Cooperative Sensitization Upconversion in Solution Dispersions of Co-Crystal Assemblies of Mononuclear Yb3+ and Eu3+ Complexes

Lanthanide upconversion luminescence in nanoparticles has prompted continuous breakthroughs in information storage, temperature sensing, and biomedical applications, among others. Achieving upconversion luminescence at the molecular scale is still a critical challenge in modern chemistry. In this work, we explored the upconversion luminescence of solution dispersions of co-crystals composed of discrete mononuclear Yb(DBM)₃Bpy and Eu(DBM)₃Bpy complexes (DBM: dibenzoylmethane, Bpy: 2,2′-bipyridine). The 613 nm emission of Eu³⁺ was observed under excitation of Yb³⁺ at 980 nm. From the series of molecular assemblies studied, the most intense luminescence was obtained for a 1 : 1 molar ratio of Yb³⁺ : Eu³⁺, resulting in a high quantum yield of 0.67 % at 2.1 W cm⁻². The structure and energy transfer mechanism of the assemblies were fully characterized. This is the first example of an Eu³⁺-based upconverting system composed of two discrete mononuclear lanthanide complexes present as co-crystals in non-deuterated solution.     

Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+-Metal-Organic Frameworks

Lanthanide-doped metal–organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺-based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺, Ho³⁺, Tb³⁺, and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺, Pr³⁺, Sm³⁺, and Dy³⁺. The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.     

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF₅ matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF₅ NCs co-doped with Yb³⁺/Tm³⁺ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.     

Frenkel Defect-modulated Anti-thermal Quenching Luminescence in Lanthanide-doped Sc2(WO4)3

Although large amount of effort has been invested in combating thermal quenching that severely degrades the performance of luminescent materials particularly at high temperatures, not much affirmative progress has been realized. Herein, we demonstrate that the Frenkel defect formed via controlled annealing of Sc₂(WO₄)₃:Ln (Ln=Yb, Er, Eu, Tb, Sm), can work as energy reservoir and back-transfer the stored excitation energy to Ln³⁺ upon heating. Therefore, except routine anti-thermal quenching, thermally enhanced 415-fold downshifting and 405-fold upconversion luminescence are even obtained in Sc₂(WO₄)₃:Yb/Er, which has set a record of both the Yb³⁺-Er³⁺ energy transfer efficiency (>85 %) and the working temperature at 500 and 1073 K, respectively. Moreover, this design strategy is extendable to other hosts possessing Frenkel defect, and modulation of which directly determines whether enhanced or decreased luminescence can be obtained. This discovery has paved new avenues to reliable generation of high-temperature luminescence.     

Vacuum ultraviolet and near-infrared excited luminescence properties of Ca3(PO4)2:RE, Na (RE=Tb, Yb, Er, Tm, and Ho)

Tb³⁺, Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped Ca₃(PO₄)₂ were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb³⁺-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb³⁺ content is comparable with that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb³⁺-Ho³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Tm³⁺ in Ca₃(PO₄)₂, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb³⁺-Tm³⁺-Er³⁺-Ho³⁺ in Ca₃(PO₄)₂, in which the cross-relaxation process between Er³⁺ and Tm³⁺, producing the ¹D₂-³F₄ transition of Tm³⁺, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams.     

A "turn-off" luminescence resonance energy transfer aptamer sensor based on near-infrared upconverting NaYF4:Yb3+,Tm3+ nanoparticles as donors and gold nanorods as acceptors

Near-infrared upconverting NaYF₄:Yb^3*,Tm^3* nanophosphors modified with poly（acrylic acid） were prepared and characterized by transmission electron microscopy and luminescence spectroscopy.Based on the observed overlap between the emission spectrum of the NaYF₄:Yb^3*,Tm^3* nanophosphors and the absorption spectrum of the gold nanorods,we believe that a new "turn-off luminescence resonance energy transfer aptamer sensor was constructed for sensing thrombin in near-infrared region.     

Designing Upconversion Nanocrystals Capable of 745 nm Sensitization and 803 nm Emission for Deep‐Tissue Imaging

A crystal design strategy is described that generates hexagonal‐phased NaYF₄:Nd/Yb@NaYF₄:Yb/Tm luminescent nanocrystals with the ability to emit light at 803 nm when illuminated at 745 nm. This is accomplished by taking advantage of the large absorption cross‐section of Nd³⁺ between 720 and 760 nm plus efficient spatial energy transfer and migration through Nd³⁺→Yb³⁺→Yb³⁺→Tm³⁺. Mechanistic investigations suggest that a cascaded two‐photon energy transfer upconversion process underlies the emission mechanism. This protocol enables deep‐tissue imaging to be achieved while mitigating the attenuation effect associated with the visible emission and the overheating constraint imposed by conventional 980 nm excitation.     

Impact of High Ytterbium(III) Concentration in the Shell on Upconversion Luminescence of Core–Shell Nanocrystals

After coating 20 Yb/2 Er:NaGdF₄ core nanocrystals with a NaYbF₄ shell, upconversion emission of the rare earth ions weakens. So far, the exact reason for this phenomenon is still unclear due to lack of the direct evidence. In this report, a core@shell@shell sandwich‐like structure is designed and fabricated to investigate this phenomenon. We find that high Yb³⁺ concentration in the shell has mainly two adverse impacts: it promotes not only the deleterious back energy transfer from Er³⁺ in the core to Yb³⁺ in the shell but also the energy transfer from Yb³⁺ in the core to Yb³⁺ in the shell. To obtain nanocrystals with high upconversion efficency, appropriate Yb³⁺ concentration should be introduced into the shell or the transition layer.     

Upconversion Luminescence from Ho3+ and Yb3+ Codoped α-NaYF4 Single Crystals

The Ho³⁺/Yb³⁺ co-doped α-NaYF₄ single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient (70-90 oC/cm) of solid-liquid interface was adopted. Upconversion emissions at green ～544 nm, red ～657 and ～751 nm were obtained under 980 nm laser diode excitation. The intensity at ～544 nm was much stronger than those of ～657 and ～751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb³⁺ concentration was about 8.08 mol% when Ho³⁺ concentration was hold at about 1.0 mol%. The results showed that Ho³⁺/Yb³⁺+ doped α-NaYF₄ single crystal was a possible candidate upconversion material for the green solid-state laser.     

ate complexes of lanthanides with aryloxide ligands: Synthesis, structures, and luminescence properties

(2-Benzox(thi)azol-2-yl)phenolate and -naphtholate ate complexes of Sc, Y, La, Sm, Tb, and Yb are synthesized. The structure of (benzoxazolyl)phenolate complexes of La, Sm, and Yb are determined by X-ray diffraction analysis. All synthesized compounds manifest ligand-centered photo- and electroluminescence in a range of 510–540 nm. In addition, the spectra of the samarium and terbium complexes exhibit narrow bands of f-f transitions characteristic of Sm³⁺ and Tb³⁺ ions.     

Intrinsic Time‐Tunable Emissions in Core–Shell Upconverting Nanoparticle Systems

Color‐tunable luminescence has been extensively investigated in upconverting nanoparticles for diverse applications, each exploiting emissions in different spectral regions. Manipulation of the emission wavelength is accomplished by varying the composition of the luminescent material or the characteristics of the excitation source. Herein, we propose core–shell β‐NaGdF₄: Tm³⁺, Yb³⁺/β‐NaGdF₄: Tb³⁺ nanoparticles as intrinsic time‐tunable luminescent materials. The time dependency of the emission wavelength only depends on the different decay time of the two emitters, without additional variation of the dopant concentration or pumping source. The time‐tunable emission was recorded with a commercially available camera. The dynamics of the emissions is thoroughly investigated, and we established that the energy transfer from the ¹D₂ excited state of Tm³⁺ ions to the higher energy excited states of Tb³⁺ ions to be the principal mechanism to the population of the ⁵D₄ level for the Tb³⁺ ions.     

Aptamer‐Based Luminescence Energy Transfer from Near‐Infrared‐to‐Near‐Infrared Upconverting Nanoparticles to Gold Nanorods and Its Application for the Detection of Thrombin

A new luminescence energy transfer (LET) system has been designed for the detection of thrombin in the near‐infrared (NIR) region by utilizing NIR‐to‐NIR upconversion lanthanide nanophosphors (UCNPs) as the donor and gold nanorods (Au NRs) as the acceptor. The use of upconverting NaYF₄:Yb³⁺,Tm³⁺ nanoparticles with sharp NIR emission peaks upon NIR excitation by an inexpensive infrared continuous wave laser diode provided large spectral overlap between the donor and the acceptor. Both the Au NRs and carboxyl‐terminated NaYF₄:Yb³⁺,Tm³⁺ UCNPs were first modified with different thrombin aptamers. When thrombin was added, a LET system was then formed because of the specific recognition between the thrombin aptamers and thrombin. The LET system was used to monitor thrombin concentrations in aqueous buffer and human blood samples. The limits of detection for thrombin are as low as 0.118 nM in buffer solution and 0.129 nM in human serum. The method was also successfully applied to thrombin detection in blood samples.     

Nd3+/Yb3+离子共掺的氧化钛基上转换发光玻璃的热学和力学性能

利用气悬浮无容器技术制备出了Nd³⁺/Yb³⁺稀土离子共掺杂的TiO₂-La₂O₃-ZrO₂(TLZ)发光玻璃. 利用差热分析(DTA)技术研究了该类新型稀土掺杂TiO₂基上转换发光玻璃的热稳定性,主要包括玻璃化转变温度、析晶起始温度以及析晶峰值温度. 并采用两种热分析动力学计算方法得到TLZ玻璃的析晶活化能值和指前因子.本文还研究了TLZ 发光玻璃的力学性能,发现其维氏硬度大小为7.50 GPa,断裂韧性大于1.20 MPa·m^1/2. 此外,还对TLZ玻璃在808 nm激光激发下的上转换发光性能进行了研究,实验结果显示光谱中有三个强发射谱峰. 优异的上转换发光性能以及良好的热稳定性和机械性能表明,这类新材料在上转换器件的实际应用中具有很大的潜力.     

Integration of high-thermal-responsive color change and invisible emission intensity ratio in Gd2Mo4O15 lattice with the desired structure

Thermal-responsive upconversion luminescence (UCL) is of interest due to its potential application in anti-counterfeiting and temperature sensing. However, integrating the multi-model emission intensity ratios with high-thermal sensitivity, especially those involving invisible UCL, into a single host lattice remains challenging. In this work, the color change of blue to bluish-purple and invisible emission intensity ratio with a temperature sensitivity as high as 13.47% K^?1, thanks to the crossover-reduced thermal quenching and the Yb³⁺-MoO₄^2- dimer sensitization, are available in the monoclinic Gd₂Mo₄O₁₅:Yb³⁺/Tm³⁺. Moreover, the temperature-dependent color response is tunable, such as the introduction of Er³⁺ results in a color change from blue to bluish-green. Our results allow promising temperature-dependent UCL applications and open the opportunity for other functional materials based on Re₂Mo₄O₁₅ with desirable phase structures.     

Sm3Cl[SiO4]2: Ein chlorarmes Chloridorthosilicat des Samariums

Sm₃Cl[SiO₄]₂: A Chlorine‐poor Chloride Orthosilicate of Samarium Pale yellow, plate‐like single crystals of Sm₃Cl[SiO₄]₂ (orthorhombic, Pnma; a = 701.74(8), b = 1800.8(2), c = 626.63(7) pm; Z = 4) are obtained upon the reaction of SmCl₃, Sm₂O₃ and SiO₂ (”︁Kieselgel”︁”︁) in 1 : 4 : 6 molar ratios, most advantageously in the presence of substantial amounts of NaCl as fluxing agent, after seven days at 850 °C in evacuated silica ampoules. The B‐type crystal structure (isotypic with e. g. Yb₃Cl[SiO₄]₂) contains discrete orthosilicate tetrahedra [SiO₄]^4– which form anionic double layers ({(Sm1)₂[SiO₄]₂}^2–) with (Sm1)³⁺. These are alternatingly sheethed along [010] with cationic monolayers ({(Sm2)Cl}²⁺) consisting of (Sm2)³⁺ and Cl^–. Both crystallographically independent Sm³⁺ cations exhibit coordination numbers of eight (Sm1: 1 Cl + 7 O; Sm2: 2 Cl + 6 O) with respect to the involved electronegative particles.     

Synthesis,crystal structure,antioxidation and fluorescence of two lanthanide complexes with a noncyclic polyether Schiff base ligand

Two lanthanide (Sm and La) complexes with the Schiff base ligand bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod) have been synthesized and characterized by physico-chemical and spectroscopic methods. [Sm(Bod)(NO₃)₃] {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine samarium(III) trinitrate} (1) is a discrete mononuclear species and [La(Bod)(NO₃)₃(DMF)]_n {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine dimethylformamide lanthanum(III) trinitrate}_n (2) formed an inorganic coordination polymer. In the two complexes, the metal ions are both ten-coordinate and the geometric structure around the Ln(III) ions can be described as distorted hexadecahedral. An antioxidant assay in vitro shows that complexes 1 and 2 exhibit better scavenging activity than both the ligand and the usual antioxidants on hydroxyl and superoxide radicals. Under excitation at room temperature, a red shift in the fluorescence band of the ligand in the complexes compared with that of the free ligand can be attributed to coordination of the rare earth ions to the ligand. Furthermore, 1 produced characteristic Sm(III) luminescence, which indicates the ligand Bod is a good organic chelator to absorb energy and transfer it to the Sm³⁺ ion.     

An efficient upconversion luminescence energy transfer system for determination of trace amounts of nitrite based on NaYF4:Yb3+, Er3+ as donor

Based on NaYF₄:Yb³⁺, Er³⁺ upconversion nanocrystals as donor and 4-((4-(2-aminoethylamino)naphthalen-1-yl)diazenyl) benzenesulfonic acid dihydrochloride (ANDBS) as acceptor, an efficient luminescence energy transfer (LET) system was developed for selective and sensitive determination of trace amounts of nitrite. Based on Griess Reaction, ANDBS was generated by the quantitative reaction of nitrite, sulfanilamide and N-(1-naphtyl)-ethylenediamine dihydrochloride (N1NED). The degree of the overlaps between the emission spectrum of NaYF₄:Yb³⁺, Er³⁺ and the absorption spectrum of ANDBS were effective for luminescence energy transfer. Under the optimal condition, the upconversion luminescence quenching of NaYF₄:Yb³⁺, Er³⁺ was in proportion to the trace amounts of nitrite. The detection limit for nitrite achieved is 0.0046 μg mL^?1 and the system shows high sensitivity towards nitrite at 0.008000–0.2500 μg mL^?1 range.     

Rare earth complexes [Ln(EDBP)<Subscript>2</Subscript>(DME)Na(DME)<Subscript>3</Subscript>] as catalysts for the polymerization of 2,2-dimethyltrimethylene carbonate

The biphenol based discrete ion-pair rare earth complexes,[Ln（EDBP）₂（DME）Na（DME）₃][Ln=Er（1）,Yb（2）, Sm（3）],were prepared and used as catalysts for the ring-opening polymerization（ROP）of 2,2-dimethyltrimethylene carbonate（DTC）.Three complexes show moderate activities for the polymerization,and the catalytic activities increase in the following sequence:（Yb2 elimination was prepared.     

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.     

Synthesis and Upconversion Luminescence in LaF3:Yb3+, Ho3+, GdF3: Yb3+, Tm3+ and YF3:Yb3+, Er3+ obtained from Sulfide Precursors

Rare earth fluorides are mainly obtained from aqueous solutions of oxygen‐containing precursors. Probably, this method is simple and efficient, however, oxygen may partially be retained in the fluoride structure. We offer an alternative method: obtaining fluorides and solid solutions based on them from an oxygen‐free precursor. As starting materials, we choose sulfides of rare‐earth elements and solid solutions based on them. The fluorination is carried out by exposure to hydrofluoric acid of various concentrations. The transmission electron microscopy images revealed the different morphologies of the products, which depend on the concentration of the fluorinating component (HF) and the host element. The solid solution particle size varied from 30–35 nm in the case of GdF₃:Yb³⁺, Tm³⁺ (4 % HF) to larger structures with dimensions exceeding 200 nm, such as that for LaF₃:Yb³⁺, Ho³⁺ (40 % HF). The thermal characteristics, such as the temperatures of the transitions and melting and enthalpies, were determined for the solid solutions and simple fluorides. Applicability of the materials obtained as biological luminescent markers was tested on the example of upconversion luminescence, and good upconversion properties were detected.