Luminescence Mode Research Articles

Photocatalysis of fenoxycarb over silver-modified zeolites

Two samples of silver doped into zeolite Y were prepared and characterized. ICP and SEM-EDS analysis indicate that the AgY1 sample contains twice the amount of silver compared to the AgY2 sample. Solid state luminescence spectroscopy shows variations in the emission modes of the site-selective luminescence where various luminophores might be excited upon selecting the proper excitation energy. The selected material effectively decomposed the pesticide fenoxycarb in aqueous solution. The photodecomposition of fenoxycarb reached 80 % upon irradiation for 60 min in the presence of the AgY1 catalyst. 2-(4-Phenoxy-phenoxy)ethyl] carbamic acid (1) and 1-amine-2-(phenoxy-4-ol) ethane (2) were identified as products for both uncatalyzed solution and the catalyzed fenoxycarb with AgY2 catalyst. Whereas, compound (2) was the only product identified in the catalyzed reaction with AgY1.

Highly luminescent dual mode rare-earth nanorod assisted multi-stage excitable security ink for anti-counterfeiting applications

Demonstration of new strategy for designing multi-stage excitable highly-luminescent Y2O3:Yb3+/Er3+ nanorod assisted security ink for protection against counterfeiting.

Acetyl protected thiol methacrylic polymers as effective ligands to keep quantum dots in luminescent standby mode

Herein, we report evidence for the promising potential of 2-(acetylthio)ethylmethacrytale (AcSEMA), a new monomer, which copolymerizes with methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) leading to well-defined multidentate protected thiol polymer ligands for CdSe QDs capping by simple ligand exchange. Among the different strategies that can be employed for coating QDs, it is found that thioacetylated polymers, in the presence of hydrophobic QDs, are able to replace trioctylphosphine oxide (TOPO) ligands, leading to hybrid CdSe@PMMA nanoparticles without covalent binding of the polymer to the QD surface. These polymer protected QDs exhibit high stability for long periods of time, in a low luminescence standby mode. Moreover, the fluorescence QD activation of these hybrids is easily achieved at any time from thioacetate hydrolysis to free thiol under mild conditions. This subsequent step, which results in the covalent attachment of PMMA thiol groups to the metallic QD surface, produces compact QDs which exhibit amazingly improved photophysical properties, yielding highly photoluminescent new hybrid materials. For comparison, the same procedure was applied to obtain brush-like QDs coated with PMMA obtained by ATRP with a final thioacetate group. It was then established that the multidentate thiolated polymers provide additional protection against external quenchers, such as 4-amino-TEMPO, to a greater extent than the brush-like PMMA coating and the pristine TOPO capping ligand.

Nonclassical dual control of circularly polarized luminescence modes of binaphthyl-pyrene organic fluorophores in fluidic and glassy media.

The fluorescent modes and signs of the circularly polarized luminescence of an axially chiral binaphthyl-pyrene organic fluorophore were successfully controlled by changing from a fluidic chloroform solution to a glassy poly(methyl methacrylate) solid film.

Lumicyano™: A new fluorescent cyanoacrylate for a one-step luminescent latent fingermark development

Latent fingermarks developed by cyanoacrylate fuming often lack contrast; therefore further enhancement is required, such as dye staining. This second step is part of the conventional detection sequences performed by forensics practitioners. Dye-staining or powder dusting aims at improving contrast and at increasing the legibility of details, yet their use may at times be limited. Indeed powder dusting may not be effective due to unexpected adherence to the background, and poor affinity to the cyanoacrylate. In the same way staining processes can dye a whole semi-porous surface or may wash the marks.To avoid that second step, a new luminescent cyanoacrylate (Lumicyano™) which allows one-step development without changing the fuming chamber settings (80% humidity rate, 120°C fuming temperature) was developed and assessed. This study aimed at comparing Lumicyano™ to a conventional two-step process. A detailed sensitivity study was conducted on glass slides, as well as the processing of various non-porous and semi-porous substrates, usually considered as problematic for a dye staining step.The results indicate that Lumicyano™ detects fingermarks with equal or better sensitivity and ridge details than currently used cyanoacrylate. Secondly in luminescent mode, good ridges clarity and excellent contrast are observed, even if Lumicyano™ is sometimes less bright than the two-step process. Furthermore, conventional enhancement can still be carried out if needed. As a conclusion, Lumicyano™ makes it possible to avoid an enhancement step which can be detrimental to further examinations, particularly on rough or semi-porous surfaces.

Few-bubble luminescence in the acoustic field of a spherical resonator in aqueous solutions of sodium and terbium compounds

Stabilization and the luminescence mode during slight motion around the equilibrium position of a few (two to eight) bubbles in 2–6 mol/L aqueous solutions of NaCl, NaOH, TbCl saturated with argon were achieved in a device for monitoring single-bubble sonoluminescence in a spherical resonator. Examples are presented of this variety of multibubble sonoluminescence illustrating various spatial-spectral distributions of cavitation bubbles, which contain either emitters comprising only the solvent continuum or also metal emitters (Na*, Tb3+*). Stabilization of bubbles in the form of closely (0.5–1 mm) located pairs of bubbles is of particular interest, in one of which only the solvent luminesces, and in the other, a metal.

Lanthanide Complex-Based Luminescent Probes for Highly Sensitive Time-Gated Luminescence Detection of Hypochlorous Acid

Two novel lanthanide complex-based luminescent probes, ANMTTA-Eu(3+) and ANMTTA-Tb(3+) {ANMTTA, [4'-(4-amino-3-nitrophenoxy)methylene-2,2':6',2"-terpyridine-6,6"-diyl] bis(methylenenitrilo) tetrakis(acetic acid)}, have been designed and synthesized for the highly sensitive and selective time-gated luminescence detection of hypochlorous acid (HOCl) in aqueous media. The probes are almost nonluminescent due to the photoinduced electron transfer (PET) process from the 4-amino-3-nitrophenyl moiety to the terpyridine-Ln(3+) moiety, which quenches the lanthanide luminescence effectively. Upon reaction with HOCl, the 4-amino-3-nitrophenyl moiety is rapidly cleaved from the probe complexes, which affords strongly luminescent lanthanide complexes HTTA-Eu(3+) and HTTA-Tb(3+) {HTTA, (4'-hydroxymethyl-2,2':6',2"-terpyridine-6,6"-diyl) bis(methylenenitrilo) tetrakis(acetic acid)}, accompanied by the remarkable luminescence enhancements. The dose-dependent luminescence enhancements show good linearity with detection limits of 1.3 nM and 0.64 nM for HOCl with ANMTTA-Eu(3+) and ANMTTA-Tb(3+), respectively. In addition, the luminescence responses of ANMTTA-Eu(3+) and ANMTTA-Tb(3+) to HOCl are pH-independent with excellent selectivity to distinguish HOCl from other reactive oxygen/nitrogen species (ROS/RNS). The ANMTTA-Ln(3+)-loaded HeLa and RAW 264.7 macrophage cells were prepared, and then the exogenous HOCl in HeLa cells and endogenous HOCl in macrophage cells were successfully imaged with time-gated luminescence mode. The results demonstrated the practical applicability of the probes for the cell imaging application.

Investigation of energy transfer in terbium doped Y 2SiO5 phosphor particles

The kinetics of luminescence of sol–gel synthesized terbium doped Y 2SiO5 (YSO) phosphor particles is investigated in detail with reference to Tb concentration in the 0.001%–10% range. By increasing the dopant concentration, the luminescence profile changes from a blue to a green peaked emission spectrum because of the energy transfer among centers. The inter-center energy transfer mechanism is well accounted for by the Inokuti–Hirayama (IH) kinetic model which is based on a statistical average of inter-center distance dependent decay modes of the donor luminescence. The distribution of the decay modes is implemented from the Förster–Dexter resonance theory of energy transfer by assuming a rate constant for the energy transfer by multipolar interactions between donors and acceptors. However, the experimental results recorded in the low concentration limit show the presence of green emission contributions in the luminescence spectrum which cannot be related to the Tb concentration; for this reason an additional internal energy transfer mechanism, occurring among levels of the same center, is proposed to account for the recorded emission properties. Thus, a new and more exhaustive model which includes both the internal and external energy transfer processes is considered; the proposed model allows a better explanation of the spectroscopic features of Tb related centers in YSO crystals and discloses the critical concentration and the quantum yields of the different energy transfer mechanisms.

Successive Nanosecond Discharges in Water

Successive discharges of alternating polarities in distilled water have been studied. Cathode-initiated discharges develop in two possible configurations: slow and weakly luminescent bushlike mode or fast and luminous treelike mode with well-pronounced branching. Under our experimental conditions, the two modes originate with approximately equal probability. Positive discharge demonstrates only one discharge morphology with two hemispherical weakly luminescent structures. Successive negative pulse results in the formation of one of the negative modes, bushlike or treelike.

Luminescence imaging using radionuclides: a potential application in molecular imaging

Nuclear and optical imaging are complementary in many aspects and there would be many advantages when optical imaging probes are prepared using radionuclides rather than classic fluorophores, and when nuclear and optical dual images are obtained using single imaging probe. The luminescence intensities of various radionuclides having different decay modes have been assayed using luminescence imaging and in vitro luminometer. Radioiodinated Herceptin was injected into a tumor-bearing mouse, and luminescence and microPET images were obtained. The plant dipped in [(32)P]phosphate solution was scanned in luminescence mode. Radio-TLC plate was also imaged in the same imaging mode. Radionuclides emitting high energy β(+)/β(-) particles showed higher luminescence signals. NIH3T6.7 tumors were detected in both optical and nuclear imaging. The uptake of [(32)P]phosphate in plant was easily followed by luminescence imaging. Radio-TLC plate was visualized and radiochemical purity was quantified using luminescence imaging. Many radionuclides with high energetic β(+) or β(-) particles during decay were found to be imaged in luminescence mode due mainly to Cerenkov radiation. 'Cerenkov imaging' provides a new optical imaging platform and an invaluable bridge between optical and nuclear imaging. New optical imaging probes could be easily prepared using well-established radioiodination methods. Cerenkov imaging will have more applications in the research field of plant science and autoradiography.

Mercurian sphalerite from Akoluk deposit (Ordu, NE Turkey): Hg as a cathodoluminescence activator

AbstractA recent investigation of sphalerite from Akoluk deposit, Ordu, NE Turkey, revealed the possible presence of a new activator element in the sphalerite structure. The sample was studied under a reflected light microscope coupled with a cold-stage cathodoluminescence (CL) system which revealed a unique banding in the sphalerite. The same sample was subsequently examined using the backscattered electron and luminescence modes in an electron microscope, the results of which were later confirmed in terms of chemical composition by electron probe microanalyses (EPMA). Detailed evaluation of the EPMA data indicated the presence of a new CL activator element in the sphalerite structure. The data also indicate that Hg2+ in the sphalerite crystal structure substitutes for Zn in a simple manner and for Cd and Cu in a coupled manner. Spectral analysis indicated a bright yellow and orange-red blend (more like brown) CL colour with λmax centred at 580 nm, probably due to Cd and Mn ions, and relatively broad emission bands ranging from 525 to 690 nm with λmax centred at 580 and 700, due probably to Cu, Cd and Hg. This study reports that Hg in the sphalerite crystal lattice behaves as an activator and/or co-activator element resulting in emissions of CL colours that range from yellow with purple shades to shades of brown, based on their varying contents.

Room-temperature broadband InAsSb flip-chip photodiodes with λcut off = 4.5 μm

Equilibrium and nonequilibrium IR images of p-InAsSbP/n-InAsSb/n +-InAs photodiodes including the images obtained in the electroluminescence and negative luminescence modes have been analyzed. The contact reflectivity has been evaluated. The influence of the substrate’s doping level and mesa depth on the quantum efficiency and sensitivity of a backside illuminated photodiode sensitive in the 2.7–4.5 μm range is discussed.

Time‐Gated Luminescence Microscopy

Autofluorescent algal samples were spiked with europium beads for analysis on a novel all-solid-state, time-gated luminescence (TGL) microscope. Pulsed UV excitation (365 nm) was provided by a high-power UV-LED source fitted to an Olympus BX51 microscope. An "Impactron" electron multiplying charge-coupled-device (CCD) camera acquired images in delayed luminescence mode. Second, we evaluated sensitivity of the instrument by acquiring images of immunofluorescently labeled Giardia cysts with a single-exposure period of 3 ms. The camera was triggered 3 micros after the LED had extinguished to yield a 14-fold increase in signal-to-noise ratio within a single 33 ms capture cycle. This novel instrument could be switched instantly from prompt epifluorescence mode to TGL mode for suppression of short-lived fluorescence.

Polarization of edge emission from III-nitride light emitting diodes of emission wavelength from 395to455nm

Polarization-resolved edge-emitting electroluminescence of InGaN∕GaN multiple quantum well (MQW) light emitting diodes (LEDs) from 395to455nm was measured. Polarization ratio decreased from 3.2 of near-ultraviolet LEDs (395nm) to 1.9 of blue LEDs (455nm). Based on TE mode dominant emissions in InGaN∕GaN MQWs, compressive strain in well region favors TE mode, indium induced quantum-dot-like behavior leads to an increased TM component. As wavelength increased, indium enhanced quantum-dot-like behavior became obvious and E‖C electroluminescence signal increased thus lower polarization ratio. Electroluminescence spectrum shifts confirmed that quantum dotlike behaviors rather than strain might be dominant in modifying luminescence mode of InGaN∕GaN MQWs from near ultraviolet to blue.

High intensity solid‐state UV source for time‐gated luminescence microscopy

The unique discriminative ability of immunofluorescent probes can be severely compromised when probe emission competes against naturally occurring, intrinsically fluorescent substances (autofluorophores). Luminescence microscopes that operate in the time-domain can selectively resolve probes with long fluorescence lifetimes (tau > 100 micros) against short-lived fluorescence to deliver greatly improved signal-to-noise ratio (SNR). A novel time-gated luminescence microscope design is reported that employs an ultraviolet (UV) light emitting diode (LED) to excite fluorescence from a europium chelate immunoconjugate with a long fluorescence lifetime. A commercial Zeiss epifluorescence microscope was adapted for TGL operation by fitting with a time-gated image-intensified CCD camera and a high-power (100 mW) UV LED. Capture of the luminescence was delayed for a precise interval following excitation so that autofluorescence was suppressed. Giardia cysts were labeled in situ with antibody conjugated to a europium chelate (BHHST) with a fluorescence lifetime >500 micros. BHHST-labeled Giardia cysts emit at 617 nm when excited in the UV and were difficult to locate within the matrix of fluorescent algae using conventional fluorescence microscopy, and the SNR of probe to autofluorescent background was 0.51:1. However in time-gated luminescence mode with a gate-delay of 5 mus, the SNR was improved to 12.8:1, a 25-fold improvement. In comparison to xenon flashlamps, UV LEDs are inexpensive, easily powered, and extinguish quickly. Furthermore, the spiked emission of the LED enabled removal of spectral filters from the microscope to significantly improve efficiency of fluorescence excitation and capture.

Visible range whispering-gallery mode in microdisk array based on size-controlled Si nanocrystals

Microdisks based on in-plane embedded size-controlled Si nanocrystal∕SiO2 superlattices (Si-NCs∕SiO2 SLs) were mass-fabricated arranged in well-ordered arrays. The microdisks were fabricated with size irregularity of below 0.2% over large-scale areas. Overlapping whispering-gallery modes (WGM) of the visible nanocrystalline-silicon luminescence were observed. A comparison between analytical calculation and experimental results is reported. We found that only one axial and one radial WGM exist due to their thin disk thickness and birefringence characteristic of Si-NCs∕SiO2 SLs, and that the mode spacing is 15nm and 6nm for microdisks with a diameter of 8.8μm and 23.7μm, respectively. The advantages of such size-controlled Si-NCs∕SiO2 embedded in microdisk arrays for Si-based photonic application will be discussed.

Raman, hyper-Raman, hyper-Rayleigh, two-photon luminescence and morphology-dependent resonance modes in a single optical tweezers system

We present a setup of optical tweezers combined with linear and nonlinear microspectroscopies that enhances the capabilities of capture and analysis of both techniques. We can use either a continuous-wave (cw) Ti:sapphire laser for Raman measurements or a pulsed femtosecond Ti:sapphire laser that permitted the observation of nonlinear results such as hyper-Raman, hyper-Rayleigh, and two-photon luminescence. Only the high peak intensity of the femtosecond laser allows the observation of all these nonlinear spectroscopies. The sensitivity of our system also permitted the observation of morphology-dependent resonance (MDR) modes of a single stained trapped microsphere of 6 microm. The possibility of performing spectroscopy in a living microorganism optically trapped in any desired neighborhood would mean that one can dynamically observe the chemical reactions and/or mechanical properties changing in real time.

Evolution of stress in GaN heteroepitaxy on AlN∕Si(111): From hydrostatic compressive to biaxial tensile

The initial steps of GaN growth on an AlN buffer layer on Si(111) substrates by metalorganic vapor phase epitaxy were investigated using field emission scanning electron microscopy, micro-photoluminescence, as well as by conventional and grazing incidence x-ray diffraction. A series of GaN layers was grown for various times ranging from 7.5 s to several minutes, doubling the growth time for each step. The AlN buffer layer is noncontinuous and consists of (0001)-oriented AlN islands with a mean diameter of about 50 nm. On top of these nucleation centers three-dimensional growth of GaN was observed. With increasing growth times up to 30 s these islands further expanded and their distribution became more homogeneous. At 60 s coalescence started with homogeneously distributed islands, and after 120 s the layer was fully coalesced. The layers grown for 7.5 and 15 s are under a high compressive hydrostatic pressure, which might be enhanced by the lattice mismatch between AlN and GaN. For longer growth times a biaxial tensile stress is observed. The occurrence of the biaxial tensile stress correlates with the onset of island coalescence. The x-ray results are in agreement with low-temperature optical measurements showing a consistent energy shift of the near band gap luminescence and longitudinal optical Raman modes with respect to relaxed GaN.

Current crowding in InAsSb light-emitting diodes

High-resolution two-dimensional infrared (IR) imaging of dynamic electronic processes in the surface-emitting p-InAsSb/n-InAsSbP light-emitting diodes (LEDs) (λ=4.3 μm, T>300 K) showed that forward current crowding drastically decreases efficiency of LEDs with point contacts. Current flows and IR emittance “forget” the emitting area size and geometry, whereas extended areas far off the point contacts become even “darker” with the current increase. Contrary to this, the reverse bias causes remarkable current spreading and uniform “negative emittance” distribution. Therefore the negative luminescence mode is more favorable for IR LEDs operating at higher temperatures.

The widespread occurrence and tissue distribution of the imidazolopyrazine luciferins.

Bioluminescence has been reported to occur in 17 phyla and at least 700 genera. However, the luciferin chemistry of the majority of luminous organisms has yet to be determined. The most common chemistry which is known to occur in deep sea bioluminescence is imidazolopyrazine bioluminescence. The main aim of this study was to examine the phyletic and tissue distribution of imidazolopyrazine luciferins. This will facilitate analysis of imidazolopyrazine bioluminescence at the cellular and molecular levels and, in particular, how and when its chemistry is controlled and expressed in vivo. Assays for both known imidazolopyrazines were established and a range of fresh organisms and tissue were analysed, i.e. fish, cephalopods, copepods, ostracods, amphipods and euphausiids. The main findings were that the number of genera in which coelenterazine has been detected has been increased from 52 to about 90. Also, for the first time, the other known imidazolopyrazine luciferin, Vargula-type luciferin, was quantified in the ostracod Cypridina dentata, but was not detected in any of its potential predators. Neither imidazolopyrazine luciferin was found in several luminous stomiiform fish assayed. Coelenterazine was measured in the livers and photophores of a number of cephalopods and it is apparent that coelenterazine is responsible for both modes of luminescence.