Synthesis of Upconversion β-NaYF₄:Nd3+/Yb3+/Er3+ Particles with Enhanced Luminescent Intensity through Control of Morphology and Phase

Assessing the Effect of Surface Coating on the Stability, Degradation, Toxicity and Cell Endocytosis/Exocytosis of Upconverting Nanoparticles

Lanthanide-doped up-converting nanoparticles (UCNPs) have emerged as promising biomedical tools in recent years. Most research efforts were devoted to the synthesis of inorganic cores with the optimal physicochemical properties. However, the careful design of UCNPs with the adequate surface coating to optimize their biological performance still remains a significant challenge. Here, we propose the functionalization of UCNPs with four distinct types of surface coatings, which were compared in terms of the provided colloidal stability and resistance to degradation in different biological-relevant media, including commonly avoided analysis in acidic lysosomal-mimicking fluids. Moreover, the influence of the type of particle surface coating on cell cytotoxicity and endocytosis/exocytosis was also evaluated. The obtained results demonstrated that the functionalization of UCNPs with poly(isobutylene-alt-maleic anhydride) grafted with dodecylamine (PMA-g-dodecyl) constitutes an outstanding strategy for their subsequent biomedical application, whereas poly(ethylene glycol) (PEG) coating, although suitable for colloidal stability purposes, hinders extensive cell internalization. Conversely, surface coating with small ligand were found not to be suitable, leading to large degradation degrees of UCNPs. The analysis of particle' behavior in different biological media and in vitro conditions here performed pretends to help researchers to improve the design and implementation of UCNPs as theranostic nanotools.

Morphology controlled synthesis of Fe3+-doped upconversion nanomaterials

This work details the synthesis of paramagnetic upconversion nanoparticles doped with Fe3+ in various morphologies via the thermal decomposition method, followed by comprehensive characterization of their structures, optical properties and magnetism using diverse analytical techniques. Our findings demonstrate that by precisely modulating the ratio of oleic acid to octadecene in the solvent, one can successfully obtain hexagonal nanodiscs with a consistent and well-defined morphology. Further adjustments in the oleic acid to octadecene ratio, coupled with fine-tuning of the Na+/F- ratio, led to the production of small-sized nanorods with uniform morphology. Significantly, all Fe3+-doped nanoparticles displayed pronounced paramagnetism, with magnetic susceptibility measurements at 1 T and room temperature of 0.15 emu g-1 and 0.14 emu g-1 for the nanodiscs and nanorods, respectively. To further enhance their magnetic properties, we replaced the Y-matrix with a Gd-matrix, and by fine-tuning the oleic acid/octadecene and Na+/F- ratios, we achieved nanoparticles with uniform morphology. The magnetic susceptibility was 0.82 emu g-1 at 1 T and room temperature. Simultaneously, we could control the nanoparticle size by altering the synthesis temperature. These upconversion nanostructures, characterized by both paramagnetic properties and regular morphology, represent promising dual-mode nanoprobe candidates for optical biological imaging and magnetic resonance imaging.

Subcellular imaging and diagnosis of cancer using engineered nanoparticles

The advances in the synthesis of nanoparticles with engineered properties are reported to have profound applications in oncological disease detection via optical and multimodal imaging and therapy. Among various nanoparticle-assisted imaging techniques, engineered fluorescent nanoparticles show great promise from high contrast images and localized therapeutic applications. Of all the fluorescent nanoparticles available, the gold nanoparticles, carbon dots, and upconversion nanoparticles are emerging recently as the most promising candidates for diagnosis, treatment, and cancer monitoring. This review addresses the recent progress in engineering the properties of these emerging nanoparticles and their application for cancer diagnosis and therapy. In addition, the potential of these particles for subcellular imaging is also reviewed here.

Barium yttrium fluoride based upconversion nanoparticles as dual mode image contrast agents

Dual labeled contrast agents could provide better complementary information for bioimaging than available solely from a single modality. In this paper we investigate the suitability of Yb³⁺ and Er³⁺-doped BaYF₅ upconversion nanoparticles (UCNPs) as both optical and X-ray micro computed tomography (μCT) contrast agents. Stable, aqueous UCNP dispersions were synthesised using a hydrothermal method with the addition of polyethyleneimine (PEI). UCNPs were single crystal and had a truncated cuboidal and/or truncated octahedral morphology, with average particle size of 47 ±9 nm from transmission electron microscopy which was further used to characterize the structure and composition in detail. A zeta potential value of +51 mV was measured for the aqueous nanoparticle dispersions which is beneficial for cell permeability. The outer hydrated PEI layer is also advantageous for the attachment of proteins for targeted delivery in biological systems. The prepared UCNPs were proven to be non-toxic to endothelial cells up to a concentration of 3.5 mg/mL, when assessed using an MTT assay. The particles showed intense green upconversion photoluminescence when excited at a wavelength of 976 nm using a diode laser. Quantitative X-ray μCT contrast imaging confirmed the potential of these UCNPs as X-ray contrast agents and confirming their dual modality for bioimaging.

Fabrication of Er3+/Yb3+ Co-Doped Bi5O7I Microsphere With Upconversion Luminescence and Enhanced Photocatalytic Activity for Bisphenol A Degradation

Er3+/Yb3+ co-doped Bi5O7I uniform porous microsphere photocatalysts were synthesized by a two-step chemical method, which possesses excellent photocatalytic performance and upconversion luminescence property. The photocatalytic performance of the photocatalysts was studied by degradation of bisphenol A in aqueous solution under visible light and different monochromatic light irradiation. The photocatalytic performance of Er3+/Yb3+ co-doped Bi5O7I sample is better than that of the pristine Bi5O7I and Er3+-doped Bi5O7I samples. Moreover, Er3+/Yb3+ co-doped Bi5O7I possesses photocatalytic ability with a red light monochromatic LED lamp (3 W, λ = 630 nm) and an infrared monochromatic LED lamp (100 W, λ = 940 nm) irradiation whose wavelength is longer than the absorption-limiting wavelength of pristine Bi5O7I sample. This phenomenon further verified that the upconversion property of Er3+ and Yb3+ causes the improved photocatalytic efficiency of Er3+/Yb3+ co-doped Bi5O7I sample.

Morphology control, spectrum modification and extended optical applications of rare earth ion doped phosphors

This review summarizes the morphology control strategy, phase transfer theory, spectrum modulation, and extended optical applications of RE³⁺-doped phosphors.

Yb,Nd,Er-doped upconversion nanoparticles: 980 nm versus 808 nm excitation

Yb,Nd,Er-doped upconversion nanoparticles (UCNPs) have attracted considerable interest as luminescent reporters for bioimaging, sensing, energy conversion/shaping, and anticounterfeiting due to their capability to convert multiple near-infrared (NIR) photons into shorter wavelength ultraviolet, visible or NIR luminescence by successive absorption of two or more NIR photons. This enables optical measurements in complex media with very little background and high penetration depths for bioimaging. The use of Nd³⁺ as substitute for the commonly employed sensitizer Yb³⁺ or in combination with Yb³⁺ shifts the excitation wavelength from about 980 nm, where the absorption of water can weaken upconversion luminescence, to about 800 nm, and laser-induced local overheating effects in cells, tissue, and live animal studies can be minimized. To systematically investigate the potential of Nd³⁺ doping, we assessed the performance of a set of similarly sized Yb³⁺,Nd³⁺,Er³⁺-doped core- and core-shell UCNPs of different particle architecture in water at broadly varied excitation power densities (P) with steady state and time-resolved fluorometry for excitation at 980 nm and 808 nm. As a measure for UCNPs performance, the P-dependent upconversion quantum yield (Φ_UC) and its saturation behavior were used as well as particle brightness (B_UC). Based upon spectroscopic measurements at both excitation wavelengths in water and in a lipid phantom and B_UC-based calculations of signal size at different penetration depths, conditions under which excitation at 808 nm is advantageous are derived and parameters for the further optimization of triple-doped UCNPs are given.

Tuning the upconversion photoluminescence lifetimes of NaYF4:Yb3+, Er3+ through lanthanide Gd3+ doping

The multiplexing capacity of conventional fluorescence materials are significantly limited by spectral overlap and background interference, mainly due to their short-lived fluorescence lifetimes. Here, we adopt a novel Gd³⁺ doping strategy in NaYF₄ host materials, realized tuning of upconversion photoluminescence (UCPL) lifetimes at selective emissions. Time-correlated single-photon counting (TCSPC), was applied to measure the photoluminescence lifetimes accurately. We demonstrated the large dynamic range of lifetimes of upconversion nanoparticles with good upconversion quantum yields, mainly owing to the dominance of high efficient energy transfer upconversion mechanism. The exceptional tunable properties of upconversion materials allow great potential for them to be utilized in biotechnology and life sciences.

808-nm-Light-Excited Lanthanide-Doped Nanoparticles: Rational Design, Luminescence Control and Theranostic Applications

808 nm-light-excited lanthanide (Ln³⁺ )-doped nanoparticles (LnNPs) hold great promise for a wide range of applications, including bioimaging diagnosis and anticancer therapy. This is due to their unique properties, including their minimized overheating effect, improved penetration depth, relatively high quantum yields, and other common features of LnNPs. In this review, the progress of 808 nm-excited LnNPs is reported, including their i) luminescence mechanism, ii) luminescence enhancement, iii) color tuning, iv) diagnostic and v) therapeutic applications. Finally, the future outlook and challenges of 808 nm-excited LnNPs are presented.

Lanthanide-Doped KLu2F7 Nanoparticles with High Upconversion Luminescence Performance: A Comparative Study by Judd-Ofelt Analysis and Energy Transfer Mechanistic Investigation

The development, design and the performance evaluation of rare-earth doped host materials is important for further optical investigation and industrial applications. Herein, we successfully fabricate KLu₂F₇ upconversion nanoparticles (UCNPs) through hydrothermal synthesis by controlling the fluorine-to-lanthanide-ion molar ratio. The structural and morphological results show that the samples are orthorhombic-phase hexagonal-prisms UCNPs, with average side length of 80 nm and average thickness of 110 nm. The reaction time dependent crystal growth experiment suggests that the phase transformation is a thermo-dynamical process and the increasing F^-/Ln³⁺ ratio favors the formation of the thermo-dynamical stable phase - orthorhombic KLu₂F₇ structure. The upconversion luminescence (UCL) spectra display that the orthorhombic KLu₂F₇:Yb/Er UCNPs present stronger UCL as much as 280-fold than their cubic counterparts. The UCNPS also display better UCL performance compared with the popular hexagonal-phase NaREF₄ (RE = Y, Gd). Our mechanistic investigation, including Judd-Ofelt analysis and time decay behaviors, suggests that the lanthanide tetrad clusters structure at sublattice level accounts for the saturated luminescence and highly efficient UCL in KLu₂F₇:Yb/Er UCNPs. Our research demonstrates that the orthorhombic KLu₂F₇ is a promising host material for UCL and can find potential applications in lasing, photovoltaics and biolabeling techniques.

Crystallization kinetics mechanism investigation of sol–gel-derived NaYF4:(Yb,Er) up-converting phosphors

The crystallization mechanism of sol–gel-derived NaYF₄:(Yb,Er) up-converting phosphors has been studied by differential scanning calorimetry analysis using both model-free and model fitting approaches.

Synergistically enhanced upconversion luminescence in Li+-doped core–shell-structured ultrasmall nanoprobes for dual-mode deep tissue fluorescence/CT imaging

The development of upconversion luminescence that allows for multimodal imaging in terms of resolution and penetration depth using a single system is attracting increasing interest for use in clinical molecular imaging and diagnostics.

The Influence of Fluorination on Nano-Scale Phase Separation and Photovoltaic Performance of Small Molecular/PC71BM Blends

To investigate the fluorination influence on the photovoltaic performance of small molecular based organic solar cells (OSCs), six small molecules based on 2,1,3-benzothiadiazole (BT), and diketopyrrolopyrrole (DPP) as core and fluorinated phenyl (DFP) and triphenyl amine (TPA) as different terminal units (DFP-BT-DFP, DFP-BT-TPA, TPA-BT-TPA, DFP-DPP-DFP, DFP-DPP-TPA, and TPA-DPP-TPA) were synthesized. With one or two fluorinated phenyl as the end group(s), HOMO level of BT and DPP based small molecular donors were gradually decreased, inducing high open circuit voltage for fluorinated phenyl based OSCs. DFP-BT-TPA and DFP-DPP-TPA based blend films both displayed stronger nano-scale aggregation in comparison to TPA-BT-TPA and TPA-DPP-TPA, respectively, which would also lead to higher hole motilities in devices. Ultimately, improved power conversion efficiency (PCE) of 2.17% and 1.22% was acquired for DFP-BT-TPA and DFP-DPP-TPA based devices, respectively. These results demonstrated that the nano-scale aggregation size of small molecules in photovoltaic devices could be significantly enhanced by introducing a fluorine atom at the donor unit of small molecules, which will provide understanding about the relationship of chemical structure and nano-scale phase separation in OSCs.

Influence of synthesis conditions on the morphologies of ReBO3 microstructures and white light emission of YBO3:Eu3+ phosphors prepared by an oleic acid-assisted hydrothermal method

YBO₃:5%Eu³⁺ phosphor prepared by the OA-assisted hydrothermal method displays the white color under excitation at 394 nm, and the light color of YBO₃:Eu³⁺ can be varied with the Eu³⁺ dopant concentration or the excitation wavelength.

Enhancing Solar Cell Efficiency Using Photon Upconversion Materials

Photovoltaic cells are able to convert sunlight into electricity, providing enough of the most abundant and cleanest energy to cover our energy needs. However, the efficiency of current photovoltaics is significantly impeded by the transmission loss of sub-band-gap photons. Photon upconversion is a promising route to circumvent this problem by converting these transmitted sub-band-gap photons into above-band-gap light, where solar cells typically have high quantum efficiency. Here, we summarize recent progress on varying types of efficient upconversion materials as well as their outstanding uses in a series of solar cells, including silicon solar cells (crystalline and amorphous), gallium arsenide (GaAs) solar cells, dye-sensitized solar cells, and other types of solar cells. The challenge and prospect of upconversion materials for photovoltaic applications are also discussed.