Radiationless Energy Transfer Research Articles

Sensitization of 5–6 μm Nd3+ luminescence in selenide glass by Tb3+ ions

This investigation proposes Tb3+ ions as efficient sensitizers of 5–6 μm Nd3+ emission in selenide glasses. Tb3+ ions can be pumped by 2.9 μm Er:YAG as well as by 1.9–2 μm Tm3+ lasers and laser diodes. It was shown, that at room temperature the radiationless energy transfer from Tb3+ to Nd3+ is combined with the reverse process. At liquid nitrogen temperature the energy transfer from Tb3+ to Nd3+ becomes irreversible. The proposed sensitization scheme should allow the development of neodymium chalcogenide glass lasers emitting at ∼6 μm.

Resonantly enhanced interatomic Coulombic electron capture in a system of three atoms

In interatomic Coulombic electron capture, the capture of a free electron at an atomic center is accompanied by the radiationless transfer of the excess energy to a neighboring atom of different species, leading to ionization of the latter. We show that this interatomic process can be strongly enhanced by the presence of an additional third atom, provided the energy of the free-bound capture transition in the first atom is resonant to a dipole-allowed excitation energy in this assisting atom. The relation of the resonantly enhanced three-center electron capture with other processes is discussed, and its dependencies on the incident electron energy and the spatial geometry of the triatomic system are illustrated.

The role of Yb2+ as a scintillation sensitiser in the near-infrared scintillator CsBa2I5:Sm2+

The feasiblity of using Yb2+ as a scintillation sensitiser for CsBa2I5:Sm2+ near-infrared scintillators has been assessed. CsBa2I5 samples with concentrations ranging from 0.3% to 2% Yb2+ and 0–1% Sm2+ have been studied. The scintillation properties have been determined and the dynamics of the scintillation mechanism have been studied through photoluminescence measurements. Radiationless energy transfer between Yb2+ ions plays a key role in increasing the ratio between the spin-forbidden and spin-allowed emission with increasing Yb2+ concentration in samples where Yb2+ is the only dopant. In samples co-doped with Sm2+, the Yb2+ 4f13[F27/2]5d1[LS] and 4f13[F27/2]5d1[HS] states both serve as donor states for radiationless energy transfer to Sm2+ with a rate of energy transfer that is inversely proportional to the luminescence lifetime the respective donor states. At a Sm2+ concentration of 1%, 85% of the Yb2+ excitations are transferred to Sm2+ through radiationless energy transfer. Almost all of the remaining Yb2+ emission is reabsorbed by Sm2+, resulting in nearly complete energy transfer.

Assessing Protein Interactions in Live-Cells with FRET-Sensitized Emission.

Förster Resonance Energy Transfer (FRET) is the radiationless transfer of energy from an excited donor to an acceptor molecule and depends upon the distance and orientation of the molecules as well as the extent of overlap between the donor emission and acceptor absorption spectra. FRET permits to study the interaction of proteins in the living cell over time and in different subcellular compartments. Different intensity-based algorithms to measure FRET using microscopy have been described in the literature. Here, a protocol and an algorithm are provided to quantify FRET efficiency based on measuring both the sensitized emission of the acceptor and quenching of the donor molecule. The quantification of ratiometric FRET in the living cell not only requires the determination of the crosstalk (spectral spill-over, or bleed-through) of the fluorescent proteins but also the detection efficiency of the microscopic setup. The protocol provided here details how to assess these critical parameters.

Single ionization of an asymmetric diatomic system by relativistic charged projectiles

We study single ionization of a heteroatomic system by charged projectiles whose velocity $v$ approaches the speed of light $c$. The system is formed by two loosely bound atomic species, $A$ and $B$, with the ionization potential of $A$ being smaller than excitation energy for a dipole-allowed transition in $B$. In such a case, three single ionization channels occur: (i) single-center ionization of atom $A$, (ii) single-center ionization of atom $B$, and (iii) two-center ionization of $A$. While (i) and (ii) are the well known mechanism of direct impact ionization of a single atom, in channel (iii) ionization of $A$ proceeds via impact excitation of $B$ with consequent radiationless transfer of excitation energy---via (long-range) two-center electron-electron correlations---to $A$, leading to its ionization. We show that, close to the resonance energy, the two-center channel (iii) is so enormously strong that its contribution remains dominant even if the range of emission energies $\ensuremath{\sim}1$ eV, which is orders of magnitude broader than its width, is considered. The influence of relativistic effects, caused by a high collision velocity, on the angular distribution of emitted electrons may be quite strong even at $\ensuremath{\gamma}=1/\sqrt{1\ensuremath{-}{v}^{2}/{c}^{2}}\ensuremath{\approx}2$. However, in the energy distribution and the total cross section, these effects become substantial only at $\ensuremath{\gamma}\ensuremath{\gg}1$. Relativistic effects arising due to a large size of the two-atomic system are shown to be very weak even for a $^{7}\mathrm{Li}\text{\ensuremath{-}}\mathrm{He}$ dimer whose mean size is about 28 \AA{}.

Step-function luminopsins for bimodal prolonged neuromodulation.

Although molecular tools for controlling neuronal activity by light have vastly expanded, there are still unmet needs which require development and refinement. For example, light delivery into the brain is still a major practical challenge that hinders potential translation of optogenetics in human patients. In addition, it would be advantageous to manipulate neuronal activity acutely and precisely as well as chronically and non-invasively, using the same genetic construct in animal models. We have previously addressed these challenges by employing bioluminescence and have created a new line of opto-chemogenetic probes termed luminopsins by fusing light-sensing opsins with light-emitting luciferases. In this report, we incorporated Chlamydomonas channelrhodopsin 2 with step-function mutations as the opsin moiety in the new luminopsin fusion protein termed step-function luminopsin (SFLMO). Bioluminescence-induced photocurrent lasted longer than the bioluminescence signal due to very slow deactivation of the mutated channel. In addition, bioluminescence was able to activate most of the channels on the cell surface due to the extremely high light sensitivity of the channel. This efficient channel activation was partly mediated by radiationless bioluminescence resonance energy transfer due to the proximity of luciferase and opsin. To test the utility of SFLMOs in vivo, we transduced the substantia nigra unilaterally via a viral vector in male rats. Injection of the luciferase substrate as well as conventional photostimulation via fiber optics elicited circling behaviors. Thus, SFLMOs expand the current approaches for manipulation of neuronal activity in the brain and add more versatility and practicality to optogenetics in freely behaving animals.

Almost complete radiationless energy transfer from excited triplet state of a dim phosphor to a covalently linked adjacent fluorescent dye in purely organic tandem luminophores doped into PVA matrix

Efficient harvesting of energy of the triplet exited state of dim organic phosphors by conjugated fluorophores is a general phenomenon that would be applicable for construction of novel photoluminescence-based sensors and organic light emitting devices.

(Invited) Metal-Organic Frameworks As Prospective Materials in Photonic Applications

Integrated photonics, using photons as information carriers on the macro -or nanosize region, has a tremendous potential to overcome the fundamental speed limitation in electronics and therefore can create new techniques, important for telecommunication, information processing, data storage or photonic computing. A key factor for the development of advanced photonic applications is the manipulation and conversion of photons. This, however, necessitates sophisticated solid-state materials which combine molecular tailoring and flexibility with low-cost solution processable thin films for device integration at the one side and extending photo-physical properties at the other side. Multi-photon absorption (MPA), amplified stimulated emission (STE), wave-guiding are fundamental processes in the specific modulation of light and therefore of immense importance for the fabrication of various photonic devices at different sizes. In particular, these processes have been studied in a number of material classes including single molecules, inorganic (nano)particles or organic polymers. Nevertheless, limiting factors include critical issues such as of concentration quenching, wavelength tunability, photo-stability, transparency or defect induced losses, if not even synthetic access and toxicity. In this regard, solid-state hybrid materials, namely metal-organic frameworks (MOFs) and coordination polymers (CPs), appear to be highly promising novel photonic materials, which could overcome such challenges. The coordination of an optically active linker to a metal-node in a CP often increases the photo-physical response induced by the weakening of radiation-less decay mechanisms or by cooperative enhancement effects between adjacent chromophores or metal nodes. The restrictive conformation of the linker between metal centers impacts the polarizability of the latter, which plays also a significant role in the photo-physical response. The building-block concept of CPs offers a huge space for rational control over such parameters. This highlights the uniqueness of MOFs compared to other photoactive materials and therefore, MOFs are supposed to be among the most promising material class exploiting photonic properties in the solid-state by a thorough choice of organic linkers and metal nodes. Furthermore, the possibility to process MOFs as thin films makes them a perfect candidate for device integration, which is a prerequisite for materials to be used in technological applications. We recently demonstrated exceptionally high two-photon absorption (2PA) action cross-section values alongside with intrinsic STE with low threshold energy from electron rich tetrakis-phenylethylene based MOFs. In a joined theoretical and experimental venture, we further derived and probed a quantitative model to predict the MPA properties of these materials, including important parameters such as charge polarization, length of π-system, fluorescence quantum yield, alignment and packing density as well as the conformation of the chromophores inside the MOF structure. We also showed that the 2PA response of MOFs can either be tuned by linker functionalization using acceptor groups or by an intermolecular approach through the interaction of different linkers via space. Moreover, we quantified below bandgap absorption on micrometer-sized MOF 2D-plates acting as low-loss optical waveguides, where the light is passed from linker to linker in a radiation-less energy transfer process. The design of exceptionally high performing and optimized optically active MOFs in photonic applications needs a thorough understanding of the structure-property relationship to guide the required MOF crystal engineering. We are successively expanding the number of MPA active linkers and MOFs at the moment to deepen our understanding of this (non-)linear optically active material class both on an experimentally and theoretically level. Our results impressively demonstrate that MOFs are a highly interesting material class in photonic research and therefore can constitute to future techniques such as quantum computing, high density data storage or ultra-fast data transmission and processing. Figure 1

Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas

Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis(1), energy-transfer-based microspectroscopies(2), nanoscale quantum entanglement(3) and photonic-mode hybridization(4). Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized(5) plasmonic modes. Analogous to the Tavis-Cummings model, two whispering-gallery-mode antennas(6) placed in the foci of an elliptical plasmonic cavity(7) fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.

Plasmon-activated intermolecular nonradiative energy transfer in spherical nanoreactors

The effect of silver nanoparticles upon intermolecular radiationless energy transfer between the dye molecules confined in the nanopores of silica was studied both experimentally and by theoretical modeling. Silver nanoparticles were synthesized directly inside the nanopores of silica from AgNO3 using aqueous solution of NaBH4 as a reducing agent. Silica samples with or without nanoparticles were soaked with ethanol solutions of dyes, Acridine Orange (AO) as a donor of electronic excitation energy, and Nile Blue as the acceptor. Studies of fluorescence spectra of samples at different acceptor concentration have shown that addition of nanoparticles decreases the relative quantum yield of fluorescence of donor accompanied by the increase of that of acceptor. This was interpreted as a plasmonic contribution to the rate of nonradiative energy transfer. A theoretical model was proposed, which describes the quenching kinetics of the excited donor molecules in the presence of accepting molecules and metal nanoparticles in a polarized spherical nanopore, as well as the changes in spectral bands of the system. Besides, simulation of the interaction of a point dipole source field with plasmonic silver nanoparticles in a silica cavity was carried out using finite-difference time-domain (FDTD) method. The results of field calculation with the two models are in a good qualitative agreement between each other and predict the regions of local electric field enhancement in the gap between silver nanoparticles and walls of pores that is supposed to account for the experimentally observed increased efficiency of the nonradiative intermolecular singlet–singlet energy transfer in porous silica matrix with silver nanoparticles. The results obtained can be of interest for FRET SNOM.

UV-induced Melanin Chemiexcitation: A New Mode of Melanoma Pathogenesis.

Mutations in sunlight-induced melanoma arise from cyclobutane pyrimidine dimers (CPDs), DNA photoproducts usually created picoseconds after an ultraviolet (UV) photon is absorbed at thymine or cytosine. Surprisingly, we found that, in melanocytes, CPDs were generated for hours after UVA or UVB exposure. These "dark CPDs" constituted the majority of CPDs in cultured human and murine melanocytes and in mouse skin, and they were most prominent in skin containing pheomelanin, the melanin responsible for blonde and red hair. The mechanism was also a surprise. Dark cyclobutane pyrimidine dimers (CPDs) arise when ultraviolet (UV)-induced superoxide and nitric oxide combine to form peroxynitrite, one of the few biological molecules capable of exciting an electron. This process, termed "chemiexcitation," is the source of bioluminescence in lower organisms. Excitation occurred in fragments of melanin, creating a quantum triplet state that had the energy of a UV photon but which induced CPDs by radiationless energy transfer to DNA. UVA and peroxynitrite also solubilized melanin and permeabilized the nuclear membrane, allowing melanin to enter. Melanin is evidently carcinogenic as well as protective. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin.

Insulinotropic Effect of Herbal Drugs for Management of Diabetes Mellitus: A Congregational Approach

Among biosensors, genetically-encoded FRET biosensors raised hope to dissect signaling pathways by monitoring enzymatic activities or second messengers levels in living cells and even in living and developing organisms. FRET (Froster resonance Energy Transfer) is a radiationless energy transfer from donor to acceptor fluorophore. For most genetically encoded donor/acceptor pair, this transfer can only occur if they are separated by a distance less than ~10 nm. A FRET based sensor is made up of an adapted bioreceptor tagged on both ends with appropriate fluorophores.

A time-resolved luminescent competitive assay to detect L-selectin using aptamers as recognition elements

L-selectin is a protein with potential importance for numerous diseases and clinical disorders. In this paper, we present a new aptamer-based luminescent assay developed to detect L-selectin. The sensing system working principle is based on Förster Resonance Energy Transfer (FRET) from a donor terbium complex (TbC) to an acceptor cyanine dye (Cy5). In the present approach, the biotinylated aptamer is combined with Cy5-labelled streptavidin (Cy5-Strep) to yield an aptamer-based acceptor construct (Apta-Cy5-Strep), while L-selectin is conjugated using luminescent TbC. Upon aptamer binding to the TbC-labelled L-selectin (L-selectin-TbC), permanent donor-acceptor proximity is established which allows for radiationless energy transfer to occur. However, when unlabelled L-selectin is added, it competes with the L-selectin-TbC and the FRET signal decreases as the L-selectin concentration increases. FRET from the TbC to Cy5 was observed with time-gated time-resolved luminescence spectroscopy. A significant change in the corrected luminescence signal was observed in the dynamic range of 10–500 ng/mL L-selectin, the concentration range relevant for accelerated cognitive decline of Alzheimer's disease, with a limit of detection (LOD) equal to 10 ng/mL. The aptasensor-based assay is homogeneous and can be realized within one hour. Therefore, this method has the potential to become an alternative to tedious heterogeneous analytical methods, e.g. based on enzyme-linked immunosorbent assay (ELISA).

A method for calculating the parameters of Förster resonance energy transfer in nanoclusters of colloidal quantum dots from data on their photoluminescence: an account of fluorescence intermittency

We have formulated and solved a system of differential equations describing the kinetics of Forster resonance energy transfer in nanoclusters of colloidal quantum dots for the case of binary particle mixture (donors and acceptors) in the presence of fluorescence intermittency. By solving the system, we have been able to develop a method to calculate all relevant parameters of radiationless energy transfer and the fraction of “dark” particles of both types from experimental data on the photoluminescence of nanoclusters.

Intermolecular Radiationless Electronic Excitation Energy Transfer Near A Conductive Film

Based on the developed mathematical model, the radiationless electronic excitation energy transfer by surface plasmons between molecules adsorbed on a conductive film is investigated. A dependence of the rate of energy transfer on the geometrical system parameters is established. It is demonstrated that the presence of the plasmon channel increases up to two orders of magnitude the probability of energy transfer in comparison with the direct dipole-dipole interaction between the donor and acceptor spaced at the same distance in vacuum.

Symmetry-Related Transitions in the Photoluminescence and Cathodoluminescence Spectra of Nanosized Cubic Y2O3:Tb3+

Herein the photoluminescence spectra of nanosized cubic Y2O3:Tb3+ having Tb3+ concentrations varying between 0.1 and 10 Mol% are described. Low temperature cathodoluminescence spectra from these materials recorded in a scanning transmission electron microscope are presented and discussed. By studying the photoluminescence-spectra recorded at room temperature and focused on the 5D4→7F5 (C2) and 5D4→7F5 (C3i) transitions, at 542.8 and 544.4 nm respectively, it was found that the critical distance for energy transfer from Tb3+ ions at C3i lattice sites to Tb3+ ions at C2 lattice sites was 1.7 nm; at distances >1.7 nm, which prevail at low Tb3+ concentration, this energy transfer virtually stops. The gradual change of the excitation spectra upon increasing the Tb3+ concentration is also explained in terms of energy transfer from Tb3+ at C3i sites to Tb3+ at C2 sites. Cathodoluminescence spectra recorded at low temperatures with the scanning transmission electron microscope provided additional evidence for this radiationless energy transfer.

The fluorescence decay times and quantum efficiencies of 1,4,5,8-naphthalisoimides

Presented herein are the luminescence properties of several 1,4,5,8- polinahthalisoimides. The luminescence decay curves after deconvolution exhibit three decay times: τ1, τ2, and τ3.The luminescence lifetimes change along with the growth of excitation energy, as well as the contribution of each luminescence decay mechanism (A1, A2, and A3). The manner of change is distinct for one sample, namely, the pure E-isomer, in comparison to the others. The radiative deexcitation coupled with radiationless vibrational energy transfer to other luminescence centers, mainly other isomer units, is discussed as a possible deexcitation mechanism of fluorescence. The Kasha–Vavilov empirical rule is not fulfilled for the studied samples, as the luminescence quantum efficiency (ΦF) distinctly depends on the excitation wavelength (λexc). The quantum yield of one sample (about 63% of Z-isomer) is quite high, at 1%.

Binding of dihydromyricetin and its metal ion complexes with bovine serum albumin

The binding mechanisms of the interaction of three dihydromyricetin (DMY)–metal complexes (DMY–Cu (II) complex, DMY–Mn (II) complex, DMY–Zn (II) complex) and DMY with bovine serum albumin (BSA) were investigated using fluorescence and ultraviolet spectroscopy at different temperatures. The results indicated some differences in the binding process between different DMY–metal complexes and BSA compared with that of free DMY. All of the complexes and DMY quenched the fluorescence of BSA based on static mode combined with radiationless energy transfer, yet having different binding distance based on the Förster theory. Different DMY–metal complexes can change the binding constants. The binding constants increase for DMY–Cu (II) and DMY–Mn (II) complexes, whereas the opposite is true for the DMY–Zn (II) complex compared to the one with free DMY. The DMY–metal complexes can also affect the types of the interaction. The van der Waals forces and hydrogen bonding may play a major role in the interaction of free DMY with BSA, while for the three complexes, the nature of the binding forces lies in hydrophobic forces and hydrogen bonding based on the thermodynamic parameters.

Quenching of tribo- and photoluminescence in a Tb2(SO4)3 · 8H2O + NaNO2 crystalline mixture

It is found that the addition of NaNO2 to Tb2(SO4)3 · 8H2O crystals quenches tribo- and photo-luminescence from the latter. In the case of triboluminescence, the glow of both Tb3+* ions (solid component of triboluminescence) and N2* molecules (gas component) is quenched. The NO2− ion is known to be an efficient quencher of Tb3+ ion luminescence by the mechanism of radiationless energy transfer in solutions. That quenching takes place when a crystalline quencher is in contact with a crystalline phosphor and also with a gaseous (molecular) phosphor seems to indicate that the excitation energy is transferred not only within individual crystals but also between contacting surfaces of the phosphor and quencher and at the gas-solid interface.

Luminescence and energy transfer processes in ensembles and single Mn or Tb doped ZnS nanowires

Zinc sulfide (ZnS) nanowires with a typical diameter of 100 to 300 nm have been doped with different concentrations of either Mn or Tb using ion implantation. Both systems show very efficient and long living intra-shell luminescence with strong non-exponential decay characteristics in the range of milliseconds. The time behavior of the corresponding luminescence is well described within a modified Förster model, taking into account the lower dimensionality of the nanowires in case of radiationless dipole-dipole energy transfer. The general applicability of this model for energy transfer processes in low dimensional systems will be shown as a function of concentration, temperature, excitation density as well as for measurements on the level of single nanowires.