Temperature Dependence Of Fluorescence Lifetime Research Articles

Concentration- and temperature- dependent luminescence quenching and optical transition of Sr2GdTaO6: Eu3+ phosphor for potential applications in white LEDs

A series of Eu3+ doped Sr2GdTaO6 (SGT) phosphors with double perovskite structure were synthesized via a high-temperature solid-state reaction approach. The crystal structure, morphology and luminescence properties were characterized by means of X-ray diffraction, transmission electron microscope, luminescence spectroscopy and fluorescence decay lifetimes, respectively. Under the excitation of 394 nm, intense red emission in the visible region was observed in Eu3+ doped SGT phosphors, and the critical quenching concentration of Eu3+ in SGT phosphors was derived to be 15 mol%. The chromaticity coordinates and color purity of SGT: 15 mol% Eu3+ were calculated to be (0.61, 0.36) an 93.82 %, respectively. Meanwhile, it was also confirmed that the electric quadrupole–quadrupole interaction is responsible for the luminescence concentration quenching of Eu3+. The internal quantum efficiency of SGT: Eu3+ phosphors with different Eu3+ concentrations were calculated. Furthermore, the crossover process was confirmed to be the main mechanism for luminescence thermal quenching based on the temperature-dependent emission spectra and temperature-dependent fluorescence lifetimes. In addition, the Judd-Ofelt parameters, radiative transition rates and branch ratios from the 5D0 emitting states to various lower energy states were evaluated with the aid of the Judd-Ofelt theory, respectively. All results indicate that SGT: Eu3+ samples are a promising red-emitting phosphor.

Realizing dual-mode luminescent thermometry with excellent sensing sensitivity in single-phase samarium (III)-doped antimonite phosphors

In this work, we synthesized the Sr 2 InSbO 6 (SISO) phosphors with good temperature sensing performances for luminescent thermometry. Both X-ray diffraction and Rietveld refinement results verified that SISO: Sm 3+ phosphors have a monoclinic structure with the P2 1 /n space group. Under the charge transfer band excitation, three dominating emission peaks which are attributed to the f-f transition of Sm 3+ ions from the 4 G 5/2 excited level to the 6 H 5/2 , 6 H 7/2 , and 6 H 9/2 levels, respectively were observed. As the main concentration quenching mechanism was controlled by dipole-dipole (d-d) interaction, the optimum doping concentration in SISO:Sm 3+ phosphors was found to be 3%. With the aid of the temperature-dependent fluorescence intensity and lifetime, the maximum relative temperature sensitivities, S R1 and S R2 , of SISO:0.03Sm 3+ phosphor were 10.9% K −1 and 2.15% K −1 at 523 K, respectively. On the account of these results, single-phase Sr 2 InSbO 6 :Sm 3+ phosphors with remarkable temperature sensing performances can be applied in dual-mode optical thermometers. • Sm 3+ -activated Sr 2 InSbO 6 phosphors were firstly synthesized. • The crystal structure and photoluminescence properties were investigated. • The concentration quenching mechanism was identified in detail. • The sensing sensitivity was 10.9% K −1 based on the fluorescence intensity ratio. • The sensing sensitivity was 2.15% K −1 based on temperature-dependent lifetime.

Reliable and Remote Monitoring of Absolute Temperature during Liver Inflammation via Luminescence-Lifetime-Based Nanothermometry.

Temperature of tissues and organs is one of the first parameters affected by physiological and pathological processes, such as metabolic activity, acute trauma, or infection-induced inflammation. Therefore, the onset and development of these processes can be detected by monitoring deviations from basal temperature. To accomplish this, minimally invasive, reliable, and accurate measurement of the absolute temperature of internal organs is required. Luminescence nanothermometry is the ideal technology for meeting these requirements. Although this technique has lately undergone remarkable developments, its reliability is being questioned due to spectral distortions caused by biological tissues. In this work, how the use of bright Ag2 S nanoparticles featuring temperature-dependent fluorescence lifetime enables reliable and accurate measurement of the absolute temperature of the liver in mice subjected to lipopolysaccharide-induced inflammation is demonstrated. Beyond the remarkable thermal sensitivity (≈ 3% °C-1 around 37 °C) and thermal resolution obtained (smaller than 0.3 °C), the results included in this work set a blueprint for the development of new diagnostic procedures based on the use of intracorporeal temperature as a physiological indicator.

Photophysical Properties of Mn-Doped InP/ZnS Nanocrystals

InP-based nanocrystals (NCs) have received considerable attention as promising candidates to replace Cd- and Pb-based NCs because they contain no heavy metal elements. However, relevant studies on the photophysical properties of InP-based NCs are still insufficient. In this work, Mn-doped InP/ZnS NCs are synthesized, and their photophysical properties have been investigated. With the help of transient absorption spectrum measurement, it is found that Mn-doped InP/ZnS NCs exhibit efficient exciton–dopant exchange interaction. Through the temperature-dependent fluorescence lifetime measurements it is revealed that some excitons may undergo reverse crossing to the conduction band of the InP core from the long-lived 4T1 state of the Mn2+ ions with increasing temperature, resulting in the exciton fluorescence lifetime of the doped NCs to be less influenced by the temperature. In addition, compared with the Mn fluorescence, the exciton fluorescence shows an opposite intensity tendency to the temperature variation as a result of the greatly decreased energy transfer efficiency at elevated temperature. Importantly, the doped NCs exhibit a bright two-photon excited Mn fluorescence in which no size selection effect is observed. The excellent photophysical properties of Mn-doped InP/ZnS NCs imply that they are promising in the applications of highly effective optoelectronic devices and biological science.

Laser site-selective spectroscopy of Nd3+-doped Y2SiO5

We report on laser site-selective spectroscopy, as well as high resolution, infrared to optical absorption, of both the six and seven -fold coordinated, C1 symmetry sites for Nd3+ doped Y2SiO5. A total of fifty three crystal-field energy levels have been determined for both sites. We also present the temperature dependencies of the spectral linewidth and line position as measured in absorption. The coupling coefficients due to Raman two-phonon and direct one-phonon processes are interpreted in terms of the phonon energies contributing and their roles in the phonon energy distribution of Y2SiO5. Finally, we analyse direct non-radiative relaxation processes as inferred from the temperature-dependent fluorescence lifetimes.

Double-Stranded DNA Matrix for Photosensitization Switching

Photosensitization, originated from the activation of triplet states, is the basis of many photodynamic applications, but often competes with a series of nonradiative processes. Herein, we communic...

Specific features of the temperature dependence of tryptophan fluorescence lifetime in the temperature range of −170–20 °C

The temperature dependence of tryptophan fluorescence lifetime in an aqueous solution, aqueous solutions of glycerol (50 and 75 %, v/v) and dimethyl sulfoxide (DMSO) (50 and 75 %), and 1 M aqueous trehalose solution was studied in the range of –170 to +20 °C. In this temperature range, the fluorescence kinetics in all samples is best approximated by three exponential terms with characteristic times τ1 ∼ 3 ns, τ2 ∼ 4 ns, and τ3 ∼ 15 ns at room temperature. Temperature dependences of fluorescence lifetimes for the fastest and medium components exhibited antisymbatic (antiphase) behavior in the temperature range of –60 to 10 °C. To explain this behavior, a model was suggested that takes into account the tryptophan (Trp) molecule transition from the excited state to the state with separated charges – charge transfer state (CTS), the transitions back to the excited state, and the radiative transitions of the CTS to the ground state. Mathematically, this model is equivalent to the model that we have suggested earlier in [Gorokhov et al. (2018) Biochemistry (Moscow), 82, 1615–1623] to describe the transitions between different rotamer forms of tryptophan. The obtained results can be used for interpreting the experimental temperature curves of tryptophan fluorescence lifetime in proteins.

Ischemic Brain Injury Leads to Brain Edema via Hyperthermia-Induced TRPV4 Activation.

Brain edema is characterized by an increase in net brain water content, which results in an increase in brain volume. Although brain edema is associated with a high fatality rate, the cellular and molecular processes of edema remain largely unclear. Here, we developed an in vitro model of ischemic stroke-induced edema in which male mouse brain slices were treated with oxygen-glucose deprivation (OGD) to mimic ischemia. We continuously measured the cross-sectional area of the brain slice for 150 min under macroscopic microscopy, finding that OGD induces swelling of brain slices. OGD-induced swelling was prevented by pharmacologically blocking or genetically knocking out the transient receptor potential vanilloid 4 (TRPV4), a member of the thermosensitive TRP channel family. Because TRPV4 is activated at around body temperature and its activation is enhanced by heating, we next elevated the temperature of the perfusate in the recording chamber, finding that hyperthermia induces swelling via TRPV4 activation. Furthermore, using the temperature-dependent fluorescence lifetime of a fluorescent-thermosensitive probe, we confirmed that OGD treatment increases the temperature of brain slices through the activation of glutamate receptors. Finally, we found that brain edema following traumatic brain injury was suppressed in TRPV4-deficient male mice in vivo Thus, our study proposes a novel mechanism: hyperthermia activates TRPV4 and induces brain edema after ischemia.SIGNIFICANCE STATEMENT Brain edema is characterized by an increase in net brain water content, which results in an increase in brain volume. Although brain edema is associated with a high fatality rate, the cellular and molecular processes of edema remain unclear. Here, we developed an in vitro model of ischemic stroke-induced edema in which mouse brain slices were treated with oxygen-glucose deprivation. Using this system, we showed that the increase in brain temperature and the following activation of the thermosensitive cation channel TRPV4 (transient receptor potential vanilloid 4) are involved in the pathology of edema. Finally, we confirmed that TRPV4 is involved in brain edema in vivo using TRPV4-deficient mice, concluding that hyperthermia activates TRPV4 and induces brain edema after ischemia.

Probing the temperature-dependent changes of the interfacial hydration and viscosity of Tween20 : cholesterol (1 : 1) niosome membrane using fisetin as a fluorescent molecular probe.

A detailed photophysical study of fisetin in a Tween20 : cholesterol (1 : 1) niosome membrane has been carried out. Fisetin is found to partition well into the Tween20 : cholesterol (1 : 1) niosome membrane at low temperature (Kp = 2.7 × 104 M-1 at 10 °C). Cetylpyridinium chloride quenching study confirms the location of fisetin molecules in the interfacial domain of Tween20 : cholesterol (1 : 1) niosome membrane. The emission from the prototropic forms of fisetin (neutral form, excited state anion, ground state anion and phototautomer form) is found to sensitively reflect the local heterogeneities in Tween20 : cholesterol (1 : 1) niosome membrane. The shift in anionic emission maximum with variation in temperature shows the sensitivity of fisetin towards water accessibility at the interfacial domain of Tween20 : cholesterol (1 : 1) niosome membrane. Zeta potential value confirms that there is no role of surface charge in the multiple prototropism of fisetin in Tween20 : cholesterol (1 : 1) niosome membrane. The microviscosity changes with temperature, as reflected in fluorescence anisotropy values of fisetin phototautomeric species FT*, give information about the temperature-induced changes in the motional resistance offered by the interfacial domain of the niosomal membrane to small molecules. A temperature-dependent fluorescence lifetime study confirms the distribution of FT* in the two different sites of niosomal interfacial domain, i.e. water-deficient inner site and water-accessible outer site. This heterogeneity in distribution of FT* is further confirmed through time-resolved fluorescence anisotropy decay resulting in two different rotational time constants (faster component of ∼1.04 ns originates from water-accessible outer site and slower component of ∼16.50 ns originates from water-deficient inner site). The interfacial location of fisetin in Tween20 : cholesterol (1 : 1) niosome membrane has an important implication with regards to antioxidant activity as confirmed from a DPPH radical scavenging study.

Molecular Level Understanding of Sodium Dodecyl Sulfate (SDS) Induced Sol-Gel Transition of Pluronic F127 Using Fisetin as a Fluorescent Molecular Probe.

The thermoreversible sol-gel transition of pluronic F127 is markedly altered even with addition of submicellar concentration of sodium dodecyl sulfate (SDS) surfactant. Multiple fluorescence parameters like fluorescence intensity, fluorescence anisotropy and fluorescence lifetime of both the prototropic forms (anion (A-*) and phototautomer FT*) of the photoprototropic fluorescent probe fisetin has been efficiently used to understand the molecular level properties like polarity and microviscosity of the PF127-SDS system as a function of temperature. The SDS-induced increase in the interfacial hydrophobicity level is seen to affect the sol-gel phase transition of PF127 (21-18 °C). The ET(30) polarity parameter value of anionic emission of fisetin suggests that there is a considerable decrease in the polarity of the PF127 medium with increase in temperature and with the addition of SDS. The microviscosity progressively increases from ∼5 mPa s (sol state, 10 °C) to ∼22.01 mPa s (gel state 35 °C) in aqueous solution of PF127. The variation in microviscosity with addition of SDS in PF127-SDS mixed system is significant in sol phase whereas in gel phase this variation is significantly less. Temperature dependent fluorescence lifetime of FT* indicates that there is heterogeneity in distribution of fisetin molecules at different domains of PF127. This work also show-cases the sensitivity of fisetin toward change in polarity and change in sol-gel transition temperature of copolymer PF127 with variation in temperature (both forward and reverse directions) and SDS.

Dual-phase nano-glass-ceramics for optical thermometry

Transparent bulk glass ceramics containing Yb/Er: YF3 and Cr: ZnAl2O4 dual-crystalline-phases were successfully fabricated via a glass crystallization strategy. X-ray diffraction, transmission electron microscopy and optical spectroscopy were used to investigate the microstructure of glass ceramics. Impressively, the detrimental energy transfers between Er3+ and Cr3+ were greatly suppressed because of the respective partition of Yb3+/Er3+ and Cr3+ dopants into YF3 and ZnAl2O4 crystals. As a consequence, Er3+ up-conversion and Cr3+ down-shifting emissions were simultaneously enhanced. To explore their possible application in optical thermometry, temperature-dependent fluorescence intensity ratio of the thermally coupled emitting states of Er3+ (2H11/2, 4S3/2) and temperature-dependent fluorescence lifetime of Cr3+ (2E, 4T2) in the Yb/Er/Cr triply doped dual-phase glass ceramics were systematically studied. Using the fabricated glass ceramics as the optical thermometric medium, the temperature sensitivities can reach as high as 0.30%K−1 at 585K for Er3+ and 0.61%K−1 at 410K for Cr3+, respectively.

Preparation and luminescent properties of one-dimensional YVO4:Eu nanocrystals

One-dimensional YVO4:Eu3+ nanofibre and nanospindle samples were fabricated by electrospinning and an ultrasonic chemistry method. The average diameter of the YVO4:Eu3+ nanofibres were 30 nm, and they mainly consisted of nanoparticles arranged in 1-d patterns. The YVO4:Eu3+ nanospindles, with central diameters and lengths of around 50 and 150 nm, were assembled from nanorods with central diameters and lengths of around 10 and 50 nm. Their luminescent characteristics including excitation and emission spectra, and temperature-dependent fluorescence lifetimes, were studied and compared. The luminescence intensities of Eu3+ in YVO4:Eu3+ nanofibres were slightly higher than those in YVO4:Eu3+ nanospindles. Both the dependence of fluorescence lifetimes on the temperature of Eu3+ 5D0 for the YVO4:Eu3+ nanofibres or nanospindles remained quasi-constant, or indeed constant, over the temperature range studied, respectively; however, the lifetimes of Eu3+ 5D0 in YVO4:Eu3+ nanofibres were always shorter than those in YVO4:Eu3+ nanospindles at the same temperature.

Temperature Cycles Unravel the Dynamics of Single Biomolecules

Temperature Cycles Unravel the Dynamics of Single Biomolecules

Near-field fluorescence thermometry using highly efficient triple-tapered near-field optical fiber probe

A novel local temperature measurement method using fluorescence near-field optics thermal nanoscopy (Fluor-NOTN) has been developed. Fluor-NOTN enables nanoscale temperature measurement in situ by detecting the temperature-dependent fluorescence lifetime of CdSe quantum dots (QDs). In this paper, we report a novel triple-tapered near-field optical fiber probe that can increase the temperature measurement sensitivity of Fluor-NOTN. The performance of the proposed probe was numerically evaluated by the finite difference time domain method. Due to improvements in both the throughput and collection efficiency of near-field light, the sensitivity of the proposed probe was 1.9 times greater than that of typical double-tapered probe. The proposed shape of the triple-tapered core was successfully fabricated utilizing a geometrical model. The detected signal intensity of dried layers of QDs was greater by more than two orders than that of auto-fluorescence from the fiber core. In addition, the near-field fluorescence lifetime of the QDs and its temperature dependence were successfully measured by the fabricated triple-tapered near-field optical fiber probe. These measurement results verified the capability of the proposed triple-tapered near-field optical fiber probe to improve the collection efficiency of near-field fluorescence.

Synthesis and physico-chemical properties of porphycenes

A new and improved synthesis for porphycenes is presented. In particular, treating pyrroles with iodine monochloride results in quantitative yields and easier work up. This key step was employed for the synthesis of different 2,7,12,17-substituted porphycenes (TPrPc, TPPc, TtBPPc). The synthetic part of this project is followed by a global analysis of the physico-chemical properties of three exemplary porphycenes, including absorption, emission, and electrochemistry. In-situ UV-vis/nIR spectroelectrochemistry was used to determine the spectral signatures of the radical anion and cation species. Temperature-dependent fluorescence lifetimes were determined under air as well as under inert atmosphere.

Fluorescence of Er^3+:AlN polycrystalline ceramic

We report what we believe to be the first preparation and optical spectroscopy of Er3+ doped into bulk AlN ceramic. The material was prepared via hot press sintering of AlN with Er2O3 and [NH4][ErF4], which yielded fully dense, translucent, hexagonal AlN. The Er3+ concentration is a small fraction of a percent, and resides in multiple sites, with one type of center dominant. A number of the energy levels of Er3+ are identified for this center. The temperature dependent fluorescence lifetime is probably radiative, and on that basis the stimulated emission and absorption cross section spectra are inferred for the 4I13/2 ↔ 4I15/2 transitions.

A Fusion-Spliced Near-Field Optical Fiber Probe Using Photonic Crystal Fiber for Nanoscale Thermometry Based on Fluorescence-Lifetime Measurement of Quantum Dots

We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se Quantum Dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a fiber probe should be reduced. In order to decrease the noise, we have fabricated a novel near-field optical-fiber probe by fusion-splicing a photonic crystal fiber (PCF) and a conventional single-mode fiber (SMF). The validity of the novel fiber probe was assessed experimentally by evaluating the auto-fluorescence spectra of the PCF. Due to the decrease of auto-fluorescence, a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection was achieved with the newly fabricated fusion-spliced near-field optical fiber probe. Additionally, the near-field fluorescence lifetime of the quantum dots was successfully measured by the fabricated fusion-spliced near-field optical fiber probe at room temperature, and was estimated to be 10.0 ns.

O-Amino Conjugation Effect on the Photochemistry of trans-Aminostilbenes

The excited-state behavior of a series of trans-2-(N-arylamino)stilbenes (aryl = phenyl (o1H), 4-methylphenyl (o1Me), 4-methoxyphenyl (o1OM), and 4-cyanophenyl (o1CN)) and trans-2-(N,N-diphenylamino)stilbene (o2) in both nonpolar and polar solvents is reported and compared to that of the parent trans-2-aminostilbene and the corresponding meta- and para-isomers (m1R and p1R, where R = H, Me, OM, and CN, and m2 and p2). Two types of torsional motions, the D-A torsion that results in a nonfluorescent twisted intramolecular charge transfer (TICT) state and the C═C torsion that leads to the cis isomers, account for the radiationless decays of o1R and o2. The relative efficiencies of these torsions can be readily evaluated from their quantum yields for fluorescence (Φ(f)) and trans → cis isomerization (Φ(tc)). The propensities of the D-A torsion are similar for the ortho and meta isomers, which is 1OM > 1Me and negligible for 1H, 1CN, and 2. The activation parameters determined from temperature-dependent fluorescence lifetimes suggest that the C═C torsion occurs mainly via the triplet state for the ortho systems, a behavior again similar to that of the meta isomers. Whereas the intersystem crossing in o1R, m1R, and m2 is essentially a nonactivated process, it encounters a barrier of 2.7-3.8 kcal mol(-1) in o2. As a result of the barriers that decelerate the radiationless decays and the slow fluorescence rate for o2 in acetonitrile, the observed long fluorescence lifetime 24.5 ns at room temperature reaches a new record for unconstrained trans-stilbenes.

Remote temperature measurements in femto-liter volumes using dual-focus-Fluorescence Correlation Spectroscopy

Remote temperature measurements in microfluidic devices with micrometer spatial resolution are important for many applications in biology, biochemistry and chemistry. The most popular methods use the temperature-dependent fluorescence lifetime of Rhodamine B, or the temperature-dependent size of thermosensitive materials such as microgel particles. Here, we use the recently developed method of dual-focus fluorescence correlation spectroscopy (2fFCS) for measuring the absolute diffusion coefficient of small fluorescent molecules at nanomolar concentrations and show how these data can be used for remote temperature measurements on a micrometer scale. We perform comparative temperature measurements using all three methods and show that the accuracy of 2fFCS is comparable or even better than that achievable with Rhodamine B fluorescence lifetime measurements. The temperature dependent microgel swelling leads to an enhanced accuracy within a narrow temperature range around the volume phase transition temperature, but requires the availability of specific microgels, whereas 2fFCS is applicable under very general conditions.

Continuous-Flow Polymerase Chain Reaction of Single-Copy DNA in Microfluidic Microdroplets

We present a high throughput microfluidic device for continuous-flow polymerase chain reaction (PCR) in water-in-oil droplets of nanoliter volumes. The circular design of this device allows droplets to pass through alternating temperature zones and complete 34 cycles of PCR in only 17 min, avoiding temperature cycling of the entire device. The temperatures for the applied two-temperature PCR protocol can be adjusted according to requirements of template and primers. These temperatures were determined with fluorescence lifetime imaging (FLIM) inside the droplets, exploiting the temperature-dependent fluorescence lifetime of rhodamine B. The successful amplification of an 85 base-pair long template from four different start concentrations was demonstrated. Analysis of the product by gel-electrophoresis, sequencing, and real-time PCR showed that the amplification is specific and the amplification factors of up to 5 x 10(6)-fold are comparable to amplification factors obtained in a benchtop PCR machine. The high efficiency allows amplification from a single molecule of DNA per droplet. This device holds promise for convenient integration with other microfluidic devices and adds a critical missing component to the laboratory-on-a-chip toolkit.