NaF-mediated controlled-synthesis of multicolor Na(x)ScF(3+x):Yb/Er upconversion nanocrystals

Photon Upconversion in Small Molecules

Upconversion (UC) is a process that describes the emission of shorter-wavelength light compared to that of the excitation source. Thus, UC is also referred to as anti-Stokes emission because the excitation wavelength is longer than the emission wavelength. UC materials are used in many fields, from electronics to medicine. The objective of using UC in medical research is to synthesize upconversion nanoparticles (UCNPs) composed of a lanthanide core with a coating of adsorbed dye that will generate fluorescence after excitation with near-infrared light to illuminate deep tissue. Emission occurs in the visible and UV range, and excitation mainly in the near-infrared spectrum. UC is observed for lanthanide ions due to the arrangement of their energy levels resulting from f-f electronic transitions. Organic compounds and transition metal ions are also able to form the UC process. Biocompatible UCNPs are designed to absorb infrared light and emit visible light in the UC process. Fluorescent dyes are adsorbed to UCNPs and employed in PDT to achieve deeper tissue effects upon irradiation with infrared light. Fluorescent UCNPs afford selectivity as they may be activated only by illumination of an area of diseased tissue, such as a tumor, with infrared light and are by themselves atoxic in the absence of infrared light. UCNP constructs can be monitored as to their location in the body and uptake by cancer cells, aiding in evaluation of exact doses required to treat the targeted cancer. In this paper, we review current research in UC studies and UCNP development.

Local Structure Engineering in Lanthanide-Doped Nanocrystals for Tunable Upconversion Emissions

Upconversion emissions from lanthanide-doped nanocrystals have sparked extensive research interests in nanophotonics, biomedicine, photovoltaics, photocatalysis, etc. Rational modulation of upconversion emissions is highly desirable to meet the requirements of specific applications. Among the diverse developed methods, local structure engineering is fundamentally feasible, through which the upconversion emission intensity, selectivity, wavelength shift, and lifetime can be tuned effectively. The underlying mechanism of the local-structure-dependent upconversion emissions lies in the degree of parity hybridization and energy level splitting of lanthanide ions as well as the interionic energy transfer efficiency. Over the past few years, there has been significant progress in local-structure-engineered upconversion emissions. In this Perspective, we first introduce the principles of upconversion emissions and typical characterization methods for local structure. Subsequently, we summarize recent achievements in tuning of upconversion emissions through local structure engineering, including host composition adjustment, external field regulation, and interfacial strain management. Finally, we propose a few perspectives that should tackle the current bottlenecks. This Perspective is expected to deepen the understanding of local-structure-dependent upconversion emissions and arouse adequate attention to the engineering of local structure for desired properties of inorganic nanocrystals.

Up-Conversion Luminescent Nanoparticles for Molecular Imaging, Cancer Diagnosis and Treatment

In the past few years, we have witnessed great development and application potential of various up-conversion luminescent nanoparticles (UCNPs) in the nanomedicine field. Based on the unique luminescent mechanism of UCNPs and the distinguishable features of cancer biomarkers and the microenvironment, an increasing number of smart UCNPs nanoprobes have been designed and widely applied to molecular imaging, cancer diagnosis, and treatment. Considerable technological success has been achieved, but the main obstacles to oncology nanomedicine is becoming an incomplete understanding of nano-bio interactions, the challenges regarding chemistry manufacturing and controls required for clinical translation and so on. This review highlights the progress of the design principles, synthesis and surface functionalization preparation, underlying applications and challenges of UCNPs-based probes for cancer bioimaging, diagnosis and treatment that capitalize on our growing understanding of tumor biology and smart nano-devices for accelerating the commercialization of UCNPs.

A high performance Sc-based nanoprobe for through-skull fluorescence imaging of brain vessels beyond 1500 nm

Optical bioimaging that works in the second near infrared region (NIR-II, 1000-1700 nm) has emerged as a next generation imaging technique with superior imaging sensitivity and spatial resolution compared to traditional optical imaging utilizing visible and near-infrared lights (below 900 nm). Herein, a new Sc-based NIR-II probe was explored for high performance NIR-II in vivo bioimaging and optical imaging-guided non-invasive brain blood vessel visualization. The lanthanide doped Sc-based probes (KSc2F7:Yb3+/Er3+) possess a pure orthorhombic phase structure with size control by adjusting the F- ion content. These probes present a dominant red upconversion (UC) emission, which is significantly different from the traditional NaYF4:Yb/Er host, which usually has a green UC emission. More importantly, apart from the dominant red UC emission, these probes also possess a strong NIR-II downconversion (DC) emission centered at 1525 nm, which is usually ignored for bioimaging applications. In vivo NIR-II imaging reveals that our explored Sc-based nanorods are promising probes for highly sensitive optical imaging. Moreover, non-invasive through-skull fluorescence bioimaging of brain vessels with high spatial resolution was demonstrated. Therefore, it is expected that Sc-based nanomaterials with unique dominant red UC and DC NIR-II emissions beyond 1500 nm are ideal probes for bio-applications.

Fixed-diameter upconversion nanorods with controllable length and their interaction with cells

A series of NaYF₄: Yb, Er upconversion nanorods with fixed diameter and controllable length were synthesized by the injection of sodium trifluoroacetate (CF₃COONa) mixed with potassium trifluoroacetate (CF₃COOK) precursor into a heated solution of ligand. We found that with the increased percentage of CF₃COOK, the length of resultant nanorods was increased from ∼40 nm to ∼200 nm whilst the diameter was kept in a narrow range of 37-42 nm. The elongation of nanorods was attributed to the specific absorption of sodium oleate on the prismatic facets, and the integration of potassium ions into the lattice as well. We further found that the elongated length affected the relative fluorescence intensity between red and green emission. More importantly, with fixed diameter, the cellular uptake of nanorods was found decreasing with the increase of their length. Meanwhile the decrease of diameter resulted in an increased cellular uptake. These results were attributed to both specific surface area and possibly varied contacting angle between nanorods and cell membrane. The current work not only suggested a synthetic method for the precise control of upconversion nanorods, but also shed light on the design of nanocrystals for cell-related biomedical applications.

One-step surfactant-free synthesis of KSc2F7 microcrystals: controllable phases, rich morphologies and multicolor down conversion luminescence properties

The obtained products show controlled phases and abundant morphologies with the increase of fluoride ion concentration.

Interconversion between KSc2F7:Yb/Er and K2NaScF6:Yb/Er nanocrystals: the role of chemistry

Interconversion between nanocrystals of orthorhombic KSc₂F₇:Yb/Er and cubic K₂NaScF₆:Yb/Er was realized by adjusting the according chemical reaction conditions.

Controlled synthesis of high quality scandium-based nanocrystals as promising recyclable catalysts for silylcyanation reaction

High quality (monodisperse and well-defined) scandium based ternary fluoride nanocrystals of NaScF₄ and KSc₂F₇ were successfully fabricated via a one-pot colloidal synthesis method. These nanocrystals can play the part of hard Lewis acid catalysts by providing Lewis acid sites on account of the unique electronic structure, i.e. the ability of polarizing double bonds by coordination. As a proof of concept application, NaScF₄ and KSc₂F₇ nanocatalysts were used to catalyze the silylcyanation reaction at room temperature, which exhibited excellent catalytic activity with outstanding recyclability.

Hydrothermal synthesis of Ba3Sc2F12:Yb3+, Ln3+ (Ln = Er, Ho, Tm) crystals and their up conversion white light emission

We have successfully synthesized Ba₃Sc₂F₁₂:Yb³⁺, Ln³⁺ (Ln = Er, Ho, Tm) crystals and achieved multicolor luminescence including the white light UC emission.

Current Advances in Lanthanide-Doped Upconversion Nanostructures for Detection and Bioapplication

Along with the development of science and technology, lanthanide-doped upconversion nanostructures as a new type of materials have taken their place in the field of nanomaterials. Upconversion luminescence is a nonlinear optical phenomenon, which absorbs two or more photons and emits one photon. Compared with traditional luminescence materials, upconversion nanostructures have many advantages, such as weak background interference, long lifetime, low excitation energy, and strong tissue penetration. These interesting nanostructures can be applied in anticounterfeit, solar cell, detection, bioimaging, therapy, and so on. This review is focused on the current advances in lanthanide-doped upconversion nanostructures, covering not only basic luminescence mechanism, synthesis, and modification methods but also the design and fabrication of upconversion nanostructures, like core-shell nanoparticles or nanocomposites. At last, this review emphasizes the application of upconversion nanostructure in detection and bioimaging and therapy. Learning more about the advances of upconversion nanostructures can help us better exploit their excellent performance and use them in practice.

From ScOOH to Sc2 O3 : Phase Control, Luminescent Properties, and Applications

In the controlled synthesis of ScOOH nanomaterials, the surfactant molecule Na3 Cit not only helps to manipulate the crystallographic structures, but also to initiate the transfer from α-ScOOH to γ-ScOOH. Further annealing of ScOOH generates cubic Sc2 O3 with morphologies inherited from respective origins. When doped with lanthanide ions, both ScOOH and Sc2 O3 can be utilized for high-temperature probing and light-emitting-diode lighting.

Smart multifunctional drug delivery towards anticancer therapy harmonized in mesoporous nanoparticles

Nanomedicine seeks to apply nanoscale materials for the therapy and diagnosis of diseased and damaged tissues. Recent advances in nanotechnology have made a major contribution to the development of multifunctional nanomaterials, which represents a paradigm shift from single purpose to multipurpose materials. Multifunctional nanomaterials have been proposed to enable simultaneous target imaging and on-demand delivery of therapeutic agents only to the specific site. Most advanced systems are also responsive to internal or external stimuli. This approach is particularly important for highly potent drugs (e.g. chemotherapeutics), which should be delivered in a discreet manner and interact with cells/tissues only locally. Both advances in imaging and precisely controlled and localized delivery are critically important in cancer treatment, and the use of such systems - theranostics - holds great promise to minimise side effects and boost therapeutic effectiveness of the treatment. Among others, mesoporous silica nanoparticles (MSNPs) are considered one of the most promising nanomaterials for drug delivery. Due to their unique intrinsic features, including tunable porosity and size, large surface area, structural diversity, easily modifiable chemistry and suitability for functionalization, and biocompatibility, MSNPs have been extensively utilized as multifunctional nanocarrier systems. The combination or hybridization with biomolecules, drugs, and other nanoparticles potentiated the ability of MSNPs towards multifunctionality, and even smart actions stimulated by specified signals, including pH, optical signal, redox reaction, electricity and magnetism. This paper provides a comprehensive review of the state-of-the-art of multifunctional, smart drug delivery systems centered on advanced MSNPs, with special emphasis on cancer related applications.

KF-mediated controlled-synthesis of potassium ytterbium fluorides (doped with Er3+) with phase-dependent upconversion luminescence

Potassium ytterbium fluorides with predictable crystal phases and architectures have been successfully synthesized by simply tuning the molar ratio of KF to Yb³⁺via a facile and general solution-based approach.