Μs Decay Time Research Articles

Enhanced luminescence encryption via Mn4+ activation with organic acid surface modification

Mn4+-activated luminescent materials exhibit high color purity red light emission, but their limited water resistance hinders practical applications. In this study, citric and oxalic acids are innovatively employed for surface modification, resulting in luminescent materials with enhanced water resistance while preserving their luminescent intensity. This enhancement provides a prerequisite for their application in anti-counterfeiting films and aqueous fluorescent inks. Furthermore, the potential for optical information storage is successfully demonstrated by utilizing the photochromic fluorescent properties of polyvinyl alcohol films deposited on oxalic acid-modified K2SiF6:Mn4+. Exploiting the 3 ms day time difference between equivalently and non-equivalently doped Mn4+ fluoride, a millisecond information encryption mode is proposed by combining oxalic acid-modified K2SiF6:Mn4+ (long decay time, τ = 8.99 ms) and K3AlF6:Mn4+ (short decay time, τ = 5.31 ms). This mode can be effectively decoded using digital cameras and editing software, achieving high-level anti-counterfeiting capabilities. This work advances the application of highly efficient Mn4+-activated red phosphors in the realm of information security.

Cu4I4-cubane cluster based on tris(p-anisyl)arsine: Synthesis, crystal structure and photophysical properties

A new cubane cluster [Cu4I4(AsAn3)4] was synthesized in 82% yield by the reaction of tris(p-anisyl)arsine (AsAn3) with CuI. At ambient temperature, this cluster exhibits bright yellow-green phosphorescence (λmax = 546 nm) with the quantum yield of 35% and 4.1 μs decay time.

Excess polymer-assisted crystal growth method for high-performance perovskite photodetectors

Defects in grain boundaries and at the surface of perovskite polycrystalline film lead to nonradiative recombination losses and ion migration, which seriously affects the performance and stability of optoelectronic devices. However, the process of passivation by using functional groups in polymers is expected to solve the problem. In this work, a tandem-like perovskite photodetector (PD) is developed, and an improved solution process is proposed to promote perovskite crystal growth and reduce the horizontal grain boundaries by using excess poly(methyl methacrylate) (PMMA) as anti-solvent. In addition, PMMA retained in perovskite grains acts as an interlayer for storing photocarriers, reducing the dark current and enhancing the PD gain. As a result, optimal perovskite PD exhibits a peak specific detectivity of 3.38 × 1012 Jones, a high responsivity of 5.65 A/W, a linear dynamic range of 80 dB, and an external quantum efficiency of 1321% under 532 nm illumination at the small bias of − 1 V. In addition, the PD has a fast response (5.90 μs rise time, 6.75 μs decay time). These results combine to provide a low-cost method for designing high-performance, ultrafast-response perovskite optoelectronic devices with low power consumption.

A reusable and self-recoverable vitrified film of an anisometric europium(III) β-diketonate complex with UV light-responsive Eu3+ emission

We report on photophysical properties of a 20 µm thick vitrified film (fabricated from a powder of an anisometric europium(III) β-diketonate complex through a melt-processing technique and sandwiched between two quartz plates), which are highly unusual for known film-type materials based on non-mesogenic lanthanide(III) β-diketonate complexes. The film excited by light in the wavelength range of 280–425 nm exhibits a bright orange-red narrow-band emission of Eu3+ ions (due to efficient ligand-to-metal energy transfer) with 530 µs decay time. The prolonged irradiation of the film with a 337 nm nitrogen laser decreases the luminescence brightness of the Eu3+ ions without decomposition of the anisometric complexes. Then the luminescence gradually recovers during storage of the film in the dark for at least 19 h at room temperature. Interestingly, the film is capable of repeatedly reversible changing the luminescence brightness upon alternating UV laser irradiation and dark storage. The observed self-recovery phenomenon can be presented as an elastic photodeformation of local structures of the film with following changes in the Eu3+ ions emission parameters. We believe that the found film properties are promising for the design and development of novel reusable luminescent sensors or dosimeters of UV radiation.

High-Resolution Phosphorescence Lifetime Imaging (PLIM) of Bones

For the first time, the time-resolved two-photon excited autophosphorescence of non-labeled biological specimens was investigated by phosphoresce lifetime imaging with microscopic spatial resolution. A modified multiphoton tomograph was employed to record both photoluminescence contributions, autofluorescence and autophosphorescence, simultaneously, induced by two-photon excitation using an 80 MHz near infrared femtosecond-pulse-laser scanning beam, an acousto-optic modulator, and a time-correlated single-photon counting module for lifetime measurements from the picosecond to the microsecond range. In particular, the two-photon-excited luminescence of thermally altered bones was imaged. A strong dependence of the phosphorescence intensity on exposure temperature, with a maximum emission for an exposure temperature of approximately 600 °C was observed. Furthermore, the phosphorescence lifetime data indicated a bi-exponential signal decay with both a faster few µs decay time in the range of 3–10 µs and a slower one in the range of 30–60 µs. The recording of fluorescence and phosphorescence allowed deriving the relative signal proportion as an unbiased measure of the temperature dependence. The measurements on thermally altered bones are of particular interest for application to forensic and archeological investigations.

Red afterglow and luminescence arising from defects in CaS:Eu2+, Tm3+

CaS:Eu2+, Tm3+ is a phosphor known to emit a long afterglow of red emission (650 nm) when excited by blue light (450 nm). It shows a long afterglow time of 700 s for Eu = 0.05% and Tm = 2%. The mechanism of this afterglow is investigated using time-resolved fluorescence (TR-F) spectroscopy from the nanosecond to millisecond region. At room temperature, it is not possible to investigate shallow levels because of the effects of thermal vibrations. The mechanism of the emission characteristics at room temperature would be affected by these levels that can be observed only at low temperatures. Therefore, the samples are cooled to 15 K for the TR-F measurements. The host material CaS emits blue light (420 nm) arising from sulfur defects, and the typical decay time is measured to be 6 ms. This blue emission becomes stronger when Tm3+ is doped. Furthermore, the doped Eu ions emit a broad red spectrum at 650 nm originating from the Eu2+-specific 4f65d1–4f7 transition. When the excitation is ceased, the red emission decays with a fast time constant of 0.6 μs. This value is a typical decay time for Eu2+. This red emission has multiple decay time constants, and a component with a decay time of 6 ms appears. This 6 ms decay time is the same as that of the blue emission from the sulfur defects, which have an important role on the red afterglow.

Highly Chiroptical Detection with Gold–Silver Bimetallic Nanoclusters Circularly Polarized Luminescence Based on G-quartet Nanofiber Self-assembly

Circularly polarized luminescence (CPL) as an intriguing luminescence phenomenon has attracted significant research interests for their chiroptical application, and CPL-active materials have been extensively explored in recent years. Herein, a highly chiroptical sensor was fabricated by the coassembly of G-quartet nanofiber and gold–silver bimetallic nanoclusters. In this, the adenosine 5′-monophosphate (AMP) templated gold–silver bimetallic nanoclusters (AuAg NCs) exhibited an enhanced fluorescence (λex = 356 nm, λem = 475 nm), a 9.42% quantum yield, and a 3.8 μs decay time compared with AMP stabilized Au NCs. In addition, a helical G-quartet-based nanofiber structure (g-fiber) was formed based on the self-assembly of guanosine 5′-monophosphate (GMP). The g-fiber was employed as chiral template for CPL emission by decorating AuAg NCs. Most interesting, the opposite CPL emission was regulated by K+ ion. The dissymmetry factor (glum) of this CPL-active material was up to 10–2. Furthermore, a CPL sensor based on the CPL emission has been developed for l-cysteine detection due to the quenching effect on AuAg NCs. The limit of detection (LOD) was as low as 95.7 nM, ranging from 0.1 to 8 μmol L–1, which was comparable with other analytical methods and materials. Our design presents a new horizon for nanoclusters and provides an entirely new approach for bioassay application.

β-Lactoglobulin amyloid fibril-templated gold nanoclusters for cellular multicolor fluorescence imaging and colorimetric blood glucose assay

β-Lactoglobulin amyloid fibril (BLGF)-capped gold nanoclusters (Au NCs) with red, green and blue emissions were fabricated via pH-dependent reduction strategy. The BLGF-Au NCs exhibited 3.2 times enhancement of fluorescence (λex = 500 nm, λem = 684 nm), a significant 42 nm red shift, a 11.57% quantum yield and a 1.4 μs decay time compared with native β-lactoglobulin (BLG)-stabilized Au NCs. Meanwhile, the multicolor Au NCs were employed for cell imaging via incubation with A549 cells for 14 h. According to the Michaelis-Menten equation, the kinetic parameters of the BLGF-Au NCs showed a lower Km value (66 μmol L-1) for 3,3,5,5-tetramethylbenzidine (TMB) and a higher vmax (3.74 × 10-8 M s-1) for H2O2, which are comparable with other artificial nanoenzymes and natural peroxidases. Based on the highly intrinsic peroxidase-like activity of the BLGF-Au NCs, a colorimetric method was developed for glucose determination with a detection limit of 1.5 μmol L-1 by determining the variation of the absorption at 652 nm, ranging from 5 to 100 μmol L-1. In addition, the glucose assay method also revealed a 101.02 to 104.16% recovery in a real human serum sample.

Fibrinogen-templated gold nanoclusters for fluorometric determination of cysteine and mercury(II).

Gold nanoclusters (Au NCs) using fibrinogen (FBG) protein as template are fabricated via one-pot reduction strategy, and applied for fluorometric detections of cysteine (Cys) and mercury(II). The modified FBG-Au NCs exhibit red fluorescence, with excitation/emission maxima at 360/620nm, a 7% quantum yield, and a 2.2μs decay time. The fluorescence of thenanoprobeis quenched by Cys and Hg(II). Cys can be determined by fluorometryin the 0.01 to 150μmolL-1 concentration range andwith a detection limit of 0.79μmolL-1. Due to the oxidation of Hg(II), it can be detected in the 0.01 to 10μmolL-1 concentration range. The properties of the FBG-Au NCs and the analytical performance are comparable with previously reported peptide/protein-templated Au NCs, supplying a promising candidate for Au NCs nanoprobes synthesis and applications. Graphical abstractSchematic representation of the preparation of gold nanoclusters (Au NCs) using fibrinogen (FBG) as the template. The modified Au NCs were applied to the fluorometric detection of cysteine (Cys) and mercury ion (Hg(II)).

Study on tower-like GaN nanostructure: Growth, optical and fast UV sensing properties

Abstract We report the fabrication and UV sensing properties of tower-like GaN nanostructures. Material properties of GaN have been characterized by X-ray diffractometer, transmission electron microscopy, and micro-Raman and photoluminescence (PL) analysis. Temperature-dependent PL measurement proves the strong band-edge emission and negligible yellow emission band of the tower-like GaN, which signifies the high crystal quality of GaN. The optimized UV photodetector in MSM structure based on the tower-like GaN shows a response current of 52 μA and a responsivity of 122.07 mA/W at 3 V bias. Furthermore, the fast UV response of the device exhibits less than 82 ms rise time and 164 ms decay time, respectively. The work indicates a promising quality of GaN nanostructure by simple and economic CVD route and its potential application in UV light sensing devices.

Chemical Vapor Deposition Method Grown All-Inorganic Perovskite Microcrystals for Self-Powered Photodetectors.

Self-powered photodetectors (SPPDs) have attracted lots of attention due to their various advantages including no external power sources, high-sensitivity, fast response speed, and so on. This study reports the fabrication and characterization results of CsPbBr3 microcrystals (MCs) grown by chemical vapor deposition (CVD) method, and the SPPDs have been fabricated on the basis of the CsPbBr3 MCs layer with the sandwich structure of GaN/CsPbBr3 MCs/ZnO. Such designed SPPD shows the detectivity ( D*) of 1014 Jones, on/off ratio of up to 105, peak responsivity ( R) of 89.5 mA/W, and enhanced stability at the incident wavelength of 540 nm. The photodetector enables the fast photoresponse speed of 100 μs rise time and 140 μs decay time. The performances of the SPPD are comparable to the best ones ever reported for CsPbBr3 based PDs but do not need external power supplies, which mainly benefit from the low trap density, long carrier diffusion of high quality CsPbBr3MCs film, and the built-in electric fields in the sandwich structure of GaN/CsPbBr3/ZnO layers.

Relaxation of intrinsic and extrinsic electronic excitations in nano- and micro-size alumina

Nanopowders consisting of mixed α-alumina and transition alumina phases were prepared by combustion synthesis and investigated using low temperature time-resolved cathodoluminescence and photoluminescence spectroscopy under VUV excitation. The onsets of the intrinsic absorption for different alumina phases were revealed in mixed phase nanopowders by analysing luminescence excitation spectra. All synthesized nanopowders possessed the intrinsic luminescence band with a maximum at 4.6 eV, which is assigned to the radiative decay of triplet self-trapped excitons with ∼750 μs decay time at 78 K. A red shift by 0.3 eV was revealed for the peak of the O2− – Cr3+ charge transfer band near 7 eV as a function of particle size. This shift is correlated with the decrease of α-alumina particle size from 180 to 80 nm. Its origin is discussed in the framework of the Kroning-Penney model.

Enhancement the sensitivity of CdS nano structure by adding of rare earth materials

Thin films of Cerium (Ce+3) doped Cadmium Sulfide (CdS) were successfully deposited on glass and silicon substrates by Chemical Spray Pyrolysis Method at different ratios with temperature 200 oC. The results shown a high quality nanoparticles and a strong orientation to the (002) plane of the wurtzite (hexagonal) phase. The fast rise and decay times of the photocurrent were confirmed that the best quality of the fabricate photodetector device. Light responsivity was at (460, 550 and 680 nm), and the device showed a good specific detectivity and quantum efficiency when illuminated by (460, 550 and 680 nm).CdS:Ce at 10% clarifies higher responsivity (0.144 A/W), quantum efficiency (38.58%), and specific detectiviy (2.7#x00D7;1011 Jones) at 460 nm illumination (3.108 mW/cm2), also the device for CdS:Ce at 10% reveals the fast with 800 ms rise time and 860 ms decay time and the sensitivity reach to 5523.

Fast chemical vapor-solid reaction for synthesizing organometal halide perovskite array thin films for photodetector applications

Preparing organometal halide perovskite array thin films from solution is a big challenge due to its soluble nature. In this work, we provide a fast chemical vapor-solid reaction (FCVR) for fabricating perovskite array thin films. An elemental Pb array thin film was firstly prepared by magnetron sputtering using a shadow mask, which then converted to CH3NH3PbI3 arrays by reacting with CH3NH3I. The related photoelectric characteristics were investigated by Uv–Vis spectroscopy, photoluminescence spectroscopy, and transient photovoltage analysis. The photodetector devices were assembled using these resultant perovskite thin films, which showed a fast response with 3 ms rise time and 3 ms decay time both under 405 nm and 660 nm light illumination. The response was faster than the commercial photodetector. This FCVR method not only provides a high quality perovskite array thin film, but also a novel synthesis strategy for new organic-inorganic hybrid perovskite photoelectric materials.

Luminescence processes in Ti-doped LiAlO2 single crystals for neutron scintillators

LiAlO2 can be considered as a good candidate for neutron scintillator host matrix due to the high Li content and high energy deposit of reaction of 6Li isotope with neutron. Low density (2.75 g/cm3) is of advantage to achieve low sensitivity of background gamma radiation in mixed radiation fields.Ti-doped LiAlO2 shows relatively high neutron light yield comparable to that of the Li-glass standard neutron scintillator. At room temperature the Ti4+ charge transfer (CT) luminescence at 375 nm with the 2.5 µs decay time is the leading emission process. Besides the CT luminescence host emission at shorter wavelengths (350 nm), defect-related emission at 440 nm and impurity Fe3+ luminescence at 740 nm are observed. Their emission spectra, excitation spectra and decay kinetics including temperature dependences were studied. Luminescence mechanism in the material and interplay between the luminescence processes are discussed together with possible role of nonstoichiometry and Mg codoping.

On the influence of calcium substitution to the optical properties of Cr3+ doped SrSc2O4

Cr3+ doped (Sr,Ca)Sc2O4 samples were synthesized and investigated in view of their potential application as luminescent converters for high power broad band near infrared (NIR) sources. The synthesis of the Cr3+ activated MSc2O4 (M=Ca, Sr) samples was performed by solid state reactions. Obtained powders show broad band near infrared emission between 700 and 1000nm under excitation in the blue spectral range. The emission is assigned to the intraconfigurational (3d3) 4T2→4A2 transition on Cr3+. As the calcium concentration in SrSc2O4 was increased, a blue shift of the emission spectra was observed. In order to gain insight in the luminescence properties, the crystal field strength, Racah parameters and phonon coupling parameters were examined. Additionally, the influence of temperature in the range between 4 and 500K on the photoluminescence of the CaSc2O4:Cr3+ and SrSc2O4:Cr3+ was investigated. At 4K a μs decay time typical of Cr3+ broad band d-d emission was observed. Between 70 and 350K the decay time and emission intensity decrease due to thermal quenching. The large Stokes shift of the Cr3+ emission (~3000cm-1) combined with the low energy position of the 4T2 excited state causes non-radiative relaxation to the ground state, already below room temperature. The low thermal quenching temperature of broad band NIR emission is a general problem and the present results provide insight in factors determining thermal quenching.

Development of Fast-Response GCaMP6 Calcium Sensors for Monitoring Neuronal Action Potential

Green Fluorescent-Calmodulin Proteins (GCaMPs) have been the reporters of choice for visualizing neuronal network activity in vivo. With the GCaMP6 generation sufficient brightness was achieved for single action potential (AP) detection1. However, the Ca2+-response kinetics of GCaMP6 probes remained limiting to separating individual APs. The aim was to accelerate the Ca2+ response kinetics of GCaMP6 probes by point mutations in the Ca2+.CaM.RS20 complex2. A series of probes retaining high fluorescence dynamic ranges was generated with in vitro dissociation constants (Kd) for Ca2+ in the μM range (0.1-3.3 μM) and Hill coefficients of 1.7 to 4.2. Two highlighted probes termed GCaMP6fast and GCaMP6bright had in vitro half times (t1/2) at 37°C for Ca2+ rise of 1.3 ms and 3.3 ± 0.2 ms and decay t1/2-s of 2.8 ± 0.1 and 3.5 ± 0.1 ms, respectively, compared to the 10 ± 1 ms rise and 63 ± 6 ms decay times for GCaMP6f. Fluorescence changes on Ca2+ association were highly cooperative and characterized by a rate limiting conformational change. In vivo Ca2+ responses associated with AP firing patterns were tested in cultured hippocampal slices by two-photon imaging at 28°C. The kinetic performance of GCaMP6fast and GCaMP6bright was compared with that of GCaMP6f. Ca2+ decay kinetics were determined by monitoring fluorescence changes evoked by 5 APs fired at 100 Hz. t1/2 values for GCaMP6fast and GCaMP6bright were 58 ms and 126 ms, respectively. With an up to 7-fold faster in vivo decay kinetics than GCaMP6f, GCaMP6fast and GCaMP6bright are promising tools for monitoring brain activity.1Podor et al., Neurophotonics, Epub 2015 Apr 30.2Helassa et al., Scientific Reports, accepted.This work was funded by Wellcome Trust (094385/Z/10/Z to KT), BBSRC (BB/M02556X/1 to KT), CIHR (MOP-123514 to AF) and NSERC (RGPIN-170421 to AF).

Blue light emission from cyclometallated iridium(III) cyano complexes: Syntheses, crystal structures, and photophysical properties

We describe the synthesis and crystal structures of four iridium compounds containing the 2-(4,6-difluorophenyl)pyridyl ligand. Cleavage of dichloro-bridged iridium(III) dimers with phosphorus ligands leads to (46dfppy)2Ir(L)(Cl) where L=PPh3 or P(OPh)3. Treatment of the chloro compounds with cyanide forms the cyano complexes (46dfppy)2Ir(L)(CN). All complexes exhibit a trans effect in their molecular structures due to the phosphorus ligands, with the phosphite having a greater effect than the phosphine. With L=PPh3, blue photoluminescence with CIE coordinates (x=0.16, y=0.24), quantum yield of 0.66±0.15 and 4.5±0.5μs decay time is measured. For L=P(OPh)3, blue photoluminescence with CIE coordinates (x=0.16, y=0.21), quantum yield of 0.65±0.15 and 2.9±0.3μs decay time is measured.

Tu1789 Brain Activation With Rectal Distention Distinguishes Irritable Bowel Syndrome From Healthy Controls and Is Independent of Psychiatric Comorbidity

gastric motility in females is due to a higher GABAergic input to gastricprojecting DMV neurons. In an in vivo anesthetized preparation, microinjections of bicuculline methiodide (BIC, 0.5-50pmoles in 60 nl) into the DMV of Sprague-Dawley rats increased gastric tone in a dose-dependent manner. In males, microinjection of 0.5 pmoles of BIC elicited a 32.0±12 mg increase in gastric tone (N=2), whereas microinjection of 50 pmoles of BIC elicited an increase of 186.0±23 mg (N=2). In females, DMV microinjections of 0.5 pmoles of BIC elicited a significantly greater increase in gastric tone compared to males (200.5±37; N=3; p<0.05). Whole-cell patch-clamp recordings were made from identified gastric-projecting DMV neurons. Female rats displayed an increased afterhyperpolarization amplitude and decay time (19.7±2mV;180.7±39ms; N=12) compared tomales (15.9±1mV afterhyperpolarization amplitude; 103.9±24 ms decay time; N=9; p<0.05), and a lower action potential frequency response to injection of 80 pA of current (13.6±1 events/s in males; 9.2±1 events/ s in females). These differences are indicative of a decreased excitability of neurons in females. Females also had a higher frequency of miniature inhibitory postsynaptic currents compared to males (1.2±0.3, N=7, and 0.7±0.04, N=4, events/s in females and males, respectively). These data indicate that gastric-projecting DMV neurons in females are less excitable and receive a higher tonic GABAergic input compared to males. These data suggest that reduced gastric motility in females may be due to an increased inhibitory input to gastric-projecting neurons.

Bridgman growth of large SrI2:Eu2+ single crystals: A high-performance scintillator for radiation detection applications

Single-crystal strontium iodide (SrI2) doped with relatively high levels (e.g., 3–6%) of Eu2+ exhibits characteristics that make this material superior, in a number of respects, to other scintillators that are currently used for radiation detection. Specifically, SrI2:Eu2+ has a light yield that is significantly higher than LaBr3:Ce3+—a currently employed commercial high-performance scintillator. Additionally, SrI2:Eu2+ is characterized by an energy resolution as high as 2.6% at the 137Cs gamma-ray energy of 662keV, and there is no radioactive component in SrI2:Eu2+—unlike LaBr3:Ce3+ that contains 138La. The Ce3+-doped LaBr3 decay time is, however, faster (30ns) than the 1.2μs decay time of SrI2:Eu2+. Due to the relatively low melting point of strontium iodide (∼515°C), crystal growth can be carried out in quartz crucibles by the vertical Bridgman technique. Materials-processing and crystal-growth techniques that are specific to the Bridgman growth of europium-doped strontium iodide scintillators are described here. These techniques include the use of a porous quartz frit to physically filter the molten salt from a quartz antechamber into the Bridgman growth crucible and the use of a “bent” or “bulb” grain selector design to suppress multiple grain growth. Single crystals of SrI2:Eu2+ scintillators with good optical quality and scintillation characteristics have been grown in sizes up to 5.0cm in diameter by applying these techniques. Other aspects of the SrI2:Eu2+ crystal-growth methods and of the still unresolved crystal-growth issues are described here.