Luminescence Response Research Articles

Colorimetric energy sensitive scintillator detectors based on luminescent multilayer designs

In this work we present a new concept for energy sensitive radiation-beam scintillator detectors based on a luminescent multilayer design, where each layer within the stack consists of a rare-earth-doped highly transparent oxide. For a given type of particle beam (i.e., protons, α particles, etc.), its penetration depth, and therefore its energy loss at a particular buried layer, depends on its initial kinetic energy. Relying on this principle and since the intensity of the luminescent response of each layer and substrate should be proportional to the energy deposited by the radiation beam, we prove that a characteristic energy dependent color emission is obtained depending on both the phosphors integrated in the luminescent stack and on the primary energy and type of particle beam. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters to achieve a broad gamut in colorimetric response. The developed scintillators are designed to operate in a transmission geometry (light detection from the opposite side of the incident radiation) which is well suited for high energy particle detection in fields such as oncotherapy, space radiation, or of fusion studies. The principles of the method are illustrated with a case example typical of ion beam accelerators devoted to materials analysis. It is obtained that the kinetic energy of protons/alpha particle beams can be distinguished and evaluated with a sensitivity of 0.06/0.25 chromaticity units per MeV in the 0.7–2.0 MeV range.

Development of oxyfluoroborate glass ceramics doped with Er3+ and Yb3+

The preparation of oxyfluoroborate glasses and glass–ceramics doped with Yb3+ and Er3+ with improved luminescent properties is reported. Glasses with compositions (100 − x − y) (MO·2B2O3) + xPbF2 + y(YbF3:ErF3) (% in mol), where M is Sr, Ba, Ca, x = 10–40% and y = 0, 1 or 5% were prepared by the melt/quenching technique. Glass crystallization was studied using thermal analysis and X-ray diffraction techniques. Optical absorption and infrared up-conversion were studied on both glasses and glass–ceramics. The incorporation of a fluoride compound into the borate glass resulted to depend on the ionic radius of the glass modifier: as it increases, glasses become more stable against crystallization. On the other hand, alkali–fluoride compounds such as BaF2 and SrF2 can be crystallized from these systems by selecting an appropriate proportion between their components. Furthermore, the up-conversion response can be tuned by changing the glass modifiers (Sr, Ba and Ca) of the borate matrix, which also influence the type of fluoride crystallized compound. The strontium glass–ceramics have the highest luminescence response due to the crystallization of SrF2 compound in the system SrO–B2O3–PbF2. Meanwhile, the lowest luminescence signal was obtained for samples in the system BaO–B2O3–PbF2 where the Pb1.33Ba2.66B11FO20 phase crystallizes. With this strategy, new materials with improved luminescence properties that can be used as up converters, were obtained.

Fabrication and Investigation of 26NCA Films Exhibiting Tunable Blue Fluorescence Based on LVPVDM

The development of metallic fluorescent materials, π-conjugated molecular systems with high-efficiency generation of blue light, and new ways to fabricate metallic/organic luminescent materials plays an important role in the fields of large-scale flat panel displays and soft optical devices. Herein, different fluorescent films have been fabricated by low vacuum physical vapor deposition method (LVPVDM), including single/two-component films. Compared with raw materials, all films show novel fluorescent behaviors, which means potential application in the fields of multicolor luminescence and thickness-optical response sensors. Meanwhile, the speculation is demonstrated in many ways that the maximum emission (λemmax) at 406 nm and 426 nm of pristine 2,6-naphthalenedicarboxylic acid (26NCA) is caused by the crystal structure, while the shoulder peak at 445 nm is caused by the self-structure of 26NCA molecule. Significantly, this speculation may afford new insight into the relationship between not only crystal structure and luminescence, but also molecular self-structure and luminescence, which means a new strategy to tune the fluorescent behaviors based on molecular self-structure by LVPVDM. Therefore, this work provides a facile way to fabricate single/multicomponent metallic/organic film materials with tunable blue luminescence properties, which have potential application in the fields of next generation of photofunctional materials.

Luminescent switch sensors for the detection of biomolecules based on metal-organic frameworks.

Metal-organic frameworks (MOFs) as sensing materials have experienced explosive growth in recent years due to their intrinsic merits, such as structural diversity, high porosity, large surface area, extraordinary adsorption affinities, etc. Biomolecules such as DNA, protein, and vitamins play vital roles in metabolism. Moreover, the sensitive detection of biomolecules is of importance in the disease prevention and treatment. This review intends to provide an update on the recent progress in the detection of various biomolecules via MOF-based luminescent sensors. MOFs are successful in the detection of DNA, RNA, protein, and other biomolecules. MOF-based luminescent sensors function by utilizing different mechanisms, including luminescent responses of enhancement and quenching, which are defined as "turn-on" and "turn-off" responses, respectively. Then, a short comparison of the "turn-on" and "turn-off" types of sensors is also made.

Tribo-induced photoluminescent behavior of graphene and YSZ:Er/graphene composite films.

In the present work, a novel method was developed to study the evolving surface state of graphene film as it is subject to friction, characterized by photoluminescence properties. We prepared the graphene film (GF) and YSZ:Er (Er3+-Y3+ co-doped ZrO2)/graphene composite films (ZGCF). The Raman spectra and photoluminescence properties of the GF and ZGCF were characterized before and after the sliding friction. A remarkable phenomenon was observed that after friction the GF generated a more pronounced luminescence response than it had prior, apparently due to graphene quantum dots which were found in the wear debris of the GF. Furthermore, the introduction of graphene into YSZ:Er nanoparticles (NPs) resulted in an unmistakable red-shift on the main luminescence bands of ZGCF after the applied friction. This is explained by the formation of considerable graphene scrolls in the wear debris of ZGCF due to the interaction of the graphene and the YSZ:Er NPs. It can be concluded that changes to the configuration of graphene greatly influence the tribo-induced photoluminescence response. Our findings justify further investigation into the composition and morphology of worn surfaces in order to better understand how photoluminescence relates to frictional effects. In addition, this work proposes the in situ fabrication of graphene quantum dots and nanoscale scrolls as a new potential application of the tribo-induced photoluminescence study.

Synthesis, photophysical properties and cation-binding studies of bipyridine-functionalized gold(i) complexes

A new family of Au(i) complexes equipped with bipyridine function demonstrate bright luminescence response to M(ii) cations in solution.

Phosphorescent iridium(iii) complexes capable of imaging and distinguishing between exogenous and endogenous analytes in living cells.

Many luminescent probes have been developed for intracellular imaging and sensing. During cellular luminescence sensing, it is difficult to distinguish species generated inside cells from those internalized from extracellular environments since they are chemically the same and lead to the same luminescence response of the probes. Considering that endogenous species usually give more information about the physiological and pathological parameters of the cells while internalized species often reflect the extracellular environmental conditions, we herein reported a series of cyclometalated iridium(iii) complexes as phosphorescent probes that are partially retained in the cell membrane during their cellular uptake. The utilization of the probes for sensing and distinguishing between exogenous and endogenous analytes has been demonstrated using hypoxia and hypochlorite as two examples of target analytes. The endogenous analytes lead to the luminescence response of the intracellular probes while the exogenous analytes are reported by the probes retained in the cell membrane during their internalization.

Chiral Discrimination through 1 H NMR and Luminescence Spectroscopy: Dynamic Processes and Solid Strip for Chiral Recognition.

The appropriate choice of the host molecules with well-defined optical activity (S-H/R-H) helps in the differentiation between two secondary ammonium ion-derivative guest molecules with different optical activities (R-G/S-G) based on the fluorescence resonance energy transfer (FRET)-based luminescence responses. Crown ether-based host molecules with opposite chiral configurations (R-H, S-H) have been derived from 1,1'-bi-2-naphthol (BINOL) derivatives that have axially chiral biaryl centers. These chiral crown ethers form host-guest complexes (i.e., [2]pseudorotaxanes) with chiral secondary ammonium ion derivatives (R-G, S-G). NMR spectroscopic studies show that the complexes are in a dynamic equilibrium in solution. Results of the 1 H NMR and fluorescence spectroscopic studies indicate a head-on orientation of the host and guest in the [2]pseudorotaxanes. The difference in the efficiency in the FRET-based responses between anthracene and the BINOL derivatives allow efficient chiral discrimination of the guests. Isothermal titration calorimetry and NMR investigations reveal that inclusion complexes between hosts and guests of the same chirality (R-H⋅R-G, S-H⋅S-G) are more stable relative to those of opposite chirality (R-H⋅S-G, S-H⋅R-G). However, FRET-based energy-transfer efficiency is higher for R-H⋅S-G and S-H⋅R-G complexes. NMR spectroscopic studies show that the relative orientation of the guest in the host cavity is significantly different when the host binds a guest of the same or opposite chirality; furthermore, the latter is more favorable for FRET, thus enabling discrimination between enantiomers. Interestingly, chiral discrimination of guest ions could also be achieved by using silica surfaces modified with chiral host molecules.

Novel water soluble cationic Au(I) complexes with cyclic PNNP ligand as building blocks for heterometallic supramolecular assemblies with anionic hexarhenium cluster units

The present work introduces synthesis, structure and spectroscopic properties of novel water soluble dicationic binuclear Au(I) complex [Au2L2]2+ with bridge P,P-coordination, where L is cyclic PNNP ligand 1,5-bis(p-tolyl)−3,7-bis(pyridine-2-yl)−1,5-diaza-3,7-diphosphacyclooctane. Its ion-pairing with anionic hexarhenium cluster complexes ([{Re6S8}(OH)6]4– and [{Re6S8}(CN)6]4–) is represented herein as a reason for bottom-up design of supramolecular heterometallic assemblies with the enhanced cluster-centered luminescence and heterometallic colloids with high luminescence response to acidification in the range of pH 6.0-5.5.

Facile synthesis of near-infrared-excited NaYF4:Yb3+, Tm3+ nanoparticles for label-free detection of dopamine in biological fluids

Rare-earth-doped upconversion nanoparticles (UCNPs) behaved advantages such as non-autofluorescence, environment-friendly synthetic route, low cost and simple detection procedures. In addition, the UCNPs show unique upconvering optical property of converting low-energy infrared photons to high‐energy visible ones. Here in our work, water and ethylene glycol at the ratio of 1/1 (v/v) were chosen as solvent. Polyethyleneimine (PEI) was chosen as surface additives to synthesize the NaYF4:Yb3+, Tm3+ UCNPs by one-pot route at 200°C. The as-prepared UCNPs exhibited a strong emission at 473nm under the continuous excitation at 980nm. Dopamine (DA), one of the important catecholamine neurotransmitters, shows a crucial role to regulate the memory and attention in brain, renal and hormonal systems. DA molecules could be gently oxidized to quinone structure (ox-DA) in air-containing buffer solution under alkaline condition. In this study, a label-free luminescent probe based on the luminescence energy transfer (LET) between the NaYF4:Yb3+, Tm3+ UCNPs and ox-DA was developed for highly sensitive and selective detection of DA. The luminescent response ratios (I0/I) increased linearly with the concentration of DA increasing in the ranges of 0.25 − 150µM. The relative standard deviation (RSD) for 11 replicate detections of 25µM DA was 0.48%, and the limit of detection was 124nM. The developed method was applied for detection of DA in biological fluids with the quantitative spike recoveries from 94.8% to 103.6%.

An -OH group functionalized MOF for ratiometric Fe3+ sensing

Iron is one of the most important elements in the biochemical processes in all living system, both deficiency or excess of iron will lead to metabolism disorder diseases. However, Fe3+ is one of the most efficient fluorescence quenchers among the transition-metal ions because of its paramagnetic nature. The realization of Fe3+ ratiometric and self-calibrated fluorescent sensor is highly-challenging. We synthesized a novel luminescent -OH functionalized EuOHBDC (Eu2(OH-BDC)3, OH-BDC=2-hydroxyterephthalic acid) by hydrothermal reaction and in situ ligand synthesis, and used it as a rare ratiomatric luminescent sensor for Fe3+ ions. The -OH functional group facilitates both electron transfer and binding interaction between EuOHBDC and Fe3+, which lead to luminescent quenching of ligand-based emission while enhancement of a new peak emission, and thus enables ratiometric detection of Fe3+. The relative fluorescent intensity ratio (I375/I427) increased linearly with increasing Fe3+ concentration in the 10–50μM range with 1.17μM (65ppb) detection limit. The EuOHBDC also shows excellent selectivity towards different metal ions, particularly can discriminate Fe3+ and Fe2+ through different luminescent responses. This result clearly demonstrates the superiority of -OH functionalized MOF for Fe3+ detection, which can contribute to develop high performance luminescent probe for detection of metal ions in environmental and biomedical applications.

Vapochromic Gold(I)–Silver(I) Cluster Protected by Alkynyl and Phosphine Ligands

Intensely luminescent coinage metal cluster [Au12Ag14(C≡CPh)20(mdppz)4(CH3OH)8](BF4)6 {1, mdppz = 2‐(3‐methylpyrazinyl)diphenylphosphine} was synthesized and structurally characterized. Twenty alkynyl ligands (PhC≡C–), four mdppz ligands, and eight methanol molecules were found to co‐stabilize the metal cluster. Interestingly, when the weakly ligated methanol molecules were removed, the green luminescence of 1 significantly redshifted to yellow; exposing the resulting yellow sample in methanol vapor immediately restores the green luminescence. Thus reversible luminescence response can be observed by removing and restoring methanol. Other small solvent molecules with weak coordination ability such as Me2CO, MeCN, and C2H5OH were also found to be good agents to trigger the vapochromism.

Structural investigation of laser luminescent response in a rotating ruby crystal

This paper presents the study of fluorescent trace in a rotating ruby crystal occurring upon irradiation of coherent emission with a wavelength λ = 532 nm. As a sample we used an oriented cylinder-shaped ruby single crystal of 5 mm in length and 10 mm in diameter.

Calibration of imaging plate detectors to mono-energetic protons in the range 1-200 MeV.

Responses of Fuji Imaging Plates (IPs) to proton have been measured in the range 1-200 MeV. Mono-energetic protons were produced with the 15 MV ALTO-Tandem accelerator of the Institute of Nuclear Physics (Orsay, France) and, at higher energies, with the 200-MeV isochronous cyclotron of the Institut Curie-Centre de Protonthérapie d'Orsay (Orsay, France). The experimental setups are described and the measured photo-stimulated luminescence responses for MS, SR, and TR IPs are presented and compared to existing data. For the interpretation of the results, a sensitivity model based on the Monte Carlo GEANT4 code has been developed. It enables the calculation of the response functions in a large energy range, from 0.1 to 200 MeV. Finally, we show that our model reproduces accurately the response of more complex detectors, i.e., stack of high-Z filters and IPs, which could be of great interest for diagnostics of Petawatt laser accelerated particles.

A windmill-like Zn3L2 cage exhibiting conformational change imparted sensing for DMA and highly selective naked-eye detection of Co2+ ion by dynamic quenching

A Zn3L2-type metal organic aggregate featuring “six leaf windmill” shaped double cages constructed from a semi-rigid tripodal carboxyl acid ligand H3TCPB (1,3,5-tri(4-carboxyphenoxy) benzene) exhibits sensitive luminescent response toward DMA with obvious intensity enhancement and red-shift. During the procedure, the host-gust interaction was supported by single-crystal-to-single-crystal transformation involving drastic conformational change of the molecular host upon μ2-bridging H2O release and the sensing mechanism was also discussed through theoretical calculations from charge separation hypothesis perspective. The DMA post-modified result of crystal transforming reveals high selective and effective naked eye reversible recognition for Co2+ ions through the dynamic and static quenching mechanisms. Moreover, the visual luminescent test paper was realized for potential application in concerns of the biology and environment.

A Smart Europium-Ruthenium Complex as Anticancer Prodrug: Controllable Drug Release and Real-Time Monitoring under Different Light Excitations.

A unique, dual-function, photoactivatable anticancer prodrug, RuEuL, has been tailored that features a ruthenium(II) complex linked to a cyclen-europium chelate via a π-conjugated bridge. Under irradiation at 488 nm, the dark-inactive prodrug undergoes photodissociation, releasing the DNA-damaging ruthenium species. Under evaluation-window irradiation (λirr = one-photon 350 nm or two-photon 700 nm), the drug delivery process can be quantitatively monitored in real-time because of the long-lived red europium emission. Linear relationships between released drug concentration and ESI-MS or luminescence responses are established. Finally, the efficiency of the new prodrug is demonstrated both in vitro RuEuL anticancer prodrug over some existing ones and open the way for decisive improvements in multipurpose prodrugs.

Effects of predator lipids on dinoflagellate defence mechanisms - increased bioluminescence capacity

Short flashes of blue light (bioluminescence) from dinoflagellates can reduce copepod grazing of light-emitting cells. Other protective strategies against grazing are toxicity, reduced cell chain length and altered swimming patterns in different phytoplankton. Both toxicity and bioluminescence capacity in dinoflagellates decrease in copepod-free cultures, but toxin production can be restored in response to chemical alarm signals from copepods, copepodamides. Here we show that strains of the dinoflagellates Lingulodinium polyedra and Alexandrium tamarense, kept in culture for 14 and 9 years respectively, are capable of increasing their total bioluminescence capacity in response to copepodamides. The luminescence response to mechanical stimulation with air bubbles also increases significantly in L. polyedra after exposure to copepodamides. Effects on size, swimming speed and rate of change of direction in L. polyedra and A. tamarense were not detected, suggesting that post-encounter mechanisms such as bioluminescence and toxin production may constitute the dominating line of defence in these taxa. To our knowledge, this study provides the first evidence of changes in bioluminescence physiology as a response to chemical cues from natural enemies and emphasizes the importance of bioluminescence as an anti-grazing strategy.

Cucurbit[7]uril Induced Formation of FRET-Enabled Unilamellar Lipid Vesicles.

A unique fluorescence resonance energy transfer (FRET) process is found to be operational in a unilamellar lipid self-assembly in the aqueous phase. A newly synthesized naphthyl based long chain lipid derivative [N-(naphthalene-1-ylmethyl)tetradecane-1-ammonium chloride, 14NA+] forms various self-assembled architectures in the aqueous phase. Controlled changes in lipid concentration lead to a transition of the self-assemblies from micelles to vesicles to rods. In the presence of cucurbit[7]uril (CB7), 14NA+ forms a host-guest [2]pseudorotaxane complex (CB7∋14NA+) and secondary interactions lead to the formation of a lipid bilayer with hydrophobic pockets situated in between the layers. The change in the structure of 14NA+ assemblies, interaction with CB7 and formation of supramolecular assemblies of CB7∋14NA+ were examined using light scattering, spectroscopic, and microscopic techniques. Entrapment of a luminescent dye, anthracene within the hydrophobic bilayer of the supramolecular assembly CB7∋14NA+ favors a modified luminescent response due to an efficient FRET process. Further, the FRET process could be controlled by thermal and chemical stimuli that induce transformation of unilamellar vesicles.

Upconversion emission of ZrO2 nanoparticles doped with erbium (Er3+) and ytterbium (Yb3+), synthesized by hydrothermal route

This paper reports the luminescent response upconversion of zirconium oxide (ZrO2) nanoparticles doped with erbium (Er3+) and ytterbium (Yb3+) ions, synthesized by hydrothermal route. X ray diffraction (DRX) showed that the synthesized material presents the face centered cubic (FCC) structure. High resolution transmission electron microscopy (HRTEM) showed the presence of crystals size smaller than 10nm. The photoluminescent analysis allowed to observe an intense upconversion luminescence emission of the samples doped with both ions Er3+ and Yb3+, when these are excited with 910nm laser source, showing the electronic transitions 4F9/2 → 4I5/2; 2H11/2 → 4I5/2; 4S3/2 → 4I15/2 of Er3+. Two decay times were observed, whose behavior can be associated to the average distance between erbium ions within the nanocrystals.

Sensitivity evaluation and selective plane imaging geometry for x-ray-induced luminescence imaging.

X-ray-induced luminescence (XIL) is a hybrid x-ray/optical imaging modality that employs nanophosphors that luminescence in response to x-ray irradiation. X-ray-activated phosphorescent nanoparticles have potential applications in radiation therapy as theranostics, nanodosimeters, or radiosensitizers. Extracting clinically relevant information from the luminescent signal requires the development of a robust imaging model that can determine nanophosphor distributions at depth in an optically scattering environment from surface radiance measurements. The applications of XIL in radiotherapy will be limited by the dose-dependent sensitivity at depth in tissue. We propose a novel geometry called selective plane XIL (SPXIL), and apply it to experimental measurements in optical gel phantoms and sensitivity simulations. An imaging model is presented based on the selective plane geometry which can determine the detected diffuse optical signal for a given x-ray dose and nanophosphor distribution at depth in a semi-infinite, optically homogenous material. The surface radiance in the model is calculated using an analytical solution to the extrapolated boundary condition. Y2 O3 :Eu3+ nanoparticles are synthesized and inserted into various optical phantom in order to measure the luminescent output per unit dose for a given concentration of nanophosphors and calibrate an imaging model for XIL sensitivity simulations. SPXIL imaging with a dual-source optical gel phantom is performed, and an iterative Richardson-Lucy deconvolution using a shifted Poisson noise model is applied to the measurements in order to reconstruct the nanophosphor distribution. Nanophosphor characterizations showed a peak emission at 611nm, a linear luminescent response to tube current and nanoparticle concentration, and a quadratic luminescent response to tube voltage. The luminescent efficiency calculation accomplished with calibrated bioluminescence mouse phantoms determines 1.06 photons were emitted per keV of x-ray radiation absorbed per g/mL of nanophosphor concentration. Sensitivity simulations determined that XIL could detect a concentration of 1mg/mL of nanophosphors with a dose of 1cGy at a depth ranging from 2 to 4cm, depending on the optical parameters of the homogeneous diffuse optical environment. The deconvolution applied to the SPXIL measurements could resolve two sources 1cm apart up to a depth of 1.75cm in the diffuse phantom. We present a novel imaging geometry for XIL in a homogenous, diffuse optical environment. Basic characterization of Y2 O3 :Eu3+ nanophosphors are presented along with XIL/SPXIL measurements in optical gel phantoms. The diffuse optical imaging model is validated using these measurements and then calibrated in order to execute initial sensitivity simulations for the dose-depth limitations of XIL imaging. The SPXIL imaging model is used to perform a deconvolution on a dual-source phantom, which successfully reconstructs the nanophosphor distributions.