, from the quenching influence of the environment. Core-only nanoparticles are susceptible to solvent overtones, which can couple with the emissive dopants on the surface and quench their intensity. This is undeniably highly undesired for any luminescence application. It was recently shown by some of us that previously unreported ion migration takes place in 2%Er,18%Yb:LiLuF4@LiLuF4 core–shell nanoparticles, which was proven both with energy-dispersive X-ray (EDX) maps and high-temperature luminescence measurements. These findings lead us to the investigation presented here, which explores in detail how to hinder the migration of Er3+ and Yb3+ ions in LiLuF4 and LiYF4 hosts by implementing an interface region. First, different synthesis routes were explored to see if the chosen approach had any effect on the ion migration process from the doped core into the inert shell in a homogeneous core–shell system. Next, a LiYF4 inert shell was grown around a 2%Er,18%Yb:LiLuF4 core forming a heterogeneous core–shell system. We observed that the heterogeneous 2%Er,18%Yb:LiLuF4@LiYF4 and LiLuF4@2%Er,18%Yb:LiYF4 core–shell combinations showed significantly less ion migration based on EDX maps and high-temperature luminescence measurements exhibiting a behavior similar to the well-studied 2%Er,18%Yb:NaYF4@NaYF4 core–shell structures that, according to previous studies, show no or very little ion migration.

Analysis of Excitation Energy Transfer in LaPO4 Nanophosphors Co-Doped with Eu3+/Nd3+ and Eu3+/Nd3+/Yb3+ Ions.

Nanophosphors are widely used, especially in biological applications in the first and second biological windows. Currently, nanophosphors doped with lanthanide ions (Ln3+) are attracting much attention. However, doping the matrix with lanthanide ions is associated with a narrow luminescence bandwidth. This paper describes the structural and luminescence properties of co-doped LaPO4 nanophosphors, fabricated by the co-precipitation method. X-ray structural analysis, scanning electron microscope measurements with EDS analysis, and luminescence measurements (excitation 395 nm) of LaPO4:Eu3+/Nd3+ and LaPO4:Eu3+/Nd3+/Yb3+ nanophosphors were made and energy transfer between rare-earth ions was investigated. Tests performed confirmed the crystal structure of the produced phosphors and deposition of rare-earth ions in the structure of LaPO4 nanocrystals. In the range of the first biological window (650-950 nm), strong luminescence bands at the wavelengths of 687 nm and 698 nm (5D0 → 7F4:Eu3+) and 867 nm, 873 nm, 889 nm, 896 nm, and 907 nm (4F3/2 → 4I9/2:Nd3+) were observed. At 980 nm, 991 nm, 1033 nm (2F5/2 → 2F7/2:Yb3+) and 1048 nm, 1060 nm, 1073 nm, and 1080 nm (4F3/2 → 4I9/2:Nd3+), strong bands of luminescence were visible in the 950 nm-1100 nm range, demonstrating that energy transfer took place.

Detection Enhancement of One Multifunctional Cd-Metal-Organic Framework toward Tetracycline Antibiotics by Simply Mixing Eu3+ in Suspension.

It is necessary to find more simple methods to improve the detection selectivity and sensitivity of antibiotics. Herein, we constructed a novel three-dimensional (3D) Cd-MOF LCU-117 assembled from p-terphenyl-4,2″,5″,4'-tetracarboxylic acid, which showed a special 3D helical structure with carboxylic acid ligands and nitrogen-containing ligands crossing each other vertically. Luminescence measurements indicated that LCU-117 has high selectivity and sensitivity toward Eu3+ through the ratiometric effect. Meanwhile, this complex itself could detect antibiotics oxytetracycline (OTC) through the turn-off mechanism. When Eu3+ was added in suspensions of LCU-117 (noted as Eu3+@LCU-117), the detection toward OTC was enhanced significantly and visually. The sensing mechanism was investigated in detail by various measurements and theoretical calculations. LCU-117 has a good effect on the logic gate, potential fingerprint detection, and mixed-matrix membranes (MMMs). The practical application for monitoring OTC in water samples also provided a satisfactory result.

Comparative study of red-emitting pyrophosphate phosphors: Site-selective replacement of Eu3+ and luminescent properties

Red phosphors play a key role in improving the optical quality of white light emitting diodes (WLEDs). In this work, Eu3+-activated red-emitting pyrophosphate phosphors of NaREP2O7:Eu3+ (RE = Sc, Lu) were prepared and the comparative investigations on crystal structures and luminescent properties were carried out. The X-ray diffraction (XRD), scanning electron microscope (SEM), and spectroscopy techniques were employed to characterize the materials. The features of crystal structures with regard to the Eu3+ doping were analyzed in detail on the basis of Rietveld crystal structure refinements. It is found that the Eu3+ tends to substitute Lu3+ in the NaLuP2O7:Eu3+, while in NaScP2O7:Eu3+ it tends to substitute Na+ due the principle of ionic size matching. The disparate selective occupation behaviour of Eu3+ ion in both crystals has resulted in a certain difference in fluorescence emission nature from each other. The doping concentration of Eu3+ was optimized for the strongest luminescence under near-ultraviolet (UV) excitation. The measurement of temperature-dependent luminescence showed that the emission of NaLuP2O7:Eu3+ at 150 °C maintained 77% of that at room temperature, and that for NaScP2O7:Eu3+ is 72%. Under the near-UV excitation, the fluorescence efficiency of the phosphors were assessed. The quantum efficiencies of NSPO:0.125Eu3+ and NLPO:0.125Eu3+ were measured to be 41.6% and 40.8%, respectively. The results imply that the Eu3+-activated pyrophosphate phosphors are promising red-emitting components in WLEDs.

Luminescence Measurements of the Hyperthermal Reactions of N/N+ + NH3.

Chemiluminescence from a system of collisions, N+/N/Kr+/Kr/Xe+/Xe + NH3, at collision energies between 10 and 170 eV (center of mass, COM), was measured in the spectral range 300-1000 nm. The energy dependence of the emission excitation cross sections was quantified, and molecular signatures were fit to known spectroscopic constants to determine vibrational-state populations. For both N and N+ collision species, the strongest features were assigned to emissions from NH (A-X) and the atomic hydrogen Balmer series. For each of the spectra resulting from collisions with primary cations, the NH (A-X) emissions had the largest cross sections reaching values of (1.0-1.5) × 10-18 cm2 by 100 eV. Additional features originating from atomic nitrogen and NH (c-a) emissions were also observed. The NH (c-a) emissions accounted for about 8%, 13%, and 15% for total excited populations in collisions with Xe+, N+, and Kr+, respectively. These transitions were consistent with short-range interactions resulting in collision-induced dissociation of the NH3 molecule with apparent energy thresholds between 20 and 30 eV and emission cross sections decreasing with ion mass. Evidence of charge exchange in the N+ + NH3 collisions was observed in the resulting spectra as broad transitions between 420 and 480 nm and were assigned to NH+ emitting from the (B) state. Differences between the spectra were observed as changes in the emission signal with the neutral collisions producing only 30% or 65% of the NH (A-X) emission cross sections compared to the cation results for xenon and krypton, respectively. For N and N+, NH (A) was created in equal amounts at lower collision energies, but the emission for the neutral system increases above that of the cation at collision energies greater than 80 eV COM. In both cases, the threshold energy for appearance was below 10 eV, suggesting an additional pathway for NH (A) formation, namely, hydrogen abstraction or charge exchange and abstraction for the N and N+, respectively. In all cases, the neutral NH (c-a) emission intensity was similar between neutral and cation pairs. The H-α emission line (n = 3-2) decreased to about 10%, 33%, and 50% of the corresponding cation spectra for xenon, krypton, and nitrogen, respectively.

High-efficiency dual-mode luminescence of metal halide perovskite Cs3Bi2Cl9:Er3+ and its use in optical temperature measurement with high sensitivity

Metal halide perovskites have attracted much attention due to their excellent optical properties and structural tunability. In this work, we synthesized the metal halide perovskite Cs3Bi2Cl9:Er3+ as the activator by solid-phase method using deionized water as the solvent. The phosphor doped with self-sensitizating of Er3+ ions emitted bright green light under the excitation of triple near-infrared laser (808 nm, 980 nm and 1550 nm). Interestingly, the upconversion emission exhibited a strong temperature dependence due to the thermally coupled energy levels 2H11/2 and 4S3/2 of Er3+, therefore is useful for optical temperature measurement. The maximum relative sensitivity in the range of 303–573 K is 1.40%K−1 (303 K, 808 nm), 1.38%K−1 (303 K, 980 nm), 1.50%K−1 (303 K, 1550 nm), respectively. By using fluorescence intensity ratiometry (FIR) methods, Cs3Bi2Cl9:Er3+ phosphor showed excellent accuracy and sensitivity and was compared very favorably with the reported temperature measurement materials. We anticipate that this new phosphor may have a range of applications in multi-mode luminescence and multi-excited light source temperature measurement.

Two Co-Based Metal–Organic Framework Isomers with Similar Metal-Carboxylate Sheets: Turn-On Ratiometric Luminescence Sensing Activities toward Biomarker N-Acetylneuraminic Acid and Discrimination of Ga3+ and In3+

Two supramolecular Co-MOF isomers, namely, {[Co(L)0.5(m-bimb)]·3H2O}n (LCU-115) and {[Co(L)0.5(p-bimb)]·3H2O}n (LCU-116), were synthesized from an amide-containing carboxylic acid N,N″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H4L) and two flexible positional isostructural N-containing ligands m-bimb and p-bimb (m-bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p-bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate sheets, which are extended further by m-bimb and p-bimb to form a 2D bilayer with parallel stacking (LCU-115) and a 3D framework (LCU-116), respectively. Luminescence measurements indicated that these two complexes exhibited interesting multiresponsive sensing activities toward pH, biomarker N-acetylneuraminic acid, and trivalent cations Ga3+/In3+. They show highly sensitive turn-on fluorescence responses in the acidic range and can also be regarded as on-off-on vapoluminescent sensors to typical acidic and basic gases HCl and Et3N. It is worth noting that these complexes have excellent turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic acid (NANA) with detection limits as low as 7.39 and 8.06 μM, respectively. Furthermore, they were successfully applied for the detection of NANA in simulated urine and serum samples with satisfactory results. For ion detection, LCU-116 could detect both Ga3+ and In3+, while LCU-115 could distinguish Ga3+ from In3+ with the latter showing luminescence quenching. The sensing mechanism was investigated in detail by XRD, UV-vis, EDS, XPS, SEM, and TEM. The results of interday and intraday precision studies gave low RSD values in the range of 1.19-3.53%, ascertaining the reproducibility of these sensors. The recoveries for the sensing analytes in simulated urine/serum or real water are satisfactory from 96.7 to 103.3% (toward NANA) and 96.6 to 115.0% (toward Ga3+ and In3+), indicating that these two complexes also possess acceptable reliability for monitoring in real samples. The results indicated that the supramolecular isomers LCU-115 and LCU-116 are promising material candidates for application in biological and environmental monitoring.

3D Printable Hybrid Gel Made of Polymer Surface-Modified Cellulose Nanofibrils Prepared by Surface-Initiated Controlled Radical Polymerization (SI-SET-LRP) and Upconversion Luminescent Nanoparticles.

A cellulose nanofibril-based hybrid gel material was developed by grafting the polymerized stearyl acrylate (PSA) and upconversion nanoparticles (UCNPs) onto cellulose nanofibrils (CNFs) via Cu0-mediated radical polymerization (SET-LRP) to create a highly cross-linked CNF system. A two-step strategy was exploited to surface-exchange the ligand of the UCNPs from a hydrophobic ligand (oleic acid) to a hydrophilic small-molecule ligand (2-acrylamido-2-methyl-1-propanesulfonic acid, AMPS) and therefore be suitable for SET-LRP. The characteristics and properties of the hybrid material (UCNP-PSA-CNF) were monitored by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), rheology, X-ray diffraction (XRD), and microscopic analysis. Those characterization techniques prove the efficient modification of the CNF, with the presence of 1.8% UCNPs. The luminescence measurement was carried out using a homebuilt confocal microscope with a 980 nm laser source. The nanostructure of UCNPs and their incorporated CNF species were measured by small-angle X-ray scattering (SAXS). In addition, this CNF-based hybrid gel has decisive rheological properties, such as good viscoelasticity (loss tangent was below 0.35 for the UCNP-PSA-CNF gel, while the PSA-CNF gel reached the highest value of 0.42), shear-thinning behavior, and shape retention, and was successfully applied to three-dimensional (3D) gel printing throughout various 3D print models.

Luminescence Temperature Quenching in Mn2+ Phosphors

AbstractNarrower band red and green emission in phosphor‐converted white light‐emitting diodes (wLEDs) can improve the efficacy and color gamut in lighting and display applications. A promising luminescent ion is Mn2+ that can have both narrowband green (tetrahedral coordination) and red (octahedral coordination) emission. Unlike in earlier lighting applications of Mn2+ phosphors, temperature quenching is important in wLEDs. Insight into the thermal quenching behavior of Mn2+ luminescence is lacking. Here systematic research is reported for a variety of Mn2+‐doped phosphors; a huge variation in the luminescence quenching temperature T50, ranging from 50 K for Mn2+ in ZnTe to 1200 K in MgAl2O4, is revealed. The value T50 shows a positive correlation with the bandgap of the host, but no correlation with the full width half maximum (FWHM) of the emission band, indicating that thermally activated photoionization, not thermal crossover, is the operative quenching mechanism. This is confirmed by thermally stimulated luminescence (TSL) measurements that show a rise in TSL signal following photoexcitation at temperatures around T50 providing evidence that quenching is correlated with generation of free charge carriers. Based on these findings, as a design rule is obtained that for temperature‐stable Mn2+ luminescence in (high power) LEDs a wide‐bandgap host material is required.

Structure and Luminescence Studies of a Ce3+-Activated Ba5La3MgAl3O15 Green-Emitting Phosphor

Novel green-emitting Ba5La3MgAl3O15:Ce3+ (BLMAO:Ce3+) is successfully obtained by a solid-state reaction. In this study, BLMAO, which is inspired from the Ba6La2A1.5Fe2.5O15 crystal structure, shows a green emission approximately peaked around 500 nm under near-ultraviolet light excitation at 412 nm by Ce3+ doping. Moreover, internal and external quantum efficiencies of BLMAO:0.02Ce3+ are found to be 27 and 22%, respectively. The emission peak deconvolution and Dorenbos model calculation reveal that the Ce3+ ion occupies on two different crystallographic sites. The potential of BLMAO:Ce3+ for phosphor-converted white LEDs (pc-wLEDs) is systematically evaluated from the results of Rietveld refinement and luminescence measurement.

Thermoluminescence and Optically Stimulated Luminescence properties of in-vitro aged dental porcelain

Among the materials applied in dentistry, porcelain is the most predominant one, as it has been used for dental restorations for decades. Towards the Thermoluminescence (TL) investigation of dental porcelain, and its capability to act as a personal accident dosimeter, the present work further examines -through a series of measurement protocols-the physical mechanisms responsible for the isothermal TL signal of its main dosimetric TL peak. Moreover, the influence of light on the TL of the same main peak is studied by means of Optically Stimulated Luminescence (OSL) measurements, while the origin of the OSL signal is further investigated. Finally, the existence of very deep traps of the material is examined and discussed via specific protocols.

Multi-Mode Lanthanide-Doped Ratiometric Luminescent Nanothermometer for Near-Infrared Imaging within Biological Windows

Owing to its high reliability and accuracy, the ratiometric luminescent thermometer can provide non-contact and fast temperature measurements. In particular, the nanomaterials doped with lanthanide ions can achieve multi-mode luminescence and temperature measurement by modifying the type of doped ions and excitation light source. The better penetration of the near-infrared (NIR) photons can assist bio-imaging and replace thermal vision cameras for photothermal imaging. In this work, we prepared core-shell cubic phase nanomaterials doped with lanthanide ions, with Ba2LuF7 doped with Er3+/Yb3+/Nd3+ as the core and Ba2LaF7 as the coating shell. The nanoparticles were designed according to the passivation layer to reduce the surface energy loss and enhance the emission intensity. Green upconversion luminescence can be observed under both 980 nm and 808 nm excitation. A single and strong emission band can be obtained under 980 nm excitation, while abundant and weak emission bands appear under 808 nm excitation. Meanwhile, multi-mode ratiometric optical thermometers were achieved by selecting different emission peaks in the NIR window under 808 nm excitation for non-contact temperature measurement at different tissue depths. The results suggest that our core-shell NIR nanoparticles can be used to assist bio-imaging and record temperature for biomedicine.

An SEM-Based Nanomanipulation System for Multiphysical Characterization of Single InGaN/GaN Nanowires

Nanomaterials possess superior mechanical, electrical, and optical properties suitable for device applications in different fields such as nanoelectronics, photonics, and sensors. Characterizing the multiphysical properties of single nanomaterials and nanostructures provides experimental guidelines for synthesis and device applications of functional nanomaterials. Nanomanipulation techniques under scanning electron microscopy (SEM) have enabled the testing of mechanical and electrical properties of various nanomaterials. However, the introduction of micro-photoluminescence ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> -PL) measurement into an SEM setup for in-situ single nanomaterial characterization is still experimentally challenging; in particular, the seamless integration of the mechanical, electrical, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> -PL testing techniques inside an SEM for multi-field-coupled characterization of single nanostructures is still unexplored. In this work, we report the first SEM-based nanomanipulation system for multiphysical characterization of single nanomaterials. A custom-made, optical-microfiber-based <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> -PL setup is integrated onto a nanomanipulation system with four nanomanipulators inside an SEM. The system is also equipped with a conductive nanoprobe and a conductive atomic force microscopy (AFM) probe for electrical nanoprobing and electroluminescence (EL) measurement of single nanomaterials with contact force feedback. Using the system, field-coupled characterization (i.e., optomechanical, optoelectronic, electromechanical, and mechano-optoelectronic testing) of single InGaN/GaN nanowires (NWs) are conducted; and, for the first time, the effect of mechanical compression applied to individual InGaN/GaN NWs on its optoelectronic property is revealed. Note to Practitioners—With the rapid advances of nanophotonics and nanoelectronics, the optical and optoelectronic characterization of semiconductive nanomaterials becomes widely used for guiding the material synthesis and improving the nanodevice performance. However, few studies on optical-relevant characterization were carried out in SEM, mainly due to the limited space of an SEM chamber, making it challenging to integrate optical components for effective optical excitation and luminescence measurement. To address this issue, space-saving optical microfibers were integrated into the SEM chamber for in-situ optoelectronic characterization of semiconductor NWs, along with the seamless integration of mechanical and electrical nanoprobing tools for electromechanical characterization. The developed nanomanipulation system will greatly facilitate the multiphysical testing of semiconductor nanomaterials, and thus expedite their synthesis optimization processes and broaden their optoelectronic device applications.

How tobacco (Nicotiana tabacum) BY-2 cells cope with Eu(III) - a microspectroscopic study.

The extensive use of lanthanides in science, industry and high-technology products is accompanied by an anthropogenic input of rare earth elements into the environment. Knowledge of a metal's environmental fate is essential for reasonable risk assessment and remediation approaches. In the present study, Eu(III) was representatively used as a luminescent probe to study the chemical environment and to elucidate the molecular interactions of lanthanides with a suspension cell culture of Nicotiana tabacum BY-2. Biochemical methods were combined with luminescence spectroscopy, two-dimensional microspectroscopic mappings, and data deconvolution methods to resolve the bioassociation behavior and spatial distribution of Eu(III) in plant cells. BY-2 cells were found to gradually take up the metal after exposure to 100 μM Eu(III) without significant loss of viability. Time-resolved luminescence measurements were used to specify the occurrence of Eu(III) species as a function of time, revealing the transformation of an initial Eu(III) species into another after 24 h exposure. Chemical microscopy and subsequent iterative factor analysis reveal the presence of four distinct Eu(III) species located at different cellular compartments, e.g., the cell nucleus, nucleolus and cell walls, which could be assigned to intracellular binding motifs. In addition, a special type of bioaccumulation occurs through the formation of a Eu(III)-containing oxalate biomineral, which is already formed within the first 24 hours after metal exposure. Oxalate crystals were also obtained in analogous experiments with Gd and Sm. These results indicate that tobacco BY-2 cells induce the precipitation of metal oxalate biominerals for detoxification of lanthanides, although they also bind to other cellular ligands at the same time.

Anthryl-functionalized cyanide-bridged Fe/Co cubes.

Two anthryl-functionalized cyanide-bridged [Fe4Co4] cube complexes, [(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]4·8MeCN·7Et2O (1) and [NEt4]3[(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]7·5MeCN·2Et2O (2) (pzTp- = tetrapyrazolylborate, TpEtOAn = 2,2,2-tris-(pyrazol-1-yl)ethoxy(9-methyl-anthracene)), were synthesized and characterized. The crystallographic study revealed that the [Fe4Co4] cubes are arranged into a linear supramolecular chain through significant anthryl-anthryl π-π stacking interactions in complex 1, whereas a zigzag supramolecular 1D assembly is observed in 2. The magnetic measurements showed that both compounds exhibited incomplete transitions from the paramagnetic {FeIIILS(μ-CN)CoIIHS} state to the diamagnetic {FeIILS(μ-CN)CoIIILS} state at about 200 K. The luminescence measurement of 1 in solution revealed an enhancement of the emission upon dilution or addition of perfluoronaphthalene (PFN) molecules, which could be attributed to the suppression of the aggregation-caused quenching (ACQ) effect, suggesting possible aggregation of the cube units in the solution.

SYNTHESIS, CRYSTAL STRUCTURE, SPECTROSCOPIC, LUMINESCENCE STUDIES AND HIRSHFELD SURFACE ANALYSIS OF BLUE LIGHT EMITTING HETEROMETALLIC MNIII-NIII COMPLEX

The synthesis, crystal structure, spectroscopic, luminescence properties and Hirshfeld surface analysis of a new heterometallic complex, [Mn(L)(H2O)(CH3CH2OH)]2[Ni(CN)4], (H2L=N,N՛-bis(3,5-di-t-butylsalicylidene)-1,2-propanediamine) was reported. Single crystal diffraction measurements showed that the heterometallic MnIII-NiII complex consists of two [(Mn(L)(H2O)(CH3CH2OH)]+ cations and one [Ni(CN)4 ]2- anion. The Mn1 and Mn2 ions are hexacoordinate by N2O4 donor sets and have a distorted octahedral geometry. The 3-D Hirshfeld surface and 2-D fingerprint plots showed that the main interactions were the H∙∙∙H intermolecular interactions with relative contributions of about 73.8%. According to solid-state luminescence measurements, the new heterometallic MnIII-NiII complex showed weak blue light emission.

Photophysical Properties of Eu3+ β-Diketonates with Extended π-Conjugation in the Aromatic Moiety

The influence of the degree of π-conjugation in biaroylmethane ligands upon Eu3+ luminescence efficiency in corresponding neutral tris-complexes was investigated in depth. The data obtained by both steady-state and time-resolved luminescence measurements gave an inside into electronic energy transfer mechanisms in the abovementioned complexes. It was shown that extension of the π-system in the naphthalene moiety in comparison to the phenyl one lead to a substantial decrease of both the S1 and T1 energy of the corresponding symmetrical β-diketones, which, in turn, led to a decrease of the total quantum yield of respective Eu3+ complexes. The obtained results are of interest for the rational design of highly luminescent complexes with NIR-emitting lanthanides, as the resonant levels energies are low and can hardly be sensitized by common ligands.

Effect of a Short, Bio-Mimetic Control Device on Aerodynamic Drag of Ahmed Body

Abstract The effects of short automatic moving deflectors (AMD) on the aerodynamic characteristics of Ahmed body are considered in this study. AMDs, known as biomimetic control devices, were added to the leading edge of the slanted surface. Its position was automatically adjusted in a separation flow. The aerodynamic drag, the pressure, and the skin-friction distribution on the slanted surface were measured for the model with three deflectors with lengths of 9%, 18%, and 30% of the slant. Particle image velocimetry was also utilized to assess the flow on the vertical symmetric plane. The Reynolds number based on the height of the model is between 1.44 × 105 and 2.80 × 105. The results showed that at a low Reynolds number, a short deflector increases the drag of the model. The effectiveness of the deflector in reducing the drag arises at a high velocity, where a maximum drag reduction of 11% was observed. The deflectors also reduced the lift coefficient by as much as 89%. Global luminescent oil-film skin-friction measurements showed that in the low drag state, the structure of the longitudinal vortexes and the separation bubble disappear on the surface. A complex flow structure is classified for the baseline model and the model with deflectors. The relationship between the surface flow, pressure distribution, and flow on the symmetric vertical plane is discussed in detail.