Short Fluorescence Lifetime Research Articles

Plasmonic-Ceria Nanoparticles as Fluorescence Intensity and Lifetime Quenching Optical Sensor.

Ceria nanoparticles have been recently used as an optical fluorescent material with visible emission under ultraviolet excitation, due to the formation of trivalent cerium ions with corresponding oxygen vacancies. This paper introduces the enhancement of both fluorescence emission and lifetime through adding gold nanoparticles. The reason is due to possible coupling between the plasmonic resonance of gold nanoparticles and the fluorescence emission of ceria that has been achieved, along with enhanced formation of trivalent cerium ions. Both factors lead to higher fluorescence intensity peaks and shorter fluorescence lifetimes. As an application, gold-ceria nanoparticles have been used as an optical sensing material for lead particles in aqueous media based on fluorescence quenching. Stern-Volmer constant of in-situ gold-ceria nanoparticles is found to be 2.424 M−1, with a relative intensity change of up to 40% at 0.2 g/L.

Well-regulated nickel nanoparticles functional modified ZIF-67 (Co) derived Co3O4/CdS p-n heterojunction for efficient photocatalytic hydrogen evolution

Well-designed functional noble metal-free Ni nanoparticles as co-catalyst to modified ZIF-67(Co) derived Co3O4 framework materials/CdS p-n heterojunction photocatalyst for efficient hydrogen evolution was successfully synthesized via photo-assisted in-situ method. The obtained noble metal-free defect-induced [Co3O4(3 wt%)/CdS/Ni] mesoporous photocatalyst exhibit excellent photocatalytic activity, namely, the maximum amount of hydrogen evolution reaches about 512 μmol for 5 h over the [Co3O4(3 wt%)/CdS/Ni] photocatalyst under visible light irradiation, which is 14.2 times higher than that of the pure CdS. Deeper further research confirms that the red shift of absorption band edge, the enhancement of light absorption intensity, the short fluorescence lifetime (2.61 ns), the faster electron injection rate (KET = 1.17 × 108 s−1), the larger efficiency of electron injection (ηinj = 30.6%), the high photocurrent response and the smaller R1 (22.3 Ω) and R2 (16,207 Ω) together accelerate the efficient spatial charges separation and transfer. The deeper characterization study results such as TEM, SEM, XPS, XRD, UV–vis DRS, Transient photocurrent and FT-IR etc. shown that the Ni nanoparticles modified on the Co3O4/CdS provided the more active sites and improved the efficiency of photo-generated charge separation, the results of which were in good agreement with each other.

Focus on nanotechnology, lasers, and imaging

Focus on nanotechnology, lasers, and imaging

Influence of acceptor strength on photoinduced charge transfer process in a newly designed molecule in bulk solvent and in β-CD microenvironment

We present a detailed photophysical properties of a synthesized charge transfer (CT) molecule (2E, 4E)-ethyl 2-cyano-5-(4-(dimethylamino) phenyl) penta-2, 4-dienoate (ECDPPD) in bulk medium and its spectral modulation inside β-Cyclodextrin cavity. Enhancement of acceptor strength of 4-(dimethylamino) cinnamaldehyde by replacing the moderate acceptor in the form of a Formyl group by two acceptors known to display greater electron withdrawing ability along with extra conjugation which may be responsible for higher dipole moment both in ground as well as in excited state. The observed excited CT process and its solvent polarity dependent emissive properties is due to simply increasing the ‘end-to-end’ length between donor and acceptor along with introduction of two different acceptors in the same site. Low fluorescence quantum yield and shorter fluorescence lifetime is due to the operation of active non-radiative channels through flexible bonds supported by viscosity and temperature dependent spectral measurement. The molecule ECDPPD easily interacts with β-CD with the formation of inclusion complex with a definite stoichiometry where the photophysics are modulated and hence can be used as fluorescence microenvironment reporter for example to evaluate the polarity as well as the micro viscosity of various regions of protein and other bimolecular systems.

Ultrabright Room-Temperature Sub-Nanosecond Emission from Single Nitrogen-Vacancy Centers Coupled to Nanopatch Antennas.

Solid-state quantum emitters are in high demand for emerging technologies such as advanced sensing and quantum information processing. Generally, these emitters are not sufficiently bright for practical applications, and a promising solution consists in coupling them to plasmonic nanostructures. Plasmonic nanostructures support broadband modes, making it possible to speed up the fluorescence emission in room-temperature emitters by several orders of magnitude. However, one has not yet achieved such a fluorescence lifetime shortening without a substantial loss in emission efficiency, largely because of strong absorption in metals and emitter bleaching. Here, we demonstrate ultrabright single-photon emission from photostable nitrogen-vacancy (NV) centers in nanodiamonds coupled to plasmonic nanocavities made of low-loss single-crystalline silver. We observe a 70-fold difference between the average fluorescence lifetimes and a 90-fold increase in the average detected saturated intensity. The nanocavity-coupled NVs produce up to 35 million photon counts per second, several times more than the previously reported rates from room-temperature quantum emitters.

Fluorescence lifetime measurement excited with ultraviolet surface plasmon resonance

We present an application of surface plasmon resonance in the ultraviolet region (UV-SPR) to lifetime measurement of fluorescent materials. Surface plasmon resonance (SPR) has been used to enhance fluorescence intensity and UV-SPR is important in the analysis of organic and biomolecules, including proteins and DNA, because UV light can excite many kinds of fluorescent dyes simultaneously or autofluorescence of biological specimens without any stain process. We obtained 16 times improvement of signal-to-noise ratio in lifetime measurement. We demonstrated the fluorescence lifetime of anthracene and CdSe/ZnS quantum dots using UV-SPR. The shortened fluorescence lifetime excited with UV-SPR compare to lifetime exited without SPR was analyzed.

Synthesis of B←N embedded indacenodithiophene chromophores and effects of bromine atoms on photophysical properties and energy levels

Developing novel fused π-conjugated chromophores has been an energetic research realm and knowing how to adjust their photophysical properties and energy levels through structure tailoring is of pivotal importance. Herein, based on the ladder-type π-conjugated indacenodithiophene (IDT) moiety, four B←N embedded IDT structures, namely, BNIDT, BNIDT-2Br, BNIDT-4Br, and BNIDT-6Br are synthesized and fully characterized. The influences of B←N unit embedded in the IDT backbone and Br atoms anchoring at the periphery on the photophysical properties and energy levels are discussed systematically. From IDT to BNIDT, a new intra-molecular charge transfer (ICT) transition band appears at lower energy (400–600 nm) in the absorption spectra with reduced optical bandgaps (Eg) from 3.25 eV to 2.11 eV and the fluorescence emission peaks red-shift from 390 nm to 565 nm along with remarkably extended fluorescence lifetimes from 1.2 ns to 12.4 ns due to the introduction of electron-deficient B←N into the backbone. Further anchoring Br atoms at the periphery of the backbone gives rise to depressed optical bandgaps, decreased fluorescence quantum yields (Φ), and shortened fluorescence lifetimes (τ) from BNIDT (Eg = 2.11 eV, Φ = 0.46, τ = 12.4 ns), BNIDT-2Br (Eg = 2.08 eV, Φ = 0.18, τ = 4.9 ns), BNIDT-4Br (Eg = 1.67 eV, non-emission) to BNIDT-6Br (Eg = 1.61 eV, non-emission). The HOMO and LUMO levels estimated from ultraviolet photoelectron spectroscopy (UPS) and optical bandgaps also experience synergetic lowering from IDT to BNIDT-6Br. This work indicates that backbone modification with electron-deficient B←N unit and side groups tailoring with halogen atoms are powerful to manipulate the optical properties and energy levels of fused π-conjugated chromophores.

Interfacial Charge Behavior Modulation in Perovskite Quantum Dot‐Monolayer MoS2 0D‐2D Mixed‐Dimensional van der Waals Heterostructures

AbstractFundamental understanding of charge behavior inside heterostructures is of vital importance for advancing high‐performance optoelectronic applications. However, the charge behavior of 0D‐2D mixed‐dimensional van der Waals heterostructures (MvdWHs) in the photoexcited state remains elusive. In this work, an energy band alignment protocol is adopted to realize effective energy band structure engineering inside 0D‐2D MvdWHs of perovskite quantum dots and MoS2 monolayer with precisely designed typical type I and type II heterostructures, respectively. A profile and in‐depth understanding of interfacial photoinduced charge behavior is determined from two opposite perspectives based on MvdWHs. Sufficient comparison of a series of optical characterization results, including Raman shift, quenched photoluminescence, visualized suppressed fluorescence intensity, and shortened fluorescence lifetime imaging, clearly verifies that interfacial charge behavior can be tailored by varying the band alignment in 0D‐2D MvdWHs. Furthermore, the photoresponse performance and the relatively stronger and weaker photogating effects of such MvdWH‐based phototransistors also demonstrate modulation of interfacial charge behavior in 0D‐2D MvdWHs via energy band structure engineering, which is still feasible for optoelectronic performance optimization. These results are expected to shed light on designing novel functional devices and advancing the development process of 0D‐2D MvdWHs in the foreseeable future.

A Stereochemically Driven Supramolecular Polymerisation.

Anthracyclines self-assemble in water into dimers. In the presence of sufficiently high salt (NaCl) concentrations, solutions of the antibiotic doxorubicin, but not those of the closely related molecules daunomycin and epirubicin, turn into gels barely compatible with the presence of small oligomers. The use of spectroscopic, scattering, imaging and computational techniques, allowed light to be shed on the self-assembly process that triggered doxorubicin gelification. A complex picture emerged, with doxorubicin molecules assembled into long, highly chiral, supramolecular aggregates made of hundreds of units, showing redshifted fluorescence spectra, very short fluorescence lifetimes and small-angle X-ray scattering profiles compatible with long cylinders. The involvement of specific chemical groups and the need for a specific stereochemistry of the monomers in the formation of a hydrogen-bond network to stabilise the supramolecular aggregates was supported by molecular dynamics calculations. A salt-induced, temperature-dependent, cooperative nucleation-elongation supramolecular polymerisation of the doxorubicin molecules is deduced.

A $16\times256$ SPAD Line Detector With a 50-ps, 3-bit, 256-Channel Time-to-Digital Converter for Raman Spectroscopy

A $16\times256$ element single-photon avalanche diode array with a 256-channel, 3-bit on-chip time-to-digital converter (TDC) has been developed for fluorescence-suppressed Raman spectroscopy. The circuit is fabricated in $0.35~\mu \text{m}$ high-voltage CMOS technology and it allows a measurement rate of 400 kframe/s. In order to be able to separate the Raman and fluorescence photons even in the presence of the unavoidable timing skew of the timing signals of the TDC, the time-of-arrival of every detected photon is recorded with high time resolution at each spectral point with respect to the emitted short and intensive laser pulse (~150 ps). The dynamic range of the TDC is set so that no Raman photon is lost due to the timing skew, and thus the complete time history of the detected photons is available at each spectral point. The resolution of the TDC was designed to be adjustable from 50 ps to 100 ps. The error caused by the timing skew and the residual variation in the resolution of the TDC along the spectral points is mitigated utilizing a calibration measurement from reference sample with known smooth fluorescence spectrum. As a proof of concept, the Raman spectrum of sesame seed oil, having a high fluorescence-to-Raman ratio and a short fluorescence lifetime of 1.9 ns, was successfully recorded.

Recent research on stimulated emission depletion microscopy for reducing photobleaching.

Stimulated emission depletion (STED) microscopy is a useful tool in investigation for super-resolution realm. By silencing the peripheral fluorophores of the excited spot, leaving only the very centre zone vigorous for fluorescence, the effective point spread function (PSF) could be immensely squeezed and subcellular structures, such as organelles, become discernable. Nevertheless, because of the low cross-section of stimulated emission and the short fluorescence lifetime, the depletion power density has to be extremely higher than the excitation power density and molecules are exposed in high risk of photobleaching. The existence of photobleaching greatly limits the research of STED in achieving higher resolution and more delicate imaging quality, as well as long-term and dynamic observation. Since the first experimental implementation of STED microscopy, researchers have lift out variety of methods and techniques to alleviate the problem. This paper would present some researches via conventional methods which have been explored and utilised relatively thoroughly, such as fast scanning, time-gating, two-photon excitation (TPE), triplet relaxation (T-Rex) and background suppression. Alternatively, several up-to-date techniques, especially adaptive illumination, would also be unveiled for discussion in this paper. The contrast and discussion of these modalities would play an important role in ameliorating the research of STED microscopy.

Ti-Doped β-Ga2O3: A Promising Material for Ultrafast and Tunable Lasers

As we know, Ti3+:Al2O3 is a very famous crystal for ultrafast and tunable lasers. However, it also has disadvantages including small segregation coefficient and short fluorescence lifetime of Ti3+. For comparison, Ti-doped β-Ga2O3 (Ti3+:β-Ga2O3) single crystals with good spectral properties have been designed and grown successfully by edge-defined film-fed growth method with larger segregation coefficient and longer fluorescence lifetime. The segregation coefficient of Ti3+ ions in the Ti3+:β-Ga2O3 crystal was calculated to be 0.49, which was much larger than that in Ti3+:Al2O3 (0.2). The thermal conductivity of Ti3+:β-Ga2O3 crystal was measured to be 24.7 W/mK along the ⟨010⟩ direction at room temperature, which is very attractive as a laser crystal. Furthermore, the polarized absorption spectra and fluorescence spectra of Ti3+:β-Ga2O3 were measured and analyzed. The full width at half-maximum of the emission peak was as large as 140 nm. The fluorescence lifetime was up to 176 ± 5 μs, which was about 50 ...

Pyrene and its selected 1-substituted derivatives revisited: A combined spectroscopic and computational investigation

Pyrene and its OH, NH2, and CN substituted derivatives were investigated experimentally by using UV/Vis absorption spectroscopy, steady state and time-resolved fluorescence spectroscopy in different polarity solvents. The computational part includes investigation of Pyrene and derivatives in excited S1 state in gas phase and in solution. Calculations were carried out with density functional theory (DFT) and time-dependent density functional theory (TDDFT) at B3LYP/6-311++G(d,p) level. Both ground and excited state geometries were fully optimized in gas phase and in solution. Solution calculations were carried out with Polarizable Continuum Model (PCM). Current results indicate that solvent polarity did not affect Py and its derivatives except PyNH2. Solvent has minor effects on PyCN and PyOH. Although PyNH2 has he smallest HOMO-LUMO energy gap, it is not the best candidate due to its shortest fluorescence lifetime. On the other hand, PyOH and PyCN have longer lifetimes. Therefore, it is concluded that investigated molecules are appropriate candidates for photosensitive applications in the order of PyNH2<PyOH < PyCN < Py.

Efficient amplified spontaneous emission based on π-conjugated fluorophore-cored molecules studied by density functional theory

Abstract The π-conjugated molecules, anthracene, pyrene and perylene with stepwise enhanced conjugation, have become a key ingredient in the design of new organic semiconductors for light emission and energy harvesting applications. Here, new biphenyl dissubstituted anthracene, pyrene and perylene derivatives are synthesized and investigated as blue-emitting materials. The designed molecules exhibited typical amplified spontaneous emission (ASE) behavior in solid thin films for the compounds dispersed in the inert polystyrene host at a rather large (5 wt%) chromophore concentration. Theoretical analysis assists in understanding the emission properties and optical gain performance. The calculations reveal enhanced transition density and increased transition dipole moment accompanying by stepwise enhanced molecular conjugation of fluorophore-cores. In addition, enhanced fluorescence quantum yield, significant shortened fluorescence lifetimes and increased radiative decay rate for designed compounds promote the occurrence of ASE behavior compared with anthracene, pyrene and perylene. As well, the vibration analysis show that the intramolecular vibrational modes of researched molecules possessed small Huang-Rhys factors, which thus bring in effective competition between radiative and non-radiative decay process in favor of optical gain. The experimental and theoretical provide evidence that the reported molecules are promising candidates for organic laser applications.

Light-assisted synthesis MoSx as a noble metal free cocatalyst formed heterojunction CdS/Co3O4 photocatalyst for visible light harvesting and spatial charge separation.

In this paper, a novel photocatalyst with visible light harvesting and spatial charge separation is reported, in which cobalt oxide (acting as a hole trap) and molybdenum sulfide (acting as an electron trap) are assembled on the surface of cadmium sulfide nanorods. The MoSx/CdS/Co3O4 composite photocatalyst shows a high H2 evolution with a yield of 537.51 μmol in 5 h, which is 35.53 times greater than over pristine CdS (15.13 μmol). The detailed underlying reason was comprehensively studied and understood by means of SEM, TEM, XRD, XPS, UV-vis DRS, BET; in particular, investigation of their photoelectrochemical properties with photocurrent, voltammetric scanning, fluorescence spectra etc. The high photocurrent response, the lower overpotential (-0.37 V vs. SCE), the faster electron transfer rate constant (ket = 4.23 × 109 s-1) and the short fluorescence lifetime (0.457 ns) supported the efficient spatial charge transfer between CdS and MoSx as well as Co3O4. The simultaneous loading of bicocatalysts can significantly improve the photo-induced spatial charge separation of CdS because MoSx nanoparticles act as an electron trap to rapidly transfer electrons from CdS while Co3O4 acts as a hole trap to quickly transfer holes, enhancing its photocatalytic performance as well.

Temperature Dependence of Tryptophan Fluorescence Lifetime in Aqueous Glycerol and Trehalose Solutions.

The temperature dependences of tryptophan fluorescence decay kinetics in aqueous glycerol and 1M trehalose solutions were examined. The fluorescence decay kinetics were recorded in the spectral region of 292.5-417.5nm with nanosecond time resolution. The kinetics curves were approximated by the sum of three exponential terms, and the spectral distribution (DAS) of these components was determined. An antisymbatic course of fluorescence decay times of two (fast and medium) components in the temperature range from-60 to+10°C was observed. The third (slow) component showed only slight temperature dependence. The antisymbatic behavior of fluorescence lifetimes of the fast and medium components was explained on the assumption that some of the excited tryptophan molecules are transferred from a short-wavelength B-form with short fluorescence lifetime to a long-wavelength R-form with an intermediate fluorescence lifetime. This transfer occurred in the indicated temperature range.

Modulation of nonradiative processes of single colloidal quantum dots by glycerol passivation

The radiative and nonradiative processes play predominant roles in the fluorescence performance of single colloidal quantum dots (QDs). In our report, we found that glycerol, a rarely studied chemical for CdSe core–shell QDs, would substantially modulate the nonradiative processes of single QDs. More specifically, the presence of glycerol would passivate the surface traps of single QDs, partly suppressing QD blinking. Simultaneously, glycerol would activate the defect states contributing to the nonradiative pathways, resulting in a shortened fluorescence lifetime and weakened fluorescence intensity. Additionally, glycerol could also stabilize single QDs, rendering enhanced chemical stability and photo stability of single QDs. As far as we know, this is a pioneering work studying on the impact of glycerol on fluorescence properties of CdSe core–shell QDs.

Fluorescence Lifetimes of Drusen in Age-Related Macular Degeneration.

The purpose of this study was to characterize fundus autofluorescence lifetimes of retinal drusen in patients with AMD. Patients with AMD and retinal drusen and healthy controls of similar age were examined. A fluorescence lifetime imaging ophthalmoscope was used. Retinal autofluorescence was excited using a 473-nm pulsed laser, and fundus autofluorescence lifetimes of the central retina (30°) were measured in two distinct spectral channels (short: 498 to 560 nm [SSC]; long: 560 to 720 nm [LSC]). Mean retinal autofluorescence lifetimes, corresponding fundus autofluorescence intensity images, spectral domain optical coherence tomography, color fundus images, and clinical data were investigated. Patients were analyzed in two distinct groups (soft drusen and reticular pseudodrusen) and compared with control subjects. Sixty-four eyes of 64 patients with AMD and retinal drusen (age: mean ± SD, 78 ± 8.5 years; range, 59 to 94 years) were investigated and compared with a control group of 20 age-matched healthy subjects. Mean retinal autofluorescence lifetimes in patients with AMD was significantly prolonged compared with the healthy control eyes (mean ± SEM: SSC, 486 ± 18 vs. 332 ± 11 ps, P < 0.0001; LSC: 493 ± 9 vs. 382 ± 17 ps, P < 0.0001). Areas of drusen featured a wide range of fluorescence lifetime values. Long lifetimes were identified in areas of atrophy and in areas of intraretinal hyperreflective deposits. Short lifetimes corresponded to deposits within the photoreceptor outer segment band. Mean retinal autofluorescence lifetimes in AMD patients are significantly prolonged. Intraretinal deposits cause prolonged lifetimes, whereas deposits in the area of the outer photoreceptor segments lead to short fluorescence lifetimes.

Application of label‐free 2‐photon fluorescence lifetime imaging microscopy to measure endogenous melanin profiles in human eye melanocytes, naevus and melanoma cells

PurposeThe progression of choroidal melanoma (CM) is complex, involving genetic and immune‐related factors. Melanin/pigmentation genes and forms (eumelanin/dark and pheomelanin/light) can also impact on CM progression. In this study, an optimised 2‐photon fluorescence lifetime imaging microscopy (FLIM), with phasor analysis, was used to identify melanin fluorescence lifetime (FL) profiles in formalin‐fixed, label‐free paraffin sections of human melanoma and naevus, with surrounding heterogeneously pigmented melanocytes.MethodsSections of ‘light CM’ (n = 3) with ‘mixed surrounding melanocytes’ and ‘dark naevi’ (n = 3) with ‘dark surrounding melanocytes’ were imaged with FLIM (3 sampled regions). Fluorescence lifetimes were measured at every pixel of captured FLIM images, Fourier transformed and presented in a ‘fit‐free’ phasor plot. These plots were segmented by 7 phasor clusters of linearly increasing fluorescence lifetimes mapped to intracellular melanin in melanocytes, naevus and melanoma cells. The mean fraction of FLIM image pixels linked to each melanin‐mapped cluster was obtained for all sampled regions to form melanin FL profiles.ResultsThe measured sampled regions displayed distinct intracellular melanin (eumelanin:pheomelanin) profiles with varying dominant melanin‐mapped clusters. The dominant ‘highest pixel fraction’ cluster measured in ‘light CM’ mapped to long FLs, implying a low eu:pheo ratio. The ‘mixed pigmented melanocytes around CM’ showed a mixed eu:pheo content based on the dominant mid‐valued FL cluster. The ‘dark naevi and surrounding melanocytes’ were mapped to mostly short FLs (high eu:pheo ratio).ConclusionsOur FLIM‐phasor method provides a fast ‘model‐free’ way to unmix melanin fluorescence lifetimes in melanocytes, naevi and CM, and provides a basis for exploring the role of melanin forms in eye melanoma pathogenesis.

Fluorescence lifetimes of drusen in age‐related macular degeneration

PurposeFluorescence Lifetime Imaging Ophthalmoscopy (FLIO) allows non‐invasive in vivo measurement of fluorescence lifetimes of natural fluorophores of the retina upon excitation with a laser light. FLIO in different retinal diseases showed that the technique is useful to detect early metabolic changes and can differentiate between retinal deposits.The aim of this study was to characterize fluorescence lifetimes in retinal drusen due to age‐related macular degeneration (AMD).MethodsFLIO imaging was performed using a Fluorescence Lifetime Imaging Ophthalmoscope (Heidelberg Engineering, Germany). Autofluorescence was elicited with a 473 nm laser and decay times were measured in a short (498–560 nm) and in a long (560–720 nm) spectral channel. Fluorescence lifetime data was compared with autofluorescence intensity images, optical coherence tomography (OCT) and color fundus images. Soft drusen and reticular pseudodrusen were analysed and compared to an age matched control group.Results64 eyes from 64 patients with AMD and retinal drusen (age: mean ± SD 78 ± 8.5 years) were investigated and compared to 20 age matched healthy controls. Mean fluorescence lifetime in patients with AMD was significantly prolonged compared to the healthy control eyes (mean ± SEM; SSC 486 ± 18 ps vs 332 ± 11 ps, p &gt; 0.0001; LSC: 493 ± 9 ps vs 382 ± 17 ps, p &gt; 0.0001). Areas of drusen featured a broader range of fluorescence lifetime values. Long lifetimes were identified in areas of atrophy and intraretinal hyperreflective deposits. Areas of short lifetime corresponded to deposits within the photoreceptor outer segment band.ConclusionsMean retinal autofluorescence lifetimes in AMD were significantly prolonged compared to healthy control eyes. Intraretinal deposits caused prolonged lifetimes whereas deposits in the area of the outer photoreceptor segments lead to short fluorescence lifetimes.