Fluorescence Decay Time Research Articles

Photophysics of 7-(diethylamino)coumarin-3-carboxylic acid in cationic micelles: effect of chain length and head group of the surfactants and urea

In this work, we have studied the effects of chain length and the head group of different cationic surfactants on the photophysics of an anionic dye, 7-(diethylamino)coumarin-3-carboxylic acid (7-DCCA), using steady state absorption and fluorescence emission spectroscopy, and time resolved emission spectroscopy. We have observed pronounced effects on the photophysics of 7-DCCA, by varying the chain length and the head group of the surfactants. The fluorescence quantum yield, decay time, solvent relaxation time, and rotational relaxation time changes with chain length and the head group of the surfactants. We have studied the effect of urea on the photophysics of 7-DCCA bound to the micellar media and found that urea causes increases in the fluorescence quantum yield, fluorescence decay time, and solvent relaxation time. These aspects clearly demonstrate that the addition of urea does not cause the removal of the dye from the micellar surface.

Luminescence properties of Ce3 +-doped lithium borophosphate glasses and their correlations with the optical basicity

Ce3+-doped lithium borophosphate glasses were prepared by melt quenching method, their luminescence properties were investigated by excitation and emission spectra, as well as X-ray excited luminescence (XEL) spectra. The broad emission band with the maximum center around 338nm attributing to 5d–4f transitions of Ce3+ ions is observed, and the optimal concentration of CeO2 is found to be 0.75wt.% in the CeO2-doped 57.5Li2O–5B2O3–37.5P2O5 scintillating glasses. Both the excitation and emission bands show a red shift in the 45Li2O–yB2O3–(55-y) P2O5–0.75wt.% CeO2 glasses due to the increasing value of the optical basicity with the increase of y. Moreover, the strongest XEL intensity of 45Li2O–yB2O3–(55-y)P2O5–0.75wt.% CeO2 glasses reaches a maximum at y=16.5, which might be associated with the decreasing concentration of the non-bridging oxygen and the change ratio between BO4 groups and total amount of borate groups by increasing B2O3. From the standpoints of the high Li+ concentration and fast fluorescence decay time (28.5ns), Ce3+-doped lithium borophosphate glasses are potential candidates for neutron detection.

Highly photostable and biocompatible graphene oxides with amino acid functionalities

Highly photoluminescent graphene oxides with various amino acid functionalities (GO–AAs) were synthesized through surface grafting reactions. The quantum yields were measured to be up to 21%. We demonstrated that their photoluminescence was highly stable against photobleaching by continuous ultraviolet (UV) light irradiation. The fluorescence decay time of GO–AAs was measured up to 9.6 ns with excitation at 375 nm. We further applied the functional graphene oxides in cell culture experiments and found that they could be readily taken up by A549 cells. MTT viability assay of GO–glutamic acid on A549 cells was also carried out to show its low cytotoxicity. Such stained cells were alive and fluoresced even after incubating for three weeks, suggesting that the graphene oxides with amino acid functionalities had high biocompatibility and low cytotoxicity.

Highly transparent Nd^3+:Lu_2O_3 produced by spark plasma sintering and its laser oscillation

Laser oscillation was demonstrated using a 1 at.% Nd3+-doped Lu2O3 (Nd3+:Lu2O3) transparent ceramic produced by spark plasma sintering. Nd2O3, Lu2O3, and LiF commercial powders were mixed by ball milling and were sintered at 1723 K using a two-step sintering profile. After the transparent Nd3+:Lu2O3 ceramic was annealed in air, its transmittance at 1076 nm reached 81.8%, which was close to the theoretical value for Lu2O3 (82.2%). The absorption cross-section at 806 nm was 1.29 × 10−20 cm2, and the fluorescence decay time at 1076 nm was 229 μs. The laser oscillation of Nd3+:Lu2O3 ceramic for the transition from 4F3/2 to 4I11/2—specifically, at 1076.7 and 1080.8 nm—was simultaneously obtained, with a laser output of 0.21 W and slope efficiency of 14%.

Terbium(III) based coordination polymer microparticles as a luminescent probe for ascorbic acid

We report on terbium coordination polymer (Tb-CP) microparticles prepared from Tb(III) ion, dipicolinic acid (DPA; acting as a bridging ligand) and tris(hydroxymethyl)aminomethane (Tris; acting as an auxiliary ligand), and show that it can be used as a luminescent probe for ascorbate in aqueous solutions. The Tb-CP emits strong fluorescence due to an intramolecular energy transfer from DPA to the Tb (III) ion, and both fluorescence intensity and decay time are quenched by ascorbate. This finding led to a method for the quantitation of ascorbic acid in the 1 μM to 1 mM concentration range and with a detection limit at ~200 nM. The strategy presented here is based on the construction of special functions directly from initial molecule/ion blocks and is expected to enable the design of various other CP materials for use as optical probes.

Quantum Dot Fluorescence in Photonic Bandgap Glassy Cholesteric Liquid Crystal Structures: Microcavity Resonance under CW-Excitation, Antibunching and Decay Time

Nanocrystal quantum dot (NQD) fluorescence in 1-D glassy cholesteric liquid crystal host is investigated: (1) Microcavity resonance is obtained under cw-excitation demonstrating coupling between NQD fluorescence and a cholesteric microcavity. Observed at a band edge of a photonic stopband, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. (2) Photon antibunching of a single NQD in a similar microcavity was observed. (3) Fluorescence decay time constants were measured at different excitation powers. These results are important in developing cholesteric lasers and single-photon sources for secure quantum communication.

Cervical cancer detection by time-resolved spectra of blood components.

Fluorescence spectral techniques are very sensitive, and hence they are gaining importance in cancer detection. The biomarkers indicative of cancer could be identified and quantified by spectral or time domain fluorescence spectroscopy. The results of an investigation of time-resolved spectra of cellular components of blood obtained from cervical cancer patients and normal controls are given. The cancer indicative biomarker in this paper is porphyrin; it has a fluorescence decay time of 60% more in samples of cancer patients than those of normal controls. Based on such measurements, a randomized set comprising samples from cancer patients and controls (N=27 in total) could be classified with sensitivity (92%) and specificity (86%).

Fluorescence and radiation response properties of Ce3+-doped CaO–Al2O3–B2O3 glass

Basic fluorescence and radiation response properties of 7.5CeO2–22.5CaO–20Al2O3–50B2O3 (in molar percent) glass were evaluated. The Ce-doped glass was prepared according to a conventional melt quenching method using a Pt crucible in air atmosphere. The photoluminescence (PL), thermoluminescence (TL), and optically stimulated luminescence (OSL) spectra showed a blue emission band due to the 5d–4f allowed transition of Ce3+. The fluorescence quantum efficiency and decay time of Ce3+ were estimated to be about 60% and 37 ns, respectively. The glass exhibited good linear TL and OSL responses in 1–1000 and 30–3000 mGy dose ranges, respectively.

Structural, optical and EPR studies of Cr3+ doped Na3Ce(PO4)2 orthophosphate

Micro-crystalline powders of Na3Ce(PO4)2 orthophosphate doped with Cr3+ ions were synthesized and characterised by means of X-ray diffraction, IR and Raman, electron absorption, magnetic and EPR studies. The emission and excitation spectra and fluorescence decay time were recorded in the temperature range 70–293K. The spectroscopic properties of Ce3+ and Cr3+ ions in the studied materials were discussed in terms of the structure and local symmetry of the optical ions. These data were compared to those obtained for NaCe(PO3)4 metaphosphate.

Metal ion influence on eumelanin fluorescence and structure

Melanin has long been thought to have an unworkably weak and complex fluorescence, but here we study its intrinsic fluorescence in order to demonstrate how metal ions can be used to control the rate of formation, constituents and structure of eumelanin formed from the well-known laboratory auto-oxidation of 3,4-dihydroxy-L-phenylalanine (L-DOPA). The effect on eumelanin absorption and fluorescence of a range of solvated metal ions is reported including Cu, Zn, Ni, Na and K. Monovalent cations and Zn have little effect, but the effect of transition metal cations can be considerable. For example, at pH 10, copper ions are shown to accelerate the onset of eumelanin formation, but not the rate of formation once it commences, and simplify the usual complex structure and intrinsic fluorescence of eumelanin in a way that is consistent with an increased abundance of 5,5-dihydroxyindole-2-carboxylic acid (DHICA). The presence of a dominant 6 ns fluorescence decay time at 480 nm, when excited at 450 nm describes a distinct photophysical species, which we tentatively assign to small oligomers. Copper is well-known to normally quench fluorescence, but increasing amounts of copper surprisingly leads to an increase in the fluorescence decay time of eumelanin, while reducing the fluorescence intensity, suggesting copper modification of the excited state. Such results have bearing on diverse areas. The most accepted morphology for melanin is that of a graphite-like sheet structure, and one which readily binds metal ions, an interaction that is thought to have an important, though as yet unclear bearing on several areas of medicine including neurology. There is also increasing interest in bio-mimicry by preparing and labelling sheet structures with metal ions for new electronic and photonic materials.

Dynamics of molecular excitons near a semiconductor surface studied by fluorescence quenching of polycrystalline tetracene on silicon

Tetracene, a molecule that undergoes singlet fission, is deposited on Si with variable thickness LiF spacer layers. In agreement with earlier work (Hayashi et al., 1983 [10]), the fluorescence intensity of the tetracene greatly increases as the LiF thickness approaches 100nm. This increase is partly due to a 30% increase in the prompt fluorescence decay time but mostly results from weaker coupling of the luminescence into the Si substrate. A decrease in the prompt fluorescence lifetime is observed as the tetracene thickness is increased on bare Si. We find no evidence for triplet energy transfer to the Si.

Luminescence and magnetic behaviour of almond like (Na0.5La0.5)MoO4:RE3+ (RE = Eu, Tb, Dy) nanostructures

Tetragonal phase (Na0.5La0.5)MoO4:RE3+ (RE=Eu, Tb, Dy) with almond like hierarchical structures assembled from nanosheets building blocks were successfully synthesized by employing disodium ethylenediaminetetraacetic acid (Na2EDTA) using hydrothermal route at 200°C for 24h. Field emission scanning electron microscope, transmission electron microscope, and X-ray diffraction patterns were used to characterize the morphology, size, and crystal structure with good resolution. The sequestering agent EDTA acts as quadridentate ligand coordinated with metal ions [Na+, La3+/RE3+] facilitating the formation of self-organized 3D networks. The growth mechanism for the formation of almond like nanostructures is explicated in four paths: dissolution, adsorption, in situ transformation in acidic and basic media and the effective collision. Photoluminescence excitation and emission spectra reveals a spectral blue shift which was observed in the nanosamples towards shorter wavelengths compared with the bulk sample. Upon UV irradiation, both bulk and nanostructure show strong luminescence in the red region due to the 5D0→7F2 transition in Eu3+. Also, Tb3+ and Dy3+ doped (Na0.5La0.5)MoO4 phosphor exhibit green and yellow luminescence due to the transitions 5D4→7F5 and 4F9/2→6H13/2, respectively. Color richness and fluorescence decay times for major emission lines in Eu3+, Tb3+, and Dy3+, that were determined to be x=0.593, y=0.326, τ=0.417ms; x=0.228, y=0.619, τ=0.411ms; x=0.3851, y=0.4334, τ=0.403ms, respectively. The as-synthesized nanophosphor exhibits weak ferromagnetic hysteresis with significant remnant magnetization (1.84E−4emu/gm) at room temperature in comparison with bulk sample. The above results suggesting these materials can serve as excellent luminescence markers which being controlled by external magnetic field.

Substituent and solvent effects on spectroscopic properties of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives

In this article, we report the photophysical properties of six, newly synthesized donor-substituted 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene fluorophores. The steady-state and time-resolved spectroscopic experiments have been used to investigate the substituent and solvent effects on the locally excited (LE) and intramolecular charge transfer (ICT) emission. We demonstrate that the spectroscopic characteristics (fluorescence quantum yields, fluorescence decay times, radiative rate constants, and ground and excited state dipole moments) of the studied D–A dyes, as well as the reorganization energies characterizing the solute–solvent interactions and intramolecular torsion motions greatly depend on different substituents and microenvironment. On the basis of the experimental results and our previous quantum-chemical calculations, it was shown that two emitting charge transfer states: non-relaxed (ICT)NR and relaxed (ICT)R exist in six biphenyl derivatives dissolved in polar solvents (e.g., THF), whereas in non-polar medium (MCH) the existence of two emissive states have been attributed to non-relaxed and relaxed, locally excited state ((LE)NR, (LE)R).

Rb2LiCeCl6할라이드 섬광체의 열형광 특성

본 논문에서는 신소재 <TEX>$Rb_2LiCeCl_6$</TEX> 할라이드 섬광체를 개발하고, 개발된 섬광체의 섬광 및 열형광 특성에 대하여 조사하였다. <TEX>$Rb_2LiCeCl_6$</TEX>의 섬광스펙트럼은 <TEX>$Ce^{3+}$</TEX> 이온의 4f <TEX>${\rightarrow}$</TEX> 5d 천이에 따라 파장범위가 350~410 nm, 피이크 파장은 368 nm 및 378 nm이었다. 섬광감쇠시간 특성은 71 ns의 빠른 시간 특성 성분(85%)과 405 ns의 느린 성분(15%)의 2개로 구성되며, 잔광에 기여한 포획준위의 물리적 변수를 열형광 측정법에서 분석한 결과, 포획 준위의 활성화에너지, 발광차수 및 주파수 인자의 평균값은 각각 0.75 eV, 1.48 및 <TEX>$3.0{\times}10^8s^{-1}$</TEX>이었다. We developed a new <TEX>$Rb_2LiCeCl_6$</TEX> scintillator and determined the scintillation and thermoluminescence properties of the scintillator. The emission spectrum of <TEX>$Rb_2LiCeCl$</TEX> is located in the range of 350 ~ 410 nm, peaking at 368 nm and 378 nm, due to the 4f <TEX>${\rightarrow}$</TEX> 5d transition of <TEX>$Ce^{3+}$</TEX> ions. The fluorescence decay time of the crystal is composed two components. The fast component is 71 ns (85%) and the slow component is 405 ns (15%) of the crystal. The after-glow is caused by the electron and hole traps in the crystal lattice. We determined physical parameters of the traps in the crystal. The determined activation energy(E), kinetic order(m) and frequency factor(s) of the trap are 0.75 eV, 1.48 and <TEX>$3.0{\times}10^8s^{-1}$</TEX>, respectively.

Structure and photoluminescence properties of Na2Y2B2O7:Ce3+,Tb3+ phosphors for solid-state lighting application

Novel phosphors of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce3+ emission properties and the crystal structure of Na2Y2B2O7 is built and the result shows that Ce3+ ions occupy two non-equivalent Y3+ sites in the host. The codoping of Tb3+ in Na2Y2B2O7:Ce3+ can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce3+→Tb3+. The energy transfer processes of Ce3+–Ce3+ and Ce3+–Tb3+ are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs.

Measurement System of Decay Time for Liquid Scintillator

The fluorescence lifetime of the molecular excited states in the liquid scintillator determines the pulse shape of the events in a detector. The fluorescence decay times of the mixtures could be measured by UV light excitation, or via ionizing particles. Both of the setups are based on the time-correlated single photon technique. In this paper we described a setup in detail for testing the fluorescence lifetime under ionizing particle to render the relatively weak neutron or ion signals detectable. In addition, we presented the time resolution of system for the setup.

Energy Transfer and Defects Study in &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\rm Ce}^{3+}$&lt;/tex&gt;&lt;/formula&gt;, &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\rm Pr}^{3+}$&lt;/tex&gt;&lt;/formula&gt; Co-doped &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\rm Lu}_{2}{\rm Si}_{2}{{\rm O}_7}$&lt;/tex&gt;&lt;/formula&gt; Crystal

Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (LPS) single crystals doped with 0.05%Ce and co-doped with 0.05%Ce, 0.05%Pr were grown by floating zone method. The segregation coefficients of Pr and Ce in LPS host were estimated through ICP-OES method. The VUV-UV excitation and emission spectra at 150 K, X-ray excited luminescence, fluorescence decay time of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> emission at room temperature and thermally stimulated luminescence (TSL) spectra of LPS:Ce and LPS:Ce,Pr were measured. The energy transfer from Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> to Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> in LPS host was observed through the VUV-UV spectra and possible transfer pathways are discussed. The luminescence intensity of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> can be improved by about 20% after Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> co-doping. Defects in LPS host are studied through TSL spectra.

Preparation and Luminescence Properties of ${\rm Bi}_{4}{\rm Si}_{3}{\rm O}_{12}\!:\!{\rm Zn}$ Powders

Bi4Si3O12:Zn2+(BSO:Zn) polycrystalline powders were successfully prepared by sol-gel method. X-ray diffraction measurements confirm that the Zn2+-doped materials are all monophasic solid solution powders. The influences of doping concentration on the photoluminescence and radioluminescence characteristics have been investigated and discussed. The Zn2+ doped material shows a better light yield than that of undoped material under X-ray excitation. The fluorescence decay time of the optimal material, excited by UV has been aslso measured. The results show that the Zn2+ ion doping has a positive effect on the light yield of BSO. But the crystal growth and characterizations of BSO:Zn polycrystalline powders prepared deserve further investigations.

Fluorescence Spectroscopy and Confocal Microscopy of the Mycotoxin Citrinin in Condensed Phase and Hydrogel Films

The emission spectra, quantum yields and fluorescence lifetimes of citrinin in organic solvents and hydrogel films have been determined. Citrinin shows complex fluorescence decays due to the presence of two tautomers in solution and interconversion from excited-state double proton transfer (ESDPT) process. The fluorescence decay times associated with the two tautomers have values near 1 and 5 ns depending on the medium. In hydrogel films of agarose and alginate, fluorescence imaging showed that citrinin is not homogeneously dispersed and highly emissive micrometer spots may be formed. Fluorescence spectrum and decay analysis are used to recognize the presence of citrinin in hydrogel films using confocal fluorescence microscopy and spectroscopy.

Up/down conversion luminescence properties of (Na0.5Gd0.5)MoO4:Ln3+(Ln = Eu, Tb, Dy, Yb/Er, Yb/Tm, and Yb/Ho) microstructures: synthesis, morphology, structural and magnetic investigation

Novel bi-pyramid-like (Na0.5Gd0.5)MoO4:Ln3+ (Ln = Eu, Tb, Dy, Yb/Er, Yb/Ho, and Yb/Tm) hierarchical microstructures are synthesized via the EDTA-aided hydrothermal route. Time-dependent experiments were carried out and the morphological evolution was discussed, which signposted that the present method corresponded to a typical Ostwald ripening process for the formation of bi-pyramid-like structures. Elemental mapping analysis confirms the incorporation and uniform distribution of all the elements. Phase purity and crystal structure of the as-synthesized phosphor were analyzed by the X-ray diffraction (XRD) technique. Fourier transform infrared spectroscopy (FTIR) results confirm that for scheelite tetragonal symmetry, F2 (ν3) modes of vibrations are IR active. (Na0.5Gd0.5)MoO4 was demonstrated to be a good host material for down- and up-conversion luminescence, which were strongly dependent on the hydrothermal reaction time interval. The down-conversion luminescence properties of (Na0.5Gd0.5)MoO4 doped with Eu3+, Tb3+, Dy3+ were studied. Under 980 nm NIR excitation intense up-converted visible emissions were observed in (Na0.5Gd0.5)MoO4:Yb3+/Ln3+ (Ln = Er, Tm, and Ho), which shows green (2H11/2 → 4I15/2 of Er3+ at 525 nm), blue (1G4 → 3H6 of Tm3+ at 474 nm), and yellow (5S2 → 5I8 and 5F5 → 5I8 of Ho3+ at 541 nm and 660 nm, respectively) luminescence. Also, Yb3+/Er3+-doped samples exhibit luminescence in the near infrared (combination of Er3+/Yb3+ at 977 nm, Er3+ at 1530 nm) region. The energy transfer process, fluorescence decay time, and colour coordinates were analyzed for both down- and up-conversion luminescence. Further, the magnetic properties of (Na0.5Gd0.5)MoO4:Ln3+ (Ln = Eu and Yb/Er) as-prepared bi-pyramid-like structure exhibit typical paramagnetic behavior.