Enhanced upconversion luminescence in NaGdF4:Yb,Er nanocrystals by Fe3+ doping and their application in bioimaging

Z-Scheme Photocatalyst Constructed by Natural Attapulgite and Upconversion Rare Earth Materials for Desulfurization

The Er³⁺:CeO₂/ATP (attapulgite) nanocomposites were prepared by a facile precipitation method. The samples were characterized by various measurements. XRD and TEM showed that Er³⁺:CeO₂ nanoparticles were well-crystallized and loaded on the surface of ATP. The visible light was converted into ultraviolet light by Er³⁺:CeO₂ as evidenced by upconversion photoluminance (PL) analysis. The mass ratio of Er³⁺:CeO₂ to ATP on the desulfurization efficiency was investigated. Results showed that the desulfurization rate reached 87% under 4 h visible light irradiation when the mass ratio was 4:10. The mechanism was put forward as follows. Er³⁺:CeO₂ and ATP formed Z-scheme heterostructure intermediated by oxygen vacancy, leading to the enhanced separation of photogenerated charges and preservation of high oxidation-reduction potential, both of which favored for the generation of radicals to oxidize sulfur species.

Lanthanide Doped Near Infrared Active Upconversion Nanophosphors: Fundamental Concepts, Synthesis Strategies, and Technological Applications

Near infrared (NIR) light utilization in a range of current technologies has gained huge significance due to its abundance in nature and nondestructive properties. NIR active lanthanide (Ln) doped upconversion nanomaterials synthesized in controlled shape, size, and surface functionality can be combined with various pertinent materials for extensive applications in diverse fields. Upconversion nanophosphors (UCNP) possess unique abilities, such as deep tissue penetration, enhanced photostability, low toxicity, sharp emission peaks, long anti-Stokes shift, etc., which have bestowed them with prodigious advantages over other conventional luminescent materials. As new generation fluorophores, UCNP have found a wide range of applications in various fields. In this Review, a comprehensive overview of lanthanide doped NIR active UCNP is provided by discussing the fundamental concepts including the different mechanisms proposed for explaining the upconversion processes, followed by the different strategies employed for the synthesis of these materials, and finally the technological applications of UCNP, mainly in the fields of bioimaging, drug delivery, sensing, and photocatalysis by highlighting the recent works in these areas. In addition, a brief note on the applications of UCNP in other fields is also provided along with the summary and future perspectives of these materials.

Extended Near-Infrared Photoactivity of Bi₆Fe1.9Co0.1Ti₃O18 by Upconversion Nanoparticles

Bi₆Fe_1.9Co_0.1Ti₃O₁₈ (BFCTO)/NaGdF₄:Yb³⁺, Er³⁺ (NGF) nanohybrids were successively synthesized by the hydrothermal process followed by anassembly method, and BFCTO-1.0/NGF nanosheets, BFCTO-1.5/NGF nanoplates and BFCTO-2.0/NGF truncated tetragonal bipyramids were obtained when 1.0, 1.5 and 2.0 M NaOH were adopted, respectively. Under the irradiation of 980 nm light, all the BFCTO samples exhibited no activity in degrading Rhodamine B (RhB). In contrast, with the loading of NGF upconversion nanoparticles, all the BFCTO/NGF samples exhibited extended near-infrared photoactivity, with BFCTO-1.5/NGF showing the best photocatalytic activity, which could be attributed to the effect of {001} and {117} crystal facets with the optimal ratio. In addition, the ferromagnetic properties of the BFCTO/NGF samples indicated their potential as novel, recyclable and efficient near-infrared (NIR) light-driven photocatalysts.

Lanthanide Yb/Er co-doped semiconductor layered WSe2 nanosheets with near-infrared luminescence at telecommunication wavelengths

Atomically thin layers of transition metal dichalcogenides (TMDs) have recently drawn great attention. However, doping strategies and controlled synthesis for wafer-scale TMDs are still in their early stages, greatly hindering the construction of devices and further basic studies. In this work, we develop the fast deposition of wafer-scale layered lanthanide ion Yb/Er co-doped WSe2 using pulsed laser deposition. WSe2 nanosheets were chosen as the host, while Yb3+ and Er3+ ions served as the sensitizer and activator, respectively. The obtained Yb/Er co-doped WSe2 layers exhibit good uniformity and high crystallinity with highly textured features. Under the excitation of a diode laser at 980 nm, down-conversion emission is observed at around 1540 nm, assigned to the emission transition between the 4I13/2 and 4I15/2 states of Er3+. Considering the significance of 1540 nm luminescence in the application of photonic technologies, this observation in the WSe2:Yb/Er nanosheets down to the monolayer provides a new opportunity for developing photonic devices at the 2D limit. Our work not only offers a general method to prepare wafer-scale lanthanide doped TMDs, but also to widely modulate the luminescence of atomically layered TMDs by introducing lanthanide ions.

Synthesis and luminescence properties of NaGdF4: Yb3+, Ce3+, and Ho3+ upconversion nanoparticles doped with Zn2+

Due to shrinkage of crystal lattice and formation of F⁻ vacancies, the luminescence intensities show a rise-and-fall change with growing Zn²⁺ concentration in β-NaGdF₄ UCNPs.

Controllable synthesis of lanthanide Yb3+ and Er3+ co-doped AWO4 (A = Ca, Sr, Ba) micro-structured materials: phase, morphology and up-conversion luminescence enhancement

The combination of CDs can mainly maintain the morphologies of AWO₄:Yb³⁺,Er³⁺ but prominently increase their up-conversion luminescence performance.

Simultaneous size adjustment and upconversion luminescence enhancement of β-NaLuF4:Yb3+/Er3+,Er3+/Tm3+ microcrystals by introducing Ca2+ for temperature sensing

β-NaLuF₄:Yb³⁺/Er³⁺ microcrystals have been obtained through a facile hydrothermal method at a relatively low temperature (180 °C) within only two hours.

Fe3+-Enhanced NIR-to-NIR upconversion nanocrystals for tumor-targeted trimodal bioimaging

Fe³⁺-Enhanced NIR-to-NIR multifunctional upconversion luminescence nanocrystals were synthesized for excellent tumor-targeted UCL/MRI/X-ray trimodal bioimaging.

Enhanced upconversion luminescence and controllable phase/shape of NaYF4:Yb/Er crystals through Cu2+ ion doping

The crystal phase/shape and upconversion luminescence properties of NaYF₄:Yb/Er crystals could be fine-tuned through doping with Cu²⁺ ions.

PEGylated GdF3:Fe Nanoparticles as Multimodal T1/T2-Weighted MRI and X-ray CT Imaging Contrast Agents

Contrast agents for multimodal imaging are in high demand for cancer diagnosis. To date, integration of T₁/T₂-weighted magnetic resonance imaging (MRI) and X-ray computed tomography (CT) imaging capabilities in one system to obtain an accurate diagnosis still remains challenging. In this work, biocompatible PEGylated GdF₃:Fe nanoparticles (PEG-GdF₃:Fe NPs) were reasonable designed and synthesized as multifunctional contrast agents for efficient T₁/T₂-weighted MRI and X-ray CT multimodal imaging. Owing to the enhanced permeability and retention effect in vivo, strong T₁ contrast, evident T₂ contrast, and X-ray CT signals in a tumor lesion can be observed after intravenous injection of PEG-GdF₃:Fe NPs. Therefore, PEG-GdF₃:Fe NPs could be used as potential multimodal contrast agents for cancer diagnosis.

Manipulating the emission intensity and lifetime of NaYF4:Yb3+,Er3+ simultaneously by embedding it into CdS photonic crystals

Photonic crystals (PCs) have long been considered effective for tuning upconversion luminescence due to their photonic band gap (PBG) and the redistribution of density of optical states (DOS). Although the emission intensity can be changed obviously by the PC effect, rarely an obvious lifetime change consistent with theory is observed due to the low refractive index of PS or SiO₂ spheres in the commonly used PCs. Herein, CdS/NaYF₄:Yb³⁺,Er³⁺ composite PCs with a high refractive index contrast are fabricated in one step with upconversion nanoparticles filled inside CdS PCs. When the upconversion emission peak lies at the edge of the PBGs of the composite PCs, a dramatic decrease in lifetime by 28% and 41% is observed for the green and red emissions, respectively. At the same time, obvious emission intensity enhancements are also observed. In contrast, PS PCs with a low refractive index contrast show a slight effect on the lifetime of upconversion luminescence with their emission peak at the edge of the PBGs. Our results agree well with theory and prove that a sufficiently large refractive index contrast is necessary for PCs to dramatically tune the luminescence lifetime and intensity simultaneously.

M2+ Doping Induced Simultaneous Phase/Size Control and Remarkable Enhanced Upconversion Luminescence of NaLnF4 Probes for Optical-Guided Tiny Tumor Diagnosis

Doping has played a vital role in constructing desirable hybrid materials with tunable functions and properties via incorporating atoms into host matrix. Herein, a simple strategy for simultaneously modifying the phase, size, and upconversion luminescence (UCL) properties of the NaLnF₄ (Ln = Y, Yb) nanocrystals by high-temperature coprecipitation through nonequivalent M²⁺ doping (M = Mg²⁺ , Co²⁺ ) has been demonstrated. The phase transformation from cubic to hexagonal is readily achieved by doping M²⁺ . Compared with Mg-free sample, a remarkable enhancement of overall UCL (≈27.5 times) is obtained by doping Mg²⁺ . Interestingly, owing to the efficient UCL, red UCL-guided tiny tumor (down to 3 mm) diagnosis is demonstrated for the first time. The results open up a new way of designing high efficient UCL probe with combination of hexagonal phase and small size for tiny tumor detection.

Yb3+,Er3+,Eu3+-codoped YVO4 material for bioimaging with dual mode excitation

We propose an efficient bioimaging strategy using Yb³⁺,Er³⁺,Eu³⁺-triplet doped YVO₄ nanoparticles which were synthesized with polymer as a template. The obtained particles possess nanoscale, uniform, and flexible excitation. The effect of Eu³⁺ ions on the luminescence properties of YVO₄:Yb³⁺,Er³⁺,Eu³⁺ was investigated. The upconversion mechanism of the prepared material was also discussed. The structure and optical properties of the prepared material were characterized by using X-ray diffraction (XRD), Fourier-transform IR spectroscopy (FTIR), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) upconversion and photoluminescence spectra. The Commission International de I'Eclairage (CIE) chromaticity coordinates was investigated to confirm the performance of color luminescent emission. The prepared YVO₄:Yb³⁺,Er³⁺,Eu³⁺ nanoparticles could be easily dispersed in water by surface modification with cysteine (Cys) and glutathione (GSH). The aqueous dispersion of the modified YVO₄:Yb³⁺,Er³⁺,Eu³⁺ exhibits bright upconversion and downconversion luminescence and has been applied for bioimaging of HeLa cells. Our developed material with dual excitation offers a promising advance in bioimaging.

Lanthanide doped ultrafine hybrid nanostructures: multicolour luminescence, upconversion based energy transfer and luminescent solar collector applications

We herein demonstrate novel inorganic-organic hybrid nanoparticles (HNPs) composed of inorganic NPs, NaY_0.78Er_0.02Yb_0.2F₄, and an organic β-diketonate complex, Eu(TTA)₃Phen, for energy harvesting applications. Both the systems maintain their core integrity and remain entangled through weak interacting forces. HNPs incorporate the characteristic optical behaviour of both the systems i.e. they give an intense red emission under UV excitation, due to Eu³⁺ in organic complexes, and efficient green upconversion emission of Er³⁺ in inorganic NPs for NIR (980 nm) excitation. However, (i) an energy transfer from Er³⁺ (inorganic NPs) to Eu³⁺ (organic complex) under NIR excitation, and (ii) an increase in the decay time of ⁵D₀ → ⁷F₂ transition of Eu³⁺ for HNPs as compared to the Eu(TTA)₃Phen complex, under different excitation wavelengths, are added optical characteristics which point to an important role of the interface between both the systems. Herein, the ultra-small size (6-9 nm) and spherical shape of the inorganic NPs offer a large surface area, which improves the weak interaction force between both the systems. Furthermore, the HNPs dispersed in the PMMA polymer have been successfully utilized for luminescent solar collector (LSC) applications.

Enhanced red upconversion emission and its mechanism in Yb3+–Er3+ codoped α-NaLuF4 nanoparticles

Red upconversion luminescence is greatly enhanced through manipulation of the initial solution pH.

Comprehensive studies of the Li+ effect on NaYF4:Yb/Er nanocrystals: morphology, structure, and upconversion luminescence

Impurity doping plays a critical role in altering the properties of target nanomaterials in terms of designed morphologies, crystal structures, and functionalities.

A novel anion doping strategy to enhance upconversion luminescence in NaGd(MoO4)2:Yb3+/Er3+ nanophosphors

A novel and efficient F⁻ anion doping strategy is proposed for enhancing upconversion luminescence in NaGd(MoO₄)₂:Yb³⁺/Er³⁺ nanophosphors.

Core@shell Fe3O4@Mn2+-doped NaYF4:Yb/Tm nanoparticles for triple-modality T1/T2-weighted MRI and NIR-to-NIR upconversion luminescence imaging agents

Core@shell structures of Fe₃O₄@Mn²⁺-doped NaYF₄:Yb/Tm nanoparticles (NPs) were prepared and then used for in vivo NIR to NIR (980 nm to 800 nm) imaging, and as dual-mode T₁/T₂-weighted MRI because of the co-existence of Fe₃O₄ and Mn²⁺ in the NPs.

Special properties of luminescent magnetic NaGdF4:Yb3+, Er3+ upconversion nanocubes with surface modifications

Gadolinium-based upconversion nanocubes with amine surface modification are made by a one-pot process. The interfacial effect on their behaviors are observed.

Transition Metal-Involved Photon Upconversion

Upconversion (UC) luminescence of lanthanide ions (Ln³⁺) has been extensively investigated for several decades and is a constant research hotspot owing to its fundamental significance and widespread applications. In contrast to the multiple and fixed UC emissions of Ln³⁺, transition metal (TM) ions, e.g., Mn²⁺, usually possess a single broadband emission due to its 3d⁵ electronic configuration. Wavelength-tuneable single UC emission can be achieved in some TM ion-activated systems ascribed to the susceptibility of d electrons to the chemical environment, which is appealing in molecular sensing and lighting. Moreover, the UC emissions of Ln³⁺ can be modulated by TM ions (specifically d-block element ions with unfilled d orbitals), which benefits from the specific metastable energy levels of Ln³⁺ owing to the well-shielded 4f electrons and tuneable energy levels of the TM ions. The electric versatility of d⁰ ion-containing hosts (d⁰ normally viewed as charged anion groups, such as MoO₆^6- and TiO₄^4-) may also have a strong influence on the electric dipole transition of Ln³⁺, resulting in multifunctional properties of modulated UC emission and electrical behaviour, such as ferroelectricity and oxide-ion conductivity. This review focuses on recent advances in the room temperature (RT) UC of TM ions, the UC of Ln³⁺ tuned by TM or d⁰ ions, and the UC of d⁰ ion-centred groups, as well as their potential applications in bioimaging, solar cells and multifunctional devices.

Detecting the origin of luminescence in Er3+-doped hexagonal Na1.5Gd1.5F6 phosphors

Understanding site-selective fluorescence is one of valuable importance for spectrum modulation. In this Letter, we observed the existence of two non-equivalent Gd-activated crystallographic sites in an Er³⁺-doped hexagonal Na_1.5Gd_1.5F₆ phosphor. It is proved that two green emissions from the S_3/24 level separately originate from the Gd1 (540 nm) and Na2/Gd2 (550-555 nm) crystallographic sites, and the 657 nm red emission from the F_9/24 level only originates from Na2/Gd2 site through using the time-resolved luminescence spectra. The 142.2% absolute enhancement of the red emission is realized through the synergistic effect of ultraviolet downconversion and infrared upconversion induced by the 370 nm and 1.54 μm dual-mode excitation.

2D Layered Materials of Rare-Earth Er-Doped MoS2 with NIR-to-NIR Down- and Up-Conversion Photoluminescence

A 2D system of Er-doped MoS2 layered nanosheets is developed. Structural studies indicate that the Er atoms can be substitutionally introduced into MoS2 to form stable doping. Density functional theory calculation implies that the system remains stable. Both NIR-to-NIR up-conversion and down-conversion light-emissions are observed in 2D transition metal dichalcogenides, ascribed to the energy transition from Er(3+) dopants.

NaGdF4:Dy3+ nanofibers and nanobelts: facile construction technique, structure and bifunctionality of luminescence and enhanced paramagnetic performances

NaGdF₄:Dy³⁺ nanofibers and nanobelts with excellent luminescence-magnetic bi-functionality were fabricated via a combination of electrospinning and calcination with fluorination technology.

Enhanced upconversion luminescence and modulated paramagnetic performance in NaGdF4:Yb, Er by Mg2+ tridoping

In this work, a new strategy to enhance upconversion emission has been realized for the first time, based on β-NaGdF₄:Yb³⁺, Er³⁺ nanocrystals (UCNC) using tridoping with magnesium (Mg²⁺) ions.

Near-infrared emissive lanthanide hybridized carbon quantum dots for bioimaging applications

Facile preparation of lanthanide hybridized carbon quantum dots (Ln-CQDs) and their potential for visible/NIR bioimagingin vivo.

Upconversion nanocomposites for photo-based cancer theranostics

Upconversion nanoparticles (UCNPs) are able to convert long wavelength excitation light into high energy ultraviolet (UV) or visible emissions, and they have attracted significant attention because of their distinct photochemical properties including sharp emission bands, low autofluorescence, high tissue penetration depth and minimal photodamage to tissues.

Controlled synthesis, bioimaging and toxicity assessments in strong red emitting Mn2+ doped NaYF4:Yb3+/Ho3+ nanophosphors

Rare earth, Yb³⁺/Ho³⁺ doped NaYF₄ nanophosphors co-doped with Mn²⁺ showed enhanced red emission under NIR irradiation and were successfully used for cancer cell imaging.

UV-visible and near-infrared active NaGdF4:Yb:Er/Ag/TiO2 nanocomposite for enhanced photocatalytic applications

A near infra-red (NIR) active NaGdF₄:Yb:Er/Ag/TiO₂ nanocomposite photocatalyst was successfully synthesized by a one-pot thermal decomposition method.

Selectively enhanced red upconversion luminescence and phase/size manipulation via Fe(3+) doping in NaYF4:Yb,Er nanocrystals

Red upconversion luminescence (UCL) is selectively enhanced by about 7 times via Fe(3+) codoping into a NaYF4:Yb,Er nanocrystalline lattice. The maximum red-to-green ratio (R/G) as well as the overall integrated UCL intensity features at an Fe(3+) content of 20 mol%. The size and phase of nanocrystals are simultaneously manipulated via Fe(3+) doping with various concentrations by a facile hydrothermal method. Contrary to the literature, the pure hexagonal phase appears when Fe(3+) concentrations are from 5 to 20 mol%, meanwhile, the size of NaYF4:Yb,Er nanocrystals reaches its maximum at 10 mol%. The intensified visible UCL especially the dominant red emission is mainly ascribed to the energy transfer (ET) from |(2)F7/2, (4)T1g > (Yb(3+)-Fe(3+) dimer) to (4)F9/2 (Er(3+)) states as well as the distortion of the crystalline field symmetry upon Fe(3+) codoping. Dynamic investigation of (4)S3/2 and (4)F9/2 states under the pulsed laser excitation of 980 nm along with the diffuse reflectance data further supports the proposed mechanism of UC processes. The results show the remarkable promise of Fe(3+)-codoped NaYF4:Yb,Er nanocrystals as upconverting nanoprobes with high sensitivity and penetrability in deeper tissue for multimodal biomedical imaging.

Multimodal cancer imaging using lanthanide-based upconversion nanoparticles

Multimodal nanoprobes that integrate different imaging modalities in one nano-system could offer synergistic effect over any modality alone to satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research. Upconversion nanoparticles (UCNPs), particularly lanthanide (Ln)-based NPs have been regarded as an ideal building block for constructing multimodal bioprobes due to their fascinating properties. In this review, we first summarize recent advances in the optimizations of existing UCNPs. In particular, we highlight the applications of Ln-based UCNPs for multimodal cancer imaging in vitro and in vivo. The explorations of UCNPs-based multimodal nanoprobes for targeting diagnosis and imaging-guided therapeutics are also presented. Finally, the challenges and perspectives of Ln-based UCNPs in this rapid growing field are discussed.

Simultaneous morphology manipulation and upconversion luminescence enhancement of β-NaYF4:Yb3+/Er3+ microcrystals by simply tuning the KF dosage

A strategy has been adopted for simultaneous morphology manipulation and upconversion luminescence enhancement of β-NaYF₄:Yb³⁺/Er³⁺ microcrystals by simply tuning the KF dosage. X-ray power diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectra (PL) were used to characterize the samples. The influence of molar ratio of KF to Y³⁺ on the crystal phase and morphology has been systematically investigated and discussed. It is found that the molar ratio of KF to Y³⁺ can strongly control the morphology of the as-synthesized β-NaYF₄ samples because of the different capping effect of F⁻ ions on the different crystal faces. The possible formation mechanism has been proposed on the basis of a series of time-dependent experiments. More importantly, the upconversion luminescence of β-NaYF₄:Yb³⁺/Er³⁺ was greatly enhanced by increasing the molar ratio of KF to RE³⁺ (RE = Y, Yb, Er), which is attributed to the distortion of local crystal field symmetry around lanthanide ions through K⁺ ions doping. This synthetic methodology is expected to provide a new strategy for simultaneous morphology control and remarkable upconversion luminescence enhancement of yttrium fluorides, which may be applicable for other rare earth fluorides.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

Upconversion of rare Earth nanomaterials

Rare earth nanomaterials, which feature long-lived intermediate energy levels and intraconfigurational 4f-4f transitions, are promising supporters for photon upconversion. Owing to their unique optical properties, rare earth upconversion nanomaterials have found applications in bioimaging, theranostics, photovoltaic devices, and photochemical reactions. Here, we review recent advances in the photon upconversion processes of these nanomaterials. We start by considering energy transfer models involved in the study of upconversion emissions, as well as well-established synthesis strategies to control the size and shape of rare earth upconversion nanomaterials. Progress in engineering energy transfer pathways, which play a dominant role in determining upconversion emission outputs, is then discussed. Lastly, representative optical applications of these materials are considered. The aim of this review is to provide inspiration for researchers to explore novel upconversion nanomaterials and extended optical applications.

Upconversion improvement by the reduction of Na+-vacancies in Mn2+ doped hexagonal NaYbF4:Er3+ nanoparticles

A method of Mn²⁺ doping for the simultaneous control of lattice defects and luminescence output in β-NaYbF₄:Er³⁺ upconversion nanoparticles with a fixed composition of both host and dopants of Ln³⁺ is demonstrated.

Probing the nature of upconversion nanocrystals: instrumentation matters

Understanding upconversion nanocrystals: this review intends to summarize instrumental matters related to the characterization of upconversion nanocrystals from surface structures to intrinsic properties to ultimate challenges in nanocrystal analysis at single-particle levels.

Phase transition, morphology transformation and highly enhanced luminescence properties of YOF:Eu3+ crystals by Gd3+ doping

We report the crystal phase transition, morphology transformation, and greatly enhanced luminescence properties of YOF crystals by Gd³⁺ doping.

The biosafety of lanthanide upconversion nanomaterials

The association between the chemo-physical properties of UCNPs and their biodistribution, excretion, and toxic effects is presented in this review.

Synthesis of a novel bifunctional nanocomposite with tunable upconversion emission and magnetic properties

A method of Co²⁺ ions codoping for significantly enhancing upconversion emission intensity and simultaneous controlling sparamagnetic properties in β-NaYF₄:Yb/Er nanoparticles, with well maintaining their morphology and highly disperse.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

The latest advances in lanthanide-doped upconversion nanoparticles were comprehensively reviewed, which covers from their fundamental photophysics to biodetection.

Energy transfer in lanthanide upconversion studies for extended optical applications

In this review, the various energy transfer pathways involved in lanthanide-related upconversion emissions are comprehensively discussed.

pH value manipulated phase transition, microstructure evolution and tunable upconversion luminescence in Yb3+–Er3+ codoped LiYF4/YF3 nanoparticles

The effects of pH value on the phase transition, microstructure evolution and upconversion properties were demonstrated in Yb³⁺–Er³⁺ codoped LiYF₄/YF₃ nanoparticles.

Combined plasmonic and upconversion rear reflectors for efficient dye-sensitized solar cells

A novel rear reflector structure that combines NIR light harvesting β-NaGdF4:Yb, Er, Fe upconversion nanoparticles (UCNPs) and light reflecting silver particles has been successfully used to improve the performance of dye-sensitized solar cells (DSSCs). The power conversion efficiency of DSSCs with a rear reflector was 7.04%, which is an increase of 21.3% compared to the cell without a rear reflector (5.8%).