Influence of Surface Coating on Structural and Photoluminescent Properties of CaMoO4:Pr Nanoparticles

CaMoO₄:Pr(core), CaMoO₄:Pr@CaMoO₄ (core/shell) and CaMoO₄:Pr@CaMoO₄@SiO₂ (core/shell/shell) nanoparticles were synthesized using polyol method. X-ray diffraction (XRD), thermogravimatric analysis (TGA), UV–vis absorption, optical band gap energy analysis, Fourier transform infrared (FTIR), FT-Raman and photoluminescence (PL) spectroscopy were employed to investigate the structural and optical properties of the synthesized core and core/shell nanoparticles. The results of the XRD indicate that the obtained core, core/shell and core/shell/shell nanoparticles crystallized well at ~150 °C in ethylene glycol (EG) under urea hydrolysis. The growth of the CaMoO₄ and SiO₂ shell (~12 nm) around the CaMoO₄:Pr core nanoparticles resulted in an increase of the average size of the nanopaticles as well as in a broadening of their size distribution. These nanoparticles can be well-dispersed in distilled water to form clear colloidal solutions. The photoluminescence spectra of core, core/shell and core/shell/shell nanoparticles show the characteristic charge transfer emission band of MoO₄ ^2? (533 nm) and Pr³⁺ 4f²?→?4f², with multiple strong ³H₄?→?³P₂, ¹D₂?→?³H₄ and ³P₀?→?³?F₂ transitions located at ~490, 605 and 652 nm, respectively. The emission intensity of the CaMoO₄:Pr@CaMoO₄ core/shell and CaMoO₄:Pr@CaMoO₄@SiO₂ core/shell/shell nanoparticles increased ~4.5 and 1.7 times,respectively, with respect to those of CaMoO₄:Pr core nanoparticles. This indicates that a significant amount of nonradiative centers existing on the surface of CaMoO₄:Pr@CaMoO₄ core/shell nanoparticles can be eliminated by the shielding effect of CaMoO₄ shells.     

Evolution of the N = 20 and N = 28 shell closures in neutron-rich nuclei

The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent approach using the Gogny force. Introducing configuration mixing, ³²Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in ⁴⁴ S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2⁺ excitation energy E_x = 1.46 MeV and the reduced transition probability B(E2;0⁺ _gs→ 2⁺ ₁)= 420 e ² fm ⁴ obtained with our approach are in good agreement with experimental data. Received: 26 July 2000 / Accepted: 30 August 2000     

Preparation and characterization of upconversion luminescent LaF3:Yb,Er/LaF3 core/shell nanocrystals

LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals were successfully synthesized using solvothermal method. The crystal structure, morphology and photoluminescence properties of as-prepared nanocrystals were investigated in detail. XRD patterns show that the obtained LaF₃:Yb³⁺,Er³⁺ core and LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals exhibit hexagonal structure. The average particle size is about 9.3 nm and 11.4 nm for core and core/shell nanocrystals, respectively. Compared with LaF₃:Yb³⁺,Er³⁺ nanocrystals, both the upconversion emission intensity and the lifetime increase in LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals. The enhancement can be attributed to the LaF₃ shell which can eliminate the nonradiative centers on the surface of LaF₃:Yb³⁺,Er³⁺ nanocrystals.     

Synthesis and Raman signature for the formation of CdO/MnO2 (core/shell) nanostructures

In the present report, bare CdO and CdO/MnO₂ core/shell nanostructures of various cores and different shell sizes were synthesized using co‐precipitation method. The phase, size, shape and structural details of the bare CdO and CdO/MnO₂ nanostructures were investigated by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy measurements. TEM micrographs confirm the formation of core/shell nanostructures. The presence of CdO (core) and MnO₂ (shell) crystal phases was determined by analyzing the Raman data of bare CdO and CdO/MnO₂ core/shell nanostructures. The Raman spectra of bare CdO nanostructures contain one broad intense convoluted envelop of three bands in the spectral range of 200–500 cm⁻¹ and a weaker band located at ~940 cm⁻¹. The intensity of these two Raman bands is decreased with the increase of shell size and disappeared completely for the shell size 5.3 ± 1 nm. Further, two new Raman bands appeared at ~451 and ~665 cm⁻¹ for the shell size 1.3 ± 0.1 nm. These two Raman bands are assigned to the deformation of Mn–O–Mn and Mn–O stretching modes of MnO₂. The intensity of these two Raman bands is enhanced with the increase of shell size and attains a maximum value for the shell size 5.3 ± 1 nm. The disappearance of characteristics Raman bands of CdO phase and the appearance of characteristics Raman bands corresponding to MnO₂ phase for nanostructures of shell size 5.3 ± 1 nm authenticate the presence of CdO as core and MnO₂ as shell in the core/shell nanostructures. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of shell structure in the fusion reactions

The fusion reactions are studied in the central collisions ⁸²Se+ + ¹³⁴Ba and ⁸²Se+ + ¹³⁸Ba by the improved isospin-dependent quantum molecular-dynamics model, where the nucleus ¹³⁸Ba has a closed neutron shell N = 82 . Comparing the shell correction energies and fusion probabilities of these two reactions with the ones of other asymmetric or more symmetric reaction systems that form the same compound nuclei, we find the dependence of the fusion reaction on the nuclear shell structure of the colliding nuclei. The experimental data of the fusion probabilities are described well by the present model. The result suggests that the neutron shell closure N = 82 promotes fusion.     

Isospin dependence of kinetic energies in light neutron-rich nuclei

Energy spectra andelectric dipole transitions ofN=7 isotones are studied by shell model calculations with isospin dependent kinetic energies for s-d shell orbits. The ground states of¹⁰Li and⁹He are predicted. Electric dipole transitions in¹³C and¹¹Be are studied by using the realistic single-particle wave functions in Woods-Saxon potential.JSPS Fellow for Japanese Junior Scientists.     

Study of N=20 shell gap with 1H(28Ne,27,28Ne) reactions

This paper reports on the ¹H(²⁸Ne,²⁸Ne) and ¹H(²⁸Ne,²⁷Ne) reactions studied at intermediate energy using a liquid hydrogen target. From the cross section populating the first 2⁺ excited state of ²⁸Ne, and using the previously determined B(E2) value, the neutron quadrupole transition matrix element has been calculated to be M_n=13.8 ±3.7 fm². In the neutron knock-out reaction, two low-lying excited states were populated in ²⁷Ne. Only one of them can be interpreted by the sd shell model while the additional state may intrude from the fp shell. These experimental observations are consistent with the presence of fp shell configurations at low excitation energy in ^27,28Ne nuclei caused by a vanishing N=20 shell gap at Z=10.     

Emergence of new magic numbers,N = 16 and 32 by tensor interaction in Skyrme–Hartree–Fock theory

Melting of N = 20 shell and development of N = 16 and 32 shells for neutron-rich nuclei have been studied extensively by including tensor interaction in Skyrme–Hartree–Fock theory optimized to reproduce the splitting Δ1f shells of ^40,48Ca and ⁵⁶Ni nuclei. Evolution of gap generated by the energy difference of single-particle levels ν2s _1/2 and ν1d _3/2 has been found to be responsible for shell closure at N = 16. The splitting pattern of spin–orbit partners 2p shell model state in Ca, Ti, Cr, Fe and Ni isotopes indicates the formation of a new shell at N = 32 region.     

Preparation of Highly Stable and Photoluminescent Cadmium-Free InP/GaP/ZnS Core/Shell Quantum Dots and Application to Quantitative Immunoassay

Indium phosphide (InP) quantum dots (QDs) are ideal substitutes for widely used cadmium-based QDs and have great application prospects in biological fields due to their environmentally benign properties and human safety. However, the synthesis of InP core/shell QDs with biocompatibility, high quantum yield (QY), uniform particle size, and high stability is still a challenging subject. Herein, high quality (QY up to 72%) thick shell InP/GaP/ZnS core/shell QDs (12.8 ± 1.4 nm) are synthesized using multiple injections of shell precursor and extension of shell growth time, with GaP serving as the intermediate layer and 1-octanethiol acting as the new S source. The thick shell InP/GaP/ZnS core/shell QDs still keep high QY and photostability after transfer into water. InP/GaP/ZnS core/shell QDs as fluorescence labels to establish QD-based fluorescence-linked immunosorbent assay (QD-FLISA) for quantitative detection of C-reactive protein (CRP), and a calibration curve is established between fluorescence intensity and CRP concentrations (range: 1–800 ng mL⁻¹, correlation coefficient: R² = 0.9992). The limit of detection is 2.9 ng mL⁻¹, which increases twofold compared to previously reported cadmium-free QD-based immunoassays. Thus, InP/GaP/ZnS core/shell QDs as a great promise fluorescence labeling material, provide a new route for cadmium-free sensitive and specific immunoassays in biomedical fields.     

Quadrupole transitions in 20Ne

Untruncated shell model calculations in the 1s-0d shell using Chung-Wildenthal effective interactions have been performed for ²⁰Ne and the electron scattering form factors for elastic scattering and for the excitation of 2₁⁺, 2₁⁺ and 2₃⁺ states have been examined. Saxon-Woods wave functions and a phase-shift analysis have been used. It is shown that within the limited space of the 1s-0d shell, it is possible to obtain vastly different momentum transfer dependence for the electro-excitation of ΔJ^π = 2⁺ transitions. The 2₁⁺ and 2₂⁺ states are seen to be adequately described by the wave functions obtained in this calculation, but 2₃⁺ is not described well.     

Particle-hole nature of the two lowest 3−states in 24Mg

Stripping and pickup reactions are performed and show the configuration for the lowest 3^?state (7.62MeV) to be mainly a hole in the 1p shell the next 3^?level (8.36 MeV) is mainly promoted into the 2p-1f shell.     

Iinelastic electron scattering calculations on N = 50 isotones

The first excited 2⁺, 3^? and 4⁺ levels in ⁸⁸Sr, ⁹⁰Zr and ⁹²Mo are described by the seniority υ = 2 shell model and by the two-quasiparticle BCS model. In both models the DWBA cross sections for inelastic electron scattering are calculated. It appears that both models often give the same cross sections, the overall normalisation being then the difference. The agreement with the experimental data for ⁹⁰Zr and ⁹²Mo for the shell model case is much better than for the BCS model.     

Study of the K shell photoelectric parameters of Dy,Yb and W atoms using low energy bremsstrahlung radiation

Low energy external bremsstrahlung (EB) photons were used to estimate the K shell photoelectric parameters; the K shell photoelectric cross section at the K edge, the K shell binding energy, the K shell jump ratio, the K shell jump factors, the Davisson-Kirchner ratio and the K shell oscillator strength for dysprosium (Dy), ytterbium (Yb) and tungsten (W) atoms. The EB photons are produced in the nickel (Ni) target by using the beta particles from a weak beta source of ⁹⁰Sr–⁹⁰Y. These photons are made to fall on these elemental targets of our interest and the transmitted spectrum is measured using GMX 10P HPGe detector coupled to an 8K multichannel analyzer. The sharp decrease at the K edge in the measured spectrum is used to determine the K shell photoelectric parameters of these elements. The experimental results are in good agreement with the theoretical values.     

Au@SiO2 core/shell nanoparticle assemblage used for highly sensitive SERS‐based determination of glucose and uric acid

The use of Au@SiO₂ core/shell nanoparticle (NP) assemblage with highly sensitive surface‐enhanced Raman scattering (SERS) was investigated for the determination of glucose and uric acid in this study. Rhodamine 6G dye molecules were used to evaluate the SERS enhancement factor for the synthesized Au@SiO₂ core/shell NPs with various silica shell thicknesses. The enhancement of SERS signal from Rhodamine 6G was found to increase with a decrease in the shell thickness. The core/shell assemblage with silica layer of 1–2 nm over a Au NP of ~36 nm showed the highest SERS signal. Our results show that the SERS technique is able to detect glucose and uric acid within wide concentration ranges, i.e. 20 ng/dL to 20 mg/dL (10⁻¹²–10⁻³ M) and 16.8 ng/dL to 2.9 mg/dL (10⁻¹¹–1.72 × 10⁻⁴ M), respectively, with associated lower detection limits of ~20 ng/dL (~1.0 × 10⁻¹² M) and ~16.8 ng/dL (~1.0 × 10⁻¹¹ M). Our work offers a low‐cost route to the fabrication of agile sensing devices applicable to the monitoring of disease progression. Copyright © 2013 John Wiley & Sons, Ltd.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.     

Microscopic Studies of Electric Dipole Resonances in 1p Shell Nuclei

Recent data on total and partial photonuclear cross sections in the GDR region of the nuclei ⁶Li to ¹⁶O are compared with theoretical predictions, mostly from shell model and continum shell model studies. The influence of the size of the configuration space, of the adopted residual interaction and of the continuous spectrum on the isovector E1 response is discussed to some detail. The observed trends of the localization, the shape and width, the isospin and the configurational structure of the GDR with increasing 1p shell occupation are related to the microscopic structure of the nuclear ground state. Particular attention is given to the partial (γ, N_i) disintegration channels. Complex-particle emission and isospin mixing in the nuclear states are discussed for a few cases. An attempt is made to bring some systematics also in the evidence on excited-state giant resonances through the 1p shell region. The photonuclear GDR is compared with other giant multipole excitations, mostly for the example of the ¹⁴C nucleus.     

Synthesis of high quality and monodisperse CdS:Mn/ZnS and CdS:Mn/CdS core–shell nanoparticles

CdS:Mn²⁺/ZnS and CdS:Mn²⁺/CdS core–shell nanoparticles were synthesized in aqueous medium via chemical precipitation method in an ambient atmosphere. Polyvinylpyrrolidone (PVP) was used as a capping agent. The effect of the shell (ZnS and CdS) thickness on CdS:Mn²⁺ nanoparticles was investigated. Inorganically passivated core/shell nanocrystals having a core (CdS:Mn²⁺) diameter of 4 nm and a ZnS-shell thickness of ∼0.5 nm exhibited improved PL intensity. Optimum concentration of doping ions (Mn²⁺) was selected through optical study. For all the core–shell samples two emission peaks were observed, the first one is band edge emission in the lower wavelength side due to energy transfer to the Mn²⁺ ions in the crystal lattice; the second emission is characteristic peak of Mn²⁺ ions (⁴T₁ → ⁶A₁). The XRD, TEM and PL results showed that the synthesized core–shell particles were of high quality and monodisperse.     

Shape transition in the neutron rich sodium isotopes

Mass spectrometer measurements of the neutron rich sodium isotopes show a sudden increase at ³¹Na in the values of the two-neutron separation energies. The spherical shell model naturally predicts a sudden decrease at ³²Na after the N = 20 shell closure. We propose that the explanation for this disagreement lies in the fact that sodium isotopes in this mass region are strongly deformed due to the filling of negative parity orbitais from the 1f_{$\text{7}\text{2}$} shell. Hartree-Fock calculations are presented in support of this conjecture.     

A study of 80,82,84Sr by (α, 2nγ) reactions

The ^AKr(α, 2nγ)^A+2Sr reactions have been studied by in-beam γ-ray spectroscopy for A = 78, 80, and 82. States with spins up to 10⁺ in ^82,84Sr and 6⁺ in ⁸⁰Sr are identified. The Sr nuclei undergo a transition from spherical to deformed ground states as neutrons are removed from the N = 50 shell. The systematics of these nuclei are compared with calculations based upon the shell model and interacting boson model.