Absorption Spectrum Of Acceptor Research Articles

Far-infrared spectroscopy of the zinc acceptor in indium phosphide

We report the absorption spectrum of Zn acceptor in InP. Fourier interferometers equipped with Si bolometers were used to collect spectra at sample temperatures down to 1.9 K. Zeeman measurements were made in the Voigt configuration at fields up to 6.5 T with the electric field of the radiation, E , polarised either parallel or perpendicular to the magnetic field, B||〈001〉 . Energies for the G and D lines, corresponding to transitions from the 1 s 3/2 (Γ 8 +) to the 2 p 3/2 (Γ 8 −) and 2 p 5/2 (Γ 8 −) states, respectively, are 241.5±0.2 and 286.0±0.2 cm −1, respectively. Data taken at higher resolution (0.05 cm −1) indicate an intrinsic line width of 0.5 cm −1 full-width at half-maximum for a carrier concentration of 4×10 16 cm −3. At low magnetic field ( B<3 T), the D line rapidly broadens, losing intensity and becoming unresolvable. At the highest fields, four components for E|| B and two for E ⊥ B are resolved for the G line. Comparing data at 1.9, 2.9, 5.4 and 10.4 K reveals thermal depopulation effects. These experimental data permit determination of g-factors for the ground and first excited state of Zn in InP.

Synthesis and Steady-State Photophysical Properties of Dye-Labeled Dendrimers Having Novel Oligothiophene Cores: A Comparative Study

Novel chromophore-labeled dendrimers with penta- and heptathiophene cores and coumarin-2 chromophores at their periphery have been shown to be very efficient light-harvesting systems. Excitation of the peripheral coumarin-2 chromophores results in energy transfer to the oligothiophene cores as a result of the large overlap between the donor emission spectrum and the acceptor absorption spectrum, as well as the large transition dipole moments of the oligothiophenes. Although these core dyes have low fluorescence quantum yields, their emission intensity is significantly enhanced by the ability of the large light-harvesting dendron to funnel absorbed energy to the core. Because of the large Stokes shift of the oligothiophenes, the emission spectrum of the dendrimers was red-shifted by 200 nm from the excitation wavelength. Additionally, it was found that oligothiophene orientationend functionalization vs central functionalizationdid not have a significant effect on energy-transfer efficiency.

Excitation energy transfer between acriflavine and rhodamine 6G as a pH sensor

Excitation energy transfer between acriflavine (donor) to rhodamine 6G (acceptor) molecules in water with varying pH has been studied by using steady state measurements. From absorption and fluorescence spectra of donor and acceptor, overlap integrals for donor fluorescence and donor absorption ( Ω DD) as well as donor fluorescence and acceptor absorption ( Ω DA) have been calculated. The corresponding critical transfer distances for dipole–dipole Forster mechanism of excitation energy transfer between donor–donor ( R 0D) and donor–acceptor ( R 0A), reduced concentration and efficiency of energy transfer have also been calculated. It has been found that the Ω DA change with pH whereas Ω DD remain unchanged, resulting in change in energy transfer from donor to acceptor with pH, but no change in energy migration. The efficiency of excitation energy transfer is maximum for a highly basic solution and it decreases with a decrease in pH. The energy transfer efficiency, reduced concentration, and overlap integrals show a linear dependence on pH. It has been proposed that the system may be used as a wide range (1.4 to 12) pH sensor with an accuracy of 0.01.

Localization and function of ferredoxin:NADP(+) reductase bound to the phycobilisomes of Synechocystis.

Each phycobilisome complex of the cyanobacterium Synechocystis PCC 6803 binds approximately 2.4 copies of ferredoxin:NADP(+) reductase (FNR). A mutant of this strain that carries an N-terminally truncated version of the petH gene, lacking the 9 kDa domain of FNR that is homologous to the phycocyanin-associated linker polypeptide CpcD, assembles phycobilisome complexes that do not contain FNR. Phycobilisome complexes, consisting of the allophycocyanin core and only the core-proximal phycocyanin hexamers from mutant R20, do contain a full complement of FNR. Therefore, the binding site of FNR in the phycobilisomes is not the core-distal binding site that is occupied by CpcD, but in the core-proximal phycocyanin hexamer. Phycobilisome complexes of a mutant expressing a fusion protein of the N-terminal domain of FNR and green fluorescent protein (GFP) contain this fusion protein in tightly bound form. Calculations of the fluorescence resonance energy transfer (FRET) characteristics between GFP and acceptors in the phycobilisome complex indicate that their donor-acceptor distance is between 3 and 7 nm. Fluorescence spectroscopy at 77K and measurements in intact cells of accumulated levels of P700(+) indicate that the presence of FNR in the phycobilisome complexes does not influence the distribution of excitation energy of phycobilisome-absorbed light between photosystem II and photosystem I, and also does not affect the occurrence of 'light-state transitions'.

Investigations on the photophysical properties of 2-methylindole and 2-methylindoline in various environments. Studies on the nature of non-radiative transitions in presence of the electron acceptor 2-nitrofluorene

Electronic absorption, steady state and time-resolved emission, in the domain of nanosecond, spectroscopic methods were employed to compare the spectroscopic and photophysical properties of the electron donors (D) 2-methylindole (2MI) and 2-methylindoline (2MIN) in the presence of the well-known acceptor (A) 2-nitrofluorene (2NF) in fluid solutions at ambient temperature (296 K). Steady-state excitation polarization and emission polarization spectra were also measured. From all the studies presently carried out it was apparent that the two lowest lying electronic excited states 1L b (S 1) and 1L a (S 2), which seem to be very closely spaced in the case of the donor 2MI, become well-separated in the case of the other donor 2MIN. Both the donors were found to undergo large fluorescence quenching in the presence of the acceptor 2NF in solvents of different polarity. The experimental evidence suggest that numerous processes might be responsible for the observed large fluorescence quenching effect of the present donors (2MIN and 2MI) in the presence of the acceptor 2NF. These processes seem to be mainly (1) photoinduced electron transfer, as evidenced from large negative values of driving energy (Δ G 0) obtained from electrochemical measurements, (2) energy transfer of Förster's type from the observed large overlapping of donor emission and acceptor absorption spectra, (3) transient-type static quenching phenomena, etc. Further investigations are now underway to reveal the exact mechanisms of the observed large quenching effect within the present D–A systems.

Energy Transfer Studies with Perylene bis-Diimide Derivatives

Singlet energy transfer between seven derivatives of perylene diimides and cobalt ions are studied. Energy transfer quenching by cobalt ions is observed for all of the perylene diimides. The rate of bimolecular quenching is found to be about, kq ≅ 1010 M−1s−1, only the N-naphthyl substitution lowered the rates to the range of, kq ≅ 109 M−1s−1. The critical transfer distances, Ro (5.8–10.4 A°), calculated from donor emission and acceptor absorption spectra, are attributed to a Forster resonance energy transfer process.

Synthesis and photophysics of diaza‐crown ether‐based bisporphyrins

AbstractThe bisporphyria N,N′‐bis[4″‐(meso‐triphenylporphyrinyl)benzyl]‐4,13‐diaza‐18‐crown‐6 and its mono‐ and dizinc derivatives were synthesized in 66%, 46% and 53% yields, respectively, from 5‐(4′‐bromomethylphenyl)‐10,15,20‐triphenylporphyrin or its zinc derivative and 4,13‐diaza‐18‐crown‐6. The zinc‐containing bisporphyrins form dimers in solution at low temperature or at high concentration. The unsymmetrical bisporphyrin; monozinc N,N′‐bis[4″‐(meso‐triphenylporphyrinyl)benzyl]‐4,13‐diaza‐18‐crown‐6 shows singlet–singlet energy transfer from the zinc porphyrin moiety to the free base moiety in both the monomeric and the dimeric form. The energy transfer rates were determined using time‐resolved fluorescence spectroscopy and were found to be 1·26 × 109 and 2·29 × 109 s−1 for the monomeric and dimeric form, respectively. The difference in energy transfer rates between the two forms can be rationalized by the difference in overlap between the donor fluorescence spectrum and acceptor absorption spectrum, donor–acceptor distance and donor–acceptor orientation.

The optical and electronic properties of semiconducting diamond

In this paper I review the evidence that shows that the optical and electronic properties of semiconducting diamond can be understood in terms of boron acceptors partially compensated by deep donors. In natural semiconducting diamond, in which the total impurity concentration is less than 1 ppm, there is a lot of fine structure in the acceptor absorption spectrum that is not fully understood, and the electrical conductivity is primarily associated with the thermally activated excitation of holes from the acceptor ground state to the valence band. Some of the problems regarding the analysis of Hall effect data in this material are discussed, including the temperature dependences of the scattering mechanisms, of the contribution from the split-off valence band and of the population of excited states. There are no adequate theoretical descriptions of any of these processes, and this leads to some uncertainties in the values of the parameters derived from the temperature dependence of the Hall coefficient. For boron-doped synthetic diamond, and thin film diamond grown by chemical vapour deposition (CVD), the defect concentrations are generally much higher, and much more inhomogeneous, than in natural semiconducting diamond. This results in a substantial broadening of the acceptor absorption spectrum and the electronic properties are greatly modified by increasing contributions from impurity band conduction as the acceptor concentrations are increased, leading to very low mobility values. For both poly crystalline and single crystal homoepitaxial CVD diamond, measurements of the electrical properties can be completely invalidated by the presence of a surface layer of non-diamond carbon.

Semiconducting diamond

Electronic properties of acceptors and donors and the valence band structure of diamond are discussed. Acceptor absorption spectra are considered in detail. Luttinger parameters deduced from the spectra and masses of the valence band gamma 1=4.24, gamma 2=0.82, gamma 3=1.71; mh=0.86 m0, m1=0.14 m0, mso=0.24 m0 are compared with known data. The specific problems of diamond doping are considered: the rigid lattice and small radius of the carbon atom prevent the introduction of dopant atoms except boron (acceptor) and nitrogen (donor). A method of effective doping is proposed for non-equilibrium conditions of laser annealing as is done successfully in silicon and other semiconductors. In diamond this process can be done under high pressure in the range of diamond stability. The dependence of the band structure of diamond on pressure is anomalous and does not follow Paul's empirical law for the family of diamond semiconductors.

Luminescence Properties of Transition-Metal Ions in Double Complex Salts

Abstract The luminescence spectra and radiative lifetimes of a series of d3 and d6 double complex compounds with bipyridine (bip), phenanthroline (phen), ammonia and ethylenediamine (en) ligands in the cations and chloride, cyanide, thiocyanide and oxalate (ox) ligands in the anions have been investigated at temperatures down to 2 K. Although energy transfer between the component ions is predicted from the Förster and Dexter theory to be effective due to the finite overlap of the donor emission and the acceptor absorption spectra, no emission could be detected for most of the double complexes. Only [Ru(bip)3]tr-[Cr(NH3)2(NCS)4]2, [Ru(bip)3][PtCl6] and [Cr(d4-en)3] [Rh(SCN)6] exhibit characteristic luminescence spectra which in part are enhanced compared to their component emissions. For rationalizing the results, radiationless deactivation by various decay channels which compete with the energy transfer mechanism must be considered.

Role of contact complexes in singlet-triplet energy transfer

(T-T) energy transfer from the acceptor to donor. If the properties of the solvent cage lead to the same probability for these two energy transfer processes between donor and acceptor molecules, there should be no accumulation of triplet acceptor molecules in solution. In this case, acceptor molecules act as a catalyst leading to an increased population of triplet donor states. In addition to the above scheme of energy conversion in a contact complex, one can also expect that during the lifetime of the solvent cage only the S-T stage of electronic energy transfer will be completed. In this case the excited complex decays before the reverse T-T energy transfer from the acceptor to donor takes place and therefore there is a high probability that the unreacted triplet acceptor molecules will migrate beyond the boundary of the solvent cage. Therefore, depending on whether or not the triplet acceptor molecules are found in solution, one can make a conclusion about the number of elementary steps responsible for the electronic excitation energy conversion in a contact complex during its lifetime in the solvent cage. Answering the above-mentioned questions is important for understanding the properties of the solvent cage and mechanisms of energy conversion in excited contact complexes. Therefore, we conducted studies on decay channels for contact complexes, in which one of the partners from a pair was in the singlet excited state. In order to simplify the problem as much as possible and reduce it to considering only two processes: the S-T energy transfer from the donor to acceptor and the reverse T-T energy transfer from the acceptor to donor, the excited complex must fulfill a number of conditions. One of them is the lack of overlap between the fluorescence spectrum of donor and the absorption spectrum of acceptor. The fulfillment of this condition allows us to neglect the sing!et-singlet (from SoD to SoA) energy transfer relative to the efficiency of S-T energy transfer between donor and acceptor. Moreover, some experimental data [i] indicate that the donor triplet level TiD of the studied pair should be considerably lower than the acceptor triplet level TiA (AE T > i000 cm-i). The larger the energy difference between TiD and TiA , the higher the probability of appearance of acceptor molecules in the triplet state in solution at the expense of S-T energy transfer relative to the probability of T-T energy transfer from the donor to acceptor.

Changes of Acceptor Absorption Spectra in Zn3P2 Due to Heat Treatments

Changes of Acceptor Absorption Spectra in Zn3P2 Due to Heat Treatments

Photoluminescence and infrared absorption studies of Ge doped with Mg

The photoluminescence spectrum of Ge doped with the double acceptor Mg reveals lines due to both bound excitons and bound multiexciton complexes, which are in some ways similar to those previously reported for Ge:Be and Ge:Zn. As in Ge:Zn, the Ge:Mg bound exciton line was found to be a doublet, showing that the Mg double acceptor in Ge also has a split ground state. Further evidence for this ground state splitting is found from the temperature dependence of the infrared absorption spectrum of the Mg double acceptor.

Gain studies on a uranine-damc dye mixture laser under nitrogen laser pumping

The radiative and Forster type of energy transfer processes in a dye mixture laser of 7-diethylamino-4-methyl coumarin (donor) and fluorescein disodium salt (acceptor) under nitrogen laser pumping were investigated. The Forster transfer rate calculated from the absorption and emission spectra of acceptor and donor is 1.3 × 10 11 liter mole −1 sec −1. The gain of acceptor at 550 nm was measured for acceptor concentrations N A from 10 −3 M to 3 × 10 −3 M for a fixed ratio F = 1 of donor to acceptor concentrations at different pump powers. The results agreed with the rate equation model proposed for the dye mixture laser. The radiative rate constant calculated from these results is 3.1 × 10 10 liter mole −1 sec −1. Numerical simulation of the rate equations showed that the acceptor reaches peak emission with a time lag of 3 ns with respect to the donor peak emission for F = 0.998, N A = 10 −5 M. This time lag decreases with increasing N A and becomes zero for N A = 10 −1 M, F = 0.048.

Energieübertragung zwischen gleich- und ungleichartigen Molekülen in Lösung.

Abstract The p-Terphenyl (donor) and 4-aminobenzophenon (acceptor) system in solvents of different static dielectric constants was studied by the fluorescence quenching due to nonradiative energy transfer. The dependence of I ṽ/n4 (I ṽ is the overlap integral of the fluorescence spectrum of donor and the absorption spectrum of acceptor, n the refractive index of the solvent) on the polarity of the solvents was investigated. From the linear relation between (ηD 0/ηD - 1) (ηD 0/ηD is the relative quantum yield of the donor fluorescence) and I ṽ/n4 the intermoleculare distance R for a given acceptor concentration in different and also mixed solvents were determined.

Electronic Raman scattering and infrared absorption spectra of shallow acceptors in ZnTe

Electronic Raman scattering and infrared absorption have been measured for shallow acceptors As, P, and Li in ZnTe. The spectra are interpreted in terms of electronic transitions between bound hole states, some of them being phonon assisted. The valence-band parameters of ZnTe have been deduced by fitting the calculation of Baldereschi and Lipari to the experimental results. Estimated values are close to those obtained from cyclotron resonance experiments. Broadening of some electronic transition bands has been observed in both Raman and infrared spectra, which can be attributed to the mixing of the two-phonon state and the electronic excitation. TO- and LO-phonon sidebands of the electronic transition from the $1s$ to $2s$ state have been observed for the three acceptors. The energy of the LO phonon associated with this transition has been found to be smaller than that corresponding to the $\ensuremath{\Gamma}$ point. The mechanism of this energy lowering is discussed.

Fluorescent derivatives of nucleotides. Metal ion interactions and pH dependency

The fluorescence parameters of ethenoadenosine derivatives are influenced by metal cations and pH, as summarized here. The pH profile of ethenoadenosine determined by fluorescence intensity gives a normal titration curve and is not affected by ionic strength. In contrast, the pH titration curves of etheno-ATP, etheno ADP, and etheno AMP depend upon ionic strength. At high ionic strength normal curves are obtained, whereas at low ionic strength anomalies are obtained; this suggests that the phosphates can interact with the ring, possibly by hydrogen binding to the ring nitrogens. The room temperature fluorescence of ethenoadenosine occurs from the base form, although excitation of either the acid or base forms can contribute to the emission. This result can be explained if the excited state pK is lower than the ground state pK, and if deprotonation occurs within the time scale of the excited state. At low pH values the fluorescence lifetime of the base form is dependent upon the buffer concentration, indicating that the reverse reaction, protonation, occurs. The affinity constants for the binding of metals to the ethenoadenosine phosphates resemble those for the corresponding adenosine phosphates. Ni(II) and Co(II) are more effective than Mn(II) in quenching the fluorescence of ethenoadenosine phosphates; this result is predicted by Förster's theory for energy transfer based upon the overlap between donor emission spectrum and acceptor absorption spectrum. The diamagnetic ions Mg(II), Ca(II), and Zn(II) do not appear to affect the fluorescence of the ethenoadenosine phosphates directly, but rather to affect the conformation of the molecule, thereby affecting the quantum yield.

Energy transfer and laser action in binary solutions excited by short and ultrashort pulses

An analysis is made of the relative contributions of radiative and nonradiative dipole-dipole energy transfer from donors to acceptors during laser action in binary solutions of polyatomic molecules excited by nanosecond and picosecond pump pulses. A study is reported of systems with overlapping donor luminescence and acceptor absorption spectra, where both donor and acceptor are capable of stimulated emission. Spectral-polarization methods are used to show that the radiative energy transfer mechanism predominates in the investigated systems.

Optical spectra and exciton coherence

The overlap of donor emission and acceptor absorption spectra has long been known as a determining factor in the rate of excitation transfer. Memory functions capable of providing short time information can be obtained in an equally direct way from spectra. We present several examples derived from both real and model systems to illustrate the effect of spectral linewidth and splitting on the coherence of excitation undergoing transfer.

Quantum efficiency of diffusion limited energy transfer in La1−x−yCexTbyPO4

In this paper, we present a detailed study of the concentration and temperature dependences of the quantum efficiency of energy transfer between Ce3+ and Tb3+ in La1−x−yCexTbyPO4. The determination of the transfer quantum efficiency in terms of the donor luminescence lifetimes is critically compared with that in terms of the donor luminescence intensities. It is shown that for the latter determination it is important to take into account any overlap in the donor and acceptor absorption spectra in the excitation wavelength region. From the exponential behavior, the concentration, and thermal dependences of the donor luminescence decay, it is shown that the diffusion of donor excitation plays an important role in the energy transfer process.