Decay Time Spectra Research Articles

Luminescent and Scintillation Characteristics of Ce-doped (Y2-xGdx)Si2O7 single crystal

Yttrium-gadolinium pyrosilicate ((Y2-xGdx)Si2O7) single crystals with different ratios of yttrium to gadolinium (x = 0.1–1.9) and 2% Ce-dopant were successfully synthesized using the floating-zone method. In this work, photoluminescence (PL) and scintillation properties of 2% Ce-doped (Y2-xGdx)Si2O7 were investigated. The conducted experiments included PL decay time and emission, X-ray-induced decay time and scintillation spectra, an afterglow analysis, as well as the total scintillation light yield by γ-ray-irradiation pulse-height spectra. Interesting results were including the considerably low afterglow at 20 ms of 40–65 ppm compared to commercial scintillator materials on the market like CdWO4. Further, the high light yield of 21,800 ph/MeV was achieved in Y0.5Gd1.5Si2O7 under 662 keV (137Cs) γ-ray-irradiation.

Express Synthesis of YAG:Ce Ceramics in the High-Energy Electrons Flow Field.

YAG:Ce ceramics by the direct action of an electron beam with 1.4 MeV energy were synthesized on a mixture of a stoichiometric composition of Y, Al, and Ce oxides without adding any substances to facilitate the process. The synthesis is realized in a time less than 1 s. The main structural phase of the obtained ceramics is YAG and YAP can be additional. The luminescence characteristics of the synthesized samples, the excitation, luminescence, decay time, and pulsed cathodoluminescence spectra, are similar to those known for YAG:Ce phosphors. The conversion efficiency of the excitation energy into the luminescence of the samples reaches 60-70% of those used for the manufacture of LED phosphors. The set of processes that determine the rate and efficiency of radiation synthesis differs from those occurring during thermal methods by the existence of a high degree of the initial compositions' ionization under the influence of a radiation flux and a high probability of the decay of electronic excitations into short-lived radiolysis products.

Development of apparatus for mean-lifetime measurement of cosmic-ray muons using plastic scintillation detectors and FLASH-ADC/FPGA-based readout electronics

Introduction: This paper presents the development and results of an apparatus for measuring the mean lifetime of cosmic-ray muons. Methods: The apparatus uses three plastic scintillation detectors and a readout electronics system based on Flash Analog Digital Converter (Flash-ADC) and Embedded Field Programmable Gate Array (FPGA). The readout system has 8-bit resolution and a 125 Msample/sec sampling rate. The system's trigger and data collection are controlled through a computer interface based on LabVIEWTM. The readout electronics are calibrated with an accuracy of 8 nsec/TDC channel. Results: Over 6000 events were recorded during the measurements performed at ground level using aluminum as the muon stopping material, and the muon decay time spectrum was obtained and fit with a combination of two exponential components and a constant background. The mean lifetimes of negative and positive muons were determined. Conclusion: Our results indicate that the mean lifetimes of negative and positive muons in aluminum are 0.70 ± 0.24 µsec and 2.05 ± 0.16 µsec, respectively.

Influence of Sintering Parameters on Spectroscopic Properties of BMW: Eu3+ Ceramic Materials Prepared by HPLT Technique.

In this work, Ba2MgWO6: Eu3+ (BMW: Eu3+) ceramic materials with a double perovskite structure were sintered using the High-Pressure Low-Temperature sintering (HPLT) technique. As part of the research, the influence of pressure (CP), sintering temperature (CT), and sintering time (CTS) on the structure and luminescence of the doped BMW were determined. Structural analysis via XRD and SEM + EDS and spectroscopic analysis via emission and excitation spectra, decay time, and absorption spectra of the obtained ceramics were performed. Dense double perovskite ceramics were obtained with a cubic structure with optimal sintering parameters: T = 500 °C, p = 8 GPa, and t = 1 min. The increase in temperature caused an increased extinction of the luminescence due to the diffusion of carbon into the ceramics. The increase in pressure led to the formation of the amorphous phase, which increased the speed of non-radiative transitions and also led to the extinction of the luminescence. The increase in sintering time from 1 to 3 min enhanced the luminescence output, but when the ceramic was sintered for 5 min, the luminescence was quenched, most likely by increasing the rate of the non-radiative process, as evidenced by reduced decay time.

Ce concentration dependence on scintillation properties of Ce-doped yttrium pyrosilicate single crystal

Yttrium pyrosilicate (Y2Si2O7) single crystals are successfully grown by the floating-zone method with 0.5–10.0% of Ce-doping concentration. X-ray diffraction patterns indicate a single phase of Y2Si2O7 without the impurity phase. The series photoluminescence (PL) and scintillation properties are systematically explored in this study, including PL emission, PL decay time, X-ray induced scintillation spectra, X-ray induced scintillation decay time, afterglow profile, and pulse height spectra. Ce-doped Y2Si2O7 is presented interesting properties including the intense emission band at 390 nm from Ce3+ 5d-4f transition on both PL emission contour maps as well as X-ray-induced scintillation spectra in all samples. The afterglow level at 20 ms after X-ray irradiation of the Ce-doped YPS is comparable with commercial scintillators such as CdWO4 and Tl-doped CsI. Under 137Cs (662 keV) γ-ray irradiation 137Cs (662 keV), the highest scintillation light yield of Ce-doped Y2Si2O7 is reach up to 17,200 ph/MeV for 2.0% Ce-doped sample.

Photophysical properties of BODIPYs with sterically-hindered nitrophenyls in meso-position

During recent years, the BODIPY core became a popular scaffold for designing of dyes with desirable properties. In this paper, we extend the library of possible modification of BODIPYs, presenting experimental data for a new family meso-substituted with nitrophenyl groups. We also present quantum chemical calculations, which complement the experimental data and give additional insight in the underlying photochemical and photophysical processes. Optical properties of novel compounds are characterized. It is shown that the fluorescence quantum yield and the efficiency of singlet oxygen generation differs by two orders of magnitude across the family. In aqueous solution, red-shifted fluorescence emission band is detected, corresponding to aggregates. This band has shorter decay time and wide excitation spectrum. We show that photolysis is not accompanied by the release of nitric oxide (NO) which was observed earlier for some dyes with nitrophenyl substituents. The experimental data presented in this paper may be useful for further designing of BODIPY dyes and NO photodonors.

A new diffusion effect correction method in pulsed neutron capture logging

The neutron diffusion effect contributed considerate bias to the sigma estimation in the pulsed neutron capture (PNC) well logging, and thus this effect must be corrected to achieve an accepted sigma prediction. This paper developed a new diffusion effect correction method for a more accurate sigma estimation in the PNC well logging method. Since the diffusion effect with a given source spacing in a PNC tool mainly depends on neutron slowing down and absorption, two parameters, the capture gamma ray counts ratio (RCAP) of the far to near detectors and the gamma ray counts ratio of inelastic scattering to capture (RIC) in the near detector, were used in the new method to effectively correct the diffusion effect. This is because RCAP is sensitive to neutron slowing down ability and RIC is sensitive to thermal neutron absorption ability. A combined expression of RCAP and RIC thus can reflect both the scattering and absorption contribution to the diffusion coefficient, which is subsequently used to correct the diffusion effect. No additional efforts are required to measure RCAP and RIC because they can be simultaneously obtained with the gamma ray decay time spectrum measurement. Computational experiments based on Monte Carlo simulations demonstrated the sigma calculated with the new correction method has shown to be more accurate than the non-corrected apparent sigma in the PNC logging. • A diffusion effect correction method developed for accurate sigma estimation. • Diffusion effect in sigma logging demonstrated by Monte Carlo simulation. • Two self-correction parameters of RCAP and RIC were used to correct the diffusion effect.

Development of photoluminescent, superhydrophobic, and electrically conductive cotton fibres.

A simple method for the preparation of multifunctional nanocomposite was developed towards the production of water-repellent, electrically conductive, and photoluminescent film onto cotton fibres. The nanocomposite was composed of lanthanide-doped strontium aluminium oxide and silicon rubber dispersed in petroleum ether. The electrically conductive fabric was woven from nickel strips twisted with cotton filaments as core yarns, which were wrapped with pure cotton yarns. The nanoparticles (NPs) of lanthanide-doped strontium aluminium oxide were mixed with environmentally friendly room-temperature vulcanizing silicon rubber (RTV-SR) dissolved in petroleum ether to give the silicon rubber/strontium aluminate nanocomposites. The produced nanocomposites were applied onto electrically conductive cotton/nickel fibres using spray-coating technology. The surface of the cotton/nickel fibres showed different hierarchical morphologies depending on the total content of the silicon rubber. Additionally, the superhydrophobic effect was found to be improved upon increasing the total content of the luminescence pigment NPs. The morphologies of the prepared phosphor NPs were determined using transmission electron microscopy (TEM). The generated transparent luminescence film demonstrated an absorbance peak at 358 nm and an emission peak at 515 nm. Photoluminescence of cotton fibres was monitored with the generation of different colours, including grey, green-yellow, bright white, and turquoise shades as recognized using CIE Laboratory colorimetric parameters. The emission, excitation, lifetime, and decay time spectra of the phosphorescent spray-coated cotton samples were studied. The surface morphologies and chemical compositions of the spray-coated cotton/nickel were investigated using wavelength-dispersive X-ray fluorescence (WD-XRF), scanning electron microscope (SEM), Fourier-transform infrared spectra (FTIR), and energy-dispersive X-ray analyzer (EDAX). The superhydrophobic effects were characterized by measuring static water contact angle. The comfort characteristics of the treated cotton/nickel substrates were assessed by investigating their air permeability and stiffness. The treated cotton/nickel fabrics also displayed an antimicrobial activity. The results displayed water repellence with high electrical conductivity and photoluminescence properties.

Optical performance test and energy resolution analysis on LaBr3(Ce) crystal

The paper used 137Cs and 60Co γ sources to measure and analyze the effects of different voltage, gain, count time of photomultiplier tube and different distance of sources on the energy resolution of LaBr3(Ce) crystal; the relationship curves were obtained quantitatively. The experiment values are in good agreement with MCNP simulation results. The results show that the energy resolution of LaBr3(Ce) is negatively correlated with voltage and gain; the gain is more influential. The energy resolution of LaBr3(Ce) is positively correlated with detection distance and count time; the detection distance is more influential. The paper used picosecond X-ray generated by pulsed power accelerator “Qiangguang-?” to excite the LaBr3(Ce) crystal and measure its fluorescence decay time and emission spectrum. The results are consistent with the available experimental data of other scholars and verify the excellent time response of LaBr3(Ce). With the increase in X-ray energy, the peak emission wavelength shifts towards infrared direction, which can better match the spectral response of photocathode.

Synthesis and luminescence properties of double perovskite Bi3+/Mn4+ co-doped Ca2GdTaO6 phosphor

Bi3+-doped, Mn4+-doped, and Bi3+/Mn4+ co-doped oxide phosphors Ca2GdTaO6 (CGT) are prepared via the solid-state reaction method. The phase purity and morphology of CGT: Bi3+, Mn4+ phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The band structure and density of state for CGT are calculated based on density functional theory (DFT). The bandgap of the CGT host is 3.72 eV. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CGT: Bi3+ and CGT: Mn4+ is investigated in detail. The overlap between the emission spectra of Bi3+ and the excitation of Mn4+ proves energy transfer from Bi3+ to Mn4+. The corresponding mechanism of the Bi3+→Mn4+ energy transfer process is investigated in detail based on the decay time and PL spectra. Energy transfer efficiency is also calculated. Upon excitation at 320 nm, Bi3+/Mn4+ co-doped CGT phosphors show dual emission attributed to the blue-violet emission (429 nm) of 3P1→1S0 transition of Bi3+ and red emission (679 nm) of 2Eg→4A2g of Mn4+. The intensity of the blue-violet and red emission peaks can be easily adjusted by controlling the concentration of Bi3+ and Mn4+ in the CGT host. The emission band is well-matched with the absorption bands of chlorophylls a and phytochrome PR under the near-ultraviolet to blue excitation, suggesting that the phosphors have great potential applications in light-emitting diodes (LEDs) to modulate plant growth.

Tm concentration dependence of scintillation characteristics on Tm-doped Lu2Si2O7 single crystal

Lutetium pyrosilicate (Lu2Si2O7) single crystals were synthesized by using the floating-zone method with 0.1, 0.5, 1.0, 2.0 and 5.0% of Tm-doping concentration. After the phase confirmation by powder XRD, photoluminescence (PL) and scintillation properties were systematically measured, including PL emission map, PL decay time, scintillation spectra, scintillation decay time and pulse height spectra. When we irradiated X-rays, we observed the scintillation emission at 360 and 460 nm caused by Tm3+ 4f-4f transitions. Under 662 keV γ-ray irradiation, we determined absolute scintillation light yield of 2340 ph/MeV for the 2.0% Tm doped sample. Taking into account whole optical and scintillation properties, 2.0% doping was the best for Tm-doped LPS crystals.

Time-resolved photoluminescence and optical properties of a specific organic azo dye

The aim of this work is to measure the photoluminescence of the Disperse Blue 79 (DB 79) deposited as thin films and study its morphological properties by the mean of the Atomic Force Microscopy technique in order to apply it as an Organic Emitting Light Diode (OLED). The films were prepared by the mean of the home-made Physical Vapor Deposition apparatus in a high vacuum on BK7 glass substrates. The linear optical properties were studied by photoluminescence and decay time spectra. The photoluminescence was measured in a broad ranged from 25 to 300 K in a high vacuum, while the decay time technique was investigated to measure the studied sample’s life-time in real time. Obtained results confirm homogeneous morphology and good optical quality of investigated organic azobenzene dye. These results allow the DB 79 dye to be used for the first time in production of the Organic Light Emitting Diodes (OLEDs).

Enhanced near/mid-infrared emission bands centered at ∼1.54 and ∼2.73 µm of Er3+-doped in transparent silicate glass-ceramics via Mn2+-Yb3+ dimer

The near/mid-infrared emission of Er3+-doped, Er3+-Yb3+ co-doped and Er3+-Mn2+-Yb3+ tri-doped in 40SiO2–(22.9-x)Al2O3–20BaF2–10LaF3–5TiO2– xMnO–0.1Er2O3–2Yb2O3 (in mol.%, x = 0, 2.0, 4.0, 6.0 and 10.0) (acronym: SGC-xMn) transparent silicate glass-ceramics were prepared. Enhanced near/mid-infrared emission intensity of Er3+-doped bands centered at ∼1.54 and ∼2.73 µm in transparent silicate glass-ceramics via Mn2+–Yb3+ dimer under 980 nm excitation were investigated. XRD results indicate that the Mn2+ ions are dispersed into the glass matrix. With the forming of Mn2+–Yb3+ dimer and the energy transfer processes from Mn2+–Yb3+ dimer and Mn2+ to Er3+ ions has led to NIR emission intensity of Er3+-doped at ∼1.54 µm was increased significantly about four-fold and the MIR emission intensity of Er3+-doped at ∼2.73 µm was increased about third-fold. In addition, based on the decay time spectra, mechanism of energy transfer processes between Mn2+–Yb3+ dimer, Mn2+ and Er3+ ions were also discussed.

Broadband near-infrared emission and energy transfer in Nd-Bi co-doped transparent silicate glass-ceramics for optical amplifiers

The Bi+-doped, Nd3+-doped, and Nd3+-Bi+ co-doped in SiO2–Al2O3–BaF2–LaF3–TiO2 transparent silicate glass-ceramics were fabricated by conventional melting-quenching technique. The super broadband near-infrared luminescence, decay time spectra in Nd3+-Bi+ co-doped transparent silicate glass-ceramics under 808 nm excitation were investigated. The interesting in this paper is due to energy transfer between Bi+ and Nd3+ ions already exists lead to super broadband NIR emission extending from 1050 to 1550 nm with a full-width at half-maximum (FWHM) of 480 nm which covered the whole O, E and S bands were observed in the Nd3+-Bi+ co-doped transparent silicate glass ceramics. In addition, based on the decay time spectra, mechanism of energy transfer processes between Bi+ and Nd3+ ions were also discussed and proposed.

Direct measurements of the lifetime of medium-heavy hypernuclei

The lifetime of a Λ particle embedded in a nucleus (hypernucleus) decreases from that of free Λ decay mainly due to the opening of the ΛN→NN weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. This paper presents a direct measurement of the lifetime of medium-heavy hypernuclei that were hyper-fragments produced by fission or break-up from heavy hypernuclei initially produced with a 2.34 GeV photon-beam incident on thin Fe, Cu, Ag, and Bi target foils. For each event, fragments were detected in coincident pairs by a low-pressure multi-wire proportional chamber system. The lifetime was extracted from decay time spectrum formed by the difference of the time zeros between the pairs. The measured lifetime from each target is actually a statistical average over a range of mass with mean about 1/2 of the target mass and appears to be a constant of about 200 ps. Although this result cannot exclude unexpected shorter or longer lifetimes for some specific hypernuclei or hypernuclear states, it shows that a systematic decrease in lifetime as hypernuclear mass increases is not a general feature for hypernuclei with mean mass up to A≈130. On the other hand, the success of this experiment and its technique shows that the time delayed fissions observed and used by all the lifetime measurements done so far on heavy hypernuclei could likely have originated from hyper-fragments lighter than the assumed masses.

Development and measurement of luminescence properties of Ce-doped Cs2LiGdBr6 crystals irradiated with X-ray, γ-ray and proton beam

The effect of higher Ce-concentration on the luminescence and scintillation properties of Cs2LiGdBr6 single crystals are studied. We used the Bridgman method for the growth of Ce-doped Cs2LiGdBr6 single crystals. Luminescence properties of the grown crystals are measured by X-ray and proton excitations. We measured the pulse height and fluorescence decay time spectra of Cs2LiGdBr6:Ce3+ with a bi-alkali photo multiplier tube (PMT) under γ-ray excitation from 137Cs source. Improvements in the scintillation properties are observed with the increase of Ce-concentration in the lattice. Detailed procedure of the crystal growth is also discussed.

State of the art timing in TOF-PET detectors with LuAG, GAGG and L(Y)SO scintillators of various sizes coupled to FBK-SiPMs

Time of flight (TOF) in positron emission tomography (PET) has experienced a revival of interest after its first introduction in the eighties. This is due to a significant progress in solid state photodetectors (SiPMs) and newly developed scintillators (LSO and its derivatives). Latest developments at Fondazione Bruno Kessler (FBK) lead to the NUV-HD SiPM with a very high photon detection efficiency of around 55%. Despite the large area of 4×4 mm2 it achieves a good single photon time resolution (SPTR) of 180±5ps FWHM. Coincidence time resolution (CTR) measurements using LSO:Ce codoped with Ca scintillators yield best values of 73±2ps FWHM for 2×2×3 mm3 and 117±3ps for 2×2×20 mm3 crystal sizes. Increasing the crystal cross-section from 2×2 mm2 to 3×3 mm2 a non negligible CTR deterioration of approximately 7ps FWHM is observed. Measurements with LSO:Ce codoped Ca and LYSO:Ce scintillators with various cross-sections (1×1 mm2 - 4×4 mm2) and lengths (3mm - 30mm) will be a basis for discussing on how the crystal geometry affects timing in TOF-PET. Special attention is given to SiPM parameters, e.g. SPTR and optical crosstalk, and their measured dependency on the crystal cross-section. Additionally, CTR measurements with LuAG:Ce, LuAG:Pr and GGAG:Ce samples are presented and the results are interpreted in terms of their scintillation properties, e.g. rise time, decay time, light yield and emission spectra.

Luminescence and energy transfer progress in Bi-Yb co-doped germanate glass

The Bi-doped and Bi-Yb co-doped germanate glasses were fabricated by high temperature melting-quenched technique. The absorption spectra, near-infrared (NIR) luminescence properties and decay time spectra are investigated. The results show that the NIR emission peak around 1030 nm of Yb3+ ions and two NIR emission bands around 1180 and 1300 nm of Bi ions are observed, under 690 nm LD excitation. Two NIR emission bands of Bi-related are ascribing in different Bi-related NIR emission centers, Bi0 for 1180 nm and Bi+ ion for 1300 nm, respectively. NIR luminescence intensity of Yb3+ ions, Bi0 and Bi+ ion is decreased. The full width at half maximum (FWHM) is broadening with the increasing in Yb2O3 concentration, and over 361 nm. The energy transfer (ET) among Yb3+, Bi0, and Bi+ NIR emission center is also investigated, under 690 nm LD excitation. It shows that Bi0 ion transfer energy to Bi+ and Yb3+ ions. The Yb3+ ion addition is benefit to Bi+ ions NIR luminescence. This could be the reason for broadening the FWHM. Yb–Bi codoped germanate glass is a promising material for broadband optical amplification.

Probing DNA-stabilized fluorescent silver nanocluster spectral heterogeneity by time-correlated single photon counting.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are promising fluorophores whose photophysical properties and synthesis procedures have received increased attention in the literature. However, depending on the preparation conditions and the DNA sequence, the DNA-AgNC samples can host a range of different emitters, which can influence the reproducibility of the optical response and the evolution over time of the populations of these emitters. We have developed a simple method to characterize the spectral heterogeneity and time evolution of these emissive species at any given point in time after preparation, by plotting the average decay time as a function of emission wavelength. These so-called average decay time spectra were acquired for different excitation wavelengths of AgNCs stabilized by an oligonucleotide containing 24 cytosines (C24-AgNCs). The average decay time spectra allowed the comparison of sample preparation and the judgment of reproducibility. Therefore, we propose the use of the average decay time spectra as a robust and easy tool to characterize and compare different as-synthesized DNA-AgNC samples. The average decay time spectra can in general also be used to characterize the spectral heterogeneity of other fluorophores, such as luminescent colloidal nanoparticles, and to assess the reproducibility of a synthetic procedure containing an unknown distribution of emissive species.

Synthesis and photoluminescence properties of tunable emission phosphors Ca4Si2O7F2:Ce3+

The Ce3+ activated phosphors Ca4Si2O7F2:Ce3+ are prepared by a solid state reaction technique. The UV–vis luminescence properties as well as fluorescence decay time spectra are investigated and discussed. The results revealed that there were two kinds of Ce3+ luminescence behavior with 408 and 470 nm emissions, respectively. Under 355 nm excitation, the Ce(1) emission (408 nm) is dominant at low doping concentration, and then the Ce(2) emission (470 nm) get more important with increasing of Ce3+ concentrations in the host. The phosphors Ca4Si2O7F2:xCe3+ show tunable emissions from blue area to green-blue area under near-ultraviolet light excitation, indicating a potential application in near-UV based w-LEDs.