Upconversion Core Research Articles

Enhance the performance of dye-sensitized solar cells by constructing upconversion-core/semiconductor-shell structured NaYF4:Yb,Er @BiOCl microprisms

Upconversion spectral converters enable the utilization of infrared photons for dye-sensitized solar cells. However, the TiO2 photoanode photoelectron trapping loss caused by defects and ligands on upconversion material surface limits the dye-sensitized solar cells efficiency. Here, we separate spatially TiO2 particles and upconverters through crafting an uniform semiconductor BiOCl shell onto NaYF4:Yb3+,Er3+ upconverters surface by a hydrothermal method. Unlike common insulate SiO2 shells, the BiOCl shell decreases little the upconversion luminescence intensity from the upconversion core, but it can inhibit the photoelectron transfer from TiO2 to upconversion particles due to its higher conduction band position than that of TiO2, which eliminates the photoelectron trapping loss. In addition, the BiOCl shell can harvest 408 nm photons from upconversion cores to generate additional photoelectrons into TiO2 photoanode film. Consequently, the incorporation of upconversion-core/semiconductor-shell structured particles into TiO2 photoanodes of dye-sensitized solar cells achieves 29.8% increase of power conversion efficiency, whereas bare upconversion particles only get 11.9% increase as compared with dye-sensitized solar cells with pure TiO2 photoanodes. We quantify that among the relative efficiency increase by the incorporation of upconversion-core/semiconductor-shell particles: 17.2% from the reduced photoelectron trapping and the harvest of upconversion 408 nm photons by BiOCl shell, 4.9% from the green and red upconversion of near infrared photons, and 7.7% from the scattering effect of the designed spectral upconverters.

Nanoparticles: Untying the Gordian Knot in Conventional Computed Tomography Imaging

X-ray computed tomography (CT) imaging plays an essential role in disease diagnosis due to its noninvasive, painless mode and superior penetration depth. However, the resolution of the soft tissue ...

Intelligent phototriggered nanoparticles induce a domino effect for multimodal tumor therapy.

Rationale: Integration of several monotherapies into a single nanosystem can produce remarkable synergistic antitumor effects compared with separate delivery of combination therapies. We developed near-infrared (NIR) light-triggered nanoparticles that induce a domino effect for multimodal tumor therapy.Methods: The designed intelligent phototriggered nanoparticles (IPNs) were composed of a copper sulfide-loaded upconversion nanoparticle core, a thermosensitive and photosensitive enaminitrile molecule (EM) organogel shell loaded with anticancer drugs, and a cancer cell membrane coating. Irradiation with an NIR laser activated a domino effect beginning with photothermal generation by copper sulfide for photothermal therapy that also resulted in phase transformation of the EM gel to release the anticancer drug. Meanwhile, the NIR light energy was converted to ultraviolet light by the upconversion core to excite the EM, which generated reactive oxygen species for photodynamic therapy.Results: IPNs achieved excellent antitumor effects in vitro and in vivo with little systemic toxicity, indicating that IPNs could serve as a safe and high-performance instrument for synergetic antitumor therapy.Conclusion: This intelligent drug delivery system induced a chain reaction generating multiple antitumor therapies after a single stimulus.

A novel upconversion core–multishell nanoplatform for a highly efficient photoswitch

Red upconversion emission is significantly increased on the premise of ensuring optimal UV-blue upconversion emission.

EDTA-Modified 17β-Estradiol-Laden Upconversion Nanocomposite for Bone-Targeted Hormone Replacement Therapy for Osteoporosis

Hormone therapy (HT) is one of the most effective treatments for osteoporosis. However, the nonselective accumulation of hormone in organs such as breast, heart and uterus other than bones causes serious side effects, which impedes the application of HT. Hence, it is critically important to develop a HT strategy with reduced non-specific enrichment of hormone drugs in non-target tissues and enhanced bone-targeting ability.Methods: Herein, a 17β-estradiol (E2)-laden mesoporous silica-coated upconversion nanoparticle with a surface modification of ethylenediaminetetraacetic acid (EDTA) (NaLuF4:Yb,Tm@NaLuF4@mSiO2-EDTA-E2, E2-csUCNP@MSN-EDTA) is developed for bone-targeted osteoporosis hormone therapy. EDTA was attached onto the surface of E2 upconversion nanocomposite to enhance its affinity and efficiency targeting bone tissue and cells to optimize hormone replacement therapy for osteoporosis. We characterized the size, cytotoxicity, loading and release efficiency, in situ and ex vivo imaging. Further, in vitro and in vivo osteogenic ability was tested using preosteoblast and ovariectomy mouse model of osteoporosis.Results: The upconversion core of E2-csUCNP@MSN-EDTA nanoparticle serves as an excellent imaging agent for tracking the loaded hormone drug in vivo. The mesoporous silica layer has a high loading efficiency for E2 and provides a relatively long-lasting drug release within 50 h. EDTA anchored on the silica layer endows the nanocomposite with a bone targeting property. The nanocomposite effectively reverses estrogen deficiency-induced osteoporosis and reduces the damage of hormone to the uterus. The bone mineral density in the nanocomposite treatment group is nearly twice that of the ovariectomized (OVX) group. Compared with the E2 group, the uterine weight and luminal epithelial height were significantly lower in the nanocomposite treatment group.Conclusion: This work demonstrated that E2-csUCNP@MSN-EDTA alleviates the side effect of hormone therapy while maintaining its therapeutic efficacy, which has great potential for developing the next generation of methods for osteoporosis treatment.

Design of core/active-shell NaYF4:Ln3+@NaYF4:Yb3+ nanophosphors with enhanced red-green-blue upconversion luminescence for anti-counterfeiting printing

Lanthanide-doped NaYF4 upconversion luminescent nanophosphors have attracted great interest for anti-counterfeiting applications. However, low luminescent intensity caused by surface defects and low extinction coefficients of lanthanide dopants greatly limits their practical applications. Herein, we developed core/active-shell NaYF4:Ln3+@NaYF4:Yb3+ (e.g. NaYF4:Er3+/Tm3+@NaYF4:Yb3+, NaYF4:Yb3+/Er3+@NaYF4:Yb3+, and NaYF4: Yb3+/Tm3+@NaYF4:Yb3+) nanophosphors with enhanced near-infrared (NIR)-to-visible upconversion luminescence by coating Yb3+-doped NaYF4 shell (active-shell) on NaYF4:Ln3+ upconversion core nanoparticles. The structure, morphology, and elemental composition of NaYF4:Ln3+@NaYF4:Yb3+ core/active-shell nanoparticles (CASNs), NaYF4:Ln3+@NaYF4 core/inert-shell nanoparticles, and NaYF4:Ln3+ core nanoparticles were characterized and compared systematically to reveal their structure-property relationship. Collective data showed that coating of a NaYF4:Yb3+ active shell on NaYF4:Ln3+ cores significantly enhanced upconversion luminescent intensity by ~21 times, while an inert (pure NaYF4) shell coated on the surface of NaYF4:Ln3+ core only resulted in 5.2 times luminescence enhancement. The enhanced upconversion luminescence intensity was mainly attributed to (i) the NaYF4 shell-reduced quenching effect and (ii) the promoted transformation of the absorbed NIR light from the pump source to the core nanoparticles by Yb3+ sensitizer in the active shell. Moreover, by tailoring dopant pairs and molar ratios of lanthanide ions in the core nanoparticles, three CASNs with enhanced red, green, and blue upconversion luminescence were obtained and fabricated into environmental benign luminescent inks. The inkjet printing of RGB CASNs inks on papers produced multiple-color, high-resolution, complex luminescent patterns under 980 nm laser. This work expands the lanthanide-doped NaYF4 materials for anti-counterfeiting applications.

Effect of Ytterbium and Erbium co-doped NaYF4@NaSmF4 upconversion core-shell nanoparticles on their luminescence and morphological properties

In this study, novel upconversion (UC) core–shell NaYF4@NaSmF4 nanoparticles were synthesized via hydrothermal route which is having a tendency to convert two or more lower energy near IR photons to single higher energy UV/Visible photon for biomedical imaging and therapeutic applications. The core (NaYF4) nanoparticles were synthesized by varying sodium fluoride concentration and temperature of the reaction. The core–shell nanoparticles were prepared by growing the shell NaSmF4/NaSmF4:Yb, Er over the as-prepared core nanoparticles with optimized precursor-fluoride ratio, without any binding. The crystalline behaviour, morphology and particle size were investigated for core–shell nanoparticles using XRD, FESEM, TEM, EDS and Particle size analyzer. Photoluminescence spectra were recorded to find the emission wavelength and luminescence intensity. NaYF4@NaSmF4, the upconversion core–shell nanoparticles shown higher intensity luminescence spectra than core NaYF4. These core–shell nanoparticles have provided a platform for the spatially confining optical process, which possesses high luminescence efficiency.

Photothermally Active Upconversion Core–Shell NaGdF4:Yb:Tm@Cu Nanostructures: Synthesis and Theranostic Properties

AbstractNear infrared (NIR) active nanostructures with applications in imaging and therapy have attracted significant attention in cancer diagnosis and treatment. NIR active structures can provide molecular images, penetrating from deep within tissue with high resolution. In addition, particles with photothermal properties can lead to a new era of cancer diagnostics. The first synthesis of core–shell NaGdF4:Yb:Tm@Cu (NGF@Cu) nanostructures is reported. NGF@Cu particles have molecular imaging and photothermal activation properties owing to an upconverting core and metallic shell. The upconversion core means that cancer cell location can be recognized and the Cu‐based photothermal therapy is subsequently able to disrupt the cells. NGF@Cu characterization studies, including scanning tunneling electron microscopy and energy dispersive X‐ray spectroscopy mapping, confirm the core–shell structure with Cu as the shell. This study demonstrates the use of a single nanostructure for diagnosis in the NIR therapeutic window (650–1400 nm) and photothermal therapy, with a core–shell particle efficiency of ≈36.3%.

In-Depth Analysis of Excitation Dynamics in Dye-Sensitized Upconversion Core and Core/Active Shell Nanoparticles

Upconversion nanoparticles (UCNPs) combining both dye sensitization and core/shell enhancement are of great interest for their ability to boost the excitation efficiency of upconversion systems. Here, we report and investigate a 20-fold upconversion luminescence enhancement in dye-sensitized core/active shell UCNPs compared to that in nonsensitized core-only UCNPs. We observe a two-component luminescence rise dynamics in the upconversion kinetics of dye-sensitized UCNPs, distinctly different from the one-component rise dynamics of the nonsensitized UCNPs. For dye-sensitized UCNPs, the fast sub-microsecond component of the upconversion luminescence rise time is attributed to the radiative pumping of Er3+ ions from the dye, whereas the slow sub-millisecond component is due to the nonradiative energy transfer from the dye predominantly to Yb3+ ions, followed by the energy migration and the nonradiative energy transfer from Yb3+ to Er3+ ions. Our studies provide an insight into the interplay between radiative...

Synergizing Upconversion Nanophotosensitizers with Hyperbaric Oxygen to Remodel the Extracellular Matrix for Enhanced Photodynamic Cancer Therapy.

Photodynamic therapy (PDT) holds great promise as a noninvasive and selective cancer therapeutic treatment in preclinical research and clinical practice; however, it has limited efficacy in the ablation of deep-seated tumor because of hypoxia-associated circumstance and poor penetration of photosensitizers to cancer cells away from the blood vessels. To tackle the obstacles, we propose a therapeutic strategy that synergizes upconversion nanophotosensitizers (UNPSs) with hyperbaric oxygen (HBO) to remodel the extracellular matrix for enhanced photodynamic cancer therapy. The UNPSs are designed to have an Nd3+-sensitized sandwiched structure, wherein the upconversion core serves as light transducers to transfer energy to the neighboring photosensitizers to produce reactive oxygen species (ROS). With HBO, photodynamic process can generate abundant ROS in the intrinsically hypoxic tumor. It is revealed for the first time that HBO-assisted PDT decomposes collagen in the extracellular matrix of tumor and thus facilitates the diffusion of oxygen and penetration of UNPSs into the deeper area of tumor. Such a synergic effect eventually results in a significantly enhanced therapeutic efficacy at a low laser power density as compared with that using UNPSs alone. In view of its good biosafety, the HBO-assisted and UNPSs-mediated PDT provides new possibilities for treatment of solid tumors.

Probing Interaction Distance of Surface Quenchers in Lanthanide-Doped Upconversion Core–Shell Nanoparticles

Core–shell structures, which employ an optically inert shell to physically separate the emitting core from the surface quenchers, are often designed to optimize the emission efficiency of nanoscale emitters. However, it remains unclear that at what distance the effects of different surface quenchers, such as defects and adsorbed moieties, can be completely screened by the shell. Here, in a model upconversion system, we examine the interaction distance of surface quenchers in core–shell nanoparticles by using upconversion spectroscopy. Steady-state as well as time-resolved spectra show that the quenching effect of surface-adsorbed hydroxyl (OH) group diminishes at a distance (shell thickness) of 3.5 nm in diameter and 8.0 nm in length, which is larger than that for oleate-capped counterparts. With the increase of pumping density, the interaction distance of the surface quenchers does not apparently change, whereas saturation of the surface-related states notably reduces the optimal shell thickness for surf...

A facile synthesis approach and impact of shell formation on morphological structure and luminescent properties of aqueous dispersible NaGdF4:Yb/Er upconversion nanorods

A general facile synthesis approach was used for fabrication of highly emissive aqueous dispersible hexagonal phase upconversion luminescent NaGdF4:Yb/Er nanorods (core NRs) through metal complex decomposition process. An inert NaGdF4 and porous silica layers were grafted surrounding the surface of each and every NRs to enhance their luminescence efficiency and colloidal dispersibility in aqueous environment. Optical properties in terms of band gap energy of core, core/shell, and silica-coated core/shell/SiO2 nanorods were observed to investigate the influence of surface coating, which was gradually decreased after surface coating because of increase crystalline size after growth of inert and silica shells. The inert shell formation before silica surface grafting, upconversion luminescence intensity was greatly improved by about 20 times, owing to the effective surface passivation of the seed core and, therefore, protection of Er3+ ion in the core from the nonradiative decay caused by surface defects. Moreover, after silica coating, core/shell nanorods shows strong upconversion luminescence property similar to the hexagonal upconversion core NRs. It is expected that these NaGdF4:Yb/Er@NaGdF4@SiO2 (core/shell/SiO2) NRs including highly upconversion emissive and aqueous dispersible properties make them an ideal materials for various photonic-based potential applications such as in upconversion luminescent bioimaging, magnetic resonance imaging, and photodynamic therapy.

Unique Upconversion Core–Shell Nanoparticles with Tunable Fluorescence Synthesized by a Sequential Growth Process

A facile sequential growth process is developed to synthesize uniform lanthanide-doped upconversion (UC) core–shell nanoparticles with controlled nanostructures and enhanced UC fluorescence, which provides an important tool for their extensive applications in the near future. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Photon Upconversion in Core—Shell Nanoparticles

AbstractReview: tutorial review; 53 refs.

The Quality of In Vivo Upconversion Fluorescence Signals Inside Different Anatomic Structures.

Fluorescence imaging is a broadly interesting and rapidly growing strategy for non-invasive clinical applications. However, because of interference from light scattering, absorbance, and tissue autofluorescence, the images can exhibit low sensitivity and poor quality. Upconversion fluorescence imaging, which is based on the use of near-infrared (NIR) light for excitation, has recently been introduced as an improved approach to minimize the effects of light scattering and tissue autofluorescence. This strategy is promising for ultrasensitive and deep tissue imaging applications. However, the emitted upconversion fluorescence signals are primarily in the visible range and are likely to be absorbed and scattered by tissues. Therefore, different anatomic structures could impose various effects on the quality of the images. In this study, we used upconversion-core/silica-shell nanoprobes to evaluate the quality of upconversion fluorescence at different anatomic locations in athymic nude mice. The nanoprobe contained an upconversion core, which was green (β-NaYF4:Yb3+/Ho3+) or red (β-NaYF4:Yb3+/Er3+), and a nonporous silica shell to allow for multicolor imaging. High-quality upconversion fluorescence signals were detected with signal-to-noise ratios of up to 170 at tissue depths of up to - 1.0 cm when a 980 nm laser excitation source and a bandpass emission filter were used. The presence of dense tissue structures along the imaging path reduced the signal intensity and imaging quality, and nanoprobes with longer-wavelength emission spectra were therefore preferable. This study offers a detailed analysis of the quality of upconversion signals in vivo inside different anatomic structures. Such information could be essential for the analysis of upconversion fluorescence images in any in vivo biodiagnostic and microbial tracking applications.

Photon upconversion in core-shell nanoparticles.

Photon upconversion generally results from a series of successive electronic transitions within complex energy levels of lanthanide ions that are embedded in the lattice of a crystalline solid. In conventional lanthanide-doped upconversion nanoparticles, the dopant ions homogeneously distributed in the host lattice are readily accessible to surface quenchers and lose their excitation energy, giving rise to weak and susceptible emissions. Therefore, present studies on upconversion are mainly focused on core-shell nanoparticles comprising spatially confined dopant ions. By doping upconverting lanthanide ions in the interior of a core-shell nanoparticle, the upconversion emission can be substantially enhanced, and the optical integrity of the nanoparticles can be largely preserved. Optically active shells are also frequently employed to impart multiple functionalities to upconversion nanoparticles. Intriguingly, the core-shell design introduces the possibility of constructing novel upconversion nanoparticles by exploiting the energy exchange interactions across the core-shell interface. In this tutorial review, we highlight recent advances in the development of upconversion core-shell nanoparticles, with particular emphasis on the emerging strategies for regulating the interplay of dopant interactions through core-shell nanostructural engineering that leads to unprecedented upconversion properties. The improved control over photon energy conversion will open up new opportunities for biological and energy applications.

Synthesis of Nd3+/Yb3+ sensitized upconversion core–shell nanocrystals with optimized hosts and doping concentrations

Dual Nd3+/Yb3+ sensitized upconversion core–shell nanocrystals with strong upconversion emissions under both 808 nm and 980 nm excitation are developed.

An upconversion NaYF4:Yb3+,Er3+/TiO2 core–shell nanoparticle photoelectrode for improved efficiencies of dye-sensitized solar cells

Novel upconversion NaYF4:Yb3+,Er3+/TiO2 core–shell nanoparticles (NPs) are synthesized and used to prepare the photoelectrode (PE) of dye-sensitized solar cells (DSSCs). The morphology, structure, photoluminescence characterization of the NaYF4:Yb3+,Er3+/TiO2 core–shell NPs and the photoelectric performance, alternating current impedance spectroscopy of DSSCs are characterized using transmission electron microscopy, X-ray diffraction, upconversion luminescence (UCL) spectrofluorimetry and electrochemistry. Compared with the pure TiO2 PE or the NaYF4:Yb3+,Er3+ upconversion NPs and TiO2 simply mixed prepared PE as the volume ratio of the core–shell structure, the DSSCs with the upconversion core–shell PE show a greater photovoltaic efficiency. The energy conversion efficiency of the DSSCs with a NaYF4:Yb3+,Er3+/TiO2 PE is 23.1% higher than with a pure TiO2 PE and 99.1% higher than with a mixed PE using the same conditions. This enhancement is due to the UCL core extending the spectral response range of DSSCs to the infrared region and their particular shell structure, retaining its semiconductor character. This method represents a novel approach to increase the efficiencies of DSSCs.

A Fully-Integrated 16-Element Phased-Array Receiver in SiGe BiCMOS for 60-GHz Communications

A phased-array transmitter (TX) for multi-Gb/s non-line-of-sight links in the four frequency channels of the IEEE 802.15.3c standard (58.32 to 64.8 GHz) is fully integrated in a 0.12-μm SiGe BiCMOS process. It consists of an up-conversion core followed by a 1:16 power distribution tree, 16 phase-shifting front-ends, and a digital control unit. The TX core is a two-step sliding-IF up-conversion chain with frequency synthesizer that features 40 dB of gain programmability, I/Q balance and LO leakage correction, and a modulator for 802.15.3c common-mode signaling. The tradeoffs involved in the implementation of a 1:16 power distribution network are analyzed and a hybrid passive/active distribution tree architecture is introduced. Each of the 16 front-ends consists of a balanced passive phase shifter and a variable-gain, 3-stage PA that features oP1dB programmability through the bias control of the its final stage. All of the chip features are digitally controllable and individual memory arrays are integrated at each front-end to enable fast beam steering through a high-speed parallel interface. The IC occupies 44 mm and is fully characterized on wafer. The TX delivers 9 to 13.5 dBm oPidB per element at 60.48 GHz with a total power consumption of 3.8 to 6.2 W. Each element attains a phase-shift range >360° with an amplitude variation <;±1 dB across phase settings and adjacent elements. Measurement results from a packaged IC in an antenna chamber are also presented including the demonstration of spatial power combining up to +40 dBm EIRP and 16-element radiation patterns.

A Fully Integrated 16-Element Phased-Array Transmitter in SiGe BiCMOS for 60-GHz Communications

A phased-array transmitter (TX) for multi-Gb/s non-line-of-sight links in the four frequency channels of the IEEE 802.15.3c standard (58.32 to 64.8 GHz) is fully integrated in a 0.12-μm SiGe BiCMOS process. It consists of an up-conversion core followed by a 1:16 power distribution tree, 16 phase-shifting front-ends, and a digital control unit. The TX core is a two-step sliding-IF up-conversion chain with frequency synthesizer that features 40 dB of gain programmability, I/Q balance and LO leakage correction, and a modulator for 802.15.3c common-mode signaling. The tradeoffs involved in the implementation of a 1:16 power distribution network are analyzed and a hybrid passive/active distribution tree architecture is introduced. Each of the 16 front-ends consists of a balanced passive phase shifter and a variable-gain, 3-stage PA that features oP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> programmability through the bias control of the its final stage. All of the chip features are digitally controllable and individual memory arrays are integrated at each front-end to enable fast beam steering through a high-speed parallel interface. The IC occupies 44 mm and is fully characterized on wafer. The TX delivers 9 to 13.5 dBm oPidB per element at 60.48 GHz with a total power consumption of 3.8 to 6.2 W. Each element attains a phase-shift range >360° with an amplitude variation <;±1 dB across phase settings and adjacent elements. Measurement results from a packaged IC in an antenna chamber are also presented including the demonstration of spatial power combining up to +40 dBm EIRP and 16-element radiation patterns.