In this work, a new Na2Se monolayer in 1H-phase, with interesting properties similar to transition metal dichalcogenides (TMDs), has been predicted using first-principles calculations. Results reveal good stability and wide direct gap semiconductor nature, with an energy gap of 0.82(1.45) eV as determined by standard PBE(hybrid HSE06) functional. This two-dimensional (2D) material exhibits poor stability under compressive strain due to the sensitive ZA acoustic phonon mode. In contrast, it only becomes unstable with tensile strain from 9% due to the elongation of chemical bonds reflected in the optical E" phonon mode. Under effects of lattice tension, the direct gap character is preserved and the band gap increases nearly linearly according to increase the strain strength. In addition, the effects of point defects associated with Na and Se atoms, including vacancies, antisites, and atom adsorption are also examined. Results indicate significant magnetization induced by Na single vacancy, SeNa antisite (one Na atom substituted by one Se atom), and Na adsorption on-top of hollow (TH) site. In these cases, feature-rich magneto-electronic properties as half-metallic and magnetic semiconductor natures are obtained. In contrast, the formation of 2Na+1Se combined vacancies as well as other defects related to Se atoms leads to an effective band gap modification, even metallization in some cases. Results introduces new promising 2D material for optoelectronic applications and proposes point defect engineering to create artificially novel features for spintronic applications.

Nanospherical upconversion luminescence particles (UCLPs) Gd2O3:Er3+ and Gd2O3:Er3+@ chitosan (CS) were prepared by step-by-step precipitation and calcination of the available nitrate rare Earth sales and chitosan. The morphology and composition of as-prepared samples were characterized by field emission electron spectroscopy (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. The synthesized UCLPs were non-agglomerate spheres in uniform nanoscale. The quantitative amount of chitosan was well coated with the gain surface of the UCLPs Gd2O3:Er3+ to obtain Gd2O3:Er3+@CS nanocomposite. The down-conversion luminescent intensity of Gd2O3:Er3+ NSP is lower than Gd2O3:Er3+@CS NSP samples, but luminescent characterizations were non-change. The photoluminescence (PL) of the green emission range of all UCLPs samples with chitosan-coated and -uncoated took the leading position. By using a diode laser excitation with 975 nm of wavelength, the detected intensity of red emission is more remarkably detected than green emissions. The two-photon mechanism for both green and red emissions of nanophosphor was observed. As a result, these might be promising opportunities to conjugate with various bio subjects that could be used in medical applications.

Transmission electron microscopy and UV–Vis spectroscopy can be used to observe the individual crystallite morphology and the origin of optical activity of quantum dots (QDs). CdSe QDs with different sizes were obtained by controlling their growth time, and the estimated sizes of the CdSe QDs ranged from 2.5 to 5.1 nm. The first excitonic absorption and photoluminescence (PL) peak shifted to lower energy with increasing QD size in the strong confinement regime. The PL spectra included a shoulder peak in the spectra of smaller QDs because of preferential adsorption. A comparison of the empirical trends and experimental results provided a fundamental understanding of the size-dependent properties of the CdSe QDs. In addition, time-resolved PL spectra in conjunction with surface characterization results showed that the PL behavior can be explained by the additional contribution of electron–phonon interaction.

In this work, novel two-dimensional BC2X (X = N, P, As) monolayers with X atoms out of the B–C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC2X monolayers have been investigated. Stability evaluation of the BC2X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC2N, BC2P and BC2As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC2X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC2N and BC2P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC2X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC2X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.

Most of the ZnS:M (M: transition metal) nanoparticles synthesized from the S2− source in organic and inorganic precursors cause defects, dangling bonds, and vacancies in the surface of nanoparticles, creating nonradiative recombination centres and reducing the photoluminescence (PL) intensity. ZnS:Mn and ZnS:Cu-PVP nanoparticles were synthesized by different methods with sources of S2− in organic and inorganic precursors of Na2S, Na2S2O3.5H2O or HSCH2COOH (TGA), and PVP. Then, the surface activation methods used ultraviolet radiation at 325 and 337 nm and visible radiation at 532 nm, 632.8 nm, and 650 nm were used to increase the photoluminescence (PL) intensity of the nanoparticles. The results of the XRD pattern analysis showed that the crystal structure and grain size of the samples did not appear to change due to the radiation annealing process. However, the FT-IR spectra showed that samples using the S2− source from the inorganic precursor Na2S, Na2S2O3, exhibited ZnSO4 formation that was attributed to the photochemical phenomena on the surface of the nanoparticles. The samples using S2− source from organic precursor TGA showed the formation of ZnSO4 and polyglycolide [CH2–COO]n (PGA) polymer on the surface of nanoparticles. This was attributed to the polymerization phenomenon. These photochemical and polymerization processes have the effect of reducing the nonradiative recombination processes of the nanoparticle surface defect states and simultaneously increasing the photoluminescence (PL) intensity of the luminescent centres (Mn2+, Cu2+) from 2.0 to 3.6 times for the ZnS:Mn system and 2.7 times for the ZnS:Cu-PVP system in comparison with the samples that were not annealed. The effects of UV and visible radiation, annealing time, and annealing power on the PL intensity of luminescence centres in the nanoparticles were also investigated and explained. The radiation annealing methods for the samples after synthesis are highly important for improving the optical properties of the nanoparticles and for studies on the fabrication of photovoltaic elements, quantum dots, and LEDs.

We measured the integrated cross sections of 110Pd(γ,n)109mPd, 110Pd(γ,n)109gPd and 110Pd(γ,x)108mRh reactions in the energy range from the reaction threshold to 70 MeV bremsstrahlung end-point energy. Measurements were performed by means of the activation method in combination with off-line γ-ray spectrometry. The induced activity of radionuclides was measured with a high-purity germanium (HPGe) detector and necessary corrections for γ-ray interferences were made. The integrated cross section of the studied reactions was measured relative to that of the monitor reaction 27Al(γ,2pn)24Na. Current results are compared with theoretical predictions using the TALYS-1.9 statistical nuclear model code. Calculations were performed using six different level density models in combination with eight γ-strength functions to determine which combinations best fit the experimental results. The present results are measured for the first time.

Herein, we present the development and characterization of Yttrium oxide (Y2O3) films and Al/Y2O3/n-Si heterojunction diodes at various substrate temperatures using a low-cost facile jet nebulizer spray pyrolysis (JNSP) technique. The X-ray powder diffraction (XRD) pattern proved polycrystalline films of Y2O3 with a cubic structure. Field emission scanning electron microscope (FESEM) images reveal very fine nanograins formation in Y2O3 films at all temperatures. Scanning probe microscopy (SPM) analysis shows very low roughness of all films. The detailed compositional/homogeneity analysis was done via energy dispersive X-ray (EDX)/e-mapping analysis. All the films exhibited a sharp absorption edge at ∼ 280 nm, and the estimated energy gap values were noticed between 4.5 to 4.9 eV. Moreover, the observed photoluminescence (PL) spectrum indicated number of emission peaks in the grown films. From the current – voltage (I-V) characteristic, the calculated ideality factor (n) value was noticed to be drastically reduced from 7.66 to 2.87 on increasing the substrate temperature. Further, the diode ideality factor, series resistance (Rs) and barrier height (ФB) were obtained from Cheung's method. The results revealed that the developed Al/Y2O3/n-Si heterojunction diode is a promising contender for optoelectronic devices.