Showing papers by "Xiaogang Liu published in 2019"
TL;DR: In this paper, a colour-tunable, ultra-long organic phosphorescence (UOP) can be tuned by varying the excitation wavelength, allowing dynamic colour tuning from the violet to the green part of the visible spectrum.
Abstract: Materials exhibiting long-lived, persistent luminescence in the visible spectrum are useful for applications in the display, information encryption and bioimaging sectors1–4. Herein, we report the development of several organic phosphors that provide colour-tunable, ultra-long organic phosphorescence (UOP). The emission colour can be tuned by varying the excitation wavelength, allowing dynamic colour tuning from the violet to the green part of the visible spectrum. Our experimental data reveal that these organic phosphors can have an ultra-long lifetime of 2.45 s and a maximum phosphorescence efficiency of 31.2%. Furthermore, we demonstrate the applications of colour-tunable UOP for use in a multicolour display and visual sensing of ultraviolet light in the range from 300 to 360 nm. The findings open the opportunity for the development of smart luminescent materials and sensors with dynamically controlled phosphorescence. Organic phosphors with ultra-long lifetimes and an emission colour that can be tuned by the excitation wavelength are reported.
467 citations
16 Jul 2019
362 citations
TL;DR: This work reports the room-temperature synthesis of a colloidal scintillator comprising CsPbBr3 nanosheets of large concentration and reveals an energy transfer process inside those stacked nanosheet solids that is responsible for their superb scintillation performance.
Abstract: Scintillators, which are capable of converting ionizing radiation into visible photons, are an integral part of medical, security, and commercial diagnostic technologies such as X-ray imaging, nuclear cameras, and computed tomography. Conventional scintillator fabrication typically involves high-temperature sintering, generating agglomerated powders or large bulk crystals, which pose major challenges for device integration and processability. On the other hand, colloidal quantum dot scintillators cannot be cast into compact solid films with the necessary thickness required for most X-ray applications. Here, we report the room-temperature synthesis of a colloidal scintillator comprising CsPbBr3 nanosheets of large concentration (up to 150 mg/mL). The CsPbBr3 colloid exhibits a light yield (∼21000 photons/MeV) higher than that of the commercially available Ce:LuAG single-crystal scintillator (∼18000 photons/MeV). Scintillators based on these nanosheets display both strong radioluminescence (RL) and long-term stability under X-ray illumination. Importantly, the colloidal scintillator can be readily cast into a uniform crack-free large-area film (8.5 × 8.5 cm2 in area) with the requisite thickness for high-resolution X-ray imaging applications. We showcase prototype applications of these high-quality scintillating films as X-ray imaging screens for a cellphone panel and a standard central processing unit chip. Our radiography prototype combines large-area processability with high resolution and a strong penetration ability to sheath materials, such as resin and silicon. We reveal an energy transfer process inside those stacked nanosheet solids that is responsible for their superb scintillation performance. Our findings demonstrate a large-area solution-processed scintillator of stable and efficient RL as a promising approach for low-cost radiography and X-ray imaging applications.
298 citations
TL;DR: This work demonstrates a highly efficient strategy for tumor therapy by utilizing pH-sensitive sodium-hyaluronate-modified calcium peroxide nanoparticles (SH-CaO2 NPs), which create an artificial calcium overloading stress in tumor cells, which is responsible for cell death.
221 citations
04 Mar 2019
TL;DR: It is demonstrated that molecularly tailored UCNPs could serve as optogenetic actuators of transcranial NIR to functionally stimulate deep brain neurons in mice, which would open the door to less-invasive optical neuronal activity manipulation with the potential for remote therapy.
Abstract: Optogenetic stimulation of neurons, driven by the development of light-gated rhodopsins, has revolutionized the experimental interrogation of neural circuits and holds promise for next-generation treatment of neurological disorders. However, it is limited by the inability of visible light to penetrate deep inside brain tissue. Optical stimulation of deep brain neurons, for example, has hitherto required the insertion of invasive optical fibers because the activating blue-green wavelengths are strongly scattered and absorbed by endogenous chromophores. Red-shifted variants of rhodopsins have been developed, but their action spectra still fall out of the near-infrared (NIR) optical window (650-1350 nm) where light has its maximal depth of penetration in brain tissue. Here, we developed a novel approach for NIR optogenetics, where lanthanide-doped upconversion nanocrystals (UCNPs) were used to absorb tissue-penetrating 980 nm NIR and emit visible light for rhodopsin activation. Due to lanthanides’ ladder-like electronic energy structure, the emission of UCNPs can be precisely tuned to a particular wavelength by control of energy transfer via selective lanthanide-ion doping. For instance, incorporation of Tm3+ into Yb3+ doped host lattices leads to blue emission (~470 nm) that matches the maximum absorption of channelrhodopsin-2 (ChR2) for neuronal activation, while the Yb3+/Er3+ couple emits green light (~540 nm) compatible with activation of halorhodopsin (NpHR) or archaerhodopsin (Arch) for neuronal inhibition. We demonstrated that molecularly tailored UCNPs could serve as optogenetic actuators of transcranial NIR to functionally stimulate deep brain neurons in mice. Transcranial NIR UCNP-mediated optogenetics evoked dopamine release from genetically tagged neurons in the ventral tegmental area, induced brain oscillations via activation of inhibitory neurons in the medial septum, silenced seizure via inhibition of excitatory cells in the hippocampus, and triggered memory recall via excitation of a hippocampal engram. UCNP technology would open the door to less-invasive optical neuronal activity manipulation with the potential for remote therapy.
168 citations
TL;DR: A new modality for enhancing immunogenic cell death through a synergistic phototherapeutic nanoplatform is established and this strategy to overcome tumor metastasis with an augmented antitumor immune response is extended.
Abstract: Synergistic phototherapy has the potential to conquer the extreme heterogeneity and complexity of difficult tumors and result in better cancer treatment outcomes than monomodal photodynamic therapy (PDT) or photothermal therapy (PTT). However, the previous approaches to combining PDT and PTT are mainly focused on primary tumor obliteration while neglecting tumor metastasis, which is responsible for about 90% of cancer deaths. It is shown that a combined PDT/PTT approach, based on upconversion-polymer hybrid nanoparticles with surface-loaded chlorin e6 photosensitizer, can enhance primary tumor elimination and elicit antitumor immunity against disseminated tumors. The specifical arrangement of an external upconversion coating over the polymer core ensures adequate photoabsorption by the upconversion nanoparticles for the generation of reactive oxygen species upon single near-infrared light irradiation. Furthermore, it is found that synergistic phototherapy can elicit robust systemic and humoral antitumor immune responses. When combined with immune checkpoint blockades, it can inhibit tumor relapse and metastasis as well as prolong the survival of tumor-bearing mice in two types of tumor metastasis models. This study may establish a new modality for enhancing immunogenic cell death through a synergistic phototherapeutic nanoplatform and extend this strategy to overcome tumor metastasis with an augmented antitumor immune response.
163 citations
TL;DR: Flexible and washable CNT-embedded polyacrylonitrile (PAN) nonwoven fabrics by a simple electrospinning route that can facilitate the construction of large-scale outdoor evaporation devices, conferring the great capacity for efficient desalination of seawater under natural sunlight.
Abstract: Nanostructured photothermal membranes hold great potential for solar-driven seawater desalination; however, their pragmatic applications are often limited by substantial salt accumulation. To solve this issue, we have designed and prepared flexible and washable carbon-nanotube-embedded polyacrylonitrile nonwoven fabrics by a simple electrospinning route. The wet fabric exhibits a strong photoabsorption in a wide spectral range (350-2500 nm), and it has a photoabsorption efficiency of 90.8%. When coated onto a polystyrene foam, the fabric shows a high seawater evaporation rate of 1.44 kg m-2 h-1 under simulated sunlight irradiation (1.0 kW m-2). With a high concentration of simulated seawater as the model, the accumulation of solid salts can be clearly observed on the surface of the fabric, resulting in a severe decay of the evaporation rate. These salts can be effortlessly washed away from the fabric through a plain handwashing process. The washing process has a negligible influence on the morphology, photoabsorption, and evaporation performance of the fabric, demonstrating good durability. More importantly, a larger fabric can easily be fabricated, and the combination of washable fabrics with various parallel PS foams can facilitate the construction of large-scale outdoor evaporation devices, conferring the great potential for efficient desalination of seawater under natural sunlight.
157 citations
146 citations
TL;DR: In this paper, the authors review the field of upconversion nanoparticles from the perspectives of fundamental luminescence mechanisms, new synthetic routes, and current practical approaches to tune emission color and enhancing upcon conversion efficiency.
135 citations
123 citations
TL;DR: Disruptive technologies such as super-resolution microscopy, optogenetics, nanolasing, and optical anticounterfeiting are focused on, which take full advantage of the upconversion nanophenomena in relation to lanthanide-doped nanocrystals.
Abstract: Advanced nanoscale synthetic techniques provide a versatile platform for programmable control over the size, morphology, and composition of nanocrystals doped with lanthanide ions. Characteristic upconversion luminescence features originating from the 4f-4f optical transitions of lanthanides can be achieved through predesigned energy transfer pathways, enabling wide applications ranging from ultrasensitive biological detection to advanced spectroscopic instrumentation with high spatiotemporal resolution. Here, we review recent scientific and technological discoveries that have prompted the realization of these peculiar functions of lanthanide-doped upconversion nanocrystals and discuss the mechanistic studies of energy transfer involved in upconversion processes. These advanced schemes include cross relaxation-mediated depletion, multipulse sequential pumping, and nanostructural configuration design. Our emphasis is placed on disruptive technologies such as super-resolution microscopy, optogenetics, nanolasing, and optical anticounterfeiting, which take full advantage of the upconversion nanophenomena in relation to lanthanide-doped nanocrystals.
TL;DR: It is demonstrated that tailoring the mode of the plasmonic cavity permits active control over the colour output of upconversion emission and may benefit the future development of rapid nonlinear image scanning nanoscopy and open up the possibility of constructing high-frequency, single-photon emitters driven by telecommunication wavelengths.
Abstract: The generation of anti-Stokes emission through lanthanide-doped upconversion nanoparticles is of great importance for technological applications in energy harvesting, bioimaging and optical cryptography1–3. However, the weak absorption and long radiative lifetimes of upconversion nanoparticles may significantly limit their use in imaging and labelling applications in which a fast spontaneous emission rate is essential4–6. Here, we report the direct observation of upconversion superburst with directional, fast and ultrabright luminescence by coupling gap plasmon modes to nanoparticle emitters. Through precise control over the nanoparticle’s local density of state, we achieve emission amplification by four to five orders of magnitude and a 166-fold rate increase in spontaneous emission. We also demonstrate that tailoring the mode of the plasmonic cavity permits active control over the colour output of upconversion emission. These findings may benefit the future development of rapid nonlinear image scanning nanoscopy and open up the possibility of constructing high-frequency, single-photon emitters driven by telecommunication wavelengths. Coupling the emission of upconversion nanoparticles to gap plasmon modes enables a direct observation of upconversion superburst with directional, fast and ultrabright luminescence.
TL;DR: A new class of quaternary piperazine substituted rhodamines with outstanding quantum yields and superior brightness is developed, by utilizing the electronic inductive effect to prevent TICT.
Abstract: Insufficient brightness of fluorophores poses a major bottleneck for the advancement of super-resolution microscopes. Despite being widely used, many rhodamine dyes exhibit sub-optimal brightness due to the formation of twisted intramolecular charge transfer (TICT) upon photoexcitation. Herein, we have developed a new class of quaternary piperazine-substituted rhodamines with outstanding quantum yields (Φ = 0.93) and superior brightness (e × Φ = 8.1 × 104 L·mol-1·cm-1), by utilizing the electronic inductive effect to prevent TICT. We have also successfully deployed these rhodamines in the super-resolution imaging of the microtubules of fixed cells and of the cell membrane and lysosomes of live cells. Finally, we demonstrated that this strategy was generalizable to other families of fluorophores, resulting in substantially increased quantum yields.
TL;DR: Wang et al. as discussed by the authors developed low-cost and washable photothermal fabrics by dyeing traditional cotton fabrics with carbon nanotube (CNT)-based ink, which exhibited strong optical absorption in 250-2500nm with a total solar absorption efficiency of 95.7%.
TL;DR: An overview of advances in developing new modalities for neural circuitry modulation utilizing upconversion‐nanoparticle‐mediated optogenetics is presented, which have led to minimally invasive optical stimulation and inhibition of neurons with substantially improved selectivity, sensitivity, and spatial resolution.
Abstract: Optogenetics is an optical technique that exploits visible light for selective neuromodulation with spatio-temporal precision. Despite enormous effort, the effective stimulation of targeted neurons, which are located in deeper structures of the nervous system, by visible light, remains a technical challenge. Compared to visible light, near-infrared illumination offers a higher depth of tissue penetration owing to a lower degree of light attenuation. Herein, an overview of advances in developing new modalities for neural circuitry modulation utilizing upconversion-nanoparticle-mediated optogenetics is presented. These developments have led to minimally invasive optical stimulation and inhibition of neurons with substantially improved selectivity, sensitivity, and spatial resolution. The focus is to provide a comprehensive review of the mechanistic basis for evaluating upconversion parameters, which will be useful in designing, executing, and reporting optogenetic experiments.
TL;DR: The utilization of dielectric microbeads are exploited to significantly enhance the photon upconversion processes in lanthanide-doped nanocrystals to enhance the luminescence efficiency of upconverting nanoparticles and show its application for optogenetics.
Abstract: Achieving efficient photon upconversion under low irradiance is not only a fundamental challenge but also central to numerous advanced applications spanning from photovoltaics to biophotonics. However, to date, almost all approaches for upconversion luminescence intensification require stringent controls over numerous factors such as composition and size of nanophosphors. Here, we report the utilization of dielectric microbeads to significantly enhance the photon upconversion processes in lanthanide-doped nanocrystals. By modulating the wavefront of both excitation and emission fields through dielectric superlensing effects, luminescence amplification up to 5 orders of magnitude can be achieved. This design delineates a general strategy to converge a low-power incident light beam into a photonic hotspot of high field intensity, while simultaneously enabling collimation of highly divergent emission for far-field accumulation. The dielectric superlensing-mediated strategy may provide a major step forward in facilitating photon upconversion processes toward practical applications in the fields of photobiology, energy conversion, and optogenetics.
TL;DR: Tunable resonator-upconverted emission (TRUE) is achieved by placing upconversion nanoparticles (UCNPs) within plasmonic nanoresonators within size-tuned gap-plasmon resonances in Al nanodisk arrays.
Abstract: Lanthanide-doped nanophosphors are promising in anti-counterfeiting and security printing applications. These nanophosphors can be incorporated as transparent inks that fluoresce by upconverting near-infrared illumination into visible light to allow easy verification of documents. However, these inks typically exhibit a single luminescent color, low emission efficiency, and low print resolutions. Tunable resonator-upconverted emission (TRUE) is achieved by placing upconversion nanoparticles (UCNPs) within plasmonic nanoresonators. A range of TRUE colors are obtained from a single-UCNP species self-assembled within size-tuned gap-plasmon resonances in Al nanodisk arrays. The luminescence intensities are enhanced by two orders of magnitude through emission and absorption enhancements. The enhanced emissive and plasmonic colors are simultaneously employed to generate TRUE color prints that exhibit one appearance under ambient white light, and a multicolored luminescence appearance that is revealed under near-infrared excitation. The printed color and luminescent images are of ultrahigh resolutions (≈50 000 dpi), and enable multiple colors from a single excitation source for increased level of security.
TL;DR: This Account attempts to provide an overview of general and emerging strategies for the design of efficient lanthanide-mediated photon upconversion nanosystems, and management of NIR photon energy injection, the optimization of efficient energy transfer pathways, and the minimization of energy flux leakage.
Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) exhibit unique optical characteristics, including a large anti-Stokes shift, a long luminescence lifetime, sharp emission bands, and high photostability. These virtues make UCNPs highly useful in many emerging applications such as biolabeling, security, multicolor displays, and optogenetics. Despite the enticing prospects of UCNPs, their practical utility is greatly hindered by the low efficiency of the conversion from near-infrared (NIR) excitation to visible emission. In a typical nanosystem codoped with sensitizers and activators, upconversion processes occur through NIR light sensitization, energy transfer from sensitizers to activators, sequential energy population at the excited states of the activators, and eventually the release of higher-energy photons. In fact, in the upconversion nanosystem, each step in the energy flux, including NIR energy injection, energy transfer and migration, and energy dissipation, has a decisive effect on the resulting luminescence intensity. Important in-depth studies have been conducted in pursuit of brighter UCNPs. Specifically, lanthanide ions possessing larger absorption cross sections (Nd3+) or organic dye molecules have been chosen as NIR light sensitizers to improve the light harvesting ability of upconversion nanostructures. The doping concentration and spatial distribution of lanthanide ions are strictly managed to mitigate detrimental energy cross-talk processes. The surfaces of UCNPs are passivated with epitaxially grown layers to block surface quenching. Therefore, rational design of energy flux manipulation, through control of excitation energy collection, transmission, and release in a three-dimensional nanospace of UCNPs, is crucial in constructing nanosystems with high upconversion efficiencies. In this Account, from an energy flux manipulation perspective, we attempt to provide an overview of general and emerging strategies for the design of efficient lanthanide-mediated photon upconversion nanosystems. With the significant progress made over the past several years, we are now able to design a series of upconversion nanoplatforms with efficient NIR light harvesting ability, sufficient energy transmission channels, and low levels of luminescence quenching at the particle's surface. In addition to providing a deep understanding of the underlying mechanism of energy flux, these discoveries will guide the development of upconversion nanosystems with significantly improved performance. The key aspects of this Account of energy flux manipulation in upconversion nanosystems mainly include the management of NIR photon energy injection, the optimization of efficient energy transfer pathways, and the minimization of energy flux leakage. Future challenges and opportunities for the development of efficient upconversion nanosystems are also discussed.
TL;DR: It is reported that the singlet-triplet emissive property can be profoundly regulated by crystal conformational distortions, probably offering new insights for design of smart crystal luminescent materials.
Abstract: Crystal-state luminophores have been of great interest in optoelectronics for years, whereas the excited state regulation at the crystal level is still restricted by the lack of control ways. We report that the singlet-triplet emissive property can be profoundly regulated by crystal conformational distortions. Employing fluoro-substituted tetrakis(arylthio)benzene luminophores as prototype, we found that couples of molecular conformations formed during different crystallizations. The deformable carbon-sulphur bond essentially drove the distortion of the molecular conformation and varied the stacking mode, together with diverse non-covalent interactions, leading to the proportional adjustment of the fluorescence and phosphorescence bands. This intrinsic strategy was further applied for solid-state multicolor emissive conversion and mechanoluminescence, probably offering new insights for design of smart crystal luminescent materials.
TL;DR: A new class of nanoparticle‐based contrast agents comprising self‐assembled NaGdF4 and CaCO3 nanoconjugates is reported, showing more than 60‐fold contrast enhancement in tumor visualization relative to the commercially used contrast agent Magnevist.
Abstract: The development of high-performance contrast agents in magnetic resonance imaging (MRI) has recently received considerable attention, as they hold great promise and potential as a powerful tool for cancer diagnosis. Despite substantial achievements, it remains challenging to develop nanostructure-based biocompatible platforms that can generate on-demand MRI signals with high signal-to-noise ratios and good tumor specificity. Here, the design and synthesis of a new class of nanoparticle-based contrast agents comprising self-assembled NaGdF4 and CaCO3 nanoconjugates is reported. In this design, the spatial confinement of the T1 source (Gd3+ ions) leads to an "OFF" MRI signal due to insufficient interaction between the protons and the crystal lattices. However, when immersed in the mildly acidic tumor microenvironment, the embedded CaCO3 nanoparticles generate CO2 bubbles and subsequently disconnect the nanoconjugate, thus resulting in an "ON" MRI signal. The in vivo performance of these nanoconjugates shows more than 60-fold contrast enhancement in tumor visualization relative to the commercially used contrast agent Magnevist. This work presents a significant advance in the construction of smart MRI nanoprobes ideally suited for deep-tissue imaging and target-specific cancer diagnosis.
TL;DR: The discovery of a new charge-transfer and separation process, namely the twisted intramolecular charge shuttle (TICS), which expands the current perspectives of charge- transfer processes and will inspire future applications.
Abstract: Charge transfer and separation are important processes governing numerous chemical reactions. Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry. Herein, we report the discovery of a new charge-transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems, the donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 90° intramolecular rotation. TICS systems thus exhibit charge shuttling. TICSs exist in several chemical families of fluorophores (such as coumarin, BODIPY, and oxygen/carbon/silicon-rhodamine), and could be utilized to construct functional fluorescent probes (i.e., viscosity- or biomolecule-sensing probes). The discovery of the TICS process expands the current perspectives of charge-transfer processes and will inspire future applications.
TL;DR: In this article, a series of acid-resistant rhodamine spirolactams with accelerated ring-closing reactions from fluorescent xanthyliums to non-fluorescent spiactams, endowing them with good photoswitchable properties even in acidic environments.
Abstract: Rhodamine spirolactam based photoswitches have been extensively applied in super-resolution single-molecule localization microscopy (SMLM). However, the ring-opening reactions of spirolactams are cross-sensitive to acid, limiting their photoswitch use to neutral pH conditions. In addition, the ring-closing reactions of spirolactams are environment-sensitive and slow (up to hours), virtually making rhodamine spirolactams caged fluorescent dyes instead of reversible photoswitches in SMLM. Herein, by introducing hydrogen bonds to stabilize spirolactams, we report a series of acid-resistant rhodamine spirolactams with accelerated ring-closing reactions from fluorescent xanthyliums to non-fluorescent spirolactams, endowing them with good photoswitchable properties even in acidic environments. By further substitution of 6-phenylethynyl naphthalimide on the spirolactam, we shifted the photoactivation wavelength into the visible region (>400 nm). Subsequently, we have successfully applied these dyes in labeling and imaging the cell surface of Bacillus subtilis at pH 4.5 using SMLM.
TL;DR: The 4-quinolones and their analogs are a heterogeneous group of biologically active compounds that have evolved in modern days to provide utilities at the forefront of antibiotic research as mentioned in this paper.
TL;DR: It is expected that the new probe present here can prompt the development of a wide variety of TP ratiometric fluorescent probes which can find application in detecting other important analytes in biological systems.
Abstract: Lysosomal pH plays an essential role in mediating various biological processes such as immunization, cell metabolism and enzyme activity Herein, by utilizing the fluorescence resonance energy transfer (FRET) strategy, a two-photon (TP) ratiometric fluorescent probe (NpLys-pH) has been developed for tracking of lysosomal pH changes in living cells, tissues, and zebrafish NpLys-pH was constructed by conjugating a pH turn-on TP fluorophore 1 (D-π-A-structured naphthalene derivative) with a pH turn-off naphthalimide fluorophore 2 via a non-conjugated linker Meanwhile, NpLys-pH has two potential pH response sites that modulate the fluorescence signal by ICT and PET, respectively The FRET process exists between the TP fluorophore 1 and naphthalimide fluorophore 2 In addition, NpLys-pH respond to pH rapidly and reversibly with high selectivity and sensitivity and has been applied for tracking lysosomal pH changes in living cells, tissues and zebrafish We expect that the new probe present here can prompt the development of a wide variety of TP ratiometric fluorescent probes which can find application in detecting other important analytes in biological systems
TL;DR: This study presents a dynamic imaging technique that fully exploits the characteristics of upconversion nanoparticles and can be used as a microscopic probe for the quantitative in-situ tracking of retrograde transport neurons with single-particle resolution in multilayered cultures.
Abstract: Cargo transport along axons, a physiological process mediated by motor proteins, is essential for neuronal function and survival. A current limitation in the study of axonal transport is the lack of a robust imaging technique with a high spatiotemporal resolution to visualize and quantify the movement of motor proteins in real-time and in different depth planes. Herein, we present a dynamic imaging technique that fully exploits the characteristics of upconversion nanoparticles. This technique can be used as a microscopic probe for the quantitative in situ tracking of retrograde transport neurons with single-particle resolution in multilayered cultures. This study may provide a powerful tool to reveal dynamic neuronal activity and intra-axonal transport function as well as any associated neurodegenerative diseases resulting from mutation or impairment in the axonal transport machinery.
TL;DR: An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species, and their staining properties were determined (Gram-positive or Gram-negative).
Abstract: An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species. When the nonemissive aggregates bound to the anionic bacteria surface, the sensor disassembled to turn on significant fluorescence. At the same time, ratiometric signals between pyrene monomer and excimer emission were controlled by different interactions with various bacteria surfaces. The resulted different fluorescent emission profiles then were obtained as fingerprints for various bacterial species. By converting emission profiles directly into output signals of two channels, fluorescence increase and ratiometric change, a two-dimensional analysis map was generated for bacteria identification. We demonstrated that our sensor rapidly identified 10 species of bacteria and 14 clinical isolated multidrug-resistant bacteria, and we determined their staining properties (Gram-positive or Gram-negative).
TL;DR: In this article, the fundamental principle for the upconversion phenomenon and the current experimental state-of-the-art for controlling photon up-conversion in lanthanidedoped nanocrystals are discussed.
Abstract: The ability to convert low-energy quanta into a quantum of higher energy is critical for a variety of applications, including photovoltaics, volumetric display, bioimaging, multiplexing sensing, super-resolution imaging, optogenetics, and potentially many others. Although the processes of second harmonic generation and multiphoton (or two-photon) absorption can be used to generate photon upconversion, lanthanide-doped upconversion nanocrystals have emerged as an attractive alternative for nonlinear upconversion of near-infrared light with pump intensities several orders of magnitude lower than required by conventional nonlinear crystals. Over the past five years, considerable efforts have been made to tune the photoluminescence of upconversion nanocrystals, and significant progress has been achieved. In this review, we focus on manipulation of the wavelength, emission intensity and lifetime of upconversion nanocrystals. Here, we outline the fundamental principle for the upconversion phenomenon, review the current experimental state-of-the-art for controlling photon upconversion in lanthanidedoped nanocrystals and highlight the prospects for multifunctional upconversion nanocrystals currently in development.
TL;DR: Rhodamine B-naphthalimide (RhB-Naph) demonstrated a distinct aggregation-induced emission (AIE) mechanism, different from the restriction of intramolecular rotations or vibrations as in traditional AIE molecules, and enabled the development of a solid-state three-color fluorescent switch upon multi-external stimuli.
TL;DR: In this article, nonradiative decay occurring at lattice defect sites may constitute an essential pathway for luminescence quenching in lanthanide-doped upconversion nanomaterials.
Abstract: Nonradiative decay occurring at lattice defect sites may constitute an essential pathway for luminescence quenching in lanthanide-doped upconversion nanomaterials. Considerable efforts have been de...
TL;DR: In this article, the authors proposed to change the surrounding of the emitting Mn2+ ions by doping alkaline-earth metal ions (A2+) into the host lattice of hexagonal-phase NaGdF4.
Abstract: DOI: 10.1002/adom.201900519 However, the multicolor integration relies almost exclusively on the manipulation of relative intensity ratios between the emission peaks. Multicolor tuning of UCNPs through modulating the band position of the emission is highly desirable for their applications in biological detection and imaging. Introducing a different type of emission with a long lifetime into conventional UCNPs is particularly attractive for lifetime-based data encoding. Such nanoparticles could allow the ease of access to a library of transient color codes for multiplexing and data encoding.[9,10] Incorporation of Mn2+ upconversion luminescence into lanthanide emission at a single-particle level may provide a much-needed solution for the abovementioned challenge.[11–13] This is because the radiative transition of T1→A1 of Mn2+ is spin-forbidden, allowing the decay lifetime of the optical transition to be much longer than that of lanthanide emitters. Additionally, the emission position and lifetime of Mn2+ ions are likely to be modulated by crystal-site engineering. Our primary design is to change the surrounding of the emitting Mn2+ ions by doping alkaline-earth metal ions (A2+) into the host lattice of hexagonal-phase NaGdF4 (Figure 1a).[14] The added dopants can induce variations in the energy gap between the T1 and A1 energy levels of Mn2+ as well as the ionic distance of Mn2+ or Gd3+, thereby enabling the color tuning of Mn2+ emission (Figure 1b). In our design, the promotion of Mn2+ ions to excited states could be enabled by trapping the excitation energy from the neighboring excited Gd3+ ions that are pumped by an energy migration through a multilayered core– shell nanoparticle (Figure S1, Supporting Information). To validate our hypothesis, we used Ca2+, Mn2+-codoped core–shell nanoparticles as a model system. We first prepared a series of NaGdF4:Ca/Mn (x/30 mol%, x = 0, 5, 20, 40, and 50) core nanoparticles by a hydrothermal method.[11] The results showed that a low Ca2+ doping concentration (<40 mol%) has a negligible impact on the size and morphology of the core nanoparticles. Transmission electron microscopy (TEM) showed that the main products are short nanorods in these cases (Figure S2a–c, Supporting Information). The diameter and length of the nanorods were estimated to be in the regions of 11–13 and 17–20 nm, respectively. Notably, high-level doping of Ca2+ (≈40 mol%) led to a shrinkage in both of the diameter (≈8–9 nm) and length (≈0–12 nm) of the nanorods (Figure S2d, Supporting Information). This morphological change is likely Crystal-site engineering of hexagonal-phase NaGdF4:Mn through alkalineearth metal (A2+) doping is used to tune the upconversion luminescence of the Mn2+ dopants. Experimental and calculated results show the ability of A2+ doping to alter the occupancy site of Mn2+ ion from Na+ to Gd3+, thus enabling an emission change from green (520 nm) to yellow (583 nm) upon excitation at 980 nm. The yellow emission of Mn2+ shows a long emission lifetime of 65 ms, more than three times longer than the green emission of Mn2+ (20 ms). The combination of tunable long-lived Mn2+ emission with lanthanide emission at a single-particle level provides a convenient route to triple transient upconversion color codes upon dynamic excitation, which offers an attractive optical feature particularly suitable for efficient document encoding.