Lifetime Measurements Of Excited States Research Articles

Emission based response of Er3+, Tb3+, and Er3+-Tb3+ co-doped 1393 bioactive glasses along with HPTS towards CO2

The HPTS serves as a versatile tool in pH and CO2 sensing studies, as well as in cell biology studies of various processes. However, the long-term photostability of HPTS as a fluorescent dye is an important consideration in its use, especially for long-term applications. In this work, sol–gel synthesized Er3+, Tb3+ and Er3+: Tb3+ co-doped 1393 bioactive glass particles were incorporated with the HPTS in the presence of ionic liquid in an ethyl cellulose matrix. The interaction of the bioactive glasses with the HPTS was investigated by steady-state luminescence and excited-state lifetime measurements. The prepared composites showed linearizable responses when exposed to different CO2 concentrations. High I0/I100 values (87, 109 and 115) were obtained for the binary blends of HPTS and bioactive glasses. When the imidazolium-based IL was used together with the offered composites, we observed improved stability and longevity for the HPTS up to 315 days. The incorporation of imidazolium-based ionic liquids as additives in HPTS-based fluorescence assays together with the bioactive glasses holds promise for enhancing the photostability of the HPTS and improving the reliability and longevity of fluorescence signals in various research applications.

Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh95

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research () Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian. Published by the American Physical Society 2024

COF‐Topological Quantum Material Nano‐heterostructure for CO2 to Syngas Production under Visible Light

AbstractEfficient solar‐driven syngas production (CO+H2 mixture) from CO2 and H2O with a suitable photocatalyst and fundamental understanding of the reaction mechanism are the desired approach towards the carbon recycling process. Herein, we report the design and development of an unique COF‐topological quantum material nano‐heterostructure, COF@TI with a newly synthesized donor‐acceptor based COF and two dimensional (2D) nanosheets of strong topological insulator (TI), PbBi2Te4. The intrinsic robust metallic surfaces of the TI act as electron reservoir, minimising the fast electron‐hole recombination process, and the presence of 6s2 lone pairs in Pb2+ and Bi3+ in the TI helps for efficient CO2 binding, which are responsible for boosting overall catalytic activity. In variable ratio of acetonitrile‐water (MeCN : H2O) solvent mixture COF@TI produces syngas with different ratios of CO and H2. COF@TI nano‐heterostructure enables to produce higher amount of syngas with more controllable ratios of CO and H2 compared to pristine COF. The electron transfer route from COF to TI was realized from Kelvin probe force microscopy (KPFM) analysis, charge density difference calculation, excited state lifetime and photoelectrochemical measurements. Finally, a probable mechanistic pathway has been established after identifying the catalytic sites and reaction intermediates by in situ DRIFTS study and DFT calculation.

COF-Topological Quantum Material Nano-heterostructure for CO2 to Syngas Production under Visible Light.

Efficient solar-driven syngas production (CO+H2 mixture) from CO2 and H2O with a suitable photocatalyst and fundamental understanding of the reaction mechanism are the desired approach towards the carbon recycling process. Herein, we report the design and development of an unique COF-topological quantum material nano-heterostructure, COF@TI with a newly synthesized donor-acceptor based COF and two dimensional (2D) nanosheets of strong topological insulator (TI), PbBi2Te4. The intrinsic robust metallic surfaces of the TI act as electron reservoir, minimising the fast electron-hole recombination process, and the presence of 6s2 lone pairs in Pb2+ and Bi3+ in the TI helps for efficient CO2 binding, which are responsible for boosting overall catalytic activity. In variable ratio of acetonitrile-water (MeCN : H2O) solvent mixture COF@TI produces syngas with different ratios of CO and H2. COF@TI nano-heterostructure enables to produce higher amount of syngas with more controllable ratios of CO and H2 compared to pristine COF. The electron transfer route from COF to TI was realized from Kelvin probe force microscopy (KPFM) analysis, charge density difference calculation, excited state lifetime and photoelectrochemical measurements. Finally, a probable mechanistic pathway has been established after identifying the catalytic sites and reaction intermediates by in situ DRIFTS study and DFT calculation.

Concentration quenching dynamics in silica glass highly doped with Er3+

In this study, quenching dynamics in RE-doped silica glass were investigated through the measurement of excited-state lifetimes of heavily doped silica micro-hemispheres fabricated directly on the end face of a multimode fiber (MMF).

Fabrication and characterization of thin 94Zr target with gold backing for nuclear lifetime measurements using DSAM

For lifetime measurements of excited nuclear states in the sub-picosecond range, a thin target with a thick backing of high-Z material is required. To meet these specifications, a thin isotopic94Zr target of thickness 1.14 ± 0.05 mg/cm2, with backing of 4.7 ± 0.2 mg/cm2 thick Au layer, has been fabricated using the cost-effective cold rolling technique at the target laboratory of Inter-University Accelerator Centre (IUAC), New Delhi. The thickness verification and purity check of the fabricated target have been carried out by non-destructive Energy Dispersive X-ray Fluorescence (EDXRF) and Rutherford Backscattering Spectrometry (RBS) techniques. The results of these measurements are in good agreement with each other. The elemental composition, purity and surface morphology have been explored by Energy Dispersive X-ray Spectrometry (EDS) and Scanning Electron Microscopy (SEM) techniques. The fabricated target has been successfully used with a16O ion beam in a recent γ-ray spectroscopy experiment for lifetime measurements using the Doppler Shift Attenuation Method (DSAM) at IUAC, New Delhi.

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Spectroscopic characterization of the interactions between poly(2-(trimethylamino)ethyl methacrylate) chloride and the xanthene dyes, 2′, 7′-difluorofluorescein and 2, 4, 5, 7-tetraiodofluorescein

Intermolecular interactions in buffered aqueous solution between the polycation, poly(2-(trimethylamino)ethyl methacrylate) chloride (pTMAEMC) and two anionic xanthene dyes, 2′, 7′-difluorofluorescein (Oregon Green 488) and 2, 4, 5, 7-tetraiodofluorescein (Erythrosin B), are characterized using multiple optical spectroscopic methods. Visible absorption spectroscopy indicates the formation of ground-state pTMAEMC-dye complexes. Benesi-Hildebrand binding isotherm analysis of visible absorption spectra for pTMAEMC-dye mixtures quantifies the strength of binding interactions producing the complexes. For both Oregon Green 488 (OG) and Erythrosin B (EB) in mixtures with pTMAEMC, the concentration of the solution’s sodium acetate buffer at a fixed pH alters the binding constants, Kb, suggesting that ionic strength plays a key role in determining the binding affinity of pTMAEMC for the dyes. Comparison of Kb, for the dyes indicates stronger binding of EB under all solution conditions. Steady-state fluorescence emission spectroscopy, fluorescence quenching, excited-state fluorescence lifetime measurements and fluorescence correlation spectroscopy provide complementary data for the interactions between pTMAEMC and the dyes. Mixtures of pTMAEMC with the dyes produce fluorescence enhancements and fluorescence quenching which exhibit a dependence on the buffer concentration used in the mixture. Excited-state lifetime analysis indicates that OG interacts with pTMAEMC through ground-state interactions while EB exhibits both ground-state and excited-state interactions with pTMAEMC. The spectroscopic measurements suggest that a polyelectrolyte effect for pTMAEMC due to ionic strength variation produced by the buffer concentration affects the dye binding profile of the polycation. This conclusion is supported by fluorescence correlation spectroscopy (FCS) analyses of the hydrodynamic diameter changes in pTMAEMC-OG binding in low buffer concentration (low ionic strength) solution. FCS analyses of pTMAEMC-OG mixtures also reveal diversity in the complexes formed in low ionic strength solution suggesting that other xanthene dyes will exhibit similar binding behaviors in mixtures with pTMAEMC as a function of solution ionic strength.

Ultra-Narrowband Near-Infrared Responsive J-Aggregates of Fused Quinoidal Tetracyanoindacenodithiophene.

Narrowband photoresponsive molecules are highly coveted in high-resolution imaging, sensing, and monochromatic photodetection, especially those extending into the near-infrared (NIR) spectral range. Here, a new class of J-aggregating materials based on quinoidal indacenodithiophenes (IDTs) that exhibit an ultra-narrowband (full width half maxima of 22nm) NIR absorption peak centered at 770nm is reported. The spectral width is readily tuned by the length of the solubilizing alkyl group, with longer chains resulting in significant spectral narrowing. The J-aggregate behavior is confirmed by a combination of excited state lifetime measurements and single-crystal X-ray diffraction measurements. Their utility as electron-transporting materials is demonstrated in both transistor and phototransistor devices, with the latter demonstrating good response at NIR wavelengths (780nm) over a range of intensities.

Polymer-mediated tuning of the monomer-aggregate equilibrium of a coumarin derivative for ratiometric sensing of protamine.

Amongst the various existing methods of analyte quantification, fluorescent-based methods, especially the ratiometric methods, continue to gain significant attention due to their high reproducibility, low environmental influence, and self-calibrating behavior. This paper presents the modulation in a monomer-aggregate equilibrium of coumarin-7 (C7) dye at pH ∼ 3, under the influence of a multi-anionic polymer, poly(styrene sulfonate) (PSS), leading to a significant modification in the ratiometric optical signal of the dye. At pH ∼ 3, cationic C7 formed aggregates in the presence of PSS via a strong electrostatic interaction, resulting in the development of a new emission peak at 650 nm at the expense of the monomer emission at 513 nm. Such contradicting changes in fluorescence intensities at two different wavelengths gave rise to a ratiometric signal, which was found to be highly sensitive towards external stimuli such as pH, and ionic strength. The stability of the C7-PSS complex was found to decrease as the pH of the solution was increased beyond 5, which indicated the decline in the electrostatic attraction between C7 and PSS due to the deprotonation of the C7 dye. Furthermore, an increase in the monomeric peak and a concomitant decrease of the aggregate peak with added salt in the solution (at pH ∼ 3) clearly justified the presence of an electrostatic attraction between C7 and PSS for the complex formation. This was further validated by the excited-state lifetime measurement of the C7-PSS complex, which showed a systematic increase in lifetime contribution from the monomeric species at the expense of aggregated species, as the concentration of NaCl increased in the solution. Thus, protamine (Pr), being a highly positively charged polypeptide, largely affected the monomer-aggregate equilibrium of the C7-PSS system, leading to a phenomenal change in the ratiometric signal, which was utilized to quantify with LOD as low as ∼2.8 nM in buffer for the bio-analyte Pr. Moreover, the ratiometric response of the C7-PSS assembly demonstrated excellent selectivity towards Pr, facilitating its practical relevance for the quantification of Pr in a 1% human serum matrix. Therefore, the studied C7-PSS can be utilized as a potential candidate for the quantification of the protamine even in complex biological media.

Fabrication of [formula omitted]As targets for heavy ion nuclear reactions

Thin uniform targets of 75As isotope with Pb/Au backing layer were fabricated for nuclear structure studies and sub-picosecond lifetime measurements of nuclear excited states using the Doppler shift attenuation method (DSAM) for nuclei populated in the heavy-ion induced fusion-evaporation reactions. The 75As targets of thickness 2.8–4.0 mg/cm2 (4.9–7.0μm) were prepared by in-vacuo sublimation of the As metal powder on to the backing (∼10 mg/cm2) of Pb (9.4μm) or Au (5.2μm), which were prepared by rolling method. The prepared targets were further rolled to improve their uniformity and avoid any interlayer gaps. The amount 75As material required for target preparation could be significantly reduced to ∼80 mg by increasing vapour flux by replacing the open dimpled tantalum boat with the pinhole tubular form. The uniformity, purity and thickness of As and Pb layers in the fabricated targets were assessed using a non-destructive Energy dispersive X-ray fluorescence (EDXRF) technique set-up. The measured thickness values of As and Pb/Au layers were found to agree within ∼3% with those deduced from the weighing method. The prepared targets have been successfully used with 28Si and 31P ion beams and the in-beam γ-ray spectroscopic studies in excited nuclear states in 98,99Rh, 99,100,101Pd and 102Ag isotopes.

Temperature-dependent excited state lifetimes of nitrogen vacancy centers in individual nanodiamonds

Nitrogen vacancy (NV) centers are fluorescent defects widely employed for thermometry, most commonly via temperature-dependent shifts of their optically detected magnetic resonance. Recently, all-optical approaches based on temperature-dependent features of the NV center fluorescence spectrum have also gained traction. Excited state lifetime thermometry is an all-optical technique that has been implemented using other fluorophores but has not previously been demonstrated for NV centers in individual nanodiamonds (NDs). Here, we report temperature-dependent excited state lifetime measurements of NV centers in individual NDs between 300 K and 500 K. We measure a 32 ± 7.0% and 35 ± 8.3% average decrease in the excited state lifetimes of individual NDs on silicon and glass substrates, respectively, over this temperature range. A linear approximation applicable to nearly all measured NDs yields temperature coefficients of −2000 ± 240 ppm/K and −2600 ± 280 ppm/K for NDs on silicon and glass, respectively. In addition to all-optical operation, single-ND excited state lifetime thermometry offers ∼100 ns temporal resolution and utilizes time-correlated single photon counting measurements ideally suited to low emission intensities, a limiting factor for other NV center thermometry techniques above 700 K. We demonstrate that atomic force microscope nanomanipulation can position individual NDs at critical locations on a sample of interest, enabling single-point temperature measurements that combine ∼100 ns temporal resolution and ∼100 nm spatial resolution. This work also has broader implications for other single-ND excited state lifetime sensing applications, where care is required to avoid conflating changes in temperature and other environmental parameters.

A fast-timing array of 2” x 2” LaBr[formula omitted]:Ce detectors for lifetime measurements of excited nuclear states

With its unique combination of excellent timing properties and good energy resolution, LaBr3:Ce detectors have proven to be effective tool in gamma spectroscopy and in particular fast-timing studies. Eight 2” x 2” LaBr3:Ce detectors used in conjunction with the 16 channel all-digital waveform 500 MHz acquisition module, PIXIE-16 were commissioned at iThemba Laboratory for Accelerator Based Sciences, South Africa. The results presented here give insight of the performance of the 2” x 2” LaBr3 detectors when used in conjunction with a digital pulse processing (DPP) module and electronic read-out module. Initial commissioning experiments were done using radioactive sources, including 60Co, 152Eu and 67Ga. The detectors were then exposed to an in-beam environment using the AFRODITE array with targets 45Sc and 64Ni, with a proton beam energy of 27 MeV.

Measurement of the tune-out wavelength for Cs133 at 880 nm

We perform a measurement of the tune-out wavelength, ${\ensuremath{\lambda}}_{0}$, between the ${D}_{1}$, ${6}^{2}{S}_{1/2}\ensuremath{\rightarrow}{6}^{2}{P}_{1/2}$, and ${D}_{2}$, ${6}^{2}{S}_{1/2}\ensuremath{\rightarrow}{6}^{2}{P}_{3/2}$, transitions for $^{133}\mathrm{Cs}$ in the ground hyperfine state $(F=3,{m}_{F}=+3)$. At ${\ensuremath{\lambda}}_{0}$, the frequency-dependent scalar polarizability is zero leading to a zero scalar ac Stark shift. We measure the polarizability as a function of wavelength using Kapitza-Dirac scattering of a $^{133}\mathrm{Cs}$ Bose-Einstein condensate in a one-dimensional optical lattice, and determine the tune-out wavelength to be ${\ensuremath{\lambda}}_{0}=880.21790{(40)}_{\text{stat}}{(8)}_{\text{sys}}$ nm. From this measurement we determine the ratio of reduced matrix elements to be ${|\ensuremath{\langle}6{P}_{3/2}\ensuremath{\parallel}d\ensuremath{\parallel}6{S}_{1/2}\ensuremath{\rangle}|}^{2}/{|\ensuremath{\langle}6{P}_{1/2}\ensuremath{\parallel}d\ensuremath{\parallel}6{S}_{1/2}\ensuremath{\rangle}|}^{2}=1.9808(2)$. This represents an improvement of a factor of 10 over previous results derived from excited-state lifetime measurements. We use the present measurement as a benchmark test of high-precision theory.

Enhanced quadrupole collectivity in doubly-magic 56Ni: Lifetime measurements of the [formula omitted] and [formula omitted] states

Lifetime measurements of excited states in doubly-magic 56Ni have been performed exploiting the Doppler-shift attenuation method in order to determine reduced transition probabilities. For the 41+ and 61+ states, the deduced B(E2) values are compared with results from shell-model calculations employing the GXPF1A and the modern PFSDG-U interactions. In addition, valence ab-initio calculations were performed using a novel realistic Hamiltonian derived from chiral perturbation theory including three-body potential contributions and are confronted with the experimental findings. The new results show maximum E2 strength in comparison with known values along the N=28 chain of isotones. The results corroborate the high collectivity for the double shell closure at N=Z=28 which was anticipated from the large B(E2;21+→0g.s.+) value despite the considerable increase of its excitation energy as compared to neighboring semi-magic nuclei. Based on similarities in the shell structures of the self-conjugate doubly-magic nuclei 56Ni and 100Sn, the new values could be an indication for an expected comparable collective behavior of the 61+ state in 100Sn.

Lifetime measurements of excited states in 169,171,173Os: Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i13/2 valence neutron

Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2;41+→21+)/B(E2;21+→0gs+) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.

Static and dynamic fluorescence spectroscopic analyses of direct yellow 27—an azo dye

In this work, the static and dynamic fluorescence analyses of direct yellow 27 [C25H20Na2O9S3] had been carried out through fluorescence spectroscopic techniques in various polar protic and polar aprotic solvents at room temperature. The prominent emission peak of the molecule observed at 355.84 nm in water, and the Stokes shift of the order of 68.84 nm (Δν = 6741 cm−1) came out. We found the recorded emission peak to be slightly redshifted with increase in polarity of the solvents. The excited-state lifetime measurement of the molecule in different solvents studied and determined that mono-azo direct yellow 27 possessed a lifetime of 12.18 ns in DMSO and 6.8 ns in the water at a concentration of 100 µM. The fluorescence quantum yield (Φf) calculated as 0.41 in water and the impact of different solvents on its value also analyzed.

Advancing understanding of actinide(iii) (Ac, Am, Cm) aqueous complexation chemistry.

The positive impact of having access to well-defined starting materials for applied actinide technologies – and for technologies based on other elements – cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac3+ and Cm3+ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H2O)6(1)(O2CMe)3(1) compound was the major species in solution for the large Ac3+. In contrast, smaller Cm3+ preferred forming an anion. There were approximately four bound O2CMe1− ligands and one to two inner sphere H2O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH4)2M(O2CMe)5 (M = Eu3+, Am3+ and Cm3+) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements).

Binding of metal ions to the curcumin mediated methoxy polyethylene glycol thiol conjugated greenly synthesized gold nanoparticles: A fluorescence spectroscopic study

Curcumin, a nontoxic molecule obtained from plant extract, was used to reduce gold salt to produce gold nanoparticles (AuNPs). First time the particles were functionalized with methoxy polyethylene glycol thiol (mPEGT), which acts as a stabilizing agent in such a manner that the methoxy group is pointed toward the aqueous solution to serve as anchor point to many metal ions. The greenly synthesized gold nanoparticles have a size between ∼40 and ∼83 nm. The prepared material was characterized in detail by SEM, XRD, TGA and FT-IR spectroscopy. These AuNPs were found to be fluorescence active similar to free curcumin suggesting that curcumin is conjugated at the surface of AuNPs. Exposure of the mPEGT functionalized AuNPs to different concentrations of metal cations in the range between 0 and 100 μM resulted in the decrease in the fluorescence intensity of the AuNPs unlike free curcumin in aqueous solution. Excited state lifetime measurements further validated quenching mechanism to be static in nature. The binding constant and number of binding sites for such interaction were evaluated. Based on observed bimolecular quenching rate constants, kQ values, the order of association of the metals studied is Pb (II) > Hg (II) >Hg (I) > Cd (II)>Al (III) >Ni (II) >Cu (II) >Na2HAsO4. These interactions between the mPEGT conjugated AuNPs and the metal ions in solution contribute a proof-of-concept that mPEGT functionalized curcumin mediated AuNPs can be used as a simple, cheap and straightforward, on-site detection system for toxic and even essential metal ions in solution.

Lifetime measurements of excited states in neutron-rich Ti53 : Benchmarking effective shell-model interactions

Level lifetimes of the yrast (5/2(-)) to 13/2(-) states in the neutron-rich nucleus Ti-53, produced in a multinucleon-transfer reaction, have been measured for the first time. The recoil distance Doppler-shift method was employed and lifetimes of the excited states were extracted by a lineshape analysis aided by GEANT4-based Monte-Carlo simulations. The experiment was performed at the Grand Accelerateur National d'Ions Lourds facility in Caen, France, by using the Advanced Gamma Tracking Array for the gamma-ray detection coupled to the large-acceptance variable mode spectrometer for an event-by-event particle identification and the Cologne plunger for deep-inelastic reactions. Reduced transition probabilities, deduced from the lifetimes, give new information on the nuclear structure of Ti-53, and are used to benchmark different shell-model calculations using established interactions in the f p shell.