State Decay Time Research Articles

Ho3+ codoping of GGAG:Ce: a detailed analysis of acceleration of scintillation response and scintillation efficiency loss.

In this study, we investigate the effects of Ho3+ codoping on the luminescence and scintillation properties of GGAG:Ce, with a particular focus on timing properties and scintillator efficiency. The research reveals that Ho3+ codoping and subsequent resonant energy transfer from Ce3+ to Ho3+ can significantly reduce the 5d1 excited state decay time of Ce3+ and shorten scintillation pulses of GGAG:Ce registered by using photomultipliers, although this reduces scintillator efficiency as well. The study presents a detailed analysis of the loss of scintillator efficiency due to Ho3+ codoping, identifying the most significant loss pathways and estimating their impact. The findings suggest that Ho3+ codoping is an effective method for accelerating the scintillation response of GGAG:Ce. Furthermore, the study presents a high level of consistency of the Ce3+ kinetics with the Inokuti-Hirayama model and with results obtained in the previous studies on similar systems, demonstrating the predictability of the effect of RE3+ codoping on scintillator properties.

Physical and spectroscopic properties of variable Yb2O3 doped phosphate glasses containing SnO as UV sensitizer for Yb3+ NIR emission

Barium phosphate glasses were prepared with variable Yb2O3 added within 0–3.0 mol% and fixed SnO at 10 mol% (quantities relative to P2O5) to assess physical and spectroscopic properties emphasizing the Sn2+-promoted ultraviolet (UV) to near-infrared (NIR) photoluminescence (PL) down-shifting. The various characterizations performed involved refractive index (d-line), density, X-ray diffraction, Raman spectroscopy, UV–Vis–NIR absorption, and PL spectroscopy (steady-state & dynamic) measurements. The refractive indices and densities increased within the ranges of ∼1.60–1.62 and ∼3.70–3.83 g/cm3, respectively, with increasing Yb2O3 contents. The glasses were shown to be X-ray amorphous, whereas Raman spectra indicated slight Yb3+-induced phosphate network depolymerization. Optical absorption was consistent with Sn2+ occurrence in the glasses while increasing the Yb3+ concentration. Visible emission spectra obtained under 290 nm excitation concurred with Sn2+ emission wherein the Yb2O3 increments caused continuous Sn2+ PL quenching. The UV to NIR down-shifting promoted by Sn2+ upon 290 nm excitation was favored with increasing Yb2O3 added within 0.5–2.0 mol%, but decreased for 3.0 mol%. From the NIR emission decay curves obtained by exciting Sn2+ at 290 nm, the Yb3+2F5/2 state decay times were estimated which decreased linearly with increasing Yb3+ concentration. Strong Yb3+-Yb3+ interactions following Sn2+ → Yb3+ energy transfer are suggested to be at the origin of the PL weakening observed at the highest Yb3+ concentration.

Enhanced NIR emission from Nd3+ ions in plasmonic & dichroic Cu nanocomposite glass

The optical properties of neodymium and copper co-doped phosphate glass were examined focusing on the impact of Cu nanoparticles (NPs) with distinct plasmonic properties on the Nd3+ near-infrared (NIR) emission. The glasses were synthesized with either merely plasmonic or plasmonic & dichroic (transmitting blue, scattering red) character. While the merely plasmonic glass exhibited Nd3+ photoluminescence (PL) quenching consistently, the dichroic glass showed an enhanced NIR emission for excitation at 747 and 803 nm. The Nd3+ 4F3/2 emitting state decay times were however similar to the melt-quenched precursor. Scattering effects from Cu NPs are suggested to produce the PL boost.

Ytterbium-doped chloride photo-thermo-refractive glass: spectral, luminescent, and gain properties

We developed a new chloride photo-thermo-refractive glass doped with ytterbium ions. The dependence of optical and spectral-luminescent characteristics on ytterbium concentration has been studied. Concentration dependence of excited state decay time has been analyzed taking into account the self-trapping and self-quenching mechanisms. The optimum concentration of ytterbium ions in chloride photo-thermo-refractive glass has been determined. Other important spectroscopic parameters such as absorption and emission cross-sections, radiative lifetimes, pump saturation, and minimum pump intensities have been obtained using absorption and emission measurements and theoretical approaches such as Fuchtbauer-Landenburg and McCumber theories. The evolution of the gain cross-section spectrum as a function of a population inversion parameter has been performed. Results of this study show that the ytterbium-doped chloride photo-thermo-refractive glass demonstrates good spectroscopic and luminescent properties for laser and gain application.

Study of foil explosion using the soft x-ray radiography

The experiments were carried out upon a research facility comprising three current generators. One of them was used to initiate the explosion of a foil and the other two, X-pinch backlighting sources were used for diagnostics. In the experiments, an upper limit has been determined for the decay time of the metastable state of a superheated metal. For aluminum, at a foil thickness of 6 μm and a deposited energy of 5.3 ± 0.5 kJ/g, the metastable state decay time was about 90 ns; for copper, at the same foil thickness and a deposited energy of 2.1 ± 0.3 kJ/g, it was about 250 ns; for nickel at the same foil thickness and a deposited energy of 1.3 ± 0.4 kJ/g, it was about 390 ns.

Magnetopolaron-state lifetime and qubit decoherence in donor-center quantum dots with the electromagnetic field

Recently, the measurement scheme of quantum dot qubit decocoherence quantized by the longitudinal optical (LO) phonon spontaneous emission rate has attracted the attention and discussion of many researchers. However, it is not difficult to see that the above-mentioned measurement scheme still has some insufficient and imperfect aspects that are to be studied urgently. Considering from the physical mechanism, the essence of the above scheme is to quantify the decoherence time of qubit by using the excited state decay time or excited state lifetime of the polaron. However, so far, there is little research on how the ground state decay time and ground state lifetime of two-state polaron affect the coherence of qubit. There is no doubt that this is an equally important research topic. This is because, firstly, for the coherence of the quantum state of polaron, both the decay of the excited state and the decay of the ground state will destroy or attenuate the qubit coherence, secondly, the transition rate of the two-state polaron from the ground state to the excited state after absorbing an LO phonon is also a function quantifying the qubit decoherence time of two-state system of which the inverse is called the ground state decay time or the ground state lifetime. It may be called a measure of qubit decoherence time quantized by the ground state decay time or ground state lifetime of polaron. In this article, the ground-state and excited-state energy and wave function of the magnetopolaron in a donor-center quantum dot with asymmetric Gaussian potential are derived by Lee-Low-Pines transformation and Pekar-type variational methodd, and then the two-level structure for a qubit is constructed. The measure of qubit decoherence time of quantum dots quantified by ground state decay time of two-state polaron is established, which is compared with the well-known measure of qubit decoherence time of quantum dots quantified by polaron excited state decay time, and their physical mechanisms are revealed. By studying the influence of dielectric constant ratio, electro-phonons coupling constant, temperature and electromagnetic field on the ground state lifetime of magnetopolaron in the donor-center quantum dots with asymmetric Gaussian potential, the influences of material properties, temperature, electromagnetic field and other environmental factors on qubit decoherence of quantum dots are revealed, thereby revealing the mechanism of qubit decoherence caused by LO phonon effect.

Foil explosion and decay of metastable state

The mechanism of decay of the superheated metastable metal produced by a thin foil explosion was investigated experimentally. The decay of the metastable metal was indicated by the occurrence of bubbles detected using soft x-ray backlighting. The experiments were carried out on a research facility comprising three current generators. One of them was used to initiate the explosion of a test foil, and the other two, X-pinch backlighting sources, were used for diagnostics. In the experiments, an upper limit has been determined for the decay time of the metastable state of a superheated metal. For aluminum, at a foil thickness of 6 μm and a deposited energy of 1.49 ± 0.08 eV/atom, the metastable state decay time was about 90 ns; for copper, at the same foil thickness and a deposited energy of 1.46 ± 0.07 eV/atom, it was about 250 ns. Analysis of the experimental results based on the classical nucleation theory has made it possible to estimate the work required for the formation of a critical bubble, the radius of the critical bubble, and the Tolman length, which characterizes the effect of the surface curvature on the surface tension. The work required for the formation of a critical bubble has been estimated to be 16.6 ± 1.5 eV for aluminum and 18.3 ± 1.2 eV for copper. The critical bubble radius and the Tolman length turned out to be several nanometers for both test metals.

Monitoring the binding of serotonin to silver nanoparticles: A fluorescence spectroscopic investigation

Serotonin (5-HT) is an important monoamine neurotransmitter that plays a vital role in the regulation of various cognitive and behavioural functions including sleep, mood, pain, depression, anxiety, aggression, learning etc. From the nanotoxicity and neurotoxicity point of view, interaction studies between serotonin and nanoparticles are highly essential to develop an indispensable understanding on the effect of nanoparticles on monoamine neurotransmitters. In the present work, steady-state and time-domain fluorescence measurements were carried out along with binding energy measurements through X-ray photoelectron spectroscopic (XPS) technique to understand the interaction of 5-HT with silver nanoparticles (AgNPs). The emergence of a week red absorption band and quenching of fluorescence intensity along with decrease in full width half maximum, but not the excited state decay time of 5-HT in the addition of AgNPs suggest the formation of a non-fluorescent complex in the ground state that indicates static quenching along with radiative energy transfer among them. This is also confirmed by the low energy shift of Ag transition in 3d3/2 and 3d5/2 in XPS measurements and a coupling of Lb transition with the surface plasmons of AgNPs in the excitation spectra. The obtained thermodynamic parameters from the fluorescence quenching reveal the nature of interaction between 5-HT and AgNPs is hydrophobic. The increase in binding constant with increasing temperature suggested an enhancement in the strength of this interaction due to rise in the mobility of the molecules and hence increases the sensitivity and association of 5-HT with AgNPs.

Metastable Fluid Decay During Electric Explosion of Metallic Foils

Results of experimental investigations into overheated metastable fluid decay during electric explosion of metallic foils are presented. Experiments have been performed using an experimental complex consisting of three current generators, one of which provides explosion of foil and two others – X-pinch-based radiographs – are used for diagnostic purposes. The upper limit of the decay time of an overheated metastable metal is determined experimentally. For aluminum conductor with deposited energy of (5.3 ± 0.5) kJ/g, the metastable state decay time is ~110 ns; for copper foil with deposited energy of (2.4 ± 0.2) kJ/g, it is ~260 ns; and for nickel foil with deposited energy of (1.3 ± 0.3) kJ/g, it is ~350 ns.

Ultrafast Excited State Dynamics in Molecular Motors: Coupling of Motor Length to Medium Viscosity

Photochemically driven molecular motors convert the energy of incident radiation to intramolecular rotational motion. The motor molecules considered here execute four step unidirectional rotational motion. This comprises a pair of successive light induced isomerizations to a metastable state followed by thermal helix inversions. The internal rotation of a large molecular unit required in these steps is expected to be sensitive to both the viscosity of the medium and the volume of the rotating unit. In this work, we describe a study of motor motion in both ground and excited states as a function of the size of the rotating units. The excited state decay is ultrafast, highly non-single exponential, and is best described by a sum of three exponential relaxation components. The average excited state decay time observed for a series of motors with substituents of increasing volume was determined. While substitution does affect the lifetime, the size of the substituent has only a minor effect. The solvent polarity dependence is also slight, but there is a significant solvent viscosity effect. Increasing the viscosity has no effect on the fastest of the three decay components, but it does lengthen the two slower decay times, consistent with them being associated with motion along an intramolecular coordinate displacing a large solvent volume. However, these slower relaxation times are again not a function of the size of the substituent. We conclude that excited state decay arises from motion along a coordinate which does not necessarily require complete rotation of the substituents through the solvent, but is instead more localized in the core structure of the motor. The decay of the metastable state to the ground state through a helix inversion occurs 14 orders of magnitude more slowly than the excited state decay, and was measured as a function of substituent size, solvent viscosity and temperature. In this case neither substituent size nor solvent viscosity influences the rate, which is entirely determined by the activation barrier. This result is different to similar studies of an earlier generation of molecular motors, which suggests different microscopic mechanisms are in operation in the different generations. Finally, the rate of photochemical isomerization was studied for the series of motors, and those with the largest volume substituents showed the highest photochemical cross section.

Shifts in the fluorescence lifetime of EGFP during bacterial phagocytosis measured by phase-sensitive flow cytometry

Phase-sensitive flow cytometry (PSFC) is a technique in which fluorescence excited state decay times are measured as fluorescently labeled cells rapidly transit a finely focused, frequency-modulated laser beam. With PSFC the fluorescence lifetime is taken as a cytometric parameter to differentiate intracellular events that are challenging to distinguish with standard flow cytometry. For example PSFC can report changes in protein conformation, expression, interactions, and movement, as well as differences in intracellular microenvironments. This contribution focuses on the latter case by taking PSFC measurements of macrophage cells when inoculated with enhanced green fluorescent protein (EGFP)-expressing E. coli. During progressive internalization of EGFP-E. coli, fluorescence lifetimes were acquired and compared to control groups. It was hypothesized that fluorescence lifetimes would correlate well with phagocytosis because phagosomes become acidified and the average fluorescence lifetime of EGFP is known to be affected by pH. We confirmed that average EGFP lifetimes consistently decreased (3 to 2 ns) with inoculation time. The broad significance of this work is the demonstration of how high-throughput fluorescence lifetime measurements correlate well to changes that are not easily tracked by intensity-only cytometry, which is affected by heterogeneous protein expression, cell-to-cell differences in phagosome formation, and number of bacterium engulfed.

Ultrafast Broadband Saturable Absorption in Sb2Se3 Nanowires

Manipulating optical nonlinearity is a very fascinating prospective for both fundamental and technological purpose; offers a potential platform to explore the saturable absorption (SA) to the nanoscale limit. In this manuscript, we have focused on the tunable wavelength and pulse width dependent ultrafast broadband SA of Sb2Se3 nanowires in the resonant and the above bandgap excitations of 120 fs and 7 ns pulses. In this context, we numerically simulated the SA of Sb2Se3 nanowire with a two-level model. The solutions of the coupled rate equations for a Gaussian shaped pulse exactly reproduced the experimental results in both temporal and spatial domains. Our model provides a precise spacio-temporal analysis of carrier populations of each photo-excited state in the system. Moreover, excited state decay time (1.5 ns) and the ratio of excited state absorption cross section (σes) to the ground state absorption cross section (σgs) is less than unity for 1-D Sb2Se3 nanowires. Hence, Sb2Se3 nanowires can be employed as passive mode-lockers and essential photodetectors for ultrashort pulsed laser and can be tuned by wavelength and pulse width. These observations advise a remarkable nonlinear optical response which is expected to be comparable or even better than the graphene and 2D TMDC’s (MX2) like MoSe2, MoS2, WSe2, WS2 etc.

Nonlinear absorption and excited state dynamics of porphyrin and phthalocyanine in the presence of explosive molecules

Nonlinear absorption (NLA) properties and excited state dynamics of a porphyrin and phthalocyanine in the presence of explosive molecules were investigated using the nanosecond Z-scan and femtosecond pump-probe techniques, respectively. The NLA coefficients Is and β increased in the presence of explosive molecules. The change in first excited state decay time was evaluated through degenerate pump-probe measurements near 700nm and it was observed that decay time decreased in the presence of explosive molecules. The reduction in decay time and increase in NLA coefficients varied with different molecules according to their absorption, emission properties and affinity towards the explosive molecule.

Ultrafast excited state dynamics of the green fluorescent protein chromophore and its kindling fluorescent protein analogue

Fluorescent proteins exhibit a very diverse range of photochemical behaviour, from efficient fluorescence through photochromism to photochemical reactivity. Remarkably this diverse behaviour arises from chromophores which have very similar structures. Here we describe measurements and modelling of the excited state dynamics in the chromophores of GFP (HBDI) and the kindling fluorescent protein, KFP (FHBMI). The methods are ultrafast fluorescence spectroscopy with sub 50 fs time resolution and the modelling is based on the Smoluchowski equation. The excited state decays of both chromophores are very fast, longer for their anions than for the neutral form and independent of wavelength. Detailed studies show the mean fluorescence wavelength to be independent of time. The excited state decay times are also observed to be a very weak function of solvent polarity and viscosity. These results are modelled utilising recently calculated potential energy surfaces for the ground and excited states as a function of the twist coordinates about the two bridging bonds of the chromophore. For FHBMI and the scarce data on the neutral HBDI the calculations are not successful suggesting the need for refinement of these potential energy surfaces. For HBDI in methanol the simulation is successful provided a strong dependence of the radiationless decay rate on the coordinate is assumed. Such dependence should be included in future calculations of excited state dynamics. When the simulations are extended to more viscous solvents they fail to reproduce the observed weak viscosity dependence. The implications of these results for the nature of the coordinate leading to radiationless decay in the chromophore and for the photodynamics of fluorescent proteins are discussed.

Emission properties of Sm3+/Bi3+-doped YPO4 phosphors

The luminescence properties of YPO4 phosphors activated with 2% Sm3+ and variable concentrations of Bi3+ (from 0 to 5%) have been investigated. Steady state emission and decay time measurements clearly evidence an increment of the emission performance as the Bi3+ content increases up to 2.5%. Quantum yield measurements provide quantitative confirmation of the experimental observations. This behavior has been associated to the effect of the Bi3+ ions on the optical properties of the host lattice.

Dimethyldiphenylamino-substituted carbazoles as electronically active molecular materials

Abstract Synthesis and properties of new dimethyldiphenylamino-substituted carbazoles are reported. A comparative experimental analysis of 2-, 2,7-substituted carbazole derivatives and 3-, 3,6-substituted analogues is performed. Disubstituted carbazole derivatives exhibit more than 2-fold higher glass transition temperatures (99–100 °C) as compared to the monosubstituted compounds (38–40 °C). Dilute solutions of the dimethyldiphenylamino-substituted carbazole compounds are found to emit in the blue region with the fluorescence quantum yield of up to 0.45. More symmetrical molecular geometry of the 2-, 2,7-substituted carbazole compounds favors closer molecular packing in the neat films thereby facilitating exciton migration and migration induced exciton quenching, which results in the significantly reduced excited state decay times (down to sub-nanoseconds) and fluorescence quantum yields (down to 0.04). The 2-, 2,7-substituted carbazole compounds are shown to demonstrate the superiority over 3-, 3,6-substituted compounds by giving rise to extended π-conjugation and expressing over one order of magnitude higher radiative decay rates. The synthesized compounds are electrochemically stable: their cyclic voltammograms show reversible oxidation behavior. The ionization energies of the synthesized compounds are in the range of 5.16–5.28 eV. Hole drift mobilities of the molecular mixtures of dimethyldiphenylamino-substituted carbazoles with bisphenol Z polycarbonate reach 10 −5 cm 2 V −1 s −1 at high electric fields.

Time-resolved photoluminescence properties of CuInS2/ZnS nanocrystals: Influence of intrinsic defects and external impurities

Photoluminescence (PL) lifetime studies of CuInS2 nanocrystals (NCs) are carried out after synthesizing core-shell and compositionally variant structures using time-resolved PL spectroscopy. Long-lived excited state decay times are observed for the NCs, and decay times are very much dependent on the size of the CuInS2 NCs. The emission bands are attributed to the surface (shorter PL lifetime) and defect (longer PL lifetime) related trap states, respectively. The decay dynamics of the CuInS2 NC’s excited-state carriers is very sensitive to the surface, intrinsic defects, and extrinsic impurities. The observed large Stokes shifts and broad PL spectra also reveal the involvement of the defect-related trapping sites in the emission process.

Saturable absorption of multi-walled carbon nanotubes/hybrid-glass composites

The saturated optical absorption of multi-walled carbon nanotube (MWNT)-doped hybrid-glass composites was studied at 1064 nm with nanosecond long pulses using the Z-scan technique. Increased transmission was demonstrated for high intensity pulses. The results were modeled for the limiting cases of a slow or a fast saturable absorber, both referring to a three-level system. The ground-state absorption cross section was estimated as 2.3x10−18 cm2, in good agreement with that of a single carbon atom. The excited state absorption cross section for carbon nanotubes (CNTs) was estimated for the first time as 6.9x10−19 cm3. The absorber's density of 2.8x1018 cm−3 is smaller by approximately a factor of 5 compared to the nominal density of carbon atoms incorporated into the glass. This could be a result of the broad band-like states formation in the MWNTs. The above figures were obtained by assuming that the excited state decay time was longer than the pulse duration of ~1 ns.

Thermally Activated Superradiance and Intersystem Crossing in the Water-Soluble Chlorophyll Binding Protein

The crystal structure of the class IIb water-soluble chlorophyll binding protein (WSCP) from Lepidium virginicum is used to model linear absorption and circular dichroism spectra as well as excited state decay times of class IIa WSCP from cauliflower reconstituted with chlorophyll (Chl) a and Chl b. The close agreement between theory and experiment suggests that both types of WSCP share a common Chl binding motif, where the opening angle between pigment planes in class IIa WSCP should not differ by more than 10 degrees from that in class IIb. The experimentally observed (Schmitt et al. J. Phys. Chem. B 2008, 112, 13951) decrease in excited state lifetime of Chl a homodimers with increasing temperature is fully explained by thermally activated superradiance via the upper exciton state of the dimer. Whereas a temperature-independent intersystem crossing (ISC) rate is inferred for WSCP containing Chl a homodimers, that of WSCP with Chl b homodimers is found to increase above 100 K. Our quantum chemical/electrostatic calculations suggest that a thermally activated ISC via an excited triplet state T4 is responsible for the latter temperature dependence.

Orientational ordering of protein particles with asymmetric introductions of ferritin in a magnetic field

The mechanism of orientational ordering of protein particles in an inhomogeneous magnetic field, proposed by the authors in Phys. Wave Phenom. 13(1), 1 (2005), was extended to ferritin inclusions in such particles, taking into account the probable appearance of superantiferromagnetic susceptibility properties. Degrees of orientational ordering, ordered state formation and decay times achievable in bioparticle suspensions were estimated for a realistic model of the resistance to motion of elliptic particles in a viscous fluid. Biotechnological applications of the effect are discussed.