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Effect of Zn substitution in Cr3+ doped MgAl2O4 mixed spinel nanoparticles on red/NIR emission properties
摘要： Red/Near-infrared (NIR) emitting Mg1-xZnxAl1.98Cr0.02O4 nanoparticles were synthesized by co-precipitation followed by firing(1200°C). Gradual shift of XRD peaks with Zn-content confirmed complete solid-solution formation. HRTEM revealed hexagonal sheet-like structures and lattice fringes revealed their single-crystallinity. Owing to refractory nature of MgAl2O4, particles were smaller(~38nm) in Mg-rich samples and gradually increased(~58nm) with Zn-substitution. Due to trigonal distortion, the fine splitting of the 4T1g level of Cr3+ manifests as asymmetric band(400nm) in the excitation spectrum. Cr3+ emission was clearly observed, comprising of R-line and multi-phonon side-bands on either side, with maximum R-line intensity for x=0.5. With increasing x, side-bands were more pronounced probably due to the band-gap difference of end members. High Dq/B(3.5-3.9), suggested Cr3+ in a strong crystal-field. Racah-parameter(B) variations suggest increased electron delocalization over molecular orbitals for higher Mg2+ substitutions. Longer lifetimes(23-34ms) are well-suited for bioimaging and optoelectronic applications. Such a simple synthesis can be easily extended to other important phosphors.
关键词： MgAl2O4,Luminescence,Nanoparticles,Phosphors,ZnAl2O4,Oxide ceramics
更新于2025-09-23 15:21:21
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Ratiometric Luminescent Sensor of Picric Acid based on the Dual-Emission Mixed-Lanthanide Coordination Polymer
摘要： Powerful explosive sensors play a key role in public security and environmental protection. Herein we report a series of isostructural lanthanide coordination polymers [Ln2L1.5(NMP)2]n (LnL, Ln = Eu , Gd, Tb, Dy, Ho and Er, H4L = [1,1′:4′,1″-terphenyl]-2′,4,4″,5′-tetracarboxylic acid, NMP = N-methyl-2-pyrrolidone) and mixed-Ln LnL (EuxTb1-xL, EuxGd1-xL, TbxGd1-xL and EuxTb0.02-xGd0.98L). Luminescence studies show that both H4L and GdL emit strong fluorescence and phosphorescence at 77 K while only fluorescence at room temperature, and TbL exhibits strong Tb3+ characteristic emission though the energy difference between the triplet excited state of H4L (20661 cm-1) and the 5D4 energy level of Tb3+ (20500 cm-1) is very small. By doping Eu3+ and Tb3+ into GdL, we obtained EuxTb0.02-xGd0.98L emitting warm white light. For TbL and Tb0.01Gd0.99L showing the dual-emission, upon addition of picric acid (PA) into their suspensions in Tris-HCl buffer, Tb3+ emission decreases slowly, however, the ligand-based emission is sharply quenched, rendering TbL and Tb0.01Gd0.99L excellent single-lanthanide and mixed-lanthanide ratiometric luminescence PA sensor materials, respectively.
关键词： picric acid (PA),ratiometric luminescence sensors,white light emission,metal-organic frameworks (MOFs),Coordination polymers (CPs)
更新于2025-09-23 15:21:21
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Apparent self-heating of individual upconverting nanoparticle thermometers
摘要： Individual luminescent nanoparticles enable thermometry with sub-diffraction limited spatial resolution, but potential self-heating effects from high single-particle excitation intensities remain largely uninvestigated because thermal models predict negligible self-heating. Here, we report that the common “ratiometric” thermometry signal of individual NaYF4:Yb3+,Er3+ nanoparticles unexpectedly increases with excitation intensity, implying a temperature rise over 50 K if interpreted as thermal. Luminescence lifetime thermometry, which we demonstrate for the first time using individual NaYF4:Yb3+,Er3+ nanoparticles, indicates a similar temperature rise. To resolve this apparent contradiction between model and experiment, we systematically vary the nanoparticle’s thermal environment: the substrate thermal conductivity, nanoparticle-substrate contact resistance, and nanoparticle size. The apparent self-heating remains unchanged, demonstrating that this effect is an artifact, not a real temperature rise. Using rate equation modeling, we show that this artifact results from increased radiative and non-radiative relaxation from higher-lying Er3+ energy levels. This study has important implications for single-particle thermometry.
关键词： upconverting nanoparticles,NaYF4:Yb3+,Er3+,thermometry,luminescence,self-heating
更新于2025-09-23 15:21:21
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<i>l</i> -Stercobilin-HCl and <i>d</i> -Urobilin-HCl. Analysis of Their Chiroptical and Conformational Properties by VCD, ECD, CPL Experiments and MD, DFT Calculations
摘要： Vibrational circular dichroism (VCD) and IR spectra of dichloromethane solutions of l-stercobilin and d-urobilin hydrochlorides have been recorded in the mid-IR region. The spectra are best interpreted by combining molecular dynamics (MD) calculations and DFT calculations within the QM/MM ONIOM-type framework, and the combined predicted results are better and more informative than the more standard analysis provided by DFT calculations. The same approach also sheds light on the Cotton effect sign inversion of room temperature versus low temperature electronic CD (ECD) spectra of the same compounds in methanol-glycerol solution. Finally, circularly polarized luminescence (CPL) spectra for l-stercobilin in chloroform solution provide information on the excited state geometry of this molecule.
关键词： Vibrational circular dichroism,electronic CD,molecular dynamics,IR spectra,QM/MM ONIOM-type framework,Cotton effect,circularly polarized luminescence,DFT calculations
更新于2025-09-23 15:21:21
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Ultrathin Y <sub/>2</sub> O <sub/>3</sub> :Eu <sup>3+</sup> nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching
摘要： Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y2O3:Eu3+. It was found that the NDs of Y2O3:Eu3+ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu3+ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the 5D0 → 7FJ (J = 0, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y2O3 NDs. The concentration quenching of the Eu3+ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.
关键词： nanodiscs,small angle x-ray scattering,europium-doped yttrium oxide,Raman spectroscopy,concentration quenching,transmission electron microscopy,luminescence
更新于2025-09-23 15:21:21
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Preparation and luminescent properties of mesoporous (SBA-15)-Eu2O3 nano materials
摘要： The CH3-(SBA-15) and (SBA-15)-Eu2O3 host-gust nanocomposite materials were synthesized by post-synthesis method, ultrasonic synthesis method (UM) and ultrasonic assisted synthesis methods (UAM). The X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscope (TEM) analysis and nitrogen adsorption-desorption method were used to observe the structure, the surface morphology and the chemical composites of the prepared products. The luminescent properties, and the luminescent intensity of the samples were studied by excitation and emission spectra. The results showed that, for the (SBA-15)-Eu2O3 composite materials, the hexagonal pore structure of the SBA-15 molecular sieve was maintained. The luminescent intensity of the UM sample was about 6 times higher than that of the mechanical mixture of SBA-15 and nano-Eu2O3 (5 wt %). The excitation spectrum intensity was 2 times higher than that of the mechanical mixture.
关键词： (SBA-15)-Eu2O3,Luminescence,SBA-15 molecular sieve,Trimethyl chlorosilane,Host-gust nanocomposite material
更新于2025-09-23 15:21:21
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Revisited Dual Luminescence of 2,2′-Dipyridylamine Hydrochloride in Solution and Physical Processes behind It
摘要： Reaction of 2,2’-dipyridylamine (dpa) with hydrochloric acid results in formation of dpa hydrochloride (dpa?HCl), leading to substantial changes in its luminescent properties. Luminescence of dpa?HCl in solution has been previously interpreted as aggregation-induced phenomenon. In this work, the emission properties of dpa?HCl in solution were revisited, focusing on the impact of methanol and chloroform solvents. Luminescence, absorption, and 1H NMR spectroscopy were used to study physical state of the solute molecules and photophysical properties associated with them. The results clearly indicate that the concentration and solvent dependencies of luminescence are due to equilibrium between protonated dpaH + and neutral dpa forms, rather than aggregation in solution. In chloroform, strong emission with λem ? 430 nm is associated with the cationic dpaH + form. Polar and hydrogen bonding methanol not only facilitates dissociation of dpaH + cation, but also seems to quench its luminescence through pyridinium hydrogen bond, and the residual weak emission at λem ? 360 nm is associated with the neutral dpa form. The obtained results can be applied in design of new dpa based materials with desirable luminescent properties in both solution and solid state.
关键词： 2,2’-dipyridylamine,protonation,hydrogen bond,absorption,luminescence
更新于2025-09-23 15:21:21
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Fluorescence Imaging for Ultrafiltration of Individual Nanoparticles from a Colloidal Solution in Track Membranes
摘要： We have used ? uorescence nanoscopy for direct imaging of adsorption of individual colloidal quantum dots of diameter ~10 nm (spherical core/shell CdSeS/ZnS semiconductor nanocrystals, functionalized by organic oleic acid ligands) in nanopores of a nuclear ? lter (a polypropylene track membrane with pores of diameter ~500 nm). We have shown that when a colloidal toluene solution passes through the pores of the membrane, the nanoparticles are completely retained at a depth of 10 μm.
关键词： nanopore,single-photon source,CdSe,membrane,nanoscopy,entangled-photon source,quantum dot,colloidal solution,microscopy,nanoparticles,ultra? ltration,oleic acid,nuclear ? lter,luminescence,polymer
更新于2025-09-23 15:21:21
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Effects of composition modulation on the structural and luminescence properties of Mn2+ doped Na2Mg1-xCaxSiO4 green-emitting phosphors
摘要： On the basis of the crystalline structural information that the matrix material has excellent physical-chemical stabilization, green-emitting Na2(Mg1-xCax)SiO4:Mn2+ (NMCS:Mn2+) phosphors were synthesized by a traditional solid-state method and systematically optimized, and their photoluminescence properties were studied. The luminescence properties of NMCS:Mn2+ phosphors as a function of Ca2+ concentrations were investigated. The structure of the as-prepared phosphors was identified by the X-ray diffraction (XRD) and the luminescent properties were characterized by the luminescence spectra, decay curve and CIE chromaticity coordinates. The emission peaks at 520nm generated by 4T1(4G)→6A1(6S) transition of the Mn2+ doped NMCS phosphors can provide a green component in the tri-color system. The emission intensity would be enhanced greatly by Ca2+-substitution and it can be observed that these emission peaks would shift to shorter wavelengths (blue-shift) with the increasing of Ca2+ content. The large enhancement of emission intensity and the shift of emission peaks due to Ca2+ substitution may provide a reference in the research of new type and more efficient phosphors for NUV-LEDs.
关键词： green phosphor,luminescence properties,Na2(Mg1-xCax)SiO4:Mn2+
更新于2025-09-23 15:21:21
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Upconversion luminescence properties of Y2O3: Yb3+/Er3+/Tm3+ nanocrystal doped PMMA nanocomposites
摘要： Y2O3 nanocrystals triply doped with Yb3+, Er3+, Tm3+ ions were synthesized via alginic acid-assisted gelation using thermal decomposition method and annealed at 800 °C for 24 h. Nanopowders were embedded into PMMA matrix via free-radical polymerization in an ultrasonic bath. X-ray diffraction and transmission electron microscopy measurements have shown that the crystal grain sizes decreased significantly with the narrow size distributions of the nanocrystals in PMMA matrix. A diode laser at 975 nm was used to measure the upconversion luminescence of the annealed nanopowders and those embedded in PMMA between the 400–850 nm wavelength region. The Er3+ concentration and the excitation power density dependencies of the relative intensities for red, green and blue upconversion luminescence in the nanopowder and PMMA nanocomposites are found to be different. The measured CIE-1931 color coordinates of the upconversion luminescence in PMMA nanocomposites show appreciable color stability under different excitation power densities, which is required for potential applications in the field of photonics.
关键词： Color Tunable Emission,Upconversion Luminescence,Polymer nanocomposites,Color Stability,Polymethyl methacrylate (PMMA)
更新于2025-09-23 15:21:21