Decay Curve Measurements Research Articles

Effect of modifier oxides on absorption and emission properties of Eu3+ doped different lithium fluoroborate glass matrices

Eu 3+ doped lithium fluoroborate glass with different modifier oxides (Li 2 B 4 O 7 –BaF 2 –NaF–MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li 2 B 4 O 7 –BaF 2 –NaF–MgO+CaO, Li 2 B 4 O 7 –BaF 2 –NaF–CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state ( 7 F 0 ) of different absorption bands of Eu 3+ are calculated. From the optical absorption measurements and using the Judd–Ofelt (J–O) theory, J–O parameters (Ω λ λ =2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities ( A ), radiative life-times ( τ R ), and branching ratios ( β r ) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections ( σ P ) are obtained for the emission transitions, 5 D 0 → 7 F 1 , 5 D 0 → 7 F 2 , 5 D 0 → 7 F 3 and 5 D 0 → 7 F 4 of Eu 3+ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the 5 D 0 → 7 F 2 transition have been measured and analyzed for all the glass matrices.

FT-IR, FT-Raman and fluorescence studies of Tb3+ ions activated lead containing sodium fluoroborate glasses

This study reports on the concentration dependent fluorescence properties of Tb3+-doped lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses and are analyzed by DSC, FT-IR, FT-Raman, optical absorption, emission and decay curve spectra. Co-existence of trigonal BO3 and tetrahedral BO4 units was evidenced by FT-IR and Raman spectroscopy. Judd–Ofelt theory was applied to the experimental oscillator strengths to evaluate the J–O intensity parameters. The fluorescence spectra of Tb3+-doped glasses have revealed prominent blue and green emissions originating from 5D3 and 5D4 excited levels to 7FJ ground state multiplet, respectively. The luminescent intensity of the transitions originating from 5D4 state increases with increase of Tb3+ concentration and no quenching effect is noticed up to 2mol% of Tb3+ ions. Chromaticity color coordinates have been calculated and the dominant emission in the green region is discussed. The nature of decay curves of 5D4 level for different Tb3+ ion concentration in all LCZSFB glasses has been analyzed. Using the J–O intensity parameters as well as from the emission and decay curve measurements, various radiative and fluorescence properties have been calculated for the 5D4 fluorescent level. Based on these results, the utility of Tb3+ ions doped LCZSFB glasses as laser active materials for high intensity emissions in the green region is discussed.

Transition intensities and excited state relaxation dynamics of Tm3+ in Tm:PbF2 crystal

High-quality Tm doped β-PbF2 crystal is grown by the Bridgman method in a nonvacuum atmosphere. Optical absorption spectra were acquired and analysed in the framework of the Judd-Ofelt theory. Values of radiative transition rates and luminescence branching ratios calculated using phenomenological intensity parameters Ωλ were compared to corresponding experimental values derived from measurement of luminescence spectra and decay curves. The emission cross-sections of the 3 F 4 → 3 H 6 transitions of the Tm3+ ions at 1.86 μm wavelengths were estimated by the use of the Fuchtbauer-Ladengurg method.

Effects of rare earth ion modifications on the photoelectrochemical properties of ZnO-based dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO film electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectroscopy and open-circuit voltage decay curve measurements were performed to investigate the photoelectrochemical characteristics of the ZnO films modified with different rare earth (La, Ce, Nd, Sm, and Gd) ions. The experimental results indicate that the rare earth oxides covered on the electrode surfaces can form energy barrier and maintain a lower charge recombination probability, and some rare earth ion modifications can passivate the surface states of ZnO electrode. Among these rare earth ions tested, the Nd-, Sm- and Gd-ion modifications can obviously enhance the open-circuit photovoltage and fill factor of the ZnO-based solar cell; whereas the La-, Ce-, Nd-, and Sm-ion modificaions lead to a decreased short-circuit photocurrent. The optimal conversion efficiency is obtained from the Gd-ion modified ZnO-based cells, with a 44.5% improvement in the efficiency as compared to the unmodified one, indicating this rare earth ion modification is promising in the ZnO-based solar cell.

Robust mapping of the myelin water fraction in the presence of noise: Synergic combination of anisotropic diffusion filter and spatially regularized nonnegative least squares algorithm

To improve the mapping of myelin water fraction (MWF) despite the presence of measurement noise, and to increase the visibility of fine structures in MWF maps. An anisotropic diffusion filter (ADF) was effectively combined with a spatially regularized nonnegative least squares algorithm (srNNLS) for robust MWF mapping. Synthetic data simulations were performed to assess the effectiveness of this new method. Experimental measurements of signal decay curves were obtained and MWF maps were estimated using the new method and compared with maps estimated using other methods. MWF mapping was substantially improved in both simulations and experimental data when ADF was combined with the srNNLS algorithm. MWF variability decreased with the use of the proposed method, which in turn resulted in increased visibility of small focal lesions and structures in the MWF maps. This study demonstrates that the benefits of ADF and srNNLS algorithms can be effectively combined in a synergic way for robust mapping of MWF in the presence of noise. Substantial improvements to MWF mapping can be made using the proposed method.

Effects of annealing conditions on the photoelectrochemical properties of dye-sensitized solar cells made with ZnO nanoparticles

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectra and open-circuit photovoltage decay curves measurements were performed to investigate the photoelectrochemical characteristics of ZnO films annealed at different temperatures. The experimental results indicate that the effects of the bulk traps and the surface states within the ZnO films on the recombination processes of the photoinjected electrons in DSSCs depend on the annealing temperature. The DSSC based on the ZnO electrode annealed at 400 °C exhibits an optimal energy conversion efficiency of 3.92% under the illumination of one sun simulated sunlight because the farthest decrease in the effects of both bulk traps and surface states at this film can maintain a lower charge recombination probability. This result indicates that the ZnO film electrode has promising application in the field of DSSCs, and the optimization of porous film fabrication condition is efficient for the improvement of ZnO-based DSSC’s performances.

Optical properties and energy transfer of Dy 3+-doped transparent oxyfluoride glasses and glass–ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass–ceramics have been synthesized and studied by X-ray diffraction, transmission electron microscope, optical spectroscopy and time-resolved decay curves measurements. From the absorption spectra, Judd–Ofelt intensity parameters have been obtained and are used to predict radiative properties for the excited states of Dy 3+ ions. From the visible emission spectra, yellow to blue intensity ratios have been calculated and their relative variations have been discussed based on the concentration of Dy 3+ ions and the heat treatment conditions used to prepare the glass–ceramics. Luminescence decay curves of the 4F 9/2 emitting level are found to be single exponential for 0.01 mol% Dy 3+-doped glass and non-exponential for the remaining samples. The nature of energy transfer processes between Dy 3+ ions, responsible for the non-exponential behavior of the decay curves, has been analyzed in the frame work of the Inokuti–Hirayama model. Lifetimes of the 4F 9/2 level are found to decrease with the concentration of Dy 3+ ions as well as with the time of heat treatment.

Transition intensities and excited state relaxation dynamics of Dy 3+ in crystals and glasses: A comparative study

A comparative spectroscopic investigation of dysprosium-doped YAl 3(BO 3) 4, LiNbO 3 single crystals, fluorosilicate glass and fluorogermanate glass was performed with special attention directed to laser potential associated with the 4F 9/2 → 6H 13/2 transition of Dy 3+ near 570 nm in the visible. Optical absorption spectra were acquired and analysed in the framework of the Judd–Ofelt theory. Values of radiative transition rates and luminescence branching ratios calculated using phenomenological intensity parameters Ω t were compared to corresponding experimental values derived from measurement of luminescence decay curves and luminescence spectra. Importance of the self-quenching of the 4F 9/2 emission was assessed for the systems under study based on results of lifetime measurement with samples containing different Dy 3+ concentrations. Feasibility of the visible laser operation was considered taking into account availability of bands accessible for optical pumping, the 4F 9/2 quantum efficiency and emission cross-section for the potential 4F 9/2 → 6H 13/2 transition. It was concluded that among considered systems the Dy:YAl 3(BO 3) 4 is the most promising material for the visible laser operation. It shows advantageously low matrix absorption in the optical pump region between 400 and 340 nm. The 4F 9/2 quantum efficiency is close to unity for a low Dy 3+ concentration and it is weakly affected by the self-quenching effect at increased concentration. The 4F 9/2 → 6H 13/2 emission consists of narrow lines with high peak emission cross-section with maximum value of 1.9 × 10 −20 cm 2 at 575.5 nm for π-polarisation.

Emission analysis of RE3+ (Eu3+, Tb3+ & Ho3+): B2O3-BaO-LiF/AIF3 glasses

We report here the luminescence spectra of certain rare earth ions (Eu3+, Tb3+ & Ho3+) doped B2O3-BaO-LiF/AiF3 based on the measurements of emission and decay curves of prominent emission transitions. For both the reference host glasses, FTIR, XRD, DTA-TG profiles have been recorded to understand their structural and thermal properties. Eu3+ doped glasses have shown five emission transitions of 5D0 → 7F01,2,3 & 4 located at 580nm, 593nm, 615nm, 655nm and 704nm respectively with an excitation at λexci = 392 nm (7F0 → 5L6). Also under an UV source, these europium glasses have displayed a bright red emission from their surfaces. Tb3+ glasses have exhibited four emission bands of 5D4 → 7F6,5,4,3 at 491nm, 547nm, 588nm and 625nm respectively with an excitation at λexci = 376 nm (7F6 → 5G6). Intense green emission from the glass surfaces has been noticed upon exposure to the UV source. Prominently bluish-green emission has been noticed from the surfaces of the holmium glasses under an UV source and same emission transition (5F4 → 5I8) at 519 nm with an excitation at λexci = 389 nm (5I8 − 5G4) has also been obtained from their measured emission spectra. For all the prominent emissions of the rare earth glasses, decay curves have been measured to compute their lifetimes.

Spectroscopic characteristics of Olgite (Ba,Sr)(Na,Sr) 2Na[PO 4] 2 crystals doped with Sm 2+ ions

Sm 3+ ions doped Olgite crystals (Ba,Sr)(Na,Sr) 2Na[PO 4] 2 were prepared by high temperature solid-state reaction. Sm 2+ ions were obtained by X-ray irradiation reduction. The samples were investigated by X-ray diffraction, SEM, photoluminescence and decay curves measurements. In (Ba,Sr)(Na,Sr) 2Na[PO 4] 2, the influence of different mole ratios of Sr to Ba atoms on the crystal structure, reducing efficiencies of Sm 3+ to Sm 2+ and luminescence properties of Sm 2+ ions were discussed. It is found that the conversion of Sm 3+ → Sm 2+ after X-ray irradiation is efficient in this phosphate. The emission of Sm 2+ in this host after excitation into the 4f 5 5d 1 levels shows 5D 0 → 7F J ( J = 0, 1, 2) emission together with a broad emission band. The characteristic of Sm 2+ ions luminescence was discussed.

Luminescence and microstructure of Sm2+ ions reduced by x-ray irradiation in Li2O–SrO–B2O3 glass

Sm 3 + -doped Li2O–SrO–B2O3 glass sample was prepared by the conventional melt quenching method in air atmosphere. Sm2+ ions in this borate glass were obtained by x-ray irradiation reduction method. The as-prepared and x-ray-irradiated samples were investigated by photoluminescence spectrum and decay curve measurements. The dependence of Sm2+ luminescence intensity on the x-ray irradiation time was investigated. It is found that the conversion of Sm3+→Sm2+ after x-ray irradiation is efficient in this borate glass. Photostability of Sm2+ ions was evaluated by the photobleaching method. Furthermore, the induced optical absorption spectrum measurement after x-ray irradiation was performed. Thermoluminescence above room temperature was also studied after x-ray irradiation. The different kinds of defect structures and the reduction mechanism of Sm2+ ions in this borate glass were discussed. The microstructure of Sm ions in the Li2O–SrO–B2O3 glass was suggested. The proposed microstructure would be helpful to understand the reduction mechanism of Sm2+ ion in borate glasses.

Preparation and luminescence properties of nano-polycrystalline Cr 3+:Lu 3Ga 5O 12

Nano-polycrystalline Cr 3+:Lu 3Ga 5O 12 (Cr:LGG) has been obtained by sintering its precursor, which was synthesized via coprecipitation method. The obtained nanopowders were charactered by X-ray diffraction (XRD), scanning electron microscopy (SEM), excitation and emission spectra and fluorescence decay curve measurements. XRD result shows that Cr:LGG precursor has translated into polycrystalline Cr:LGG after being sintered at 1000 °C for 3 h. Three broad excitation bands locate around 462, 608 and below 300 nm, respectively. The emission spectrum shows a broadband from 600 to 840 nm with maximum at 708 nm. The fluorescence decay time is determined as 890 μs.

The luminescence properties of Sm 2+ doped sodium barium strontium phosphate

Sm 3+ ions doped NaSm 0.01Ba 0.78Sr 0.21(PO 4) was prepared by high-temperature solid-state reaction method. Sm 2+ ions were obtained by X-ray irradiation reduction. The samples were investigated by X-ray diffraction, photoluminescence, and decay curves measurements. It is found that the conversion of Sm 3+ → Sm 2+ after X-ray irradiation is very efficient in this phosphate. NaSm 0.01Ba 0.78Sr 0.21(PO 4) is a suitable host for Sm 3+ → Sm 2+ conversion. The emission of Sm 2+ in this host after excitation into the 4f 55d 1 levels shows 5D 0 → 7F J ( J = 0, 1, 2) emission together with the broad 5d → 4f emission band at room temperature, while only the 5D 0 → 7F J ( J = 0, 1, 2) emission is observed at lower temperature.

Experimental study of induced polarization relaxation time spectra of shaly sands

The induced polarization decay curve contains much more information than chargeability which is often used in traditional induced polarization logging tool. The singular value decomposition algorithm makes it possible to transform induced polarization decay data into relaxation time spectrum. The spectrum logging tool can be used as an in-situ method to estimate pore structure, permeability, formation water resistivity and shaliness of reservoir with deep investigation depth and high signal-to-noise ratio. In order to use this new logging method in practice, effect of some factors on the relaxation time spectrum should be investigated. The induced polarization decay curve measurements have been performed on seven samples from Daqing Oil Field using a four-electrode technique. The effects of temperature, overburden pressure, electrolyte and salinity on the relaxation spectra of the core samples were analyzed qualitatively. When we discussed the effect of one parameter on the spectra, the others were fixed. The results show that the spectra shift to low time constants with temperature increasing, but the shape is almost the same. The temperature dependence of the spectrum can be corrected. When the overburden pressure increases, the relative amplitudes of low relaxation time constants are the same, and those of high constants decrease. When pressure is diminished again, the amplitudes of high time constants do not recover to the original distribution. The salinity has small influence on the spectra. The electrolyte has the influence on the spectra because of the diffusion coefficient different. This influence of electrolyte can also be corrected.

Application of Time‐Resolved Polarization Fluorescence Spectroscopy in the Femtosecond Range to Photosynthetic Systems†

Time-resolved polarization fluorescence spectroscopy in the femtosecond range was applied to a photosynthetic antenna system. Specific signals of excited states were obtained by simultaneous measurements of fluorescence rise and decay curves and polarized spectroscopy. Relaxation processes of carotenoids, energy transfer from carotenoids to chlorophyll (Chl) a, and energy migration among pigment pools of Chl a and Chl b were clearly resolved. Two new characteristics of carotenoid molecules were revealed only by anisotropy measurements. A new singlet excited state between the well known S2 (1Bu(+)) and S1 (2Ag(-)) states was resolved by an intermediary anisotropy (r(t) = 0.30) for siphonaxanthin in chloroplasts of Codium fragile. Time-dependent changes in anisotropy with an initial value of 0.52 (r(0) = 0.52) were recorded during the relaxation of lutein molecules in the light-harvesting complexes II of Arabidopsis thaliana, and this was interpreted as a strong interaction between two lutein molecules in the pigment-protein complexes. Other examples of the application of this method were also discussed.

Multi-Exponential Inversion and Laboratory Study of Induced Polarization Relaxation Time Spectra of Shaly Sands

Abstract According to the traditional Induced Polarization (IP) logging method, the IP relaxation time spectrum can give much more information about a reservoir, such as the pore structure, permeability, formation water resistivity, and shaliness. In this paper, the Singular Value Decomposition (SVD) algorithm is used to inverse the IP multi-relaxation data of the rock samples. The appropriate number of relaxation arrangement points in the relaxation data inversion is from 32 to 64. All of the relaxation spectra show a multi-peak shape. IP decay curve measurements have been performed on 30 samples from the Daqing Oil Field using the four-electrode technique. The effects of charging current, charging and discharging time, brine salinity, and water saturation on the relaxation spectra of the rock were analyzed qualitatively, so that we could develop a new IP spectra logging tool that could be used successfully in practice. When we discussed the effect of one parameter on the relaxation time spectra, the others remained fixed. The results show that the relaxation spectrum relates with the charging time, discharging time, and depends strongly on water saturation. The salinity of NaCl brine and the charging current density are shown to have a small influence on the relaxation spectra in the special ranges. Introduction Induced polarization (IP) phenomena were observed more than 80 years ago, which may be caused by metallic minerals or clay Content(1–8). The detection of IP in the time-domain is made by measuring both the maximum voltage during the charging period of a dc current flow, and the transient decay of the electrical potential as a function of time, after the current is turned off. IP logging is traditionally used to determine the formation water resistivity and shaliness parameter (Qv), which is defined as the cation exchange capacity of the shaly sands per unit pore volume(9–12). But up to now, no IP logging has successfully been used commercially to evaluate or locate petroleum reservoirs. The theory analysis shows that the IP relaxation characteristics relate to the pore structure of the rock and the IP decay curve is a superposition of signals coming from all pores with different sizes(13). So, the curve can be fitted with multi-exponential decay function and a relaxation spectrum can be obtained. The spectrum contains much more information than the traditional IP method. The IP spectra of full water-saturated rock gives a quick, easy, and nondestructive way to characterize the rock, such as the pore structure, permeability, and Qv. On the other hand, we can develop a new time-domain IP spectra logging tool. This kind of IP spectra logging can be also used to obtain the formation water resistivity and shaliness parameter, Qv, as the traditional time-domain IP logging tool. In order to transfer the lab results downhole, the borehole effects, such as rugosity and mud, should also be considered. This can be achieved by using focusing technology as well as technologies used in traditional lateral logging tools.

Anomalous Tb3+ luminous spectrum in the TiO2 nanocrystals

In order to get Tb 3+ luminescence in the TiO 2 nanocrystals, nanoaggregate of terbium oxide in the TiO 2 nanocrystal has been produced using a reverse micelles and solvothermal method in toluene solution. Transmission electron microscopy and X-ray diffraction measurements have identified particles with average size of 6.7–10.2 nm in the anatase phase corresponding to the sintering temperature. The time-resolved spectroscopic technique has been used for the measurement of luminescence spectra and decay curves. No emission from Tb 3+ ions was observed from the sample with Tb 3+ ions dispersed in TiO 2 . However, from the sample that terbium oxide is formed a colony of aggregates in the TiO 2 solution strong emissions from 5 D 4 levels of Tb 3+ ions were observed. The PL spectrum was very anomalous, extraordinarily it has a very strong emission band due to the transition of 5 D 4 → 7 F 2 . It was proposed to describe anomalous spectrum that two kinds of energy migrations ( 5 D 4 – 7 F 6 and 5 D 4 – 7 F 2 ) are occurred among Tb 3+ ions, and quenching centers located at the boundary of titanium oxide powerfully operate to higher energy.

Dynamics of removal of organosulfur compounds from diesel by adsorption on carbon aerogels for fuel cell applications

Carbon aerogels (CAs) were investigated as adsorbents for the desulfurization of liquid hydrocarbon fuels for fuel cell applications. Synthetic mixtures of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in n-hexadecane (n-HD) were used as models for sulfur contaminated diesel fuel. Carbon aerogels were found to have good adsorption capacity for both DBT and 4,6-DMDBT. Both the thermodynamics and dynamics of adsorption were investigated by the measurement of adsorption isotherms and concentration decay curves in batch mode. A theoretical model was developed to describe the dynamics of adsorption of both DBT and 4,6-DMDBT on CAs from model diesel and it was found to represent the experimental data fairly well. The model takes into account pore diffusion and assumes local equilibrium within the pores. The tortuosities of 22nm pore diameter CA and 4nm pore diameter CA were found to be 3.5 and 4.0, respectively. For the latter, a restrictiveness factor had to be included due to the closeness of the size of the solute, DBT, to the pore size. The simulations indicated that the particle diameter and the pore size of the carbon aerogel adsorbent were critical parameters in design of large-scale fixed-bed adsorbers for sulfur removal.

Photoluminescence properties of Tb 2O 3 embedded in the TiO 2 nanocrystals

Nanosize terbium oxide embedded in the TiO 2 nanocrystal has been produced using a reverse micellar synthesis. High-resolution transmission electron microscopy and X-ray diffraction measurements have identified particles with a size of 4.5–5.5 nm in the anatase phase. The time resolved spectroscopic technique has been used for the measurement of luminescence spectra and decay curves. Strong emissions from 5D 4 levels of Tb 3+ ions were detected at the sample having core (Tb 2O 3)–shell (TiO 2) structure. The structure of this luminescence spectrum was anomalous which has very strong emission band due to the transition of 5D 4 → 7F 2. It was ascribed to two kinds of energy migration among Tb 3+ ions ( 5D 4 → 7F 6 and 5D 4 → 7F 2) in terbium oxide nanoparticle and quenching centers located at the boundary between core and shell. The excitation energy corresponding to the transition of 5D 4 → 7F 2 may be able to migrate among Tb 3+ ions for a long time, since the quenching centers operate upon higher excitation energy than that of this migration.

Luminescence and scintillation characteristics in the CsI:Br crystal on Br concentrations

Cesium Iodide (CsI) doped with Cesium Bromide (CsBr) was grown, using the Bridgman technique, varying the concentration of the Br from 10−2 to 2×10−1 mol. The Br dopant composition was analyzed by chemical and optical methods. A good uniformity of the Br dopant distribution over the height was observed inside each ingot. To evaluate the crystal obtained [CsI(Br)], systematic measurements of optical transmittance, emission spectra, pulse heights and luminescence decay curves were carried out.