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-Ca2SiO4 (from here on C2S) particle from Pechini (C2SP) and hydrothermal (C2SH) 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 C2SH. 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 SiO44– tetrahedra in C2SH. 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 C2SP to C2SH 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 C2S were discussed. The charge state and concentration of europium ions in C2SP and C2SH were determined using X-ray photoelectron spectroscopy measurements. The C2S 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 C2SH has been hypothesized on the basis of the microscopy images. This study provides insights that are needed for further understanding the structure of C2S and thereby improves the applications in optical and biomedical areas and cement hydration.
Ca2SiO4 is a phase-change material, and γ- and β-Ca2SiO4 usually coexist in the sintered product. The overlap of the diffraction data between the two polymorphs makes the relevant phase identification difficult. In this work, the Eu3+ rear-earth fluorescence probe is introduced in the preparation of Ca2SiO4, and the obtained result indicates that the introduction of Eu3+ ions facilitates the increase in the content of β-Ca2SiO4 in the final product. In addition, the differences of the local coordination environments between the two Ca2SiO4 phases obviously influence the crystal-field splittings of Eu3+ ions, especially in the 5D0 → 7F0 nondegenerate and 5D0 → 7F1 magnetic dipole transition regions. On the basis of the excitation from the Eu3+–O2– charge-transfer band, the low-temperature spectral changes are systematically discussed. The transition area ratios of 5D0 → 7F0/5D0 → 7F2 and 5D0 → 7F1/5D0 → 7F2 present a positive and negative correlation with the increase of the excitation wavelength, respectively. The four nonequivalent 5D0 → 7F0 emission peaks with low to high wavelengths are identified as Eu3+ ion-occupied Ca(β-2) (571.8 nm), Ca(β-1) (573.8 nm), Ca(γ-2) (577.6 nm), and Ca(γ-1) (578.9 nm) sites. Besides, the relationship between the phase content of γ-Ca2SiO4 and the spectral change for the 5D0 → 7F0 emissions of the Eu3+ ions is also built. It is fitted by an exponential correlation function and is quite suitable for the prediction of the phase content of γ-Ca2SiO4 based on the measured spectra. The findings in this study manifest the promising application of the Eu3+ fluorescent probe in phase identification and enrich the analysis method in inorganic phase-change materials.
3D-printed bioceramics derived from silicone resin are of great interest in bone tissue engineering owing to their simple processes and low cost. Herein, PCN-224, as a subclass of metal−organic frameworks (MOFs), is successfully fabricated and deposited on the surface of 3D-printed porous β-Ca 2 SiO 4 (C 2 S) scaffolds. The composite scaffolds possess uniform interconnected macropores (≈400 μm), with increased porosity and slower degradation. The results indicate that deposition of PCN-224 significantly promotes cell proliferation and the expression of osteogenesis-related genes. Moreover, the composite scaffolds significantly improve calvarial defect healing in rats, compared with C 2 S scaffolds. Therefore, the PCN-224-modified 3D-printed porous C 2 S composite scaffolds are promising candidates for bone tissue engineering.
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