No abstract

The europium ion probes the symmetry disorder in the crystal structure, although the distortion due to charge compensation in the case of aliovalent dopant remains interesting, especially preparation involves low and high temperatures. This work studies the preparation of the β-CaSiO (from here on CS) particle from Pechini (CSP) and hydrothermal (CSH) methods, and its luminescence variance upon doping with Eu and Eu ions. The blue shift of the charge-transfer band (CTB) in the excitation spectra indicates a larger Eu-O distance in Eu doped CSH. The changes in vibrational frequencies due to stretching and bending vibrations in the FTIR and the Raman spectra and binding energy shift in the XPS analysis confirmed the distorted SiO tetrahedra in CSH. The high hydrothermal temperature and pressure produce distortion, which leads to symmetry lowering although doping of aliovalent ion may slightly change the position of the Ca atoms. The increasing asymmetry ratio value from CSP to CSH clearly indicates that the europium ion stabilized in a more distorted geometry. It is also supported by Judd-Ofelt analysis. The concentration quenching and site-occupancy of Eu ions in two nonequivalent sites of CS were discussed. The charge state and concentration of europium ions in CSP and CSH were determined using X-ray photoelectron spectroscopy measurements. The CS particles were studied by X-ray powder diffraction, FTIR, Raman, BET surface area, TGA/DTA, electron microscopy, XPS, and luminescence spectroscopy. The impact of citrate ion on the morphology and particle size of CSH has been hypothesized on the basis of the microscopy images. This study provides insights that are needed for further understanding the structure of CS and thereby improves the applications in optical and biomedical areas and cement hydration.

Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.

A superstructure was formed on form I of 6-chloro-2, 4-dinitroaniline crystals. It was observed using a slow evaporation solution growth technique and crystals grown from slow evaporation of the filtrate in anti-solvent precipitation. The thickness of 2D petals in the superstructure is about 100 nm.