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Bonds in atomic crystals, energy levels, quantum chemistry and electronegativity visualized by light emitting diodes (LED)
摘要： Chemical bonds are discussed with the example of the group 15 elements N, P and As in light emitting diodes (LED). The colour resp. the light energy visualizes the electronegativity. Pairing LED of different colour as emitters and absorbers (detectors) allows a comparison between their different light energy. Electrons require energy above a given threshold to be excited to the conducting band: That is the (inner) photoelectric effect, an indication of the quantification of energy also in relation to chemical bonds.
关键词： inner photoelectric effect,chemical bonds of the elements N, P and As,visualisation of ionisation energy and electronegativity
更新于2025-09-19 17:13:59
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Ligand induced anomalous emission shift of size-controlled CsPbBr <sub/>3</sub> nanocrystals
摘要： CsPbX3 perovskite nanocrystals (NCs) have attracted much attention from researchers because of their excellent photoelectric properties like high quantum yield, large absorption cross section, and simple preparation process. The addition of ligands in the synthesis process has a significant effect on the microstructure and photophysical properties of solution-processed NCs, which needs further extensive studies. In this Letter, the effects of ligand electronegativity on the size and photoluminescence (PL) properties of CsPbBr3 NCs were reported. One is typical oleic acid with weak electronegativity, and another is 2-acrylamide-2-methylpropionic sulfonic acid with strong electronegativity. The third is their typical mixture with a molar ratio of 1:1. With the increase in ligand electronegativity, the size of CsPbBr3 NCs increases significantly. However, in contrast to the traditional quantum size confinement effect, the PL peak exhibits an abnormal blue shift gradually and the ligand passivation effect on NC surface defects also becomes more significant. The physical mechanism of this anomalous PL shift phenomena of CsPbBr3 NCs was investigated using the time-resolved PL spectrum and transient absorption spectrum.
关键词： transient absorption spectrum,quantum size confinement,photoluminescence,CsPbX3 perovskite nanocrystals,ligand electronegativity,time-resolved PL spectrum
更新于2025-09-16 10:30:52
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A Novel Despeckling Method for Medical Ultrasound Images Based on the Nonsubsampled Shearlet and Guided Filter
摘要： Porous maghemite (PM) was prepared by two-step calcinations. The crystallographic and magnetic changes of PM upon SO4^2? and CO3^2? adsorption were investigated. The crystallite size (~ 27 nm) and PM texture remain unchanged after adsorption. Fourier transform infrared spectra showed that SO4^2? and CO3^2? are adsorbed on the PM mainly through outer- and inner-sphere surface complexations, respectively. X-ray photoelectron spectra showed the increase and decrease of binding energy for Fe 2p3/2 electrons after SO4^2? and CO3^2? adsorption, respectively. Sulfate adsorption increases the magnetic susceptibility (χ) of PM by ~ 4.5%, and decreases the saturation magnetization (Ms) of PM by 24.6%. By comparison, carbonate adsorption decreases χ by ~ 3.7% and increases Ms by 17.8%. The magnetic changes upon SO4^2? and CO3^2? adsorption are attributed both to the electronegativity of anions and the size distribution of PM.
关键词： Adsorption,Electronegativity,Inorganic anion,Porous maghemite,Magnetic property
更新于2025-09-11 14:15:04