Role of Synthesis Method on Luminescence Properties of Europium(II, III) Ions in β-Ca 2 SiO 4 : Probing Local Site and Structure.

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-Ca2 SiO4 (from here on C2 S) particle from Pechini (C2 SP) and hydrothermal (C2 SH) methods, and its luminescence variance upon doping with Eu2+ and Eu3+ ions. The blue shift of the charge-transfer band (CTB) in the excitation spectra indicates a larger Eu3+ -O2- distance in Eu3+ doped C2 SH. 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 SiO4 4- tetrahedra in C2 SH. 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 C2 SP to C2 SH 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 Eu3+ ions in two nonequivalent sites of C2 S were discussed. The charge state and concentration of europium ions in C2 SP and C2 SH were determined using X-ray photoelectron spectroscopy measurements. The C2 S 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 C2 SH has been hypothesized on the basis of the microscopy images. This study provides insights that are needed for further understanding the structure of C2 S and thereby improves the applications in optical and biomedical areas and cement hydration.