Efficiency Of Energy Transfer Process Research Articles

A mini-review on recent progress of new sensitizers for luminescence of lanthanide doped nanomaterials

Trivalent lanthanide (Ln3+) doped luminescent nanocrystals are promising for applications ranging from biosensor, lasing, super-resolution nanoscopy, information security and so on. Although the utility prospect is of great attractions, the light absorption of these lanthanide doped nanocrystals is inherently weak due to the electric dipole-forbidden 4f → 4f transitions. Even worse, the quantum yields of upconverison nanocrystals are very low, which will unavoidably hinder their further applications. In a typical lanthanide luminescent nanosystem, both sensitizers as light absorption centers and activators as light emitting centers are necessary and important for desired luminescence properties. Among various sensitization systems, only Yb3+ and Nd3+ are considered as the most efficient sensitizers. Thus, the corresponding excitation wavelengths are strictly limited around 980 and 808 nm. To enrich excitation wavelengths and boost luminescence intensity, exploring more sensitization units that possess larger absorption cross section, higher efficiency of energy transfer process and independent excitation is imperative and beneficial for the demands of different applications, such as broadened absorption in near infrared (NIR) region for higher conversion efficiency of solar cells, prolonged excitation wavelength to second near infrared windows region (NIR II, 1,000–1,700 nm) for in vivo fluorescence imaging with deeper tissue depth and higher spatial resolution, more orthogonal excitations and emissions to improve optical multiplexing, and so on. Therefore, in the review, we primarily conclude several major energy transfer mechanisms from sensitizers to activators. Then we present three kinds of sensitizers, including lanthanide ions, organic dyes and quantum dots (QDs), and introduce the newly designed sensitization system that allows us to exploit superior excitation wavelength and amplify luminescence intensity. Finally, several future challenges and opportunities for the sensitizing strategies are discussed in hope of directing and broadening the applications of lanthanide nanosystem.

Spectroscopic analysis of the riboflavin—serum albumins interaction on silver nanoparticles

Spectrophotometric behavior of riboflavin (RF) adsorbed on silver nanoparticles as well as its interaction with two serum albumins, BSA and HSA, respectively, has been evidenced. The time evolution of the plasmonic features of the complexes formed by RF/BSA/HSA and Ag(0) nanoparticles having an average diameter of 10.0 ± 2.0 nm have been investigated by UV–Vis absorption spectroscopy. Using steady-state and time-resolved fluorescence spectroscopy, the structure, stability, and dynamics of the serum albumins have been studied. The efficiency of energy transfer process between RF and serum albumins on silver nanoparticles has been estimated. A reaction mechanism of RF with silver nanoparticles is also proposed and the results are discussed with relevance to the involvement of the silver nanoparticles to the redox process of RF and to the RF–serum albumins interaction into a silver nanoparticles complex.

Peculiarities of the structure of lanthanide chloride complexes with heterocyclic diimines and the efficiency of energy transfer processes

Two families of lanthanide chlorides LnCl3L2(H2O)n and LnCl3L(H2O)m where L is 1,10-phenanthroline or 2,2′-bipyridine were synthesized. Their luminescence properties were investigated in the solid state and 1-dodecyl-3-methylimidazolium chloride solution. The structural peculiarities of lanthanide chlorides were elucidated by joint analysis of the X-ray, vibrational and luminescence data including the lifetime measurements. As a result the analysis of efficiency of energy transfer processes was performed and the correlation between the structure and the luminescence intensity was demonstrated in the systems studied.

Synthesis and photophysical studies of covalently linked porphyrin-21-thiaporphyrin dyads

The synthesis and photophysical properties of four covalently linked unsymmetrical porphyrin dyads containing two different porphyrin cores such as N 4 and N 3S are reported. The covalently linked dyads were prepared by the coupling of appropriate porphyrin having ethynylphenyl functional group at meso-position with porphyrin having iodophenyl or bromo functional group at meso-position under mild palladium coupling conditions. The photophysical study indicated an intramolecular singlet–singlet energy transfer from N 4/ZnN 4 porphyrin sub-unit to N 3S porphyrin sub-unit in all four dyads with an efficiency of energy transfer process was typically ⩾97%. To probe the role of linker in through bond electronic communication between the two porphyrin sub-units in dyads, the linker was varied from diphenylethyne to phenylethyne and the study revealed that the energy transfer rates and efficiencies were much higher for phenylethyne-bridged porphyrin dyads compared with diphenylethyne-bridged porphyrin dyads.

Energy transfer between Eu 3+ ions in sol–gel derived silica glasses

Time-resolved fluorescence line narrowing technique has been used to analyse the evolution of the 5D 0→ 7F 0 emission of Eu 3+ ions in sol–gel derived silica glasses. These samples were doped with 2.5 mol% of Eu 3+ and heat treated at different temperatures. Background fluorescence, coming from Eu 3+ ions excited by energy transfer processes, was observed in these experiments. Using a previously proposed equation model, a study of the multipole character of the interaction between Eu 3+ ions was performed. The annealing process carried out in the samples causes important changes in the efficiency of energy transfer process and in its multipole character, varying from S=6 (in a sample treated at 400°C) to S=10 (in a sample treated at 600°C), indicating that the environment of Eu 3+ ions has been modified.