Nonradiative Resonance Energy Transfer Research Articles

Solid State Synthesis and Characterization of Yb3+/Ho3+ Doped GdPO4 Nanophosphor for Luminescence Properties

A reliable solid-state method for synthesizing GdPO4:Yb3+/Ho3+ nanophosphor is presented, exhibiting both up and down conversion luminescent properties. The peaks were observed at 460, 550, 640, and 750 nm after excitation at 300 nm, which is followed by nonradiative resonance energy transfer (ET) with the P-O charge transfer band of Ho3+ ions. A significant up-conversion nanophosphors by enhancing Ho3+ ion emissions is accomplished. The Ho3+ ion peaks at 542 and 635 nm were identified using a strong 980 nm laser source, leading to well-crystalline nanoparticles. The present results demonstrated an enormous potential of GdPO4:Yb3+/Ho3+ for high-quality, widespread luminescence. Due to their significant quantum yield when excited at a wavelength of 300 nm, these materials exhibit a diverse array of potential applications and hold considerable potential for advancement across several industries.

Role of energy transfer in a nanoinitiator complex for upconversion-driven polymerization

Upconversion nanoparticle (UCNP)-driven polymerization attracts great attention due to the ability of near-infrared light to penetrate deeper into biological media and synthetic materials than ultraviolet or visible light. Despite significant progress, the limitation of near-infrared light-triggered polymerization is associated with a key element of the photocurable composition, a UCNP/photoinitiator complex or a nanoinitiator. To determine the impact of resonance energy transfer from UCNPs to photoinitiator (PI) and its effect on polymerization, we developed two different photocurable compositions consisting of the polyethylene glycol diacrylate (PEG-DA), ultraviolet- and blue-emitting NaYF4: Yb3+, Tm3+ UCNPs with hydrophobic surface combined with water-soluble or insoluble PI. We found that transfer energy in these nanoinitiators proceeds differently: in UCNP/water-soluble PI (lithium phenyl-2,4,6-trimethylbenzoylphosphinate or LAP), it occurs through the photon-mediated transfer while in UCNP/water-insoluble PI (2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone or Irgacure 369), it takes place via the non-radiative resonant energy transfer. The impact of these processes in homolytic decomposition of initiator is extremely important in terms of the precisely controlled fabrication of polymer structures. PEG-DA facilitates the affinity between hydrophilic and hydrophobic components of the photocurable composition, which provides UCNP-driven cross-linking of biopolymers such as methacrylated hyaluronic acid and gelatin. 3D structures were prototyped to demonstrate the one-step rapid procedure of nanoinitiator preparation and emphasize the control of the energy transfer in UCNP/PI complexes for further development of UCNP-driven polymerization.

Tuning green-to-red ratio of Ho3+ Activated YPO4 dual-mode luminescence through Yb3+ sensitized nano phosphors

INTRODUCTION: Yb3+/Ho3+co-doped YPO4 nano phosphors were synthesized by polyol route, which has both up-conversion (UC) and down-conversion (DC) characteristics and excellent luminescent properties. DC peaks were seen at ~460, ~550, and ~650 nm. METHOD: Switching at ~750 with 300 nm excitation, a very faint P-O charge-transfer (CT) band of the Ho3+ ion and a minute non-radiative resonant energy transfer were observed. We found that YPO4: Yb3+/Ho3+ is an up-converting (UC ) nano phosphor capable of large-scale generation and enhancement of luminescence with green and red emissions.RESULT: Under strong laser irradiation at 980 nm, the up-conversion emission spectrum shows obvious peaks expected for Ho3+ ions at ~550 and ~650 nm. This process produces high-quality nanocrystalline materials with sizes in the range of tens of nm. Considering the results obtained under excitation at 300nm, YPO4:Yb3+/Ho3+ yielded high quantum yield values CONCLUSION: This finding can be used to manufacture high-efficiency phosphors and demonstrates that the nano-phosphor materials covered by this method have a wide range of applications.

Polariton-assisted resonance energy transfer beyond resonant dipole-dipole interaction: A transition-current-density approach

Using electric dipoles to describe light-matter interactions between two entities is a conventional approximation in physics, chemistry, and material sciences. However, the lack of material structures makes the approximation inadequate when the size of an entity is comparable to the spatial extent of electromagnetic fields or the distance between two entities. In this study, we develop a unified theory of radiative and non-radiative resonance energy transfer based on transition current density in a theoretical framework of macroscopic quantum electrodynamics. The proposed theory allows us to describe polariton-assisted resonance energy transfer between two entities with arbitrary material structures in spatially dependent vacuum electric fields. To demonstrate the generality of the proposed theory, we rigorously prove that our theory can cover the main results of the transition density cube method and the plasmon-coupled resonance energy transfer. We believe that this study opens a promising direction for exploring light-matter interactions beyond the scope of electric dipoles and provides new insights into material physics.

High-Performance X-Ray Imaging using Lanthanide Metal-Organic Frameworks.

Scintillating materials that convert ionizing radiation into low-energy photons hold great potential for radiation detection, nondestructive inspection, medical radiography, and space exploration. However, organic scintillators are characterized by low radioluminescence, while bulky inorganic scintillators are not suitable for the development of flexible detectors. Here, high-resolution X-ray imaging using solution-processable lanthanide-based metal-organic frameworks as microscale scintillators is demonstrated. Mechanistic studies suggest that lanthanide ions absorb X-rays to generate high-density molecular triplet excitons, and excited linkers subsequently sensitize lanthanide ions via nonradiative resonance energy transfer. Furthermore, the crystalline nature offers a delocalized electronic feature rather than isolated subunits, which enables direct trapping of charge carriers by lanthanide emitters. By controlling the concentration ratio between Tb3+ and Eu3+ ions, efficient and color-tunable radioluminescence of lanthanide ions can be achieved. When coupled with elastic, transparent polymer matrices, these metal-organic framework-based microscintillators allow the fabrication of flexible X-ray detectors. Such detectors feature a detection limit of 23 nGy s-1 , which is 240 times lower than the typical radiation dose for medical diagnosis. X-ray imaging with resolution higher than 16.6 line pairs per millimeter is further demonstrated. These findings provide insight into the future design of hybrid scintillators for optoelectronics and X-ray sensing and imaging.

Interaction of Ibuprofen with Partially Unfolded Bovine Serum Albumin in the Presence of Ionic Micelles and Oligosaccharides at Different λex and pH: A Spectroscopic Analysis.

The interaction between the plasma protein bovine serum albumin (BSA) and the drug ibuprofen (IBU) has been investigated at three different pH values (7.4, 6.5, and 8.0) in the presence of oligosaccharides and surfactants. The interaction analysis of BSA with oligosaccharides and surfactants has also been studied in the absence of the drug ibuprofen. The results obtained give convenient and efficient access to understand the mechanism of binding of ibuprofen to BSA, and the major forces involved are found to be hydrophobic forces, hydrogen bonding and ionic interactions. In addition to that, the formation of inclusion complexes of ibuprofen with oligosaccharides (β-CD and 2-HP-β-CD) has been observed, which has depicted that due to the hydrophobic nature of ibuprofen, it becomes more soluble in the presence of oligosaccharides, but due to the larger size of the inclusion complexes, these could not be able to access the hydrophobic pocket of BSA where tryptophan-212 (Trp-212) resides. The binding interaction between BSA and ibuprofen is observed in the presence of surfactants (SDS and CTAB), which partially unfold the protein. Non-radiative fluorescence resonance energy transfer (FRET) from Trp and Tyr residues of BSA in the presence of an anionic surfactant SDS to ibuprofen has depicted that there is a possibility of drug binding even in the partially unfolded state of BSA protein. Furthermore, the distance between the protein and the drug has been calculated from the FRET efficiency, which gives a comprehensive overview of ibuprofen binding to BSA even in its partially denatured state. The hydrophobic drug binding to the partially unfolded serum albumin protein (BSA) supports the "necklace and bead structures" model and opens up a new direction of drug loading and delivery system, which will have critical therapeutic applications in the efficient delivery of pharmacologically prominent drugs.

Study of FRET between Zn-Cu-In-S/ZnS core/shell quantum dots-Cresyl violet dye system

This study reports the fluorescence resonance energy transfer between Zn-Cu-In-S/ZnS core–shell quantum dots and Cresyl Violet dye. The quenching of Zn-Cu-In-S/ZnS core–shell QD (donor) emission and lifetime and simultaneous enhancement in Cresyl Violet (acceptor) emission validates and confirms the non-radiative resonance energy transfer from Zn-Cu-In-S/ZnS QDs to Cresyl violet. The values of spectral overlap, Förster distance, the distance between donor and acceptor pair and FRET efficiency were determined using the steady state as well as time-resolved fluorescence spectroscopic techniques. This study demonstrates that this systemexhibits efficient FRET and can act as a very sensitive chemical sensor. Since Zn-Cu-In-S/ZnS QDs are nontoxic compared to popular cadmium-based quantum dots, the application of FRET in biological systems will be advantageous. It can find vast applications in photonics and biomedical applications.

Luminescence Properties of Yb3+/Ho3+ doped GdPO4 Nanocomposites Prepared by Hydrothermal Method using PEG(6000)

By using hydrothermal synthesis, a novel Yb3+/Ho3+ co-doped GdPO4 nanophosphors were prepared which shows both upconversion (UC) and downconversion (DC) with excellent luminescence properties. DC peaks were observed at ~460, ~550, ~650 and ~750 nm. By excitation at 300 nm, a very faint P-O charge transfer (CT) band of Ho3+ ions, as well as a tiny non-radiative resonance energy transfer was observed. It is discovered that GdPO4: Yb3+/Ho3+, an upconversion (UC) nanophosphor, enables the production and enhancement of luminescence on a vast scale. On strong 980 nm laser illumination, the upconversion emission spectra show a conspicuous expectant peak of the Ho3+ ion at ~550 and ~650 nm. This process yields high-quality nanocrystalline materials with sizes between a few to tens of nm range. Considering the results of the study at 300 nm excitation, GdPO4: Yb3+/Ho3+ produced a high quantum yield value. The findings are useful for creating efficient phosphors and it proves applications of nanophosphor materials covered by this method are numerous.

Exploring the HSA/DNA/lung cancer cells binding behavior of p-Synephrine, a naturally occurring phenyl ethanol amine with anti-adipogenic activity: multi spectroscopic, molecular dynamic and cellular approaches

As a phenolic amine, p-Synephrine (SN) is known to exhibit lipolytic properties as well as enhancing energy expenditure, which can be an excellent alternative to ephedra as a dietary supplement. This study aimed to explore the subtle yet profound complex qualities and aspects of the interaction between SN, human serum albumin (HSA), and calf thymus DNA (ctDNA). To achieve a full comprehension on these fine-point distinctions, a nuanced and detail-oriented approach was implemented through a combination of different biophysical methods and molecular dynamics simulation techniques. The fluorescence spectroscopy revealed the binding of SN to HSA that led to the inducement of conformational changes. The quenching constants (KSV) of SN-HSA complex at 298, 303, and 308 K and were evaluated to be 2.95 × 104, 2.21 × 104 and 0.85 × 104 M−1, respectively. The thermodynamic parameters indicated the spontaneous formation of SN-HSA complex along with its regulation through H-bonding and van der Waals forces. The distance between SN and Trp residue of HSA was estimated at 3.91 nm by the Forster’s theory of non-radiative resonance energy transfer. According to CD spectroscopy, the binding of SN to HSA results in stabilization and promotes its functionality. Various spectroscopy methods and viscosity measurements proved the propensity of SN for binding to the grooves of ctDNA. Thermodynamic parameters indicate that the SN binds to DNA via a spontaneous and entropy-driven process that is mainly regulated by hydrophobic interactions. In conformity to the molecular modeling of HSA-SN complex, SN can be located in the active site of HSA and make a firm interaction, while the outcomes of ctDNA-SN interaction also indicated its tendency towards binding in DNA groove. In comparison to normal cells, SN caused a more pronounced reduction in lung cancer cell viability by increasing the expression of Bax and p53 at the mRNA and protein levels. Moreover, the incubation of H460 cells with the IC50 concentration of SN induced a notable decease in mRNA levels of PI3K, AKT, and mTOR, as well as protein levels of PI3Kγ-P110, P-AKT, and P-m TOR. These data indicate the potential of SN in binding with HSA, which reduces the proliferation of lung cancer cells mediated by apoptosis through the down regulation of PI3K/AKT/m TOR signaling pathway.

Graphene Quantum Dot-Based Optical Sensing Platform for Aflatoxin B1 Detection via the Resonance Energy Transfer Phenomenon.

An optical sensing platform for the detection of an important mycotoxin, aflatoxin B1 (AFB1), in the absence of a bioactive environment is explored. In this work, a fluorescence-based sensing technique was designed by combining graphene quantum dots (GQDs) and AFB1 via fluorescence quenching, where AFB1 acts as the quencher of GQD fluorescence. GQDs were synthesized through a single-step hydrothermal reaction from the leaves of "curry tree" (Murraya Koenigii) at 200 °C. The fluorescent GQDs were quenched by AFB1 (quencher), which itself is detecting the analyte. Hence, this study reports the direct sensing of the mycotoxin AFB1 without the involvement of inhibitors or biological entities. The possible mode of quenching is the nonradiative resonance energy transfer between the GQDs and the AFB1 molecules. This innovative sensor could detect AFB1 in the range from 5 to 800 ng mL-1 with a detection limit of 0.158 ng mL-1. The interferent study was also carried out in the presence of different mycotoxins and carbohydrates (d-fructose, cellulose, and starch), which demonstrated the high selectivity and robustness of the sensor in the complex sample matrix. The recovery percentage of the spiked samples was also calculated to be up to 106.8%. Thus, this study reports the first GQD based optical sensor for AFB1.

Luminescence and energy transfer processes in LuNbO4:Bi, Eu

Microcrystalline powders of LuNbO4:Bi3+, Eu3+ with the same nominal Bi3+ concentration (2 at.%) and different nominal Eu3+ concentrations (varying from 0 to 8 at.%) are synthesized and analyzed by the X-ray diffraction method. Photoluminescence characteristics of the co-doped LuNbO4:Bi, Eu powders are investigated by the steady-state and time-resolved luminescence spectroscopy methods in a wide temperature range (4.2–500 K) and compared with those of the undoped and bismuth-doped LuNbO4. It is found that owing to the overlap of the intrinsic and Bi3+-related emission bands with the absorption bands of Eu3+, an effective non-radiative (resonance) energy transfer from both the host and the Bi3+-related exciton-like states to Eu3+ ions, resulting in the appearance of the luminescence in the 1.6–3.8 eV energy range, takes place in LuNbO4:Bi, Eu. The exchange interaction is found to be responsible for the energy transfer process. The possible application of LuNbO4:Bi, Eu in white light-emitting diodes is discussed.

Brilliant Nonlinear Optical Response of Ho3+ and Yb3+ Activated YVO4 Nanophosphor and Its Conjugation with Fe3O4 for Smart Anticounterfeit and Hyperthermia Applications.

YVO4:Ho3+/Yb3+ nanophosphors prepared by an effective polyol-mediated route show dual-mode behavior in photoluminescence. Upon 980 nm excitation, the upconversion red emission spectrum exhibits a bright red peak at ∼650 nm, characteristic of the electronic transition of the Ho3+ ion via involvement of two-photon absorption, which has been confirmed by the power-dependent luminescence study. Moreover, at 300 nm excitation, downconversion emission peaks are observed at 550, 650, and ∼755 nm. The nonradiative resonant energy transfer occurs from the V–O charge transfer band to Ho3+ ions, resulting in an improved emission of Ho3+ ions. Moreover, polyethylene glycol-coated nanoparticles make it suitable for water dispersibility; and these particles are conjugated with Fe3O4 nanoparticles to form magnetic–luminescent hybrid nanoparticles. Highly water-dispersible magnetic–luminescent hybrid material attained the hyperthermia temperature (∼42 °C) under an applied AC magnetic field. The specific absorption rate value is found to be high (138 W/g), which is more than that of pure superparamagnetic Fe3O4 nanoparticles. At 300 nm excitation, the high quantum yield value of ∼27% is obtained from YVO4:Ho3+/Yb3+, which suggests that it is a good phosphor material. By employing the neutron activation analysis technique, it is shown that nanophosphor particles can absorb Au3+ up to the ppm level. Interestingly, such nanophosphor also shows the potentiality for anticounterfeiting applications.

Influence of plasmonic resonant wavelength on energy transfer from an InGaN quantum well to quantum dots

We demonstrated the enhanced nonradiative resonant energy transfer (NRET) process by localized surface plasmon (LSP) in the hybrid InGaN quantum well (QW) and CdSe/ZnS quantum dot (QD) structures. The LSP resonant wavelengths could be adjusted by silver (Ag) nanoparticle (NP) arrays annealed from different thicknesses of Ag films. The LSP resonant wavelengths that are close to the peak QD emission helped to enhance the NRET between the QW and QDs. Compared to the original NRET in the absence of Ag NPs, the LSP-enhanced NRET rate was improved by 6.9 times at the resonant wavelength of 600 nm. The calculated efficiency of the LSP-enhanced NRET was 73.1%, which was almost twice that of the original efficiency. Although Ag NPs exhibited a quenching effect, the LSP-enhanced NRET at the resonant wavelength of 465 nm enhanced QD luminescence, which demonstrated their potential use in energy conversion devices.

Three-Dimensional High Spatial Localization of Efficient Resonant Energy Transfer from Laser-Assisted Precipitated Silver Clusters to Trivalent Europium Ions

We report on the 3D precipitation, using a direct laser writing approach, of highly fluorescent silver clusters in a Eu3+-doped silver-containing zinc phosphate glass. Micro-spectroscopy of fluorescence emission shows the ability to continuously adjust the local tri-chromatic coordinates in the CIE (Commission Internationale de l’Éclairage) chromaticity diagram between red and white colors, thanks to the laser-deposited dose and resulting tunable combination of emissions from Eu3+ and silver clusters. Moreover, continuous-wave and time-resolved FAST-FLIM spectroscopies showed a significant enhancement of the fluorescence emission of Eu3+ ions while being co-located with UV-excited laser-inscribed silver clusters. These results demonstrate the ability to perform efficient resonant non-radiative energy transfer from excited silver clusters to Eu3+, allowing such energy transfer to be highly localized on demand thanks to laser inscription. Such results open the route to 3D printing of the rare earth ions emission in glass.

Temperature Driven Plasmon-Exciton Coupling in Thermoresponsive Dextran-Graft-PNIPAM/Au Nanoparticle/CdTe Quantum Dots Hybrid Nanosystem

The temperature-driven plasmon-exciton coupling in thermoresponsive dextran-graft-PNIPAM/Au nanoparticle/CdTe quantum dot (D-g-PNIPAM/Au NPs/CdTe QDs) hybrid nanosystem was studied. A significant (0.84 eV) splitting of the absorption peak was observed in the absorption spectrum of the nanosystem, which reflects the fact of formation of plexcitons, occurring due to strong plasmon-exciton coupling. An increasing with time plasmonic enhancement of the photoluminescence of CdTe QDs was revealed, as a result of the penetration of quantum dots into the volume of the D-g-PNIPAM/Au NP hybrid nanosystem and bonding to it. The heating–cooling cycle of the aqueous solution of the studied nanosystem leads to a reversible quenching-recovery alteration of the QD photoluminescence. The quenching was rationalized as a result of an increased probability of nonradiative resonance energy transfer (RET) from CdTe QDs to Au NPs, which occurs due to shortening of the NP-QD distance, caused by shrinking of the macromolecule due to cooling-induced lower critical solution temperature phase transition. Increasing the NP-QD distance in the heating stage recovers the QD PL intensity. The observed effect opens up opportunities for the controlled reversible temperature-driven tuning of the photoluminescence intensity of D-g-PNIPAM/Au NP/CdTe QD nanosystem, which is highly important for its potential use in photonics and biomedical applications.

Effect of Eu3+ doping on luminescence properties of a KAlSiO4:Sm3+ phosphor

This study presents the photoluminescence characteristic analysis of a series of red phosphors of KAlSiO4:1.5 mol%Sm3+,x mol%Eu3+ (x = 2, 3, 4, 5, 6, 7) prepared via high-temperature solid-phase reaction. The results show that the X-ray diffraction (XRD) refinement results are reliable. The unit cell parameters and volume gradually decrease as the Eu3+ concentration increases, resulting in a grain size reduction of 10.22%. When x = 6, the emission peaks of Sm3+ at 564, 601, and 651 nm disappear completely, and the corresponding full width at half maximum becomes 0. At 610 nm, the emission peak intensity of Eu3+ is increased by a factor of 4.8. The resonant non-radiative energy transfer effect is greater than the co-excitation effect. A maximum energy transfer efficiency of 97.8% is achieved. The integral area at 610 nm is as high as 85%. The color purity of the phosphor is as high as 92.97%, and the internal quantum yield gradually changes from 32% to 51%. Ultimately, these results confirm that the silicate phosphor is suitable for the red component in the three primary color phosphors of white light-emitting diodes.

Temperature features of non-radiative energy transfer in hybrid associates of CdS/TGA quantum dots with methylene blue molecules

The paper presents the study results of non-radiative resonance energy transfer of electronic excitation from colloidal CdS quantum dots passivated with thioglycolic acid (CdS/TGA QDs) with an average size of 2.9 nm to methylene blue (MB+) molecules in temperature ranging from 300 to 80 K. In an aqueous MB+ and colloidal CdS/TGA QDs mixture, the increase in (MB+)2 dimers fraction and shift of the absorption band peaks of monomers (MB+) from 662 to 676 nm and dimers (MB+)2 from 606 to 590 nm were found. It is concluded that the hybrid associates of CdS/TGA+MB+ and CdS/TGA+(MB+)2 are formed. Luminescence quenching at CdS/TGA QDs band and MB+ luminescence enhancement under increase in MB+ molecules concentration were observed. A decrease in average lifetime of CdS/TGA QDs luminescence from 25 to 4 ns was found for MB+ concentration of 42 μ M. The Stern–Volmer constant, determined from the data on luminescence quenching, is 0.36 ∗ 106 M− 1. It is concluded that there is non-radiative resonance energy transfer (FRET) from the luminescence center of CdS/TGA quantum dots to MB+ molecule. Decreasing in temperature value to 80 K led to an increase in the luminescence intensity by 12 times. At the same time, the average lifetime of luminescence for pure CdS/TGA QDs increases from 25 to 72 ns. The Stern–Volmer constant increased to 0.64 ∗ 106 M− 1. It is concluded that its increase is due to an increase in average lifetime of CdS/TGA QD luminescence. In the framework of FRET theory, the rate constant of non-radiative energy transfer was estimated for an even distribution of CdS/TGA quantum dots and MB molecules in solution. Its is much smaller (6.7 ∗ 104 s− 1) than the experimentally determined value (2.5 ∗ 108 s− 1). This fact confirms the conclusion about the formation of CdS/TGA+MB hybrid system with effective FRET.

Excitation Transfer in Hybrid Nanostructures of Colloidal Ag2S/TGA Quantum Dots and Indocyanine Green J-Aggregates.

The regularities of the electron excitations exchange in hybrid associates of colloidal Ag2S quantum dots, passivated with thioglycolic acid (Ag2S/TGA QDs) with an average size of 2.2 and 3.7 nm with Indocyanine Green J-aggregates (ICG) were studied in this work by methods of absorption and luminescence spectroscopy. It was shown that IR luminescence sensitization of Ag2S/TGA QDs with an average size of 3.7 nm in the region of 1040 nm is possible due to non-radiative resonance energy transfer from Ag2S/TGA QDs with an average size of 2.2 nm and luminescence peak at 900 nm using ICG J-aggregate as an exciton bridge. The sensitization efficiency is 0.33. This technique provides a transition from the first therapeutic window (NIR-I, 700-950 nm) to the second (NIR-II, 1000-1700 nm). It can allow high to increase the imaging in vivo resolution.

FRET probe for selective and sensitive detection of vitamin A by cadmium free quantum dots (ZnS).

Vitamin A as a powerful antioxidant plays an important role in human body functions including bone remodeling regulation, healthy immune system and cell growth reproduction. An accurate determination of vitamin A is taken into consideration because of its importance for human health. In this paper, we reported a fluorescence resonance energy transfer (FRET) probe, MPS-capped ZnS QDs, for sensitive and selective detection of vitamin A. The colloidal MPS-capped ZnS QDs were prepared from Zinc acetate and sodium sulfide by employing 3-mercaptopropyltrimethoxysilane (MPS) molecules as the stabilizer or capping agent at the pH condition of 10. The synthesized MPS-capped ZnS QDs were characterized by means of FT-IR, UV-Vis, DLS, and TEM techniques. The sensing behavior of MPS-capped ZnS QDs for selective and sensitive detection of vitamin A, vitamin B2, vitamin B6, vitamin E, vitamin K, vitamin H, vitamin D3 and vitamin C was investigated using fluorescence spectroscopy. The detection mechanism involves photoinduced charge transfer from the surface of ZnS QDs to Vitamin resulting in the fluorescence quenching of ZnS QDs followed by nonradiative fluorescence resonance energy transfer. An excellent selectivity was observed for vitamin A versus other tested species. A linear relationship was observed between the fluorescence intensity of MPS-capped ZnS QDs and the concentration of vitamin A in the range of 3.33-36.66μM with detection limit of 1.062μM.

Femtosecond dynamics of photoexcitation in hybrid systems of CdS quantum dots with methylene blue

Abstract The dynamics of electronic excitation in hybrid associates of colloidal CdS quantum dots passivated by thioglycolic acid (CdS/TGA) with methylene blue cationic dye molecules (MB + ) was studied by femtosecond transient absorption spectroscopy and nanosecond time-resolved spectroscopy. From the luminescence decays it was found that non-radiative resonance energy transfer (FRET) from the recombination luminescence centers accompanied by acceptor fluorescence is observed in the CdS/TGA-MB + systems with MB + monomers. It was found that in the exciton decay dynamics of the hybrid systems based on CdS/TGA QDs and methylene blue, there is substantial competition between the resonance energy transfer in MB + and the energy transfer to MB • and MBOH • forms.