Search

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

A heterostructure nanoplatform was designed for NIR-responsive production of ONOO−via direct lanthanide-triplet photosensitization to realize enhanced tumor therapy.

Upconversion nanocrystals have been extensively investigated for optical imaging and biomedical applications1,2. However, their photoluminescence is strongly attenuated by surface quenching as the nanocrystal size diminishes3. Despite considerable efforts4,5, the quenching mechanism remains poorly understood. Here we report that surface coordination of bidentate picolinic acid molecules to NaGdF4:Yb/Tm nanoparticles enhances four-photon upconversion by 11,000-fold. Mechanistic studies indicate that surface ligand coordination reconstructs orbital hybridization and crystal-field splitting, minimizing the energy difference between the 4f orbitals of surface and inner lanthanide sensitizers. The 4f-orbital energy resonance facilitates energy migration within the ytterbium sublattice, impeding energy diffusion to surface defects and ultimately enhancing energy transfer to the emitters. Moreover, ligand coordination can exert energy-level reconstruction with a ligand–sensitizer separation of over 2 nm. These findings offer insights into the development of highly emissive nanohybrids and provide a platform for constructing optical interrogation systems at single-particle levels. Strong lanthanide-doped upconversion luminescence enhancement is achieved by the use of surface molecules which enhance four-photon upconversion emission. The results may lead to new, highly emissive, nanohybrid systems.

Summary Photosensitization under near-infrared (NIR) excitation is attractive for applications in photocatalysis and theragnostics because NIR light offers deeper penetration depth through various media, including biological tissues. Nevertheless, most photosensitization processes can only be stimulated by ultraviolet or visible light. Here, we demonstrate a new paradigm, based on the coupling of lanthanide inorganic nanoparticles and organic photosensitizers, for NIR photosensitization through lanthanide-triplet sensitization. We show that the triplet levels of a series of porphyrin and phthalocyanine sensitizers can be effectively populated by energy transfer from lanthanide nanoparticles. This approach allows to directly active lower-lying triplet states of photosensitizers without the need to populate their higher-lying excited singlet states. It enables photosensitization to generate singlet oxygen at ultralow NIR irradiance with over 100-fold improved performance compared with conventional upconversion-based NIR photosensitization, which may provide new opportunities for applications such as deep-tumor phototherapy and NIR-light driven photosynthesis.

The discovery of X-ray-charged persistent luminescence (PersL) in fluoride nanoparticles enables these materials to emit photons without real-time excitation, which provides a great possibility for the development of new luminescent nanotechnologies. In this work, we developed NaLuF

Due to the complex environmental conditions of inland ports, it is of great significance to adopt associated protection to ensure the safe and reliable operation of the shore-to-ship power supply system. To accurately simulate the operating conditions of the shore-to-ship power supply system, the simulation model of the ship power system is established completely. According to the characteristics of the inland port, the simulation model of the shore-based power supply system is designed and established. Based on the established simulation model of a low voltage shore-to-ship power supply system, to meet its protection requirements of it, an associated protection method including safety interlock, under-voltage protection, and short-circuit protection is proposed. To verify the effectiveness of the associated protection, power faults are set in the shore-to-ship power supply system, and the action of the associated protection during the fault is analyzed by comparing the voltage and current waveforms of the shore-to-ship power supply system with associated protection and unprotected ones. The results show that the associated protection can effectively detect the power failures of the shore-to-ship power supply systems and take timely protection measures to ensure equipment safety.

Two-dimensional (2D) ferromagnetic half-metals hold tremendous potential for use in nanoelectronics and spintronic devices. However, their experimental realization remains a big challenge. In this article, we study electron- and hole-doping effects on a 2D Cr2Ge2Te6 (CGT) monolayer via performing first-principles calculations to investigate its electronic and magnetic properties. Electron-doping has tremendous effects both on the electronic and the magnetic properties. The results show that electron-doping not only induces half-metallicity but it also enhances magnetism in the CGT monolayer. Furthermore, it greatly increases the ferromagnetic stability of the CGT layer. In addition, we manipulated the electron-doping effects via the adsorption of alkali and alkaline-earth metals. The alkali metals act like dopants. Due to charge-transfer, the Fermi level is pushed up, allowing the spin-up channel to conduct while the spin-down channel remains insulating. The half-metallicity is robust, as it does not depend on the adatom concentration. However, the adsorption energy gets reduce with an increase in the concentration of adatoms. In this scenario, the adsorbates tend to repel each other in order to avoid agglomeration, thus leading to a more stable system configuration. More importantly, the local magnetic moment is enhanced because adsorption increases the magnetism. In addition, hydrogen adsorption modifies the band gap at different concentrations but it reduces the magnetic moment of the CGT monolayer.

Impurity doping has been widely applied in nanomaterial synthesis for modulating the crystallographic phase, morphology, and size of nanocrystalline materials, but mostly by altering thermodynamic equilibria of final products. Here, we report the use of lanthanide dopants to manipulate the growing kinetics of halide perovskite nanocrystals to enable the preparation of highly anisotropic two-dimensional (2D) CsPbBr3-based nanoplatelets with precisely controlled thickness. We demonstrate that the incorporation of trivalent lanthanides increases the energy barrier in growing three-monolayer (3 ML) CsPbBr3 from a 2 ML intermediate. It enables the growth of thermodynamically unfavorable 2 ML CsPbBr3 products through kinetic control. This finding provides a novel approach for dimensional control of perovskite nanocrystals with strong quantum confinement. It offers opportunities to generate deep-blue emitting (at 430 nm) CsPbBr3:Lu3+ nanoplatelets with good structural- and photo-stabilities potentially useful for many applications including light-emitting, lasers, and photocatalysis.

The electrical control of two-dimensional (2D) van der Waals ferromagnets is a step forward for the realization of spintronic devices. However, using this approach for practical applications remains challenging due to its volatile memory. Herein, we adopt an alternative strategy, where the bistable ferroelectric switches (P↑ and P↓) of Sc2CO2 (SCO) assist the ferromagnetic states of Cr2Ge2Te6 (CGT) in order to achieve non-volatile memories. Moreover, MXene SCO, being an aided layer in multiferroic CGT/SCO hetero-structures, also modifies the electronic properties of CGT to half metal by its polarized P↓ state. In contrast, the P↑ state does not change the semiconducting nature of CGT. Hence, non-volatile, electrical-controlled switching of ferromagnetic CGT can be engineered by the two opposite ferroelectric states of single layer SCO. Importantly, the magnetic easy axis of CGT switches from in-plane to out-of-plane when the direction of electric polarization of SCO is altered from P↓ to P↑.

Suspended matter and organic contaminants would prevent short-wavelength UV/visible light from penetrating deeper into real wastewater. This has hindered the practical use of photocatalysts in wastewater remediation. Construction of near-infrared light responsive photocatalysts can partially overcome this issue, due to the larger penetration depth of near-infrared light into the waste media. However, the development of near-infrared responsive photocatalysts is constrained by low photoconversion efficiency. In this work, we developed an approach to enhance the performance of NIR-responsive photocatalysis of a lanthanide-doped upconversion nanoparticle–TiO2 hybrid system through coupling the surface adhesion capability of heavy lanthanides with a NIR to UV/vis light upconversion process. We demonstrated that a Gd3+-rich nanoparticle surface can enhance the adhesion of organic compounds on the heterogeneous catalysts, resulting in more complete cycloreversion of organic chromophores. We systematically investigated the photooxidation pathways of the upconversion nanoparticle–TiO2 hybrid catalysts in degradation of rhodamine B through liquid chromatography-mass spectrometry analysis. The results reveal that Gd3+ ions on the catalyst surface could facilitate the complete mineralization of the organic molecules to achieve a total organic carbon removal efficiency of around 70%, which is three times higher than that of the conventional upconversion nanoparticle–TiO2 systems. The results offer new opportunities for near-infrared light driven photocatalysis in water remediation, which is potentially applicable for large quantity deep wastewater treatment.

NaYF4:Ln3+, due to its outstanding upconversion characteristics, has become one of the most important luminescent nanomaterials in biological imaging, optical information storage, and anticounterfeiting applications. However, the large specific surface area of NaYF4:Ln3+ nanoparticles generally leads to serious nonradiative transitions, which may greatly hinder the discovery of new optical functionality with promising applications. In this paper, we report that monodispersed nanoscale NaYF4:Ln3+, unexpectedly, can also be an excellent persistent luminescent (PersL) material. The NaYF4:Ln3+ nanoparticles with surface-passivated core–shell structures exhibit intense X-ray-charged PersL and narrow-band emissions tunable from 480 to 1060 nm. A mechanism for PersL in NaYF4:Ln3+ is proposed by means of thermoluminescence measurements and host-referred binding energy (HRBE) scheme, which suggests that some lanthanide ions (such as Tb) may also act as effective electron traps to achieve intense PersL. The uniform and spherical NaYF4:Ln3+ nanoparticles are dispersible in solvents, thus enabling many applications that are not accessible for traditional PersL phosphors. A new 3-dimensional (2 dimensions of planar space and 1 dimension of wavelength) optical information-storage application is demonstrated by inkjet-printing multicolor PersL nanoparticles. The multicolor persistent luminescence, as an emerging and promising emissive mode in NaYF4:Ln3+, will provide great opportunities for nanomaterials to be applied to a wider range of fields.

The efficacy of dynamic therapy for solid tumors suffers daunting challenges induced by tumor hypoxia. Herein, we report a biocompatible nanosystem containing Fe(OH)3-modified upconversion nanoparticles (UCNPs) for promoting synergetic chemo- and photodynamic therapy with the modulation of tumor hypoxia. In this system, UCNPs convert 808 nm near-infrared excitation to visible photon energy, which stimulates chlorin-e6 photosensitizers to generate toxic reactive oxygen species (ROS) by consumption of dissolved oxygen in cancer cells. Importantly, we employ Fe(OH)3 compounds to enable continuous oxygen generation in cancer cells and, meanwhile, induce extra ROS formation through the Fenton-like reaction. The system consequently improves the tumor treatment efficacy in vitro and in vivo. This study puts forward a novel combinatorial therapeutic platform for tumor microenvironment modulation and enhanced cancer therapy.

The electrical control of two-dimensional (2D) van der Waals ferromagnets is a step forward for the realization of spintronic devices. However, using this approach for practical applications remains challenging due to its volatile memory. Herein, we adopt an alternative strategy, where the bistable ferroelectric switches (P↑ and P↓) of Sc

Quantification of nanoparticle-molecule interaction at a single-molecule level remains a daunting challenge, mainly due to ultra-weak emission from single molecules and the perturbation of the local environment. Here we report the rational design of an intraparticle-surface energy transfer (i-SET) process, analogous to high doping concentration-induced surface quenching effects, to realize single-molecule sensing by nanoparticle probes. This design, based on a Tb3+-activator-rich core-shell upconversion nanoparticle, enables a much-improved spectral response to fluorescent molecules at single-molecule levels through enhanced non-radiative energy transfer with a rate over an order of magnitude faster than conventional counterparts. We demonstrate a quantitative analysis of spectral changes of one to four fluorophores tethered on a single nanoparticle through i-SET spectroscopy. Our results provide opportunities to identify photoreaction kinetics at single-molecule levels and provide direct information for understanding behaviors of individual molecules with unprecedented sensitivity., Single-molecule sensing is very challenging due to weak emitted signals and environmental interference. Here the authors design a method (i-SET) for single molecule sensing with core-shell upconverting nanoparticles, which relies on signal enhancement by the activator-rich probes to quantify fluorophores attached to a single nanoparticle.

The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission1, optoelectronics2,3, photon frequency conversion4,5 and photocatalysis6,7. Molecular triplet excitons (bound electron-hole pairs) are 'dark states' because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels8. Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin-orbit coupling9-11 or tuning of the singlet-triplet energy splitting12,13 via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle-molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide-triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research.

Surface modification with organic dye molecules is a useful strategy to manipulate the optical properties of lanthanide-doped nanoparticles (LnNPs). It enables energy transfer between dyes and LnNPs, which provides unprecedented possibilities to gain new optical phenomena from the dye-LnNPs composite systems. This has led to a wide range of emerging applications, such as biosensing, drug delivery, gene targeting, information storage, and photon energy conversion. Herein, the mechanism of energy transfer and the structural-dependent energy-transfer properties in dye-coupled LnNPs are reviewed. The design strategies for achieving effective dye-LnNP functionalization are presented. Recent advances in these composite nanomaterials in biomedicine and energy conversion applications are highlighted.

The stringent distance dependence of Forster resonance energy transfer (FRET) has limited the ability of an energy donor to donate excitation energy to an acceptor over a Forster critical distance (R0) of 2–6 nm. This poses a fundamental size constraint (

The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission

The existing white light-emitting diodes (WLEDs) are mostly fabricated with downshifting phosphors and ultraviolet (UV) or blue light LED chips. To achieve unconventional upconversion white-light-emitting phosphors, a novel strategy by encapsulating upconversion nanoparticles and organic dyes into metal–organic frameworks (MOFs) at room temperature is put forward. Herein, lanthanide-doped upconversion nanoparticles (NaYF4:Yb,Tm@NaYF4 core–shell UCNPs), dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) and dye Coumarin 6 (C6) with blue, red and green light emission, respectively, are encapsulated together into ZIF-8 through a facile one-pot solid-confinement conversion process. Owing to their appropriate spectral overlaps and efficient energy transfer processes between two pairs of UCNPs/DCM and UCNPs/C6 within ZIF-8, the optimized UCNP/DCM/C6@ZIF-8 thin film exhibits high-quality white-light emission upon a commercial 980 nm LED chip with ideal CIE coordinates of (0.33, 0.33), high color rendering index (CRI) value of 93 and moderate correlated color temperature (CCT) value of 5567 K. This strategy paves the way for other upconversion phosphorous nanoparticles and fluorescent molecules for WLEDs applications excited by near infrared light.

Optical tuning of lanthanide-doped upconversion nanoparticles has attracted considerable attention over the past decade because this development allows the advance of new frontiers in energy conversion, materials science, and biological imaging. Here we present a rational approach to manipulating the spectral profile and lifetime of lanthanide emission in upconversion nanoparticles by tailoring their nonlinear optical properties. We demonstrate that the incorporation of energy distributors, such as surface defects or an extra amount of dopants, into a rare-earth-based host lattice alters the decay behavior of excited sensitizers, thus markedly improving the emitters' sensitivity to excitation power. This work provides insight into mechanistic understanding of upconversion phenomena in nanoparticles and also enables exciting new opportunities of using these nanomaterials for photonic applications.

Upconversion luminescence at ~800 nm based on Thulium-doped NaYF4 nanoparticles excited by a 980 nm laser has been experimentally demonstrated. Under different concentrations, the fluorescence power is proportional to the pump power.

Developing light-harvesting materials with tunable emission colours has always been at the forefront of colour display technologies. The variation in materials composition, phase and structure can provide a useful tool for producing a wide range of emission colours, but controlling the colour gamut in a material with a fixed composition remains a daunting challenge. Here, we demonstrate a convenient, versatile approach to dynamically fine-tuning emission in the full colour range from a new class of core-shell upconversion nanocrystals by adjusting the pulse width of infrared laser beams. Our mechanistic investigations suggest that the unprecedented colour tunability from these nanocrystals is governed by a non-steady-state upconversion process. These findings provide keen insights into controlling energy transfer in out-of-equilibrium optical processes, while offering the possibility for the construction of true three-dimensional, full-colour display systems with high spatial resolution and locally addressable colour gamut.

Optical characteristics of luminescent materials, such as emission profile and lifetime, play an important role in their applications in optical data storage, document security, diagnostics, and therapeutics. Lanthanide-doped upconversion nanoparticles are particularly suitable for such applications due to their inherent optical properties, including large anti-Stokes shift, distinguishable spectroscopic fingerprint, and long luminescence lifetime. However, conventional upconversion nanoparticles have a limited capacity for information storage or complexity to prevent counterfeiting. Here, we demonstrate that integration of long-lived Mn2+ upconversion emission and relatively short-lived lanthanide upconversion emission in a particulate platform allows the generation of binary temporal codes for efficient data encoding. Precise control of the particle’s structure allows the excitation feasible both under 980 and 808 nm irradiation. We find that the as-prepared Mn2+-doped nanoparticles are especially useful for multilevel anti-counterfeiting with high-throughput rate of authentication and without the need for complex time-gated decoding instrumentation., Luminescent materials that are capable of binary temporal coding are desirable for multilevel anti-counterfeiting. Here, the authors engineer nanoparticles that produce binary color codes on different timescales by combining the long-lived luminescence of Mn2+ with the relatively short-lived emission of lanthanides.

The enthusiasm for research on lanthanide-doped upconversion nanoparticles is driven by both a fundamental interest in the optical properties of lanthanides embedded in different host lattices and their promise for broad applications ranging from biological imaging to photodynamic therapy. Despite the considerable progress made in the past decade, the field of upconversion nanoparticles has been hindered by significant experimental challenges associated with low upconversion conversion efficiencies. Recent experimental and theoretical studies on upconversion nanoparticles have, however, led to the development of several effective approaches to enhancing upconversion luminescence, which could have profound implications for a range of applications. Herein we present the underlying principles of controlling energy transfer through lanthanide doping, overview the major advances and key challenging issues in improving upconversion luminescence, and consider the likely directions of future research in the field.

Tuning the luminescence lifetimes of upconversion nanocrystals through lanthanide doping provides new opportunities for optical multiplexing in the time domain for applications in imaging and security marking.

A new fluorescent chemosensor (1a), derived from anthracene, was designed and synthesized. It has been found that 1a could be used to detect Zn2+ ratiometricly in a HEPES buffered methanol/water (9/1, v/v) solution with a large hypsochromic shift from 515 to 433 nm, while it could also be applied to sense Cu2+ with the phenomenon of fluorescence quenching of 1a completely. Moreover, adding other univalent or divalent metal ions such as Na+, K+, Li+, Ca2+, Mg2+, Ba2+, Co2+, Mn2+, Pb2+, Cr3+ or Hg2+ ions into the solution of 1a did not cause any distinct change to the emission spectra of 1a.

When you have discovered something unusual, trust your instinct and pursue it with determination and enthusiasm, says Renren Deng.

The enthusiasm for research on lanthanide-doped upconversion nanoparticles is driven by both a fundamental interest in the optical properties of lanthanides embedded in different host lattices and their promise for broad applications ranging from biological imaging to photodynamic therapy. Despite the considerable progress made in the past decade, the field of upconversion nanoparticles has been hindered by significant experimental challenges associated with low upconversion conversion efficiencies. Recent experimental and theoretical studies on upconversion nanoparticles have, however, led to the development of several effective approaches to enhancing upconversion luminescence, which could have profound implications for a range of applications. Herein we present the underlying principles of controlling energy transfer through lanthanide doping, overview the major advances and key challenging issues in improving upconversion luminescence, and consider the likely directions of future research in the field.

The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescence applications.

Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants. This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission. These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy. The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene. Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth. The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants. The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion.

We report the synthesis of luminescent crystals based on hexagonal-phase NaYF4 upconversion microrods. The synthetic procedure involves an epitaxial end-on growth of upconversion nanocrystals comprising different lanthanide activators onto the NaYF4 microrods. This bottom-up method readily affords multicolor-banded crystals in gram quantity by varying the composition of the activators. Importantly, the end-on growth method using one-dimensional microrods as the template enables facile multicolor tuning in a single crystal, which is inaccessible in conventional upconversion nanoparticles. We demonstrate that these novel materials offer opportunities as optical barcodes for anticounterfeiting and multiplexed labeling applications. © 2014 American Chemical Society.

A new type of core-shell upconversion nanoparticles which can be effectively excited at 795 nm has been designed and synthesized through spatially confined doping of neodymium (Nd(3+)) ions. The use of Nd(3+) ions as sensitizers facilitates the energy transfer and photon upconversion of a series of lanthanide activators (Er(3+), Tm(3+), and Ho(3+)) at a biocompatible excitation wavelength (795 nm) and also significantly minimizes the overheating problem associated with conventional 980 nm excitation. Importantly, the core-shell design enabled high-concentration doping of Nd(3+) (~0 mol %) in the shell layer and thus markedly enhanced the upconversion emission from the activators, providing highly attractive luminescent biomarkers for bioimaging without autofluorescence and concern of overheating.

The applications of lanthanide-doped upconversion nanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb(3+) content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er(3+) with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy.

Uyghur location for tilted text is of great significance for character recognition. Existing text region localization method is not effective for Uyghur text region. This paper proposed a new method to solve this problem. Firstly extracting rule feature of candidate regions, striking out the noise, then correcting the angle of the tilted text to detect the non-text area; Finally proposing polygon-location algorithm based on the special writing style of Uyghur, which can reduce the interference coming from the background in the process of recognition. The location accuracy is more than 91%.

A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photo-electrochemical cells. By spatially coating upconversion nanoparticles and quantum dot photosensitizers onto TiO2 inverse opal, this architecture allows direct irradiation of upconversion nanoparticles to emit visible light that excites quantum dots for charge separation. Electrons are injected into TiO2 with minimal carrier losses due to continuous electron conducting interface.

Although all of these attempts were successfulin principle, there were significant limitations associated withthe use of high-intensity UV or visible light in the photo-activation process. Excessive exposure to UV light can causephotoreactions in nucleic acids and result in cellular damage.Furthermore, short-wavelength UV or visible light does notpenetrate into tissue very far, which limits its utility for deep-tissue imaging by photoactivation of the caged compounds.Alternatively, multiphoton photolysis with long-wavelengthexcitation has been used to enable deep-tissue imaging and totarget gene expression

We report a novel design, based on a combination of lanthanide-doped upconversion nanoparticles and manganese dioxide nanosheets, for rapid, selective detection of glutathione in aqueous solutions and living cells. In this approach, manganese dioxide (MnO(2)) nanosheets formed on the surface of nanoparticles serve as an efficient quencher for upconverted luminescence. The luminescence can be turned on by introducing glutathione that reduces MnO(2) into Mn(2+). The ability to monitor the glutathione concentration intracellularly may enable rational design of a convenient platform for targeted drug and gene delivery.

Photon upconversion is promising for applications such as biological imaging, data storage or solar cells. Here, we have investigated upconversion processes in a broad range of gadolinium-based nanoparticles of varying composition. We show that by rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of lanthanide activators without long-lived intermediary energy states. Furthermore, the use of the core-shell structure allows the elimination of deleterious cross-relaxation. This effect enables fine-tuning of upconversion emission through trapping of the migrating energy by the activators. Indeed, the findings described here suggest a general approach to constructing a new class of luminescent materials with tunable upconversion emissions by controlled manipulation of energy transfer within a nanoscopic region.