Nonradiative Energy Transfer Process Research Articles

Fluorescence resonance energy transfer from serum albumins to 1-anthracene sulphonate entrapped in reverse micellar nanocavities

Fluorescence resonance energy transfer (FRET) between anionic probe 1-anthracene sulphonate (1-AS) and transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA) solubilized in reverse micelles of sodium 1,4-bis (2-ethylhexyl) sulphosucccinate (AOT) in heptane was studied where the donor and acceptor pair comes in close proximity within the smaller water pools. The mechanism of fluorescence quenching of transport proteins by 1-AS in reverse micelles has been ascribed to the non-radiative energy transfer process. The probable binding site of the probe with proteins has been ascertained from FRET study. Circular dichroism study suggests that the number of folding of the protein increases markedly due to binding of the proteins with 1-AS.

Interaction of Er3+ ions in Er-doped calcium — niobium — gallium garnet crystals

The processes of nonradiative energy transfer in calcium — niobium — gallium garnet (CNGG) crystals doped with Er3+ ions are studied. It is found that the energy of erbium ions in the Er:CNGG crystal with the erbium atomic concentrations CEr=6% and 11% is transferred via the nonradiative co-operative processes 4I11/2→ 4I15/2, 4I11/2→ 4F7/2, 4I11/2→ 4I15/2, 4I13/2→ 4F9/2; and 4I13/2→ 4I15/2, 4I13/2→ 4I9/2, whose efficiency increases with increasing intensity of exciting radiation. It is shown that the cross-relaxation processes 4S3/2→4I9/2, 4I15/2→4I13/2, whose intensity depends on the concentration of Er3+ ions, are characteristic for Er:CNGG crystals with the Er atomic concentration above 1%.

Indirect activation of porphyrin by semiconductor quantum dots with two-photon excitation

Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with 800-nm femtosecond laser pulses. The luminescent intensity and lifetime of the QDs decrease intensively in the QD-porphyrin mixture, whereas those of the TPP increase, suggesting occurence of a nonradiative fluorescence resonance energy transfer (FRET) process between the excited states of the donors and acceptors. An energy transfer efficiency of 0.27 is estimated from quenching of the excited-state radiative lifetime of the QDs. A 4-nm red shift in the emission spectrum of the CdSe QDs is observed after mixing with TPP, which is speculated to be caused by the energy transfer from QDs of small size to large. This study could be valuable for developing a QD-based drug system for application in two-photon excitation photodynamic therapy.

Temperature dependence of the crossover between the near-infrared Er and defect-related photoluminescence bands of Ge-rich Er-dopedSiO2layers

Temperature-dependent photoluminescence of Ge-rich ${\text{SiO}}_{2}$ in the presence or absence of Er shows a crossover between defect-related (15--150 K) and Er-related (150--295 K) emission within 1525 and 1440 nm. The origin of the near-infrared defect-related bands is discussed in the light of recombination of localized excitons in luminescence centers at the Ge $\text{cluster}/{\text{SiO}}_{2}$ interface. Time-resolved photoluminescence further enables us to illustrate the observed $1.53\text{ }\ensuremath{\mu}\text{m}$ Er emission above 150 K in terms of a phonon-assisted nonradiative energy-transfer process from the luminescence centers to the ${\text{Er}}^{3+}$ ions.

Towards in vivo imaging of intramolecular fluorescence resonance energy transfer parameters

Fluorescence resonance energy transfer (FRET) is a nonradiative energy transfer process based on dipole-dipole interaction between donor and acceptor fluorophores that are spatially separated by a distance of a few nanometers. FRET has proved to be of immense value in the study of cellular function and the underlying cause of disease due to, for example, protein misfolding (of consequence in Alzheimer's disease). The standard parameterization in intramolecular FRET is the lifetime and yield, which can be related to the donor-acceptor (DA) distance. FRET imaging has thus far been limited to in vitro or near-surface microscopy because of the deleterious effects of substantial scatter. We show that it is possible to extract the microscopic FRET parameters in a highly scattering environment by incorporating the FRET kinetics of an ensemble of DA molecules connected by a flexible or rigid linker into an optical diffusion tomography (ODT) framework. We demonstrate the efficacy of our approach for extracting the microscopic DA distance through simulations and an experiment using a phantom with scattering properties similar to tissue. Our method will allow the in vivo imaging of FRET parameters in deep tissue, and hence provide a new vehicle for the fundamental study of disease.

White light emission via cascade Förster energy transfer in (Ga, In)N quantum well/polymerblend hybrid structures

We have studied the room-temperature non-radiative energy transfer processes in hybridstructures composed of (Ga, In)N/GaN single quantum wells and semiconductingpolymer blend films placed in nanometre-scale proximity. The blends consistof three polyfluorene materials with concentrations adjusted so that they emitwhite light. Power-dependent photoluminescence (PL) measurements are used toinvestigate the process of energy transfer from the quantum wells to the differentcomponents of the polymer blend. We show that energy distribution among the hybridstructures involves competition between nanoscale range non-radiative energy transferprocesses from the inorganic well to the polymer components and within the blenditself.

Population inversion between the 3H 4 and the 3F 4 excited states of Tm 3+ investigated by means of numerical solutions of the rate equations system in Tm 3+-doped and Tm 3+, Ho 3+-codoped fluoride glasses

Population inversion between the 3H 4 and the 3F 4 excited states of Tm 3+ ions responsible for the 1.5 μm emission in Tm 3+ singly doped (0.5%) and Tm 3+, Ho 3+-codoped fluoride (ZBLAN) glasses and its dependence on the Ho 3+ concentration ( x=0.2–1%) was investigated by means of numerical solution of the rate equations system for continuous pumping at 797 nm. Mean lifetimes of donor and acceptor states were evaluated by using the integration method applied to the best fitting of fluorescence curves previously reported. Lifetime values were used to obtain the rate constants of all non-radiative energy-transfer processes involved and a complete set of rate equations better describing the observations was given. The rate equations were solved by numerical method and the population inversion between the 3H 4 and the 3F 4 excited states of Tm 3+ was calculated to examine the beneficial effects on the gain associated with Ho 3+ codoping. The results have shown that Tm 3+ population inversion is reached only for high Ho 3+-codoping (⩾0.3 mol%). Highest population inversion (∼1.6×10 18 Tm 3+ ions cm −3) was obtained in Tm(0.5%), Ho(1%)-codoped (ZBLAN) pumped by 2.8 kW cm −2. This population inversion density is ∼6.4 times higher than that one observed in Tm:Tb:GLKZ, Tm:Tb:Ge–Ga–As–S–CsBr and Tm:Ho:Ge–Ga–As–S–CsBr for a similar pumping condition (∼2.5×10 17 cm −3). In addition, Tm(0.5%):Ho(1%):ZBLAN presents the highest population inversion that linearly increases with the pumping intensity; this behavior does not show saturation effect at least for the maximum intensity of 12 kW cm −2 employed. The use of 1 mol% of Ho 3+-codoping maximizes the potential gain of Tm 3+-doped (0.5%) ZBLAN to produce stimulated emission near 1.5 μm, making this material suitable for using it as fiber optical amplifier and/or fiber laser operating in 1.4–1.5 μm region of the spectrum.

Yb 3+ quenching effects in co-doped polycrystalline BaTiO 3:Er 3+, Yb 3+

Luminescent properties of single and co-doped samples of sol–gel polycrystalline BaTiO 3 with trivalent Er 3+ and Yb 3+ ions are reported. Under 520 nm pumping, visible radiative emission from 2H 7/2, 4S 3/2 → 4I 15/2, and 4F 9/2 → 4I 15/2; and near infrared emission from 4S 3/2 → 4I 13/2, 4I 11/2 → 4I 15/2 and 4I 13/2 → 4I 15/2 of Er 3+ and from 2F 5/2 → 2F 7/2 of Yb 3+ ions were measured. For single Er 3+ doped samples, concentration quenching was observed from the 4S 3/2 state, whereas emissions in the 1.0 and 1.5 μm regions increase with concentration due to the cross-relaxation mechanism 4S 3/2 + 4I 15/2 → 4I 9/2 + 4I 13/2. Upon addition of Yb 3+ ions quenching is enhanced, as corroborated by the luminescence decay time curves and emission spectra. This is so because an additional non-radiative energy transfer process from the thermally coupled states ( 2H 11/2, 4S 3/2) of Er 3+ to the 2F 7/2 state of Yb 3+ takes place.

The energy transfer from Eu2+ to Tb3+ in calcium chlorapatite phosphor and its potential application in LEDs

Energy transfer from Eu2+ to Tb3+ was observed by investigating the optical properties from photoluminescence spectra and decay time curves in Tb3+ singly doped and Eu2+–Tb3+ co-doped calcium chlorapatite, Ca5(PO4)3Cl (CPCl). It is dominated by the cooperation of a phonon-assisted energy transfer process and a non-radiative resonant energy transfer process caused by the exchange interaction. Eu2+–Tb3+ co-doped calcium chlorapatite phosphors in which Tb3+ can be efficiently excited by 400 nm are potential candidates for phosphor-converted LED.

New light from hybrid inorganic–organic emitters

We present the highlights of a research programme on hybrid inorganic–organic light emitters. These devices combine recent developments in III–V nitride technology (including UV emitting micro-arrays and specifically tailored quantum wells) with conjugated polymers to access the entire visible spectrum. Two types of devices are studied, those based on down conversion of the quantum well emission by radiative transfer and those based on non-radiative resonant energy transfer. The spectral and operating characteristics of the devices are described in detail. Selectable colour micro-arrays and bar emitters are demonstrated. The nature of the non-radiative energy transfer process has also been studied and we find transfer efficiencies of up to 43% at 15 K, with a 1/R2 dependence on the distance between quantum well and polymer layer, suggesting a plane–plane interaction. The relative importance of the non-radiative resonant energy transfer process increases with temperature to be up to 20 times more efficient, at 300 K, than the radiative transfer process.

INTERLAYER TRANSFER AND QUENCHING OF EXCITATION ENERGY IN LANGMUIR-BLODGETT FILMS, DEPOSITED ONTO ELECTRODES OF ELECTROCHEMILUMINESCENT SENSOR

Processes of nonradiative excitation energy transfer and excited states quenching in electrochemiluminescent sensor with working electrode, modified by Langmuir-Blodgett film with incorporated electrochemiluminescer molecules, are investigated by means of mathematical modeling. Comparison with experimental results revealed that considered model is applicable for Langmuir-Blodgett films thinner than 10 monolayers. The optimal thickness of the film for electrochemiluminescent sensor operation was estimated as 3-5 monolayers.

Effects of annealing on morphology of polymer/polymer (PS/PMMA) blend; a fluorescence study

AbstractSteady state fluorescence (SSF) technique conjunction with optical microscopy were used to study the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend upon annealing above glass transition in elevated time intervals. The PS/PMMA blends were prepared from dissolution of pyrene (P) and naphthalene (N) labeled PS and PMMA particles, respectively. Monte Carlo simulations were performed to model the N and P fluorescence intensities (IN and IP), using photon diffusion theory. Number of N and P photons (NN and NP) emerging from the front surface of the blend are calculated when only N is excited, where NP photons are combined of photons from radiative (NPR) and nonradiative (NPNR) energy transfer processes. Optical microscopy images were taken at each annealing step to support our findings from fluorescence measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2104–2110, 2006

Cross-relaxation processes and structural modifications in Ga–Ge–S:Er 3+ chalcogenide glasses

Various processes of non-radiative energy transfer between erbium ions in Ga–Ge–S:Er 3+ chalcogenide glasses using the time-resolved luminescence spectroscopy are considered. The evaluation of the energy transfer constants C SA and C SS for the 4I 9/2, 4F 9/2 and 4S 3/2 Er 3+ levels is presented. The variation of the studied glasses structure with an increase of erbium ions concentration is shown by means of estimation of the minimum distance between Er 3+ ions as permitted by the glass matrix ( R min).

Fluorescence resonance energy transfer from Fluorescein to Safranine T in solutions and in micellar medium

Energy transfer by dipole–dipole interaction between anionic dye Fluorescein and cationic dye Safranine T (3,6 diamino-2,7-dimethyl-5-phenyl phenazinium chloride) solubilised in aqueous solution and micellar solution of cetyl trimethyl ammonium bromide (CTAB) was studied where donor–acceptor Förster critical radius ( R 0) is larger than the micellar diameter ( d m). The mechanism of quenching of fluorescence of Fluorescein by Safranine T in aqueous solution and in normal micellar medium has been related to the non-radiative energy transfer processes. The value of overlap integral and critical energy transfer distance is higher in CTAB micellar medium compared to that in the aqueous solution. The variation of quantum yield and efficiency of energy transfer between two dyes in micellar medium and aqueous solution has been compared. Effect of viscosity on the fluorescence resonance energy transfer (FRET) between the dye pairs has been determined from fluorescence anisotropy study.

Visible light emission under UV and IR excitation of rare earth doped ZrO2 nanophosphor

Abstract Strong visible emission under UV (320 nm) and IR (967 nm) excitation on ZrO 2 :Sm 3+ and ZrO 2 :Er 3+ nanophosphors were obtained and the concentration effect on the luminescence and crystalline structure is reported. Experimental results shows that phase composition depend on the ion concentration. The visible emission obtained under UV excitation is produced by the transitions 4 G 5/2 → 6 H 5/2,7/2,9/2 of Sm 3+ through a non-radiative energy transfer process from the host to the active ion. Energy transfer and quenching effect due to ion concentration was confirmed by measuring the fluorescence decay time. Green (545 nm) and red (680 nm) emissions bands were observed under IR excitation troughs an upconversion process. It was proved that visible emission for both nanophosphor could be tuned by controlling the ion concentration. The nature of this behavior is discussed taking into account the phase composition for ZrO 2 :Sm 3+ and two photon absorption and cross-relaxation process was considered for ZrO 2 :Er 3+ nanophosphor.

Optical properties of single doped Cr3+ and co-doped Cr3+–Nd3+ aluminum tantalum tellurite glasses

The optical properties for single doped Cr3+ and co-doped Cr3+–Nd3+ aluminum tantalum tellurite glasses have been studied as a function of temperature. For the single doped glass, the existence of two bands in the emission spectra at low temperature indicates the presence of two different sites for the Cr3+ ions, labelled as usual as low- and high-field sites. The broad band centred in the Near Infrared region, corresponds to low-field sites transition 4T2→4A2, and the narrow band centred at approximately 715nm to the high-field sites transition 2E→4A2. The emission intensity for both high- and low-field sites shows a strong decrease with increasing temperature, with the emission for the former sites vanishing at RT. In both cases the quenching observed with the increase of temperature can be ascribed to the presence of non-radiative relaxation mechanisms. Experimental observations for the co-doped glass show that both radiative and non-radiative energy transfer processes from Cr3+ to Nd3+ are present.

Synthesis and spectroscopic characterization of CaF2:Er3+ single crystal for highly efficient 1.53 μm amplification

A CaF2:Er3+ single crystal was grown by the Tammann–Stober method. The potential of this material as a laser crystal for 1530 nm emission was established by quantitative analysis of the optical absorption and emission spectra. Assuming the tetragonal symmetry of the Er3+ sites, the Bkq crystal field parameters, Racah parameters, spin–orbit interaction parameters, and configuration interaction parameters were derived by fitting the experimental absorption band positions with the model energy Hamiltonian. Judd–Ofelt parametrization was done to compute the radiative decay time and fluorescence branching ratio of various meta stable transitions. Using the measured fluorescence decay time and computed radiative decay time, 100% quantum efficiency is obtained for the 1530 nm band, which is reasonable due to the low multiphonon relaxation, and absence of nonradiative energy transfer processes at the 0.01 at.% Er3+ concentration. The narrow bandwidth (13 nm) and high stimulated emission cross section (3.2×10−20 cm2) support the suitability of CaF2:Er3+ for use in high gain optical amplifiers.

Luminescence and visible upconversion in nanocrystalline ZrO2:Er3+

The structural and luminescence properties of erbium doped zirconium oxide prepared by the sol-gel processes were analyzed. The annealed powders presented a concentration dependent crystallite sizes and crystalline phase, ranging from 28 to 46 nm and from 40 to 96% for the monoclinic phase, respectively. Green (545 nm) and red (680 nm) emissions bands were observed with 489 and 962 nm excitation. Experimental results showed that the emission bands can be tuned by controlling the Er3+ concentration and that the red band is almost quenched with 489 nm whereas it is enhanced with 962 nm excitation. The nature of this behavior is discussed taking into account the nonradiative energy transfer and cross-relaxation process.

Energy transfer in clustered sites of Er^3+ ions in LiNbO_3 crystals

We investigated energy-transfer processes associated with clustered sites of Er3+ ions in LiNbO3 crystals leading to upconverted blue-green fluorescence and cross relaxation with the analyses of fluorescence transients measured by site-selective excitations. We found two clustered sites with distinct lifetimes of 3 and 16 μs at room temperature for the green fluorescing levels (4S3/2), which were much shorter than the lifetimes of isolated sites (27 μs) that are due to nonradiative energy-transfer processes. The green upconverted fluorescence originates from the energy transfer of one clustered site in the 4I7/2 levels, and/or of the other clustered site in the 4I11/2 levels. Our analyses verified that the fluorescence efficiencies of Er3+ ions in the clustered sites are significantly decreased because of their interionic nonradiative energy transfers. Therefore, the formation of clustered sites in Er3+-doped LiNbO3 crystals gives rise to deleterious effects on laser and amplifier applications.

Energy transfer in Sm3+:Eu3+ system in zinc sodium phosphate glasses

The mechanism of nonradiative energy transfer process in zinc sodium phosphate glass system co-doped with samarium and europium ion has been examined under cw laser excitation. Donor–acceptor distance and quantum efficiency of transfer have been evaluated using the relevant theoretical expressions. Transfer probabilities have been determined using the overlap integral and relative fluorescence methods. The Forster–Dexter theoretical predictions are found to be in excellent agreement with experimental results. The nonresonant energy transfer assisted by phonons is the dominant transfer mechanism in the concentration range taken. Excitation spectra and the decay profile of the samarium ion also support the energy transfer from samarium to europium.