Site-selected doping of upconversion luminescent Er3+ into SrTiO3 for visible-light-driven photocatalytic H2 or O2 evolution

A series of upconversion luminescent erbium-doped SrTiO(3) (ABO(3)-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er(3+) ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO(6) octahedra promoted energy transfer from the high-energy excited states of Er(3+) with B-site occupancy to the host SrTiO(3) and thus enhanced the band-to-band transition of the host SrTiO(3). Consequently, the erbium-doped SrTiO(3) species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H(2) or O(2) evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H(2) and O(2) evolution and that the site occupancy of doped elements in ABO(3)-type perovskite oxides greatly determines the photocatalytic activity.     

Confining Excitation Energy in Er3+‐Sensitized Upconversion Nanocrystals through Tm3+‐Mediated Transient Energy Trapping

A new class of lanthanide‐doped upconversion nanoparticles are presented that are without Yb³⁺ or Nd³⁺ sensitizers in the host lattice. In erbium‐enriched core–shell NaErF₄:Tm (0.5 mol %)@NaYF₄ nanoparticles, a high degree of energy migration between Er³⁺ ions occurs to suppress the effect of concentration quenching upon surface coating. Unlike the conventional Yb³⁺‐Er³⁺ system, the Er³⁺ ion can serve as both the sensitizer and activator to enable an effective upconversion process. Importantly, an appropriate doping of Tm³⁺ has been demonstrated to further enhance upconversion luminescence through energy trapping. This endows the resultant nanoparticles with bright red (about 700‐fold enhancement) and near‐infrared luminescence that is achievable under multiple excitation wavelengths. This is a fundamental new pathway to mitigate the concentration quenching effect, thus offering a convenient method for red‐emitting upconversion nanoprobes for biological applications.     

Green and red upconversion luminescence in CeO2:Er powders produced by 785 nm laser

CeO₂:Er³⁺ powders were prepared by Pechini type sol-gel method. The structural properties of CeO₂:Er³⁺ were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The results show that CeO₂:Er³⁺ has low phonon cutoff energy, which indicate that CeO₂:Er³⁺ may have high luminescent efficiency. The green and red upconverted luminescence spectra of Er³⁺ were investigated under excitation into the ⁴I_9/2 level by 785 nm laser. The upconversion mechanisms were studied in detail through laser power dependence and Er³⁺ ions concentration dependence of upconverted emissions, and results show that excited state absorption and energy transfer process are the possible mechanisms for the upconversion. The upconversion properties indicate that CeO₂:Er³⁺ may be used in upconversion phosphors.     

Thermal Enhancement of Upconversion by Negative Lattice Expansion in Orthorhombic Yb2W3O12

Thermal quenching of photoluminescence represents a significant obstacle to practical applications such as lighting, display, and photovoltaics. Herein, a novel strategy is established to enhance upconversion luminescence at elevated temperatures based on the use of negative thermal expansion host materials. Lanthanide‐doped orthorhombic Yb₂W₃O₁₂ crystals are synthesized and characterized by in situ X‐ray diffraction and photoluminescence spectroscopy. The thermally induced contraction and distortion of the host lattice is demonstrated to enhance the collection of excitation energy by activator ions. When the temperature is increased from 303 to 573 K, a 29‐fold enhancement of green upconversion luminescence in Er³⁺ activators is achieved. Moreover, the temperature dependence of the upconversion luminescence is reversible. The thermally enhanced upconversion is developed as a sensitive ratiometric thermometer by referring to a thermally quenched upconversion.     

Bi3+‐Er3+ and Bi3+‐Yb3+ Codoped Cs2AgInCl6 Double Perovskite Near‐Infrared Emitters

Bi³⁺ and lanthanide ions have been codoped in metal oxides as optical sensitizers and emitters. But such codoping is not known in typical semiconductors such as Si, GaAs, and CdSe. Metal halide perovskite with coordination number 6 provides an opportunity to codope Bi³⁺ and lanthanide ions. Codoping of Bi³⁺ and Ln³⁺ (Ln=Er and Yb) in Cs₂AgInCl₆ double perovskite is presented. Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows Er³⁺ f‐electron emission at 1540 nm (suitable for low‐loss optical communication). Bi³⁺ codoping decreases the excitation (absorption) energy, such that the samples can be excited with ca. 370 nm light. At that excitation, Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows ca. 45 times higher emission intensity compared to the Er³⁺ doped Cs₂AgInCl₆. Similar results are also observed in Bi³⁺‐Yb³⁺ codoped sample emitting at 994 nm. A combination of temperature‐dependent (5.7 K to 423 K) photoluminescence and calculations is used to understand the optical sensitization and emission processes.     

Photocatalytic degradation of organic dyes by Er<Superscript>3+</Superscript>: YAlO<Subscript>3</Subscript>/Co- and Fe-doped ZnO coated composites under solar irradiation

In this work, the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites were prepared by the sol-gel method. Then, they were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). Photo-degradation of azo fuchsine (AF) as a model dye under solar light irradiation was studied to evaluate the photocatalytic activity of the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites. It was found that the photocatalytic activity of Co- and Fe-doped ZnO composites can be obviously enhanced by upconversion luminescence agent (Er³⁺: YAlO₃). Besides, the photocatalytic activity of Er³⁺: YAlO₃/Fe-doped ZnO is better than that of Er³⁺: YAlO₃/Co-doped ZnO. The influence of experiment conditions, such as the concentration of Er³⁺: YAlO₃, heat-treatment temperature and time on the photocatalytic activity of the Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites was studied. In addition, the effects of solar light irradiation time, dye initial concentration, Er³⁺: YAlO₃/Co- and Fe-doped ZnO amount on the photocatalytic degradation of azo fuchsine in aqueous solution were investigated in detail. Simultaneously, some other organic dyes, such as Methyl Orange (MO), Rhodamine B (RM-B), Acid Red B (AR-B), Congo Red (CR), and Methyl Blue (MB) were also studied. The possible excitation principle of Er³⁺: YAlO₃/Co- and Fe-doped ZnO coated composites under solar light irradiation and the photocatalytic degradation mechanism of organic dyes were discussed.     

A New Class of Blue‐LED‐Excitable NIR‐II Luminescent Nanoprobes Based on Lanthanide‐Doped CaS Nanoparticles

Lanthanide (Ln³⁺)‐doped luminescent nanoparticles (NPs) with emission in the second near‐infrared (NIR‐II) biological window have shown great promise but their applications are currently limited by the low absorption efficiency of Ln³⁺ owing to the parity‐forbidden 4f→4f electronic transition. Herein, we developed a strategy for the controlled synthesis of a new class of NIR‐II luminescent nanoprobes based on Ce³⁺/Er³⁺ and Ce³⁺/Nd³⁺ co‐doped CaS NPs, which can be effectively excited by using a low‐cost blue light‐emitting diode chip. Through sensitization by the allowed 4f→5d transition of Ce³⁺, intense NIR‐II luminescence from Er³⁺ and Nd³⁺ with quantum yields of 9.3 % and 7.7 % was achieved, respectively. By coating them with a layer of amphiphilic phospholipids, these NPs exhibit excellent stability in water and can be exploited as sensitive NIR‐II luminescent nanoprobes for the accurate detection of an important disease biomarker, xanthine, with a detection limit of 32.0 nm .     

TiO2 Nanotube Arrays Modified with Cr‐Doped SrTiO3 Nanocubes for Highly Efficient Hydrogen Evolution under Visible Light

In recent decades, solar‐driven hydrogen production over semiconductors has attracted tremendous interest owing to the global energy and environmental crisis. Among various semiconductor materials, TiO₂ exhibits outstanding photocatalytic properties and has been extensively applied in diverse photocatalytic and photoelectric systems. However, two major drawbacks limit practical applications, namely, high charge‐recombination rate and poor visible‐light utilization. In this work, heterostructured TiO₂ nanotube arrays grafted with Cr‐doped SrTiO₃ nanocubes were fabricated by simply controlling the kinetics of hydrothermal reactions. It was found that coupling TiO₂ nanotube arrays with regular SrTiO₃ nanocubes can significantly improve the charge separation. Meanwhile, doping Cr cations into SrTiO₃ nanocubes proved to be an effective and feasible approach to enhance remarkably the visible‐light response, which was also confirmed by theoretical calculations. As a result, the rate of photoelectrochemical hydrogen evolution of these novel heteronanostructures is an order of magnitude larger than those of TiO₂ nanotube arrays and other previously reported SrTiO₃/TiO₂ nanocomposites under visible‐light irradiation. Furthermore, the as‐prepared Cr‐doped SrTiO₃/TiO₂ heterostructures exhibit excellent durability and stability, which are favorable for practical hydrogen production and photoelectric nanodevices.     

Infrared‐to‐Visible Light Conversion in Er3+–Yb3+:Lu3Ga5O12 Nanogarnets

Er³⁺–Yb³⁺ co‐doped Lu₃Ga₅O₁₂ nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb³⁺ concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near‐infrared light. The decay curves for the (⁴S_3/2, ²H_11/2) and ⁴F_9/2 levels of the Er³⁺ions exhibit a non‐exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb³⁺ concentration from 1.0 to 10.0 mol %. The non‐exponential decay curves are well fitted to the Inokuti–Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole–quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red‐to‐green intensity ratio of Er³⁺ ions was observed with an increase in Yb³⁺ concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two‐photon upconversion processes for the green and red emissions.     

Photon avalanche upconversion in LiKYF5 crystals doubly doped with Tm3+ and Er3+

For the first time red-to-blue photon avalanche upconversion has been discovered and investigated in LiKYF₅ crystals doubly doped with Tm³⁺ and Er³⁺ under laser excitation at the liquid nitrogen temperature. On the basis of the optical studies, an original model of the luminescent mechanisms, within which the Er³⁺ ions act as both donor and acceptor, and as a result sensitize the photon avalanche effect in Tm³⁺ by converting the optical excitation energy in its diffusion among the Tm³⁺ ions, is presented. It is assumed that all these mechanisms can be realized when the Er³⁺ concentration in crystals is relatively low in order to avoid direct interactions between the Er³⁺ ions.     

Synthesis,properties and mechanism of photodegradation of core–shell structured upconversion luminescent NaYF4:Yb3+,Er3+@BiOCl

Microspherical bismuth oxychloride (BiOCl) can only utilize ultraviolet (UV) light to promote photocatalytic reactions. To overcome this limitation, a uniform and thin BiOCl nanosheet was synthesized with a particle size of about 200 nm. As results of UV–visible diffuse reflectance spectroscopy showed, the band gap of this nanostructure was reduced to 2.78 eV, indicating that the BiOCl nanosheet could absorb and utilize visible light. Furthermore, the upconversion material NaYF₄ doped with rare earth ions Yb³⁺ and Er³⁺ emitted visible light at 410 nm following excitation with near‐infrared (NIR) light (980 nm), which could be utilized by BiOCl to produce a photocatalytic reaction. To produce a high‐efficiency photocatalyst (NaYF₄:Yb³⁺,Er³⁺@BiOCl), BiOCl‐loaded NaYF₄:Yb³⁺,Er³⁺ was successfully synthesized via a simple two‐step hydrothermal method. The as‐synthesized material was confirmed using X‐ray diffraction, scanning electron microscopy, X‐ray photoelectron spectroscopy as well as other characterizations. The removal ratio of methylene blue by NaYF₄:Yb³⁺,Er³⁺@BiOCl was much higher than that of BiOCl alone. Recycling experiments verified the stability of NaYF₄:Yb³⁺,Er³⁺@BiOCl, which demonstrated excellent adsorption, strong visible‐light absorption and high electron–hole separation efficiency. Such properties are expected to be useful in practical applications, and a further understanding of the NIR‐light‐responsive photocatalytic mechanism of this new catalytic material would be conducive to improving its structural design and function.     

Gd_2O_3∶Er~(3+)上转换发光粉在染料敏化太阳电池中的应用

采用沉淀-煅烧法制备了Gd2O3∶Er3+上转换发光粉,通过X射线衍射、扫描电子显微镜、能谱和荧光光谱对其进行了表征,并利用该发光粉具有上转换发光的特性将其应用于染料敏化太阳电池(DSSC)。结果表明,管状Gd2O3∶Er3+上转换发光粉可增加电池对太阳光的吸收范围和吸收效率,提高电池的光电流和光电压。研究了掺杂量对电池性能的影响,当掺杂量为5wt%时,光电转换效率从5.93%升高到7.55%,提高约27%。     

Novel Au/La‐SrTiO3 microspheres: Superimposed Effect of Gold Nanoparticles and Lanthanum Doping in Photocatalysis

Novel multielement Au/La‐SrTiO₃ microspheres were synthesized by a solvothermal method using monodisperse gold and La‐SrTiO₃ nanocrystals as building blocks. The porous Au/La‐SrTiO₃ microspheres had a large surface area of 94.6 m² g^?1. The stable confined Au nanoparticles demonstrated strong surface plasmon resonance effect, leading to enhanced absorption in a broad UV/Vis/NIR range. Doping of rare‐earth metal La also broadened the absorption band to the visible region. Both the conduction and valence bands of Au/La‐SrTiO₃ microspheres thus show favorable potential for proton reduction under visible light. The superimposed effect of Au nanoparticles and La doping in Au/La‐SrTiO₃ microspheres led to high photocurrent density in photoelectrochemical water splitting and good photocatalytic activity in photodegradation of rhodamine B. The photocatalytic activities are in the order of the following: Au/La‐SrTiO₃ microspheres>Au/SrTiO₃ microspheres>La‐SrTiO₃ microspheres>SrTiO₃ microspheres.     

Lanthanide‐Doped LiLuF4 Upconversion Nanoprobes for the Detection of Disease Biomarkers

Lanthanide‐doped upconversion nanoparticles (UCNPs) have shown great promise in bioapplications. Exploring new host materials to realize efficient upconversion luminescence (UCL) output is a goal of general concern. Herein, we develop a unique strategy for the synthesis of novel LiLuF₄:Ln³⁺ core/shell UCNPs with typically high absolute upconversion quantum yields of 5.0 % and 7.6 % for Er³⁺ and Tm³⁺, respectively. Based on our customized UCL biodetection system, we demonstrate for the first time the application of LiLuF₄:Ln³⁺ core/shell UCNPs as sensitive UCL bioprobes for the detection of an important disease marker β subunit of human chorionic gonadotropin (β‐hCG) with a detection limit of 3.8 ng mL⁻¹, which is comparable to the β‐hCG level in the serum of normal humans. Furthermore, we use these UCNPs in proof‐of‐concept computed tomography imaging and UCL imaging of cancer cells, thus revealing the great potential of LiLuF₄:Ln³⁺ UCNPs as efficient nano‐bioprobes in disease diagnosis.     

Synthesis and luminescence properties of Yb and Er doped KLa(WO4)2 nanoparticles

The luminescent nanocrystalline Yb³⁺ and Er³⁺ codoped KLa(WO₄)₂ has been prepared by Pechini method. X-ray diffraction and transmission electron microscope were used to study the structure of the obtained samples. The average grain size of these samples depended on the annealing temperature, increasing with the increase of the temperature. The cell parameters and the crystallite size of KYb_xEr_0.02La_0.98−x(WO₄)₂ nanocrystalline decreased with the increase of x value. Luminescence studies showed that the intensity of upconversion emission of the Yb³⁺ and Er³⁺ codoped samples was much stronger than that of the Er³⁺ single doped samples (pumped by 980 nm LD). The upconversion emission mechanisms suggested that all the three bands of upconversion emissions were two-photon process.     

Rare‐Earth Single Erbium Atoms for Enhanced Photocatalytic CO2 Reduction

The solar‐driven photocatalytic reduction of CO₂ (CO₂RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO₂ emissions. However, low catalytic efficiency and poor selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO₂RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er₁/CN‐NT) with a tunable dispersion density of single atoms. Er₁/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO₂RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO₂RR.     

Gd2O3:Er3+上转换发光粉在染料敏化太阳电池中的应用

采用沉淀-煅烧法制备了Gd₂O₃:Er³⁺上转换发光粉,通过X射线衍射、扫描电子显微镜、能谱和荧光光谱对其进行了表征,并利用该发光粉具有上转换发光的特性将其应用于染料敏化太阳电池(DSSC)。结果表明,管状Gd₂O₃:Er³⁺上转换发光粉可增加电池对太阳光的吸收范围和吸收效率,提高电池的光电流和光电压。研究了掺杂量对电池性能的影响,当掺杂量为5wt%时,光电转换效率从5.93%升高到7.55%,提高约27%。     

Er3O2F5: Ein Erbiumoxidfluorid mit Vernier‐Struktur

Er₃O₂F₅: An Erbium Oxide Fluoride with Vernier‐Type Structure Attempts to synthesize multinary erbium‐trifluoride derivatives (e. g. Er₃F[Si₃O₁₀], Er₄F₂[Si₂O₇][SiO₄], CsEr₂F₇, and RbEr₃F₁₀) from mixtures of ErOF‐contaminated erbium trifluoride (ErF₃) itself and appropriate other components (such as Er₂O₃ and SiO₂ or CsF and RbF, respectively) frequently resulted in the formation of pale pink, transparent, lath‐shaped single crystals of Er₃O₂F₅ (orthorhombic, Pnma; a = 562.48(5), b = 1710.16(14), c = 537.43(4) pm; Z = 4) as by‐product, typically after seven days at 800 °C and regardless of the applied reaction‐container material (evacuated torch‐sealed silica or silica‐jacketed arc‐welded tantalum capsules). Its crystal structure, often described as a vernier‐type arrangement consisting of two interpenetrating and almost misfitting lattices (ErOF and ErF₃), contains two crystallographically different Er³⁺ cations in the eight‐ and seven‐plus‐one‐fold anionic coordination of bicapped trigonal prisms. Whereas (Er1)³⁺ carries four O^2? and F^? anions each, (Er2)³⁺ resides in the neighbourhood of only two O^2?, but five plus one F^? anions. As the main structural feature, however, one can consider O^2?‐centred (Er³⁺)₄ tetrahedra which share common edges to form linear double strands of the composition . Running parallel to the [100] direction and assembling like a hexagonal closest rod‐packing, their electroneutralization and three‐dimensional interconnection is achieved by three crystallographically independent F^? anions (d(F^??Er³⁺) = 221 ? 251 plus 281 pm) in three‐ and two‐plus‐two‐fold coordination of the Er³⁺ cations, respectively.     

Synthesis of Upconverting Hydrogel Nanocomposites Using Thiol‐Ene Click Chemistry: Template for the Formation of Dendrimer‐Like Gold Nanoparticle Assemblies

The synthesis of upconverting hydrogel nanocomposites by base‐catalyzed thiol‐ene click reaction between 10‐undecenoic acid capped Yb³⁺/Er³⁺‐doped NaYF₄ nanoparticles and pentaerythritol tetrakis(3‐mercaptopropionate) (PETMP) as tetrathiol monomer is reported. This synthetic strategy for nanocomposite gels is quite different from works where usually the preformed gels are mixed with the nanoparticles. Developing nanocomposites by surface modification of capping ligands would allow tuning and controlling of the separation of the nanoparticles inside the gel network. The hydrogel nanocomposites prepared by thiol‐ene click reaction show strong enhancement in luminescence intensity compared to 10‐undecenoic acid‐capped Yb³⁺/Er³⁺‐doped NaYF₄ nanoparticles through the upconversion process (under 980 nm laser excitation). The hydrogel nanocomposites display strong swelling characteristics in water resulting in porous structures. Interestingly, the resulting nanocomposite gels act as templates for the synthesis of dendrimer‐like Au nanostructures when HAuCl₄ is reduced in the presence of the nanocomposite gels.     

Micelle‐Directing Synthesis of Ag‐Doped WO3 and MoO3 Composites for Photocatalytic Water Oxidation and Organic‐Dye Adsorption

In this paper, an Ag‐doped WO₃ (and MoO₃) composite has been prepared by following a simple micelle‐directed method and high‐temperature sintering route. The as‐prepared samples were characterized by X‐ray diffraction, inductively coupled plasma, transmission electron microscopy, X‐ray photoelectron spectroscopy, UV/Vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller, photoluminescence spectroscopy, and electrochemical impedance spectroscopy techniques. The photocatalytic experiments reveal that their oxygen‐production rates are up to 95.43 μmol (75.45 μmol) for Ag‐doped WO₃ (MoO₃), which is 9.5 (7.3) times higher than that of pure WO₃: 9.012 μmol (MoO₃: 9.00 μmol) under visible‐light illumination (λ ≥420 nm), respectively. The improvement of their photocatalytic activity is attributed to the enhancement of their visible‐light absorption and the separation efficiency of photogenerated carriers by Ag doping. Moreover, Ag‐doped WO₃ (MoO₃) also shows excellent adsorption of rhodamine B (RhB) and methylene blue (MB) in aqueous solution, with maximum adsorption capacities towards RhB and MB of 822 and 820 mg g⁻¹ for Ag‐doped WO₃, and 642 and 805 mg g⁻¹ for Ag‐doped MoO₃, respectively.