Nonradiative Energy Transfer Process Research Articles

Hydroxychloroquine-Loaded Chitosan Nanoparticles Induce Anticancer Activity in A549 Lung Cancer Cells: Design, BSA Binding, Molecular Docking, Mechanistic, and Biological Evaluation.

The current study describes the encapsulation of hydroxychloroquine, widely used in traditional medicine due to its diverse pharmacological and medicinal uses, in chitosan nanoparticles (CNPs). This work aims to combine the HCQ drug with CS NPs to generate a novel nanocomposite with improved characteristics and bioavailability. HCQ@CS NPs are roughly shaped like roadways and have a smooth surface with an average size of 159.3 ± 7.1 nm, a PDI of 0.224 ± 0.101, and a zeta potential of +46.6 ± 0.8 mV. To aid in the development of pharmaceutical systems for use in cancer therapy, the binding mechanism and affinity of the interaction between HCQ and HCQ@CS NPs and BSA were examined using stopped-flow and other spectroscopic approaches, supplemented by molecular docking analysis. HCQ and HCQ@CS NPs binding with BSA is driven by a ground-state complex formation that may be accompanied by a non-radiative energy transfer process, and binding constants indicate that HCQ@CS NPs-BSA was more stable than HCQ-BSA. The stopped-flow analysis demonstrated that, in addition to increasing BSA affinity, the nanoformulation HCQ@CS NPS changes the binding process and may open new routes for interaction. Docking experiments verified the development of the HCQ-BSA complex, with HCQ binding to site I on the BSA structure, primarily with the amino acids, Thr 578, Gln 579, Gln 525, Tyr 400, and Asn 404. Furthermore, the nanoformulation HCQ@CS NPS not only increased cytotoxicity against the A549 lung cancer cell line (IC50 = 28.57 ± 1.72 μg/mL) compared to HCQ (102.21 ± 0.67 μg/mL), but also exhibited higher antibacterial activity against both Gram-positive and Gram-negative bacteria when compared to HCQ and chloramphenicol, which is in agreement with the binding constants. The nanoformulation developed in this study may offer a viable therapy option for A549 lung cancer.

Effective role of Co-dopants (Dy3+, Sm3+) on Tunable multicolour emission of Tb3+ doped telluroborate glasses for Natural White light applications

In the current work the efficacy of incorporation of Dy3+ and Sm3+ ions into Tb3+ doped new telluroborate glass as well as their interactions was investigated. In this study, Tb3+ ions were employed as activators and sensitizers for both Dy3+ and Sm3+ ions emissions, which emanate from the excited states of Dy3+ (4F9/2) and Sm3+ (4G5/2) ions through a non-radiative energy transfer process. To validate the emission gamut of the prepared glasses, distinct emission colours were inspected with the CIE 1931 chromaticity analysis and the appropriate correlated colour temperature (CCT) values were estimated. The emission decay profile relating to the Tb3+ ions (5D4 state) of the glasses was investigated. The energy transfer efficiency, which stems from Tb3+ ion to Dy3+ and Sm3+ ions were found to be 49 and 54% respectively. The IH model was successfully used to analyse the interaction mechanism.

Effect of radiative and nonradiative energy transfer processes of light-emitting diodes combined with quantum dots for visible light communication

Though light-emitting diodes (LEDs) combined with various color conversion techniques have been widely explored for VLC (visible light communication), E-O (electro-optical) frequency responses of devices with quantum dots (QDs) embedded within the nanoholes have rarely been addressed. Here we propose LEDs with embedded photonic crystal (PhC) nanohole patterns and green light QDs for studying small-signal E-O frequency bandwidths and large signal on–off keying E-O responses. We observe that the E-O modulation quality of PhC LEDs with QDs is better than a conventional LED with QDs when the overall blue mixed with green light output signal is considered. However, the optical response of only QD converted green light shows a contradictory result. The slower E-O conversion response is attributed to multi-path green light generation from both radiative and nonradiative energy transfer processes for QDs coated on the PhC LEDs.

Optical properties of AIE organic chromophores embedded erbium-doped glass composites fabricated by spark plasma sintering

Encapsulation strategies can isolate the organic chromophores and prevent chemical or photochemical degradation. Inorganic transparent glass matrix has excellent utility as encapsulation matrices. Although the sol-gel method can make this encapsulation, the unclear sol-gel synthetic mechanism limits the synthesis of multi-component glass whose properties can be modified. A novel technique to encapsulate organic chromophores within multi-component glasses is required. In this letter, an organic chromophore was successfully encapsulated within a multi-component glass matrix by spark plasma sintering (SPS). The glass composite has great chemical and photochemical stability. Besides, a non-radiative energy transfer process between rare earth ions and organic chromophores was observed in the glass composites. These results indicate that the glass composite has great potential for optical application, and SPS can be a novel technique for encapsulating organic chromophores.

Nonradiative energy transfer between Yb3+ and Tm3+ ions in Y2O3:Tm, Yb ceramics

The work is aimed to study the processes of nonradiative energy transfer from Yb3+ ions to Tm3+ ions, as well as the processes of interaction between Tm3+ ions in Y2O3:Yb, Tm (CYb = 6, 10, 15 at. %, CTm = 1 at. %), Y2O3: Yb, Tm (СYb = 6, 10, 15 at. %, CTm = 3 at. %) ceramics.The luminescence spectra due to the 1G4→3H6, 1G4→3F4, 3F3→3H6, 3H4→3H6 transitions of the Tm3+ ions, as well as the luminescence decay curves from the 2F5/2 level of Yb3+ and 1G4, 3F3, 3H4, 3F4 levels of the Tm3+ ions recorded upon excitation of the level of the Yb3+ ions, were analyzed for concentration series Y2O3: Yb, Tm (CYb = 6, 10, 15 at. %, CTm = 1 at. %), Y2O3:Yb, Tm (СYb = 6, 10, 15 at. %, CTm = 3 at. %. %) ceramics. On the basis of this, the mechanisms of population and unloading of the corresponding levels of Tm3+ ions were proposed.

Structure and luminescent properties of Sm/Dy‐doped Sr2MgSi2O7 glass–ceramics

AbstractSm3+‐doped and Sm3+/Dy3+ codoped SiO2–SrO–MgO glasses were prepared by conventional melt quenching and Sr2MgSi2O7 based glass–ceramics from sintering and crystallization of the glass powders. The thermal, structural, and optical properties of the glasses and glass–ceramics were investigated as a function of the dopant concentration. The optical characterization includes the photoluminescence spectra and the lifetimes of the 4G5/2 (Sm3+) and 4F9/2 (Dy3+) excited states. In Sm3+ single‐doped samples, the emission intensity increases up to a concentration of 0.3 mol% Sm3+ ions and then decreases due to nonradiative energy transfer processes. The emission spectra in the glass–ceramics show a more resolved structure and higher intensity compared to the glass samples, suggesting a different and crystalline environment for the Sm3+ ions. The non‐radiative processes also influence the experimental decays of the glass samples which deviate from a single exponential with lifetimes decreasing as Sm3+ concentration increases. The emission and excitation spectra of the codoped samples do not show significant energy transfer between Sm3+ and Dy3+ ions. Different emitting colors can be obtained in the codoped glasses by changing the excitation wavelength. The studied glass–ceramics could be applied as enamels on ceramic or metallic substrates.

Photoluminescence Properties of CdSe/ZnS Quantum Dot Donor-Acceptor via Plasmon Coupling of Metal Nanostructures and Application on Photovoltaic Devices.

Hybrid nanostructures composed of quantum dots (QDs) and metal nanoparticles (MNS) have gained immense research interest because of their unique optical properties. In optoelectronic applications, quenching and enhancement in QD photoluminescence (PL) are critical parameters. Herein, gold nanoparticles coating a silica layer decorated with quantum dots (AuNPs@SiO2@QDs) are prepared with diverse SiO2 thickness and QD diameter for investigating the exciton-plasmon interaction. This reveals the charge interaction between QDs and AuNPs@SiO2 resulting from different impacts of the Föster energy-transfer process and plasmon resonance enhancement. The variation in both radiative and nonradiative energy-transfer processes in CdSe/ZnS QDs donor-acceptor pairs clarifies the impact of AuNPs@SiO2. In addition, the hybrid structures are plainly incorporated with silicon solar cells, which activated the improvement in the power conversion efficiency (PCE). With the significant tunability of the PL intensity in the visible and near-infrared regions, this hybrid nanostructure provides potential strategies for developing efficient optoelectronics via facile methods.

Investigation of FRET from organic dyes to silver nanoparticles and structural properties using the DFT/TD-DFT approach

The Forster resonance energy transfer involving a fluorescence molecule and organic quencher is constrained to a distance of ∼10 nm. However, with the coupling plasmonic materials, a significant amount of energy transfer can take place over substantially larger separations. The authors have studied intermolecular interactions using the nonradiative energy transfer process between organic dyes as donors and silver nanoparticles as acceptors. DFT and TD-DFT calculations were used to explore the atomic charges and the related properties. Theoretically determined ground and excited state dipole moments indicated that the increase in excited state dipole moment was due to the intramolecular charge transfer (ICT) character in the dyes.

Warm-white, reddish-orange and orange light generation from lithium-aluminum-zinc phosphate glass tri-doped with Sm3+, Tb3+and Eu3+

Spectroscopic evaluation of Sm3+/Tb3+/Eu3+ doped lithium-aluminum-zinc phosphate glass (LAZSTE), based on photoluminescence spectra and emission decay profiles, is particularly focused on W-LED technology. Tauc's method is employed to find direct and indirect allowed band gap and Urbach energy values. The Judd-Ofelt parameters were evaluated from measured oscillator strengths and subsequently used to estimate various radiative properties for the prominent fluorescent transitions (4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2) of Sm3+ ions. The LAZSTE glass excited at 346, 377 and 408 nm, displays warm-white light emission of 2497 K, orange light emission of 1949 K and reddish-orange light emission of 1667 K respectively, according to (0.4753, 0.4121), (0.5306, 0.4130) and (0.6077, 0.3767) CIE1931 chromaticity coordinates, respectively. The Tb3+ and Sm3+ emission decay shortening in presence of Sm3+ and Eu3+, and Eu3+, respectively, suggests that non-radiative energy transfer processes could take place from Tb3+ to Sm3+ and/or Eu3+, and from Sm3+ to Eu3+. The analysis of the Sm3+ and Tb3+ emission decays, performed with the Inokuti-Hirayama model, suggests that all these energy transfer processes are predominantly mediated through an electric dipole-dipole interaction, inside Sm3+-Tb3+-Eu3+ clusters.

Giant Ln 30 -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Giant Ln ₃₀ -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Multicolor emission in [formula omitted] clusters and Eu3+ activated ZnO–P2O5 glasses achieved under near ultraviolet light excitation

The structural and photoluminescence properties of zinc phosphate glasses activated with Agmn+ clusters and Eu3+ are studied. The addition of Ag+ and Eu3+ does not significantly modify the glassy structural properties evaluated by X-ray diffraction (XRD) patterns and Raman spectroscopy. The only change observed by Raman spectroscopy, is ascribed to the creation of molecular oxygen. The photoluminescence spectra, recorded under near ultraviolet (NUV) light excitation, display the feature broad band attributed to Agmn+ clusters. With the Eu3+ addition, Eu3+ bands located at 578, 591, 611, 652 and 701 nm, appear on the Agmn+ cluster emission, achieving the highest intensity at 0.8 mol% of Eu3+. This behavior is accompanied by a gradual reduction of the Agmn+ cluster emission. Sinks related to Eu3+ absorption on Agmn+ cluster emission and shortening of Agmn+ cluster: S1 → S0 and T1,T2 → S0 emission decays, suggest respectively the existence of radiative and non-radiative energy transfers from Agmn+ clusters to Eu3+. The Burstein model points out that the non-radiative energy transfer processes are predominantly mediated by electric dipole-dipole interaction for the Agmn+ :S1 → S0 transition. The emission tonality, estimated from the CIE1931 chromaticity coordinates and correlated color temperature (CCT) can be tuned from the cold white region to the warm white one, with effective quantum yield measurements up to 48%, depending on the excitation wavelength and Eu3+ doping content. Emission tonalites out of the white light region (orange-pink, purple-pink and pink) are obtained at higher amounts of Eu3+ (0.8 and 1.0 mol%) as well.

Spectroscopic studies of K2GdF5:Nd3+ single crystals for incredibly strong NIR emission at 864 nm

K2GdF5 single crystals doped with 5.0 at.% of Nd3+ ions (K2GdF5:Nd3+) were synthesized by the hydrothermal technique. The identification and control of the phase purity of synthesized crystals were performed using powder X-ray diffraction analysis. The spectroscopic characteristics of Nd3+ ions in K2GdF5 were analyzed through the absorption and luminescence spectra as well as decay curves. Upconversion luminescence spectra of K2GdF5:Nd3+ in the visible region were recorded under excitation by laser radiation with a wavelength of 785 nm. The nature of the Nd3+- ligand bonding and Judd-Ofelt intensity parameters were estimated using the absorption spectrum. The Ω4/Ω6 ratio was used to predict the structure of the emission spectrum of the K2GdF5:Nd3+ crystal. The application capability of the 4F3/2 → 4I9/2 emission band (864 nm) for laser action in K2GdF5:Nd3+ is proposed based on the radiative parameters such as the experimental branching ratio (βexp), integrated emission cross-section (ΣJJ’) and stimulated emission cross-sections (σλp). The nonradiative energy transfer process between Nd3+ ions in K2GdF5:Nd3+ is also discussed in detail using the Inokuti-Hirayama and Yokota-Tamimoto models.

Enhancement of solar-driven photocatalytic activity of oxygen vacancy-rich Bi/BiOBr/Sr2LaF7:Yb3+,Er3+ composites through synergetic strategy of upconversion function and plasmonic effect

For better use of solar energy, the development of efficient broadband photocatalyst has attracted extraordinary attention. In this study, a ternary composite consisting of Sr2LaF7:Yb3+,Er3+ upconversion (UC) nanocrystals and Bi nanoparticles loaded BiOBr nanosheets with oxygen vacancies (OVs, SLFBB) was designed and synthesized by multistep solvent-thermal method. Mechanisms of in-situ formation of Bi nanoparticles and OVs in BiOBr/Sr2LaF7:Yb3+,Er3+ composites (SFLB) are clarified. The Bi metal and OVs enhanced the light-harvesting capacity in the region of visible-near-infrared (Vis-NIR), and promoted the separation of electron–hole (e−/h+) pairs. Furthermore, the surface plasmon resonance (SPR) effect of Bi metal can improve the energy transfer from Sr2LaF7:Yb3+,Er3+ to BiOBr via nonradiative energy transfer process, resulting in enhancing the light utilization from upconverting NIR into Vis light. Due to the synergistic effects of UC function, SPR and OVs, the SFLBB exhibited obviously enhanced photocatalytic ability for the degradation of BPA with a rate of 8.9 × 10−3 min−1, which is about 2.78 times higher than 3.2 × 10−3 min−1 of BiOBr (BOB) under UV–Vis-NIR light irradiation. This work provides a novel strategy for the project of high-efficiency Bismuth-based broadband photocatalysts, which is helpful to further understand the mechanism of enhanced photocatalysis by UC function and plasmonic effect.

Effect of Dimer Structure and Inhomogeneous Broadening of Energy Levels on the Action of Flavomononucleotide in Rigid Polyvinyl Alcohol Films.

The results of time-resolved fluorescence measurements of flavin mononucleotide (FMN) in rigid polyvinyl alcohol films (PVA) demonstrate that fluorescence intensity decays are strongly accelerated in the presence of fluorescent dimers and nonradiative energy transfer processes. The fluorescence decay originating both from H and J dimer states of FMN was experimentally observed for the first time. The mean fluorescence lifetimes for FMN dimers were obtained: = 2.66 ns (at λexc = 445 nm) and = 2.02 (at λexc = 487 nm) at λobs = 600 nm and T = 253 K from H and J state of dimers, respectively. We show that inhomogeneous orientational broadening of energy levels (IOBEL) affects the shape of the fluorescence decay and leads to the dependence of the average monomer fluorescence lifetime on excitation wavelength. IOBEL affected the nonradiative energy transfer and indicated that different flavin positioning in the protein pocket could (1) change the spectroscopic properties of flavins due to the existence of “blue” and “red” fluorescence centers, and (2) diminish the effectiveness of energy transfer between FMN molecules.

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.

Coexistence of Parallel and Rotary Stackings in the Lamellar Crystals of a Perylene Bisimide Dyad for Temperature-Sensitive Bicomponent Emission.

Coexistence of rotationally π-π stacked columns and discrete slip-stacked dimers of perylene bisimide (PBI) chromophores is revealed by single crystal X-ray diffraction in the lamellar crystal of a head-to-tail linked PBI dyad. The rotary π-π stacked columnar moieties show H-type spectral character with relatively higher excitation energy, while the discrete slip-stacked π-π dimers have J-type spectral behavior with lower excitation energy. The lamellar crystals show relatively low photoluminescence efficiency of 12% at room temperature, while this dramatically increases to ∼90% at low temperature (80 K). Both of the rotary and slip-stacked moieties are emissive, and the nonradiative energy transfer processes between them are suppressed at low temperature, ensuring the highly efficient excimer-like long-lived fluorescence.

Tuning the Optical Properties of MEH–PPV/PFO Hybrid Thin Films via the Incorporation of CsPbBr3 Quantum Dots

The current work examines the effects of cesium lead bromide (CsPbBr3) perovskite quantum dots (PQDs) on the structural and optical properties of conjugated polymer blends of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH–PPV) and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). MEH–PPV/PFO composite thin-films containing PQDs with weight ratios between 0.5 wt.% and 10 wt.% were prepared via a solution-blending method prior to spin-coating on glass substrates. The MEH–PPV/PFO composites’ crystallinity was improved, and the roughness was dramatically increased with higher PQDs content, as confirmed by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Conversely, a higher PQDs content resulted in a gradual reduction of the Urbach tail and an increase in the steepness parameter, thereby reducing the localized density of the electronic states within the forbidden bandgap of the hybrids. Moreover, a slight reduction in the direct and indirect bandgaps was found in PQDs/(MEH–PPV/PFO) composite films containing a higher PQDs content and provided evidence of the low concentration of the localized states. The incorporation of the PQDs resulted in enhanced non-radiative energy transfer processes in the MEH–PPV/PFO hybrids, which are very important for the development of optimized optoelectronic devices.

Evaluation of the interaction of levothyroxine with bovine serum albumin using spectroscopic and molecular docking studies

Bovine serum albumin (BSA) acts as a carrier for many endogenous and exogenous compounds, such as thyroid hormones or corresponding drugs. Binding of the hydrophilic levothyroxine drug (LT4) to BSA is of significant pharmacological importance. In this work, UV-vis measurements were used to determine the pH value at which LT4 interacts optimally with proteins. The binding mechanism and affinity of the interaction between LT4 and BSA were investigated using Fourier-transform infrared spectroscopy (FT-IR), fluorescence, fluorescence resonance energy transfer (FRET), Surface Plasmon Resonance (SPR), supplemented by molecular docking analysis. Fluorescence measurements revealed the quenching effect of LT4 on the BSA intrinsic fluorescence and LT4 binding with BSA is driven by a ground-state complex formation that may be accompanied by a nonradiative energy transfer process. The thermodynamic parameters correspond to an enthalpic process, driven mainly by hydrogen bonds and van der Waals forces. Using SPR, the adsorbed amount of biomolecules was calculated and the binding affinity of LT4 with confined-BSA was characterized, indicating that the BSA immobilization plays an important role in LT4 binding. Docking studies confirmed the formation of the LT4-BSA complex with LT4 bound to site I on the BSA structure mainly with amino acid residues Trp 213, Tyr 137, Tyr 147. The calculation of the apparent association constant confirms the result obtained in SPR. Communicated by Ramaswamy H. Sarma

Visible emission and energy transfer in Tb3+/Dy3+ co‐doped phosphate glasses

AbstractIn this work, we systematically study the spectroscopic properties of Tb3+/Dy3+ co‐doped phosphate glasses in the visible spectral region and explore the sensitization role of Dy3+ in the enhancement of visible fluorescence of Tb3+ ions. Judd‐Ofelt parameters Ω2 and Ω4/Ω6 of the phosphate glass as host for Tb3+ are calculated as 21.60 × 10‐20 cm2 and 0.73, respectively, based on the measured spectral absorption. Multiple energy transfer (ET) routes from Dy3+ to Tb3+ and their efficiencies are characterized, and the enhanced fluorescence properties of Tb3+ are investigated, including the emission spectral strength and the spontaneous emission lifetime as functions of Dy3+ doping concentration. The efficient nonradiative ET processes between Dy3+ and Tb3+ allow a moderate concentration level of Tb3+ to achieve favorably stronger spectral absorption at blue and ultraviolet wavelengths. Tb3+/Dy3+ co‐doped phosphate glass shows promising potential for phosphors and lasing operation at visible wavelengths.

Optical Absorption and NIR Photoluminescence of Nd3+-Activated Strontium Phosphate Glasses

Strontium phosphate glasses with various concentrations of Nd2O3 have been prepared by melt quenching method. Absorption and photoluminescence spectra and lifetime measurements have been carried out to obtain the optical properties of these glasses. From the absorption spectrum, intensity and radiative parameters have been evaluated using Judd–Ofelt analysis. Near-infrared photoluminescence spectra consist of three bands centered at 875 nm, 1056 nm and 1327 nm, among which the highest intensity has been noticed for the band at 1056 nm that corresponds to the 4F3/2 → 4F11/2 transition of Nd3+ ion. Laser parameters such as branching ratio, band width, stimulated emission cross section and gain bandwidth for the 4F3/2 → 4F11/2 transition are found to be 0.52, 28 nm, 2.31 × 10−20 cm2 and 6.5 × 10−26 cm3, respectively. Decay curves of the 4F3/2 level of Nd3+ ions exhibit a single exponential nature at lower concentrations, while they become non-exponential at higher concentrations (≥ 0.1 mol.%) due to non-radiative energy transfer processes. This feature is also associated with shortening of lifetime from 307 μs to 82 μs when the Nd3+ ion concentration increases from 0.1 mol.% to 4.0 mol.%. The results have been compared with those of barium and magnesium phosphate glasses and commercial glasses. The results suggest that these glasses have potential applications as infrared laser materials at 1.05 μm.