Dipole-dipole Process Research Articles

Research on energy transfer mechanism and ∼1 μm broadband luminescence properties in Nd3+/Yb3+ co-doped Bi2O3–B2O3–BaF2 glass

Through the traditional molten method, we designed and fabricated Nd3+/Yb3+ co-doped bismuth borate glasses, and completed the study of the luminescence mechanism of rare earth ions in 1 μm band as well as the doping concentration on the luminescence performance of the glass. Firstly, the thermodynamic properties of the glass sample was evaluated by utilizing DSC curve. Subsequently, the spectral properties of BBFNY-2 glass sample was revealed by analyzing the absorption spectra, fluorescence spectra, fluorescence lifetimes and Judd-Ofelt (J-O) theory. Finally, the energy transfer mechanism between rare earth ions Nd3+→Yb3+ was analyzed in detail. The increase of fluorescence intensity at 1008 nm in the glass was calculated corresponding to the broadening of Δλeff from 103 nm to 107 nm, and the obtainable OCT (optical coherence tomography) axial resolution increased from 4.4 μm to 4.1 μm. In this work, the small absorption cross section of Yb3+ at 980 nm in 55Bi2O3–35B2O3–10BaF2 (mol%) glass is effectively solved by Nd3+→Yb3+ energy transfer. Meanwhile, the relevant parameters of the prepared BBFNY-2 glass sample were calculated, and the results suggested that the fabricated glass samples have large microscopic parameters, high transfer efficiency and long fluorescence lifetime. In the results, it was revealed that the via non-radiative electric dipole-dipole process was responsible for the energy transfer and was proportional to the concentration of the Nd3+ donor ions. With all the results, the prepared BBFNY-2 glass sample is a high-potential candidate material for ∼1 μm laser applications.

Efficient Nd3+→Yb3+ energy transfer processes in high phonon energy phosphate glasses for 1.0 μm Yb3+ laser

Efficient Nd3+→Yb3+ resonant and phonon-assisted energy transfer processes have been observed in phosphate glasses and have been studied using steady-state and time-resolved optical spectroscopies. Results indicate that the energy transfer occurs via nonradiative electric dipole-dipole processes and is enhanced with the concentration of Yb3+ acceptor ions, having an efficiency higher than 75% for the glass doped with 1 mol% of Nd2O3 and 4 mol% of Yb2O3. The luminescence decay curves show a nonexponential character and the energy transfer microscopic parameter calculated with the Inokuti-Hirayama model gives a value of 240 × 10−40 cm6 s−1, being one of the highest reported in the literature for Nd3+-Yb3+ co-doped matrices. From the steady-state experimental absorption and emission cross-sections, a general expression for estimating the microscopic energy transfer parameter is proposed based upon the theoretical methods developed by Miyakawa and Dexter and Tarelho et al. This expression takes into account all the resonant mechanisms involved in an energy transfer processes together with other phonon-assisted nonvanishing overlaps. The value of the Nd3+→Yb3+ energy transfer microscopic parameter has been calculated to be 200 × 10−40 cm6 s−1, which is in good agreement with that obtained from the Inokuti-Hirayama fitting. These results show the importance of the nonresonant phonon-assisted Nd3+→Yb3+ energy transfer processes and the great potential of these glasses as active matrices in the development of multiple-pump-channel Yb3+ lasers.

Enhancement of Rydberg Atom Interactions Using ac Stark Shifts

The ac Stark effect was used to induce resonant energy transfer between translationally cold 85Rb Rydberg atoms. When a 28.5 GHz dressing field was set at specific field strengths, the two-atom dipole-dipole process 43d5/2+43d5/2-->45p3/2+41f was dramatically enhanced, due to induced degeneracy of the initial and final states. This method for enhancing interactions is complementary to dc electric-field-induced resonant energy transfer, but has more flexibility due to the possibility of varying the applied frequency.

A functionalized noncovalent macrocyclic multiporphyrin assembly from a dizinc(II) bis-porphyrin receptor and a free-base dipyridylporphyrin.

The bis-porphyrin system ZnP(2), in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cis DPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP(2)(4'-cis DPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6x10(8) M(-1) was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match between the two interacting units. The macrocycle was crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity of the two components. Photoinduced energy transfer from the singlet excited state of the zinc porphyrin chromophores to the free-base porphyrin occurs with an efficiency of 98 % (k(en)=2x10(10) s(-1) in toluene, ambient temperature) with a mechanism consistent with a dipole-dipole process with a low orientation factor.

Fast 1H NMR relaxation in some ruthenium hydrides

Abstract We report here the synthesis of the new hydride complexes (C5H4CH(CH2CH2)2NMe)- RuH(PPh3)2 (1) and [(C5H4CH(CH2CH2)2NHMe)-RuH(PPh3)2](BF4) (2), the X-ray crystal structures of 1 and 2, and an unprecedented observation of extremely short relaxation times in a monohydride complex as well as in the reaction of CpRuH(PPh3)2 with a variety of acidic proton donors. The relaxation is much faster than expected for a dipole-dipole process involving the two dihydrogen-bonded protons, but no origin for the effect could be suggested.

Direct Kinetic Evidence for Triplet State Energy Transfer from Escherichia coli Alkaline Phosphatase Tryptophan 109 to Bound Terbium

The addition of excess Tb3+ to metal-depleted Escherichia coli alkaline phosphatase results in enhanced luminescence from enzyme-bound terbium, which increases with sample deoxygenation and exhibits a tryptophan-like excitation spectrum. Following pulsed excitation at 280 nm, the time-resolved terbium emission shows a negative prefactor associated with a submillisecond rise time, which is independent of the concentration of dissolved oxygen. The absence of a build-up phase and similarity in lifetime in the decay kinetics of directly excited (488 nm) terbium allows for the assignment of the submillisecond component in the 280 nm excited sample to bound terbium. The results of the steady state and time-resolved experiments suggest that the time evolution of alkaline phosphatase-bound terbium emission is determined by energy transfer (kET approximately 360 and 120 s-1) from the triplet state of tryptophan to terbium followed by terbium decay. This model is based on the observations that 1) the tryptophan phosphorescence lifetime (previously assigned to Trp109) corresponds to the longer component of the terbium emission and 2) the long-lived emission is enhanced, as is the Trp109 phosphorescence, by deoxygenation. An energy transfer mechanism involving the Trp109 triplet state is shown to be inconsistent with a dipole-dipole process and is best understood as a through-space electron exchange over a donor-acceptor distance of 9-10 A.

Excited state relaxation and energy transfer between Tb3+ → Nd3+ and Tb3+ → Ho3+ in POCl3:SnCl4

Excited state relaxation in Tb3+ in POCl3:SnCl4 aprotic solvent has been examined. It is found that at a concentration of 10−1 M Tb3+, the fluorescence exclusively originates from the5D4 level. The appreciable increase in the decay times of Tb3+ in this solvent compared to its values in H2O or D2O, suggests that the decrease in non-radiative relaxations is due to the low energy vibrations characteristic of this solvent. Non-radiative transfer of energy from Tb3+ → Nd3+ and from Tb3+ → Ho3+ in this solvent has been established by examining the lifetime data. Calculated values of energy transfer probabilities (Pda) in the liquid air temperature are analysed to obtain a clue regarding the nature of excitation transfer mechanism. In both the systems, the energy transfer from Tb3+ donors to Nd3+ as well as Ho3+ acceptors, occurs predominantly via a dipole-dipole process. At high temperature the energy transfer is increased.