Luminescent Properties of (Ca 7 ZrAl 6 O 18 -Ca 3 Al 2 O 6 -CaZrO 3 ):Eu 3+ Composite Ceramics and Tracing in the Hydration Process.

In this work, solid-state reaction sintering was used to fabricate Ca 7 ZrAl 6 O 18 -Ca 3 Al 2 O 6 -CaZrO 3 :Eu 3+ ternary composite ceramics and cements. The structural, microstructural, and spectroscopic properties of the ceramics with different Eu 2 O 3 content were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and spectrofluorimetry, respectively. The XRD patterns analyzed with Rietveld refinement confirm the presence of the orthorhombic phase of Ca 7 ZrAl 6 O 18 and the cubic phase of Ca 3 Al 2 O 6 in all the samples, indicating that doping of Eu 3+ slightly changes the crystalline structure of both aluminate phosphors. EDS analysis revealed that the Eu doping element was strongly concentrated to the two phases, i.e., Ca 7 ZrAl 6 O 18 and Ca 3 Al 2 O 6 , with the Eu concentrations of 8.45 wt.% and 8.26 wt.%, respectively. The luminescent properties of the ceramics doped with different Eu 3+ ion concentrations were investigated by excitation and emission spectroscopy at room temperature. These results were compiled using a laser with an optical parametric oscillator (OPO) system. The obtained spectra indicated changes in the luminescence intensity and shape occurring with phase composition and Eu 2 O 3 concentration. The emission spectra of the ceramics exhibit a strong dependence on the excitation wavelength in the range from 210 to 300 nm, and invariably, five peaks were assigned to the 5 D 0 → 7 F J (J = 0, 1, 2, 3, 4) transitions of Eu 3+ . The luminescence spectroscopy was then used to trace the early and long-term hydration behavior of cements. Thus, luminescence spectroscopy may provide a new tool for non-destructive testing of cement-based structures.