Homo–hetero/core–shell structure design strategy of NaYF4 nanocrystals for superior upconversion luminescence

A comprehensive strategy has been developed to construct nano-sized homogeneous and heterogeneous core/shell structures of NaYF₄ host. Synthesis conditions of cubic phase/α-NaYF₄ and hexagonal phase/β-NaYF₄ are discussed. Pure cubic NaYF₄:Yb,Er nanocrystals were synthesized with different average sizes extending from 7 nm to 15 nm by varying the reaction time. Temperature and time thresholds of hexagonal nucleation were determined and utilized for controlled core/shell structures of different phases. α-NaYF₄:Yb,Er@α-NaYF₄, α-NaYF₄:Yb,Er@β-NaYF₄, β-NaYF₄:Yb,Er@α-NaYF₄, and β-NaYF₄:Yb,Er@β-NaYF₄ core/shell structures were prepared by adopting the required conditions to achieve the desired phase. Excess sodium was used to grow hexagonal shell over metastable cubic core under controlled conditions of reaction time and temperature to prevent the structural transition of the core. Upconversion emission spectra have also been obtained. UCL integrated intensities demonstrated about 5-fold enhancement for α-shell over α-core as compared to the core alone and 22-fold enhancement with β-shell. On the other hand, α-shell over β-core exhibited 5-fold enhancement and β-shell over β-core exhibited 6-fold enhancement.

Establishment of essential conditions of different phases of NaYF₄ and their utilization for the synthesis of core/shell structures to achieve the enhancement of UCL intensities.     

Upconversion of transparent glass ceramics containing β-NaYF4:Yb3+, Er3+ nanocrystals for optical thermometry

β-NaYF₄ nanocrystal embedded glass ceramics were fabricated by a melt-quenching method with subsequent heat-treatment. Structural characterizations and spectrographic techniques were performed to verify the successful precipitation of β-NaYF₄ nanocrystals and partition of dopants. Upon excitation of 980 nm, bright green upconversion emission could be achieved in Yb³⁺, Er³⁺ codoped β-NaYF₄ nanocrystal embedded glass ceramics. Furthermore, the temperature-dependent upconversion behaviour based on thermally coupled energy levels was also examined in the range of 300–773 K with the maximum relative sensitivity of 1.24% K⁻¹ at 300 K. Accordingly, it has been proved to be a promising candidate for application in optical thermometry.

β-NaYF₄:Yb³⁺, Er³⁺ nanocrystals embedded glass ceramics have been fabricated and demonstrates excellent performance for optical thermometry.     

Near-infrared light-driven photocatalytic NaYF4:Yb,Tm@ZnO core/shell nanomaterials and their performance

Herein, the infrared-responsive photocatalyst NaYF₄:Yb,Tm@ZnO has been successfully synthesized by combining semiconductor ZnO with an upconversion material, NaYF₄:Yb,Tm. In this composite, NaYF₄:Yb,Tm emits intense ultraviolet and blue upconversion luminescence upon excitation by a 980 nm laser and provides the necessary energy of ultraviolet light to ZnO. The photocatalytic activity of NaYF₄:Yb,Tm@ZnO composites has been studied using methylene blue by irradiation with a 980 nm laser, and the results indicate that the NaYF₄:Yb,Tm@ZnO composite is an advanced near-infrared-driven photocatalyst; this study presents a promising strategy to utilize the near-infrared-responsive upconversion materials for photocatalytic applications.

Herein, the infrared-responsive photocatalyst NaYF₄:Yb,Tm@ZnO has been successfully synthesized by combining semiconductor ZnO with an upconversion material, NaYF₄:Yb,Tm.     

One-step synthesis of amino-functionalized up-converting NaYF4:Yb,Er nanoparticles for in vitro cell imaging

The emerging up-conversion nanoparticles (UCNPs) offer a wide range of biotechnology applications, from biomarkers and deep tissue imaging, to single molecule tracking and drug delivery. Their successful conjugation to biocompatible agents is crucial for specific molecules recognition and usually requires multiple steps which may lead to low reproducibility. Here, we report a simple and rapid one-step procedure for in situ synthesis of biocompatible amino-functionalized NaYF₄:Yb,Er UCNPs that could be used for NIR-driven fluorescence cell labeling. X-ray diffraction showed that UCNPs synthesized through chitosan-assisted solvothermal processing are monophasic and crystallize in a cubic α phase. Scanning and transmission electron microscopy revealed that the obtained crystals are spherical in shape with a mean diameter of 120 nm. Photoluminescence spectra indicated weaker green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) and stronger red emission (⁴F_9/2 → ⁴I_15/2), as a result of enhanced non-radiative ⁴I_11/2 → ⁴I_13/2 Er³⁺ relaxation. The presence of chitosan groups at the surface of UCNPs was confirmed by Fourier transform infrared spectroscopy, thermogravimetry and X-ray photoelectron spectroscopy. This provides their enhanced internalization in cells, at low concentration of 10 μg ml⁻¹, without suppression of cell viability after 24 h of exposure. Furthermore, upon 980 nm laser irradiation, the amino-functionalized NaYF₄:Yb,Er UCNPs were successfully used in vitro for labeling of two human cell types, normal gingival and oral squamous cell carcinoma.

The emerging up-conversion nanoparticles (UCNPs) offer a wide range of biotechnology applications, from biomarkers and deep tissue imaging, to single molecule tracking and drug delivery.     

NaYF4:Yb,Tm@TiO2 core@shell structures for optimal photocatalytic degradation of ciprofloxacin in the aquatic environment

The removal of antibiotic residues in the aquatic environment is still a big challenge in environmental protection. Here, we developed NaYF₄:Yb,Tm@TiO₂ as a highly efficient photocatalyst for photocatalytic degradation of ciprofloxacin (CIP), a representative antibiotic in water under simulated solar irradiation. NaYF₄:Yb,Tm@TiO₂ can efficiently utilize a broad spectrum of solar energy to improve the efficiency of ciprofloxacin removal from an aquatic environment. The optimum operation conditions of photocatalyst dosage, pH value, and initial concentrations of CIP were determined by a series of contrast experiments. The dynamic process of CIP removal was monitored by UV-vis spectrophotometry, and can be well predicted by a pseudo first order model. The optimal conditions of photocatalyst dosage, initial concentration of CIP and pH value for CIP photocatalytic degradation were 1 g L⁻¹, 10⁻⁵ M and 8, respectively. This study provides an efficient method for antibiotic removal and enables a promising strategy for other organic water pollutant treatments.

The study indicated the optimum operation conditions to effectively remove ciprofloxacin from aquatic environment by NaYF₄:Yb,Tm@TiO₂ structures.     

Dispersing upconversion nanocrystals in PMMA microfiber: a novel methodology for temperature sensing

This paper reports the synthesis of a β-NaYF₄:Yb³⁺/Tm³⁺ phosphor by a thermal decomposition method and focuses on the fabrication of microfibers by the co-doping of nanocrystals with PMMA solution via a facile drawing method. The structural characteristics of the nanocrystals are studied by XRD and TEM techniques. Meanwhile, the optical properties of the microfibers are probed by wave guiding performance and upconversion spectroscopy. With the excitation of a 980 nm laser source, the microfiber presented blue upconversion emission of Tm³⁺ ions. The fluorescence intensity ratio (FIR) method is utilized for the non-thermally coupling transition (¹D₂ → ³F₄ (452 nm) and ¹G₄ → ³H₆ (476 nm)) levels to carry out the optical thermometry. The maximum sensitivity is recorded at 298 K and is 0.00157 K⁻¹. The results suggest that the microfibers have potential applications in thermometry with high sensitivity.

The synthesis of a β-NaYF₄:Yb³⁺/Tm³⁺ phosphor by a thermal decomposition method, focusing on the fabrication of microfibers by the co-doping of nanocrystals with PMMA solution.     

Core–shell structured NaYF4:Yb,Tm@CdS composite for enhanced photocatalytic properties

NaYF₄:Yb,Tm upconversion nanocrystals with hexagonal structure possess excellent photoluminescence emission characteristics. Under near infrared (NIR) light irradiation, the Yb³⁺ ions act as sensitizers to absorb the NIR light and transform NIR light into ultraviolet (UV) and visible (Vis) light continuously. Hybrid NIR-activated photocatalysts can be fabricated by combining upconversion nanocrystals with various semiconductor nanocrystals. In this paper, NaYF₄:Yb,Tm micro-rods were hydrothermally synthesized with oleic acid as capping ligand. The NaYF₄:Yb,Tm@CdS composite was fabricated by in situ generation of CdS nanoclusters on the surface of NaYF₄:Yb,Tm micro-rods. The morphologies and structures of NaY₄:Yb,Tm and NaYF₄:Yb,Tm@CdS were characterized by XRD, SEM, TEM, XPS, UV-Vis and PL spectroscopy. The results of photocatalytic experiments indicated that the NaYF₄:Yb,Tm@CdS composite displayed photocatalytic activity under NIR irradiation. In comparison with pure CdS, the photocatalytic ability of NaYF₄:Yb,Tm@CdS composite under Vis-NIR irradiation was obviously enhanced. 82% of RhB was degraded by NaYF₄:Yb,Tm@CdS catalyst within 75 min under Vis-NIR irradiation, which was more effective than pure CdS (65% degradation of RhB).

NaYF₄:Yb,Tm upconversion nanocrystals with hexagonal structure possess excellent photoluminescence emission characteristics.     

Solvothermal synthesis and modification of NaYF4:Yb/Er@NaLuF4:Yb for enhanced up-conversion luminescence for bioimaging

Water-soluble NaYF₄:Yb/Er@NaLuF₄:Yb up-converting nanoparticles (UCNPs) with a strong green emission were successfully prepared by a solvothermal method in a short period of time and at a low temperature. First, the hydrophobic UCNPs were prepared by a simple solvothermal method, then modified using a polyetherimide (PEI) surfactant or oxidation of the oleic acid ligands with the Lemieux-von Rudloff reagent. The modified UCNPs, having an average particle diameter of 60 ± 5 nm, showed a high dispersity. The oleic acid ligand on the sample surface was oxidized azelaic acid (HOOC(CH₂)₇COOH), identified from Fourier transform infrared (FTIR) spectroscopy, which results in the generation of free carboxylic acid, hence conferring a high solubility in water. The 3-4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) method and cell-targeted labeling proved that oleic acid-capped UCNPs after oxidation (UCNPs-OAO) have a higher biocompatibility than polyetherimide-capped UCNPs (UCNPs-PEI). Therefore, the UCNPs-OAO have a great potential in biomedical applications, such as multimodal imaging, targeted therapy, and gene therapy.

The NaYF₄:Yb/Er@NaLuF₄:Yb nanosphere were synthesized by a solvothermal method in a short time and low temperature, and applied to cell imaging.     

Upconversion from fluorophosphate glasses prepared with NaYF4:Er3+,Yb3+ nanocrystals

The direct doping method was applied to fabricate upconverter fluorophosphate glasses in the system (90NaPO₃-(10-x)Na₂O-xNaF) (mol%) by adding NaYF₄:Er³⁺,Yb³⁺ nanocrystals. An increase in the network connectivity, a red shift of the optical band gap and a decrease in the thermal properties occur when Na₂O is progressively replaced by NaF. To ensure the survival and the dispersion of the nanocrystals in the glasses with x = 0 and 10, three doping temperatures (T_doping) (525, 550 and 575 °C) at which the nanocrystals were added in the glass melt after melting and 2 dwell times (3 and 5 minutes) before quenching the glasses were tested. Using 5 wt% of the NaYF₄:Er³⁺,Yb³⁺ nanocrystals, green emission from the NaYF₄:Er³⁺,Yb³⁺ nanocrystals-containing glasses was observed using a 980 nm pumping, the intensity of which depends on the glass composition and on the direct doping parameters (T_doping and dwell time). The strongest upconversion was obtained from the glass with x = 10 prepared using a T_doping of 550 °C and a 3 min dwell time. Finally, we showed that the upconversion, the emission at 1.5 μm and of the transmittance spectra of the nanocrystals-containing glasses could be measured to verify if decomposition of the nanocrystals occurred in glass melts during the preparation of the glasses.

The direct doping method was applied to fabricate upconverter fluorophosphate glasses in the system (90NaPO₃-(10-x)Na₂O-xNaF) (mol%) by adding NaYF₄:Er³⁺,Yb³⁺ nanocrystals.     

Investigation on optical temperature sensing behaviour via Ag island-enhanced luminescence doped β-NaGdF4:Yb3+/Tm3+ films/microfibers

In this study, silver (Ag) island modified up-conversion nano-particle (NaGdF₄:Yb³⁺/Tm³⁺) thin films were prepared via electrostatic layer by layer (LBL) and spin coating techniques. The spectroscopic results indicated that adding Ag nanoparticles could significantly enhance the up-conversion emission of NaGdF₄:Yb³⁺/Tm³⁺ thin films at 452 nm and 476 nm. The maximum enhancement factor of ∼15.6 was reached at 476 nm. Furthermore, we prepared microfibers from upconverting nanoparticles solution, the application of microfibers as active and passive waveguides was analyzed by observing the performance of microfibers with and without Ag under 980 nm excitation of the laser source. The fluorescence intensity ratio (FIR) method was adopted to evaluate microfiber sensitivity. The intensity-based temperature sensitivity of blue emission from a single microfiber containing up-conversion nanomaterials (NaGdF₄:Yb³⁺/Tm³⁺) and Ag nanoparticles reached up to 0.018 K⁻¹ at 310 K compared to 0.0029 K⁻¹ in Ag-free microfiber. Our results suggest that the novel material can be used to construct new nano-thermometers, useful both in biological experiments as well as industrial research.

In this study, silver (Ag) island modified up-conversion nano-particle thin films were prepared via electrostatic layer by layer (LBL) and spin coating techniques.     

Understanding differences in Er3+–Yb3+ codoped glass and glass ceramic based on upconversion luminescence for optical thermometry

Optical thermometry has attracted growing consideration due to its outstanding performance. In this research, precursor glass with compositions of 50SiO₂–20Al₂O₃–30CaF₂–0.5ErF₃–1YbF₃ and the corresponding CaF₂ glass ceramic were prepared for optical temperature sensing comparison. A large enhancement in upconversion luminescence originated from thermally coupled energy levels (²H_11/2 and ⁴S_3/2) and ⁴F_9/2 was confirmed in the transparent glass ceramic (GC). Importantly, the temperature-dependent upconversion fluorescence intensity ratios of glass and GC were investigated from 303 K to 573 K under a 980 nm laser with constant pumping power. It was found that GC shows weaker optical thermometry ability than the precursor glass in terms of temperature sensitivity, the maximum relative sensitivity of GC reached to 10.6 × 10⁻³ K⁻¹ at 303 K while that of the glass is 11.15 × 10⁻³ K⁻¹ at 303 K, the thermally coupled energy gap reduced about 34.2 cm⁻¹ after crystallization, we attribute this change to the crystal field effect. Furthermore, the FIR value variation of glass shows weaker pumping power dependence than GC in terms of thermal effect induced by laser. The temperature-cycle measurements suggest that both glass and GC exhibit favorable thermal stability. Consequently, our results may contribute to enriching our understanding of the optical temperature sensing properties of glass and glass ceramic in other systems and provide a comprehensive perspective to design practical optical thermometry materials.

Optical thermometry comparison between glass and corresponding glass ceramic and understand difference for optimized temperature sensing materials.     

A multi-color persistent luminescent phosphor β-NaYF4:RE3+ (RE = Sm,Tb, Dy,Pr) for dynamic anti-counterfeiting

Conventional luminescent materials generally exhibit uni-color and transient emission under UV excitation, which makes them mediocre in the field of anti-counterfeiting. The high-level anti-counterfeiting techniques are always becoming more complicated and in need of multi-color and persistent luminescent materials. Herein, we report a series of β-NaYF₄:RE³⁺ (RE = Sm, Tb, Dy, Pr) persistent luminescent phosphors with multi-color emitting and ultra-long persistent luminescence under the irradiation of X-rays. The effects of doping concentrations of RE³⁺ on the size, morphology, radioluminescence and afterglow performance of the products are investigated in detail. Hexagonal structured rod-like β-NaYF₄:Tb³⁺ crystals show super strong X-ray response and the afterglow signal lasts for up to seven days after X-rays are turned off. Upon X-rays irradiation, some of the F⁻ ions are expected to escape from the crystal lattice by elastic collisions, leading to the generation of Frenkel defects: the F vacancies and interstitials , which capture electrons and release them slowly to achieve different afterglow emission times. Taking advantages of the extraordinary radioluminescence performance of the β-NaYF₄:RE³⁺ persistent luminescent phosphors, the dynamic anti-counterfeiting patterns that containing rich time-resolved information were successfully designed.

A dynamic anti-counterfeiting pattern was successfully designed by using the excellent luminescence characteristics of long afterglow materials under X-ray excitation.     

MgTiO3:Mn4+ a multi-reading temperature nanoprobe

MgTiO₃ nanoparticles doped with Mn⁴⁺, with homogeneous size ranging about 63.1 ± 9.8 nm, were synthesized by a molten salt assisted sol gel method. These nanoparticles have been investigated as optical thermal sensors. The luminescence of tetravalent manganese ion in octahedral environment within the perovskite host presents drastic variations with temperature. Three different thermometry approaches have been proposed and characterized. Two luminescence intensity ratios are studied. Firstly between the two R-lines of Mn⁴⁺ emission at low temperature (−250 °C and −90 °C) with a maximal sensitivity of 0.9% °C⁻¹, but also secondly between ²E → ⁴A₂ (R-line) and the ⁴T₂ → ⁴A₂ transitions. This allows studying the temperature variation within a larger temperature range (−200 °C to 50 °C) with a sensitivity between 0.6% °C⁻¹ and 1.2% °C⁻¹ over this range. The last proposed method is the study of the lifetime variation versus temperature. The effective lifetime value corresponds to a combination of transitions from two excited energy levels of the tetravalent manganese (²E and ⁴T₂) in thermal equilibrium toward the fundamental ⁴A₂ state. Since the more energetic transition (⁴T₂ → ⁴A₂) is spin-allowed, contrary to the ²E → ⁴A₂ one, the lifetime drastically decreases with the increase in temperature leading to an impressive high sensitivity value of 4.1% °C⁻¹ at 4 °C and an exceptional temperature resolution of 0.025 °C. According to their optical features, MgTiO₃:Mn⁴⁺ nanoparticles are indeed suitable candidates for the luminescence temperature probes at the nanoscale over several temperature ranges.

Luminescence properties of MgTiO₃ nanoparticles doped with Mn⁴⁺ ions are investigated for precise temperature determination.     

Anthracene derivatives as broadband nonlinear optical materials: nonlinear absorption and excited-state dynamics analysis

Two anthracene derivatives, AN-1 and AN-2, with different π-bridge lengths were designed and synthesized to investigate their optical nonlinearities. The nonlinear absorption (NLA) properties of both derivatives were measured via the femtosecond Z-scan technique with the wavelength range from 532 nm to 800 nm. The reverse saturable absorption (RSA) of both compounds results from two-photon absorption induced excited-state absorption (TPA-ESA). At all wavelengths, the reverse saturable absorption of AN-2 is superior to that of AN-1 due to a better molecular planarity for AN-2. Compared with the results of AN-1, the two-photon absorption coefficient of AN-2 can be increased by nearly 8 times (from 0.182 × 10⁻² cm GW⁻¹ for AN-1 to 1.42 × 10⁻² cm GW⁻¹ for AN-2) at 600 nm by extending the π-bridge. The evolution of femtosecond transient absorption (TA) spectra reveals the relaxation process from the singlet local excited-state (LES) to charge transfer state (CTS) for both compounds. The results imply that anthracene derivatives may be potential candidates for applications in future laser photonics.

Expanding the π-bridge to adjust the molecular planarity via increasing the amount of ethylene can modulate the nonlinear optical response.     

Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF₄ sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF₄ coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb³⁺, Er³⁺ and Dy³⁺. NaGdF₄:Yb,Er@NaDyF₄ core–shell nanoparticles with ultrathin layer shells exhibited a better T₁-weighted MR contrast.

In this work, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process.     

Synthesis and characterization of magnetic mesoporous Fe3O4@mSiO2–DODGA nanoparticles for adsorption of 16 rare earth elements

In this study, novel magnetic mesoporous Fe₃O₄@mSiO₂–DODGA nanoparticles were prepared for efficiently adsorbing and recycling REEs. Fe₃O₄@mSiO₂–DODGA was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The adsorption behavior of Fe₃O₄@mSiO₂–DODGA was investigated by ICP-OES. The results showed that the content of DODGA in the adsorbent was 367 μmol g⁻¹. Fe₃O₄@mSiO₂–DODGA exhibited the highest adsorption rates for 15 REEs, except Tm, in a 2 mol L⁻¹ nitric acid solution. Among these elements, the adsorption rates for Nd, Sm, Eu, Dy, Ho, Yb, Lu, Y and Sc ranged from 85.1% to 100.1%. The desorption rates for all 16 REE ions reached their maximum values when 0.01 mol L⁻¹ EDTA was used as the eluent. The desorption rates for Nd, Ce, Sm, Eu, Ho, Yb, Lu, Y, and Sc were 87.7–99.8%. Fe₃O₄@mSiO₂–DODGA had high stability in 2 mol L⁻¹ HNO₃ and could be used five times without significant loss of adsorption capacity. Moreover, these nanoparticles had high selectivity, and their adsorption rate was not affected even in a high-concentration solution of a coexisting ion. Therefore, 8 REE ions (Nd, Sm, Eu, Ho, Yb, Lu, Y, and Sc) were selected for the study of adsorption kinetics and adsorption isotherm experiments. It was demonstrated that the values of Q_e (equilibrium adsorption capacity) for Nd, Sm, Eu, Ho, Yb, Lu, Y, and Sc were 14.28–60.80 mg g⁻¹. The adsorption of REEs on Fe₃O₄@mSiO₂–DODGA followed the pseudo-second-order kinetic model, Elovich model and Langmuir isotherm model, which indicated that the adsorption process of Fe₃O₄@mSiO₂–DODGA for REEs comprised single-layer adsorption on a non-uniform surface controlled by chemical adsorption. It was concluded that Fe₃O₄@mSiO₂–DODGA represents a new material for the adsorption of REEs in strongly acidic solutions.

The high selectivity magnetic mesoporous Fe₃O₄@mSiO₂–DODGA nanomaterials were prepared for adsorption of 16 rare earth elements.     

Pressure-driven thermoelectric properties of defect chalcopyrite structured ZnGa2Te4: ab initio study

The pressure induced structural, electronic, transport, and lattice dynamical properties of ZnGa₂Te₄ were investigated with the combination of density functional theory, Boltzmann transport theory and a modified Debye–Callaway model. The structural transition from I$\bar{4}$ to I$\bar{4}$2m occurs at 12.09 GPa. From the basic observations, ZnGa₂Te₄ is found to be mechanically as well as thermodynamically stable and ductile up to 12 GPa. The direct band gap of 1.01 eV is inferred from the electronic band structure. The quantitative analysis of electron transport properties shows that ZnGa₂Te₄ has moderate Seebeck coefficient and electrical conductivity under high pressure, which resulted in a large power factor of 0.63 mW m⁻¹ K⁻² (750 K). The ultralow lattice thermal conductivity (∼1 W m⁻¹ K⁻¹ at 12 GPa) is attributed to the overlapping of acoustic and optical phonon branches. As a result, the optimal figure of merit of 0.77 (750 K) is achieved by applying a pressure of 12 GPa. These findings support that ZnGa₂Te₄ can be a potential p-type thermoelectric material under high pressure and thus open the door for its experimental exploration.

ZnGa₂Te₄ is a stable vacancy ordered defect chalcopyrite structured direct band gap semiconductor which can act as a good p-type thermoelectric material with zT of 0.77 under 12 GPa applied pressure.     

Microwave hydrothermal synthesis of α-MnMoO4 nanorods for high electrochemical performance supercapacitors

Pristine α-MnMoO₄ nanorods were facilely prepared via co-precipitation (Cp) and microwave hydrothermal (MH) methods. X-ray diffraction (XRD) patterns showed pure monoclinic crystalline phase α-MnMoO₄ for the heat treated powder at 500 °C. Fourier Transform Infrared (FTIR) spectra showed that the chemical bond structure of α-MnMoO₄ corresponds to the strong vibrational modes of Mo–O–Mo, Mo–O and Mo O. Raman spectra showed the structural bonding and crystalline nature of α-MnMoO₄. Field Emission Scanning Electron Microscope (FE-SEM) images exposed the nanorod shape of the α-MnMoO₄ powder, with diameters of ∼200 nm and lengths of ∼1.6 μm. Electrochemical studies of the Cp- and MH-MnMoO₄ nanorods with 2 M NaOH as the electrolyte showed specific capacitances of 143 F g⁻¹ and 551 F g⁻¹, respectively, at a 1 A g⁻¹ constant discharge current density. Cyclic voltammetric (CV) studies of the MH-MnMoO₄ nanorods at various scan rates revealed the presence of redox pairs, suggesting a pseudocapacitive nature. The structural stability at different current densities demonstrated the high rate performances and good reversible capacity retention of the calcined MH-MnMoO₄ nanorods. A cycling life stability study of MH-MnMoO₄ demonstrated a good capacity retention of 89% of the initial specific capacitance at 5 A g⁻¹ after 1000 cycles.

Pristine α-MnMoO₄ nanorods were facilely prepared via co-precipitation (Cp) and microwave hydrothermal (MH) methods.     

Development of a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran by magnetic separation

The contents of both pesticide residues and dextran are important parameters for evaluating the quality of sugarcane. In this study, a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran was established on the basis of magnetic separation. Antigens of thiamethoxam and dextran were coupled to magnetic nanoparticles as the separation elements. Monoclonal antibodies of thiamethoxam (6C7D12) and dextran (3C6F7) were conjugated with the upconversion nanoparticles of NaYF₄:Yb,Er with an emission wavelength at 544 nm and NaYF₄:Yb,Tm with an emission wavelength at 477 nm to prepare the signaling elements, respectively. Due to the difference in the emission wavelength, the signaling elements bound on the separation elements could be detected simultaneously after separation by an external magnetic field. After optimization, the half-maximal inhibitory concentration (IC₅₀) values of the immunoassay for thiamethoxam and dextran were 0.46 and 49.33 ng mL⁻¹, respectively. The assay showed no cross-reactivity with the analogs of thiamethoxam and dextran except for clothianidin (8.7%). The average recoveries of thiamethoxam and dextran in sugarcane juice were 82.9–93.3% and 87.5–97.2%, respectively. The results indicated that the immunoassay could meet the requirements for the simultaneous quantitative detection of thiamethoxam and dextran.

The anti-thiamethoxam and anti-dextran monoclonal antibodies were prepared to develop a multicolor upconversion fluorescence immunoassay for the simultaneous determination of thiamethoxam (544 nm) and dextran (477 nm).     

Multifunctional BiF3:Ln3+ (Ln = Ho,Er, Tm)/Yb3+ nanoparticles: an investigation on the emission color tuning,thermosensitivity, and bioimaging

Pure cubic phase and uniform BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ nanoparticles (NPs) were prepared by coprecipitation. The growth mechanism of BiF₃:2%Er³⁺/20%Yb³⁺ NPs was proposed based on evolution analysis of the time-dependent morphology, in which BiF₃:2%Er³⁺/20%Yb³⁺ was formed through the growth process of “nucleation to crystallization and Ostwald ripening”. The upconversion luminescence (UCL) properties and mechanism of BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ under dual-wavelength excitation were also systematically investigated. The emission intensity of BiF₃:2%Er³⁺/20%Yb³⁺ by dual-wavelength excitation (λ = 980 nm + 1550 nm) was 1.49 times more than that excited by 1550 nm or 980 nm individually. Furthermore, the properties of the bright white and multicolor UCL showed that yellow, purple, green, or pinkish light could be observed by controlling the doping concentration of Ln³⁺ (Ln = Yb, Er, Tm, and Ho), indicating that they had potential applications in backlight sources of color displays and security labeling. The temperature sensitivity of BiF₃:2%Er³⁺/20%Yb³⁺ exhibited a downward tendency and its max value was about 0.0036 K⁻¹ at 273 K. Cell toxicity tests showed that the UCNPs in phospholipid aqueous solution presented low cytotoxicity. Also, in vivo imaging and X-ray imaging revealed that the BiF₃:2%Er³⁺/20%Yb³⁺ NPs had deep penetration and high contrast, which meant it could be used as a potential probe and contrast agent in in vivo optical bioimaging.

Multifunctional BiF₃:Ln³⁺(Ln = Ho, Er, Tm)/Yb³⁺ UCLNPs presented better performances in dual-wavelength synergy, thermosensitivity, emission color tuning, and bioimaging.