Observation Of Energy Transfer Research Articles

Spectral studies of thermally stable Dy3+/Sm3+ co-doped Li2Ba5W3O15 phosphors for warm white LEDs

In the current study, a series of Li2Ba5W3O15: RE3+ (RE = Dy, Sm) [LBW:Dy3+/Sm3+] phosphors were prepared using a high-temperature solid-state method. X-ray diffraction, Scanning electron microscopy with energy-dispersive x-ray analysis scans showed that the crystal form was consistent with the standard LBW and comprised small irregularly shaped particles. Diffuse reflectance spectral (DRS) data was utilized to calculate the band gaps. Fluorescence study shows that LBW material doped with Dy3+ and Sm3+ yield distinct colors at 496 nm (blue) for Dy3+ and 582 nm (green-yellow), 612 nm (yellow), and 669 nm (red) for Sm3+ when excited by near-ultraviolet (336 nm) light. The observation of energy transfer between Dy3+ and Sm3+ ions play a role in modifying the luminescence of LBW:Dy3+/Sm3+ co-doped phosphors. With a constant excitation wavelength (λ Ex), different levels of activator doping lead to a change in the emission colors from their neutral white light to a deep orange-red region for LBW:Dy3+/Sm3+ phosphors. The decay curves demonstrate a decrease in lifetime with an increase in the concentration of activator ions (Sm3+). For D3S5 phosphor, the temperature-dependent photoluminescence characteristics were analyzed under λ Ex = 336 nm excitation. The results indicate excellent luminescence thermal stability with an activation energy of 0.16 eV at λ Ex = 336 nm. With its low color-correlated temperature and good thermal stability, the prepared phosphor sample shows potential as a solid-state emitting phosphor that can be used with UV chip stimulation for warm white LED applications.

Observation of energy transfer from Eu2+ to Eu3+ and tunable luminescence in phosphors YF3:Eu prepared by hydrothermal method

Eu2+ and Eu3+ co-activated YF3:Eu phosphors were prepared by a traditional hydrothermal method with citric acid as reducing agent. Products with bitter gourd like morphology comprised of numerous nanoparticles show a blue emission of Eu2+ and a red emission of Eu3+ simultaneously. The relative amount of Eu2+ and Eu3+ can be tuned by adjusting Eu concentration, citric acid concentration and hydrothermal reaction time. Obvious energy transfer from Eu2+ to Eu3+ can be observed. Through energy transfer, Eu2+ and Eu3+ can be effectively excited by the ultraviolet light in the range of 275–400 nm and a tunable luminescence color from red, white to blue can be achieved. The work will provide an alternative solution for the development of new LED phosphors.

Observation of energy transfer at optical frequency to an ultrathin silicon waveguide.

Energy transfer from a submonolayer of rhodamine 6G molecules to a 130 nm thick crystalline silicon (Si) waveguide is investigated. The dependence of the fluorescence lifetime of rhodamine on its distance to the Si waveguide is characterized and modeled successfully by a classical dipole model. The energy transfer process could be regarded as photon tunneling into the Si waveguide via the evanescent waves. The experimentally observed tunneling rate is well described by an analytical expression obtained via a complex variable analysis in the complex wavenumber plane.

Observations of energy transfer and anisotropic behavior in ZnO nanoparticles surface-modified by liquid-crystalline ligands

Here we report the fabrication of a novel nano-level hybrid of ZnO nanoparticles (NPs) and liquid crystals (LCs) by the attachment of organic LC molecules with a mercapto moiety, namely, 4′-n-(6-mercaptohexyloxy)-4-cyanobiphenyl (6CNBP-SH), to the surface of ZnO nanoparticles. The dispersion of modified ZnO NPs (6CNBP-SH@ZnO) is greatly improved by the surface modification of 6CNBP-SH ligands. The photoluminescence (PL) measurement shows that the ultra-violet emission of ZnO can be enhanced by the surface modification of 6CNBP-SH ligands and annealing at liquid crystal state temperature of 6CNBP-SH@ZnO (110°C). Meanwhile, defect-related emission of ZnO in 6CNBP-SH@ZnO almost disappears. We attribute this observation to the energy transfer between the ZnO NPs and 6CNBP-SH, surface passivation of the ZnO and formation of ZnO nano-dispersing structure induced by 6CNBP-SH molecules. The anisotropic behavior of 6CNBP-SH@ZnO is also investigated. The results indicated that the 6CNBP-SH liquid-crystalline ligands could endow the 6CNBP-SH@ZnO hybrid obvious mesoscopic behavior. In addition, the increased optical anisotropy of 6CNBP-SH@ZnO is also observed upon thermal treatment at 110°C.

Observation of Energy Transfer from Host to Rare-Earth Ions in Ca2SnO4:Pr3+ Phosphor

Red optical properties of Pr3+-doped Ca2SnO4 compounds prepared by the solid-state reaction at different atmospheres were investigated. Comparing with the air-sintered phosphor, a significant enhancement of the red emission intensity was observed for the vacuum-sintered phosphor. This improvement could be attributed to the increased oxygen vacancies, which act as the sensitizers for the effective energy transfer (ET) from Ca2SnO4 host to Pr3+. This study demonstrated that the ET process between the host and rare-earth ions in Ca2SnO4 was closely related to the oxygen vacancies.

Observation of energy transfer between InAs quantum dots by pump-and-probe micro-photoluminescence measurement

Using pump-and-probe micro-photoluminescence measurement, we observed the nonlinear photoluminescence (PL) of multilayer InAs quantum dots (QDs), which originated from energy transfer between dots. In double- and five-layered InAs QDs, the differential PL intensity, Δ I/I probe, became negative at certain pump intensity. With changes in the pump intensity, Δ I/I probe decreases or increases. This is explained by the generation of a non-radiative path and the saturation of non-radiative sites by the pump pulses. Our experimental results suggest that InAs QDs can act as AND- and NOT-gates by using suitable thresholds and control lights.

MspA Porin−Gold Nanoparticle Assemblies: Enhanced Binding through a Controlled Cysteine Mutation

In this study, the interactions of two gold nanoparticles of different sizes (average diameters of 3.7 +/- 2.6 and 17 +/- 3 nm) with octameric mycobacterial porin A from Mycobacterium smegmatis (MspA) and a mutant of MspA featuring a cysteine mutation in position 126 (Q126C) are investigated. From the observation of enhanced photoluminescence quenching, it is inferred that the presence of eight cysteines in the MspA Q126C mutant significantly enhances the binding of selected small gold nanoparticles within the inner pore of MspA. The large gold nanoparticle/porin complex shows photoluminescence enhancement, which is expected since the larger nanoparticles cannot dock within the homopore of MspA due to size exclusion. In addition to the fluorescence experiments, observation of energy transfer from the small gold nanoparticles to the MspA shows the close proximity of the small gold nanoparticles with the porin. Interestingly, the energy transfer of the large nanoparticle/MspA complex is completely missing. From high-performance liquid chromatography data, the estimated binding constants for small Au@MspA, large Au@MspA, small Au@MspAcys, and large Au@MspAcys are 1.3 x 10 (9), 2.22 x 10 (10), > 10 (12) (irreversible), and 1.7 x 10 (10), respectively.

Observation of energy transfer from host to rare earth ions in Pr 3+-doped CdSiO 3 long-lasting phosphor

The observation of energy transfer from host to rare earth ions in Pr 3+-doped CdSiO 3 long-lasting phosphor is reported in this Letter. The important role of persistent energy transfer from the CdSiO 3 host to the Pr 3+ is demonstrated experimentally through photoluminescence spectra, time-resolved emission spectra and fluorescence decay curves. A significant spectral overlap between the emission of host and the absorption of Pr 3+ (4d–5f) has been observed. By utilizing the principle of energy transfer, a promising approach for controlling the color-emitting is proposed to develop the multi-color long-lasting phosphors via persistence energy transfer from the long-lasting luminescent host to rare earth ions.

First Observation of NIR 4f–4f Luminescence through the Energy Transfer from the SOMO π* Doublet in Nitronyl Nitroxide Radical Lanthanide(III) Complexes

AbstractThis study demonstrates the first observation of energy transfer from the doublet state of the nitronyl nitroxide radical ligand in LnIII complexes, exerting the light‐harvesting antenna effect on the NIR luminescence for the first time. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Investigation of Energy Transfer between CdTe Nanocrystals on Polystyrene Beads and Dye Molecules for FRET-SNOM Applications

We report results on the observation of energy transfer between CdTe nanocrystals and AlexaFluor dye molecules. The nanocrystals were attached to the surface of polystyrene latex beads of 450 nm in diameter by means of the layer-by-layer technique. Energy transfer was observed as signal enhancement in confocal imaging of a single bead covered with an AlexaFluor film. This was verified by detecting quenching of the donor emission and enhancement of the acceptor emission in spectral measurements. A fluorescence-resonance energy transfer scanning near-field optical microscopy (FRET-SNOM) tip was made from a single bead coated with CdTe attached to a near-field tip. We report first results on FRET-SNOM imaging with this tip.

Observation of Energy Transfer at D2O Ice/CO/Pt(111) Interface by Time-resolved SFG Spectroscopy

Dynamic behavior of cyclohexane adsorbed on Ni(111) under the irradiation of NIR pulses (1064 nm) was studied by time-resolved sum-frequency generation (SFG). Two types of adsorbed cyclohexane were observed on Ni(111), which were attributed to the ordered cyclohexane domains at high coverage and disordered cyclohexane molecules. When the surface was temporally heated up by the irradiation with the NIR pulses, the disordered cyclohexane molecules were thermally excited to form the ordered structure.

Observation of Energy Transfer Between Al[sup 3+] and Pr[sup 3+] in SrTiO[sub 3] Phosphor

Observation of Energy Transfer Between Al[sup 3+] and Pr[sup 3+] in SrTiO[sub 3] Phosphor

Observation of Energy Transfer between Identical-Frequency Laser Beams in a Flowing Plasma

We report enhanced transmission of a low intensity laser beam when crossed with an identical-frequency beam in a plasma with a flow velocity near the ion sound speed. The time history of the enhancement and the dependence on the flow velocity strongly suggest that this is due to energy transfer between the beams via a resonant ion wave with zero frequency in the laboratory frame. The maximum energy transfer has been observed when the beams cross in a region with Mach-1 flow.

Observation of energy transfer between frequency-mismatched laser beams in a large-scale plasma.

The observation of energy transfer between two frequency-mismatched laser beams crossing in a low-density, large-scale plasma is described. The beams cross at an angle of 53\ifmmode^\circ\else\textdegree\fi{} from parallel, with the average intensity in the blue beam equal to $2\ifmmode\times\else\texttimes\fi{}{10}^{15}$ W/c${\mathrm{m}}^{2}$. A redshifted probe beam is amplified by interaction with the blue beam and a stimulated ion acoustic wave. Significant energy is transferred to the probe when the difference in the frequencies of the two beams is comparable to the frequency of the acoustic wave. As much as 52% of the pump energy is transferred to the probe.

Observation of energy transfer between Ce3+ and Eu3+ in YAIO3:Ce, Eu

Observation of energy transfer between Ce3+ and Eu3+ in YAIO3:Ce, Eu

Does slow energy transfer limit the observed time constant for radical pair formation in photosystem II reaction centers?

We have used spectrally photoselective femtosecond transient absorption spectroscopy on photosystem II reaction centers to show that there are at least two pools of chlorin molecules/states which can transfer excitation energy to P680, the primary electron donor in photosystem II. It has previously been shown that one chlorin pool equilibrates with P680 in 100 fs [Durrant et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 11632-11636], and we report here the observation of energy transfer from a second more weakly coupled chlorin pool. The effect of the weakly coupled pool is to increase the apparent time constant for radical pair formation from 21 ps when P680 is selectively excited to 27 ps when the accessory chlorins are excited. We conclude that it is possible to observe both radical pair formation somewhat slowed by an energy transfer step and radical pair formation not limited by this slow energy transfer, depending upon which chromophores are initially excited. These observations provide evidence that when using photoselective excitation of P680, the observed 21 ps time constant for radical pair formation is not limited by a slow energy transfer step.

Picosecond and nanosecond observations of energy transfer in the radiolysis of aromatic systems

Picosecond and nanosecond observations of energy transfer in the radiolysis of aromatic systems

Energy transfer between protochlorophyllide molecules: Evidence for multiple chromophores in the photoactive protochlorophyllide-protein complex in vivo and in vitro

The absorption and fluorescence properties of dark-grown bean leaves, of isolated prolamellar body membranes and of an isolated, active protochlorophyllide-protein complex (protochlorophyll holochrome) were examined at 77 °K. The leaf is characterized by two main forms of protochlorophyll(ide) absorbing at about 650 and 637 nm respectively and a minor form absorbing at 628 nm. PChl-650 †2 †2 Abbreviations used: PChl-650, PChl-637 and PChl-628, protochlorophyll forms having absorption maxima at 650 nm, 637 nm and 628 nm, respectively; PChl-H, protochlorophyll holochrome. and PChl-637 are photoconvertible to chlorophyllide a at room temperature, but PChl-628 is non-convertible. Prolamellar body membranes closely resemble the whole leaf in their spectroscopic properties, but the soluble protochlorophyll holochrome shows an absorption maximum at 637 nm and minor components at 650 nm and 628 nm. The fluorescence emission spectra at 77 °K of dark-grown bean leaves and prolamellar bodies show two main bands at 655 and 630 to 632 nm. The emission at 655 nm emanates from PChl-650, but it is activated by light absorbed both by PChl-650 and PChl-637. Energy absorbed by PChl-637 is transferred to PChl-650 with high efficiency. Fluorescence emitted at 630 nm originates from PChl-628. Protochlorophyll holochrome gave a fluorescence emission spectrum which resembled the spectra obtained with leaves and prolamellar bodies, except for an additional emission band at 643 nm. We concluded that at 77 °K the main form of protochlorophyllide in the holochrome (PChl-637) transfers a large proportion of its excitation energy to PChl-650. After the photoconversion of part of the protochlorophyllide in the holochrome, excitation energy is transferred to the newly formed chlorophyllide a, and the efficiency of transfer increases as the fraction of chlorophyllide a molecules increases. The observation of energy transfer among the chromophores of protochlorophyll holochrome indicates that a number of protochlorophyllide molecules are organized into a unit or attached to the single apoprotein molecule. The observed efficiencies of energy transfer are consistent with a model of protochlorophyll holochrome containing at least four chromophores.