Interfacial Energy Transfer Research Articles

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods

SiO2:Tb3+@Lu2O3:Eu3+ Core-Shell Phosphors: Interfacial Energy Transfer for Enhanced Multicolor Luminescence.

Uniform and well-dispersed SiO2:x%Tb3+@Lu2O3:y%Eu3+ core-shell spherical phosphors were synthesized via a solvothermal method followed by a subsequent calcination process. The structure, phase composition, and morphology of the samples were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the Lu2O3:Eu3+ layer was evenly coated on the surface of SiO2:Tb3+ spheres and the shell thickness was about 45-65 nm. The PL spectra and fluorescence lifetimes of the samples were further studied. It was proved that the multicolor luminescence of the samples could be realized by changing the doping concentration ratio of Eu3+ or by changing the excitation wavelengths. Compared with SiO2@Lu2O3:3%Tb3+,6%Eu3+, SiO2:3%Tb3+@Lu2O3:6%Eu3+ showed stronger luminescence intensity, longer fluorescence lifetime, and higher energy transfer efficiency, which was attributed to the effective interfacial energy transfer, and the interfacial energy transfer mechanism from Tb3+ to Eu3+ was a dipole-dipole interaction mechanism. The XPS results indicated that the sample contained a high content of Si-O-Lu bonds, which proved that there was a strong interaction between the SiO2 core and the Lu2O3 shell, making the interfacial energy transfer possible. These results provided a new idea for luminescence enhancement and multicolor luminescence.

Tunable upconversion of holmium sublattice through interfacial energy transfer for anti-counterfeiting.

Photon upconversion is a fascinating phenomenon that can convert low-energy photons to high-energy photons efficiently. However, most previous relevant research has been focused on upconversion systems with a sufficiently low lanthanide emitter concentration, such as 2 mol% for Er3+ in an Er-Yb coupled system. Realizing the upconversion from lanthanide heavily doped systems in particular, the emitter sublattice is still a challenge. Here, we report a mechanistic strategy to achieve the intense upconversion of the holmium sublattice in a core-shell-based nanostructure design through interfacial energy transfer channels. This design allowed a spatial separation of Ho3+ and sensitizers (e.g., Yb3+) into different regions and unwanted back energy transfers between them could then be minimized. By taking advantage of the dual roles of Yb3+ as both a migrator and energy trapper, a gradual color change from red to yellowish green was achievable upon 808 nm excitation, which could be further markedly enhanced by surface attaching indocyanine green dyes to facilitate the harvesting of the incident excitation energy. Moreover, emission colors could be tuned by applying non-steady state excitation. Such a fine-tunable color behavior holds great promise in anti-counterfeiting. Our results present a facile but effective conceptual model for the upconversion of the holmuim sublattice, which is helpful for the development of a new class of luminescent materials toward frontier applications.

Constructing a small core–multishell nanostructure for Ho-based red upconversion emission

Ho-based red dominant emission can be obtained through Tb3+-mediated interfacial energy transfer and energy migration.

Spectroscopic evidence of preferential excitation of interfacial EuIII by interfacial energy transfer process on core@shell nanoparticles

The hierarchical core@shell nanostructure in upconversion nanoparticle (UCNP) has allowed high intensities of upconversion emission by interfacial energy transfer (IET) mechanism, which can also account for high downshifting emission intensities observed for core@shell nanostructures. It is well accepted that the emission of active ions, sensitized by IET is originated from ions located into narrow core@shell interface, which has been shown by physically separation of donor and acceptor ions in the core@shell nanostructure. Herein we have spectroscopic proof of the preferential sensitization of the ions into the core@shell interface by IET. We have analyzed the excitation and emission spectra profiles of the EuIII sensitized by GdIII ions on hierarchically structured β-NaYF4 nanoparticles. In this work, EuIII emission occurs through a downshifting mechanism that is like the last step of the energy transfer pathway from GdIII to active ions in nanostructured UCNPs as part of a known UC-IET processes. Photophysical results indicate that IET sensitizes mainly the EuIII ions located at the core@shell interface, where these ions experience a variety of distorted chemical environments. Such a non-symmetrical electrical fields results in an inomogeneous broadening of 5D0 → 7F2 transition emission band. The preferential, but not unique, sensitization of EuIII ions by energy transfer from GdIII ions located at distorted interface may shine light on the upconversion emission bands intensities observed in several works describing the IET in UCNPs and spectrocopically confirms that GdIII -mediated emission occurs spatially in a narrow core@shell interfacial region.

Charge and energy transfer in the context of colloidal nanocrystals

As the number of hybrid systems comprising quantum-confined semiconductor nanocrystals and molecules continues to grow, so does the need to accurately describe interfacial energy and charge transfer in these systems. The earliest work often successfully captured at least qualitative trends in the rates of these processes using well-known results from Forster, Dexter, and Marcus theories, but recent studies have showcased how unique properties of nanocrystals drive interfacial energy transfer (EnT) and charge transfer (CT) to diverge from familiar trends. This review first describes how the nanocrystal-ligand system fits, at least superficially, into conventional models for EnT and CT, and then gradually introduces individual properties of nanocrystals that complicate our understanding of EnT and CT mechanisms. The review then explores instances in which features of nanocrystals that seem detrimental, such as trap states that introduce non-radiative recombination pathways and strong spin–orbit coupling, can be controlled or used synergistically to produce a wider range of functionality than available in all-molecular donor-acceptor systems.

Dynamic photonic barcodes for molecular detection based on cavity-enhanced energy transfer

Optical barcodes have demonstrated a great potential in multiplexed bioassays and cell tracking for their distinctive spectral fingerprints. The vast majority of optical barcodes were designed to identify a specific target by fluorescence emission spectra, without being able to characterize dynamic changes in response to analytes through time. To overcome these limitations, the concept of the bioresponsive dynamic photonic barcode was proposed by exploiting interfacial energy transfer between a microdroplet cavity and binding molecules. Whispering-gallery modes resulting from cavity-enhanced energy transfer were therefore converted into photonic barcodes to identify binding activities, in which more than trillions of distinctive barcodes could be generated by a single droplet. Dynamic spectral barcoding was achieved by a significant improvement in terms of signal-to-noise ratio upon binding to target molecules. Theoretical studies and experiments were conducted to elucidate the effect of different cavity sizes and analyte concentrations. Time-resolved fluorescence lifetime was implemented to investigate the role of radiative and non-radiative energy transfer. Finally, microdroplet photonic barcodes were employed in biodetection to exhibit great potential in fulfilling biomedical applications.

Energy Manipulation in Lanthanide-Doped Core-Shell Nanoparticles for Tunable Dual-Mode Luminescence toward Advanced Anti-Counterfeiting.

Developing advanced luminescent materials and techniques is of significant importance for anti-counterfeiting applications, and remains a huge challenge. In this work, a new and efficient approach for achieving efficient dual-mode luminescence with tunable color outputs via Gd3+ -mediated interfacial energy transfer, Ce3+ -assisted cross-relaxation, and core-shell nanostructuring strategy is reported. The introduction of Ce3+ into the inner core not only serves the regulation of upconversion emission, but also facilitates the ultraviolet photon harvesting and subsequent energy transfer to downshifting (DS) activators in the outer shell layer. Furthermore, the construction of the core@shell nanoarchitecture enables the spatial separation of upconverting activators and DS centers, which greatly suppresses their adverse cross-relaxation processes. Consequently, efficient and multicolor-tunable dual-mode emissions can be simultaneously observed in the pre-designed NaGdF4 :Yb/Ho/Ce@NaYF4 :X (X = Eu, Tb, Sm, Dy) core-shell nanostructures under 254 nm ultraviolet light and 980 nm laser excitation. The proof-of-concept experiment demonstrates that 2D-encoded patterns based on dual-mode emitting nanomaterials are very promising for anti-counterfeiting applications. It is believed that this preliminary study will advance the development of the fluorescent materials for potential applications in anti-counterfeiting and optical multiplexing.

Enhanced luminescence through interface energy transfer in hierarchical heterogeneous nanocomposites and application in white LEDs

Highly efficient light-emitting materials are essential for achieving high-performance devices. Here, a novel composite system, as well as enhanced luminescence processes, was designed, where NaLn(MoO4)2 ultra-small nucleus can be effectively isolated by In(OH)3 to form NaLn(MoO4)2@In(OH)3 composite nanoclusters due to the different nucleation rate between NaLn(MoO4)2 and In(OH)3, and then these small composite clusters gradually self-assemble into hierarchical structures. As we expected, the enhanced luminescence was achieved from hierarchical NaLn(MoO4)2 nanostructures with adjusting the distance among NaLn(MoO4)2 ultra-small nucleus by inserting In(OH)3. A series of spectroscopy results show that the In(OH)3 not only acts as an energy transfer bridge from CTB Eu3+ → O2− (or MoO42− absorption) to Eu3+, but also can effectively alleviate the concentration quenching of Ln3+ and change the J-O parameters. The Raman peak at 134 cm−1 is helpful to populate the 5D0 level of Eu3+ or the excited states of Er3+, resulting in stronger up/down-conversion emissions. The use of NaLn(MoO4)2@In(OH)3 in white light-emitting diodes (LEDs) has been demonstrated. The combination of red emission from NaLn(MoO4)2@In(OH)3 with blue, green, and yellow emission from halide perovskites could achieve white light with excellent vision performance (an LER of 376 lm/W) and superior color quality (CRI > 92). The findings of this experiment provide a new idea for the design of composite interface materials.

Red-to-blue photon upconversion based on a triplet energy transfer process not retarded but enabled by shell-coated quantum dots.

Charge and/or energy transfer from photoexcited quantum dots (QDs) is often suppressed by a wide-bandgap shell. Here, we report an interesting, counter-intuitive observation that interfacial triplet energy transfer from QDs is not retarded but rather enabled by an insulating shell. Specifically, photoluminescence of red-emitting CdSe QDs could not be quenched by surface-anchored Rhodamine B molecules; in contrast, after ZnS shell coating, their emission was effectively quenched. Time-resolved spectroscopy reveals that the shell eliminates ultrafast hole trapping in the QDs and hence opens up the triplet exciton transfer pathway. The triplet energy of Rhodamine B can be reversely transferred back to QDs by thermal activation, or it can be passed to triplet acceptors in the solution. Capitalizing on the latter, we demonstrate red-to-blue photon upconversion based on QD-sensitized triplet-triplet annihilation with an efficiency of 2.8% and an anti-Stokes shift of 1.13 eV.

Efficient dual-mode luminescence from lanthanide-doped core–shell nanoarchitecture for anti-counterfeiting applications

Fluorescent anti-counterfeiting technique is generally based on the development of luminescent materials, which generally exhibit single-mode emissions under single-wavelength excitation, thus resulting in a poor anti-fake effect. To improve the anti-forgery performance of fluorescent anti-counterfeiting approaches, dual-mode luminescent nanoparticles with the form of a β-NaGdF4:Yb/Ho/Ce@β-NaYF4:Tb/Eu core–shell structure have been skillfully designed and synthesized by a co-precipitation strategy. Through the cross-relaxation process between Ce3+ and Ho3+ ions in the inner core region, the up-conversion luminescence colors of the as-synthesized samples can be turned from green to yellow and finally to red when adjusting the dopant concentration of Ce3+ in the core. By selecting Ce3+ as the sensitizer for harvesting the energy of incident ultraviolet (UV) light and introducing Gd3+ as the ideal intermediate for subsequent energy migration, the down-converting emission colors of the as-obtained samples are also regulated from green to red via a Gd3+-assisted interface energy transfer processes (Ce3+ → Gd3+ → Tb3+, Ce3+ → Gd3+ → Tb3+ → Eu3+). Consequently, dual-mode luminescence with multi-color outputs can be achieved in the pre-designed core–shell nanostructure under the excitation of a 980 nm near-infrared laser and 254 nm UV light. The designed nanoarchitecture with bright dual-mode emissions and tunable colors greatly improves the ability of modern anti-counterfeiting, demonstrating its promising applications in anti-fake and optical multiplexing.

Tri-channel photon emission of lanthanides in lithium-sublattice core-shell nanostructures for multiple anti-counterfeiting

Lithium-sublattice nanoparticles have recently shown to be a promising nano-sized host candidate for photon upconversion of lanthanides. However, it remains a challenge for the controllable synthesis of high-quality lithium-sublattice core-shell nanostructures due to its tetragonal crystal structure in contrast to the commonly investigated hexagonal (or cubic) sodium-sublattice counterparts. Herein, we present a novel synthetic strategy of using the pre-synthesized optically-active (sensitive or emissive) seeds to guide the epitaxial growth of LiGdF4-based core-shell nanostructures. By further constructing the Gd3+-mediated interfacial energy transfer in such nanoparticles, both upconverting and down-shifting emissions from a set of lanthanide ions including Eu3+, Tb3+, Dy3+, Sm3+ and Nd3+ were realized. Such core-shell nanoparticles also show good spectral Stark-splitting feature owing to their lower local structural symmetry compared to other nano-sized hosts. Moreover, the tri-channel emission from a single nanoparticle was achieved by integrating upconverting and down-shifting emissions under the dual wavelength excitations (980/254 nm), exhibiting a great promise in the multiple anti-counterfeiting identification. These results open a door to the research on new kinds of efficient luminescent nanomaterials, and further help the design of multi-functional nanostructures towards emerging cutting-edge applications.

Coupling Photothermal Effect into Efficient Photocatalytic H2 Production by Using a Plate‐like Cu@Ni Core‐shell Cocatalyst

AbstractThe general moderate reaction condition in solar photocatalytic hydrogen production (i. e., near ambient pressure, room temperature) makes interfacial mass and energy transfer extremely slow, even by employing a cocatalytic material (usually in the form of noble metal nanoparticles or their counterparts). Herein, by fabricating well‐defined Cu@Ni core‐shell nanoplate cocatalyst and further incorporating it with a g‐C3N4 photocatalyst, we demonstrate that interfacial processes could be significantly improved by coupling localized photothermal effect into a cocatalyst. Specifically, Cu nanoplate can induce localized strong hot spots on Ni nanoparticles via a visible‐light‐driven surface plasma resonance effect. As a result, photogenerated electrons transferred from g‐C3N4 to Ni, could be elevated to a more energetic state, leading to a substantially improved photocatalytic activity toward H2 evolution from water. The highest hydrogen generation rate reaches 55 μmol h−1 g−1, 110 times of that pristine g‐C3N4. This work indicates that photoelectric and photothermal effects can be effectively coupled by integrating metal hetero‐nanoparticles.

Interfacial Microlasers: Lasing‐Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer (Advanced Optical Materials 7/2020)

Interfacial Microlasers: Lasing‐Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer (Advanced Optical Materials 7/2020)

In Situ Growth of MAPbBr3 Nanocrystals on Few-Layer MXene Nanosheets with Efficient Energy Transfer.

The performance of perovskite nanocrystals (NCs) in optoelectronics and photocatalysis is severely limited by the presence of large amounts of crystal boundaries in NCs film that greatly restricts energy transfer. Creating heterostructures based on perovskite NCs and 2D materials is a common approach to improve the energy transport at the perovskite/2D materials interface. Herein, methylamine lead bromide (MAPbBr3 , MA: CH3 NH3 + ) perovskite NCs are homogeneously deposited on highly conductive few-layer MXene (Ti3 C2 Tx ) nanosheets to form heterostructures through an in situ solution growth method. An optimal mixed solvent ratio is essential to realize the growth of perovskite NCs on Ti3 C2 Tx nanosheets. Time-resolved photoluminescence spectroscopy, transient absorption spectroscopy, and the photoresponse of electron- and hole-only photoelectric conversion devices reveal the interfacial energy transfer behavior within MAPbBr3 /Ti3 C2 Tx heterostructures. The present investigation may provide a useful guide toward use of halide perovskite/2D material heterostructures in applications such as photocatalysis as well as optoelectronics.

Enhancing multiphoton upconversion through interfacial energy transfer in multilayered nanoparticles

Photon upconversion in lanthanide-doped upconversion nanoparticles offers a wide variety of applications including deep-tissue biophotonics. However, the upconversion luminescence and efficiency, especially involving multiple photons, is still limited by the concentration quenching effect. Here, we demonstrate a multilayered core-shell-shell structure for lanthanide doped NaYF4, where Er3+ activators and Yb3+ sensitizers are spatially separated, which can enhance the multiphoton emission from Er3+ by 100-fold compared with the multiphoton emission from canonical core-shell nanocrystals. This difference is due to the excitation energy transfer at the interface between activator core and sensitizer shell being unexpectedly efficient, as revealed by the structural and temperature dependence of the multiphoton upconversion luminescence. Therefore, the concentration quenching is suppressed via alleviation of cross-relaxation between the activator and the sensitizer, resulting in a high quantum yield of up to 6.34% for this layered structure. These findings will enable versatile design of multiphoton upconverting nanoparticles overcoming the conventional limitation.

Fast atom effect on helium gas/graphite interfacial energy transfer

Energy transfer between gases and solid surfaces plays a vital role in many technologies. Thermal accommodation coefficient (TAC), which specifies the energy transferred between a surface composed of thermally-vibrating atoms and a colliding gas molecule, can be calculated by sampling the incident velocities of gas molecules by the Maxwell-Boltzmann (MB) distribution. However, the MB distribution describes gas behavior in free space rather than near a solid surface. In this work, we calculated the TAC between helium and graphite by a modified Maxwell-Boltzmann distribution accounting for the fast atom effect where gases of higher out-of-plane velocity have a larger chance of reaching the solid surface at the same period. A significant reduction in TAC is found by correcting the MB distribution with the modified-MB distribution, 32.7% for helium at 500 K and 10.74% at 300 K. Further analysis shows that the out-of-plane velocity component dominates the scattering process and energy transfer. This result underlines the importance and necessity to correct the MB distribution to incorporate the fast atom effect. Moreover, the lower and upper boundaries of the scattering events were depicted. These findings can provide a fundamental understanding of gas-surface energy transfer and guidelines for molecular dynamics simulations for TAC.

Lasing‐Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer

AbstractMicrolasers are emerging tools for biomedical applications. In particular, whispering‐gallery‐mode (WGM) microlasers are promising candidates for sensing at the biointerface owing to their high quality‐factor and potential in molecular assays, and intracellular and extracellular detection. However, lasing particles with sensing functionality remain challenging since the overlap between the WGM optical mode and external gain medium is much lower compared to internal gain inside the cavity. To overcome this problem, the concept of Förster resonant energy transfer (FRET) is exploited on WGM droplet microlaser by separating donor and acceptor molecules at the cavity–surface interface. It is first discovered that the interfacial FRET laser not only originates from conventional FRET but utilizes coherent radiative energy transfer (CRET) to excite acceptor molecules by inducing light‐harvesting effect near the cavity interface. Simulations and experiments have revealed that the absorption spectrum of individual analyte plays a crucial role in interfacial FRET laser. Distinct lasing spectra can therefore distinguish molecules of different absorption properties upon binding. Finally, detection of small fluorescent molecules and photosynthetic protein is performed. The results presented here not only demonstrate the wide‐ranging potential of microlaser external cavity implementation in molecular sensing applications, but also provide comprehensive insights into cavity energy transfer in laser physics.

Ethanedithiol treatment on zinc oxide films for highly efficient quantum dot light-emitting diodes by reducing exciton quenching

Surface modification of ZnO nanoparticles with ethanedithiol (EDT) has been studied to minimize exciton loss at the ZnO/quantum dots (QDs) interface and to improve the efficiency of QD light-emitting diodes (QLEDs). The EDT treatment has been demonstrated to fill oxygen vacancies and reduce carboxylate and hydroxyl ligands on the surface of the ZnO nanoparticles from the x-ray photoelectron spectroscopy analysis. The reduction of oxygen vacancies makes the ZnO films more hydrophobic and maintains the optical bandgap under ambient conditions. EDT treatment shifts the energy level up by 0.47 eV by modifying the surface of ZnO. Non-radiative recombination processes at the ZnO/QDs interface such as interfacial charge transfer and energy transfer are reduced through the upshifted energy level and reduced surface defects. The brightness of the QLED with EDT treatment on ZnO was improved by more than 330% having a maximum luminance of 59 , 500 c d / m 2 compared to the QLED with pristine ZnO. The maximum current efficiency of the QLEDs has been improved from 54.3 cd/A to 73.4 cd/A, which is 35% higher than ZnO-based QLEDs.

Reversible and Continuous Color-Tunable Persistent Luminescence of Metal-Free Organic Materials by "Self"-Interface Energy Transfer.

Persistent luminescence from metal-free organic materials is attractive for their ultralong exciton lifetimes. Color-tunable persistent luminescence from single-component organic materials is fascinating but still challenging. By utilizing an efficient approach of "self"-interface energy transfer (IET), the persistent luminescence color of an organic phosphor (CTXO) can be reversibly and continuously tuned by external physical stimuli. Its color circularly changes between green (lifetime = 0.24 s) and deep-yellow (lifetime = 0.10 s) when CTXO is repeatedly triggered with thermal annealing and mechanical grinding. Self-IET from the crystalline part (donor), which exhibits persistent room-temperature phosphorescence, to the amorphous part (acceptor) inside its semicrystal during these treatments is found to be the key exciton process for such novel color modulation. This also provides opportunity for designing stimuli-responsive smart materials with controlled persistent luminescence.