| Abstract [eng] |
In the last several decades, many different preparation techniques have been used for the preparation of AMoO4 (A = Mg, Ca, Sr and Ba) ceramics. Nowadays, the results of obtained compounds, depending on the preparation route, are important and have significant influence to the science and technologies. Therefore, the choice of synthesis technique usually depends on variety factors that can shorten, facilitates and reduce the preparation way. From this point of view, the solution-based synthetic methods play a crucial role in the design and production of fine ceramics and they have been successful in overcoming many of the limitation of the traditional solid-state, high-temperature methods. Thus, the development of the aqueous sol-gel synthesis technique for the preparation of M’–Mo–O tartrate (M’=Mg, Ca, Sr and Ba) gel precursors and Powellite type CaMoO4:xEu3+ compounds in the sol-gel processing using tartaric acid as a complexing agent is the main object of these investigations. Thus, in this case, for the first time in our knowledge the aqueous tartaric acid-assisted sol-gel synthesis technique was successfully proposed for the preparation of M–Mo–O tartrate gel precursors and MMoO4 ceramic materials (M=Mg, Ca, Sr and Ba) as well as europium oxide doped CaMoO4 double oxide. TG and DSC analysis of Mg–Mo–O, Ca–Mo–O, Sr–Mo–O and Ba–Mo–O tartrate gels clearly showed that the crystallization of final double oxides starts below 500 oC. Besides, the combustion of volatile components and the burning of carbon residue occurs up to 600 ° C. Using X-ray diffraction (XRD), it has been observed that the characteristic peaks of MgMoO4, CaMoO4, SrMoO4 and BaMoO4 compounds are observed at temperatures between 500 oC and 1000 oC. According to the scanning electron microscopy, the morphology of the surface of ceramic compounds depends really much from the nature of alkaline earth metal in M–Mo–O tartaric precursor. The FT–IR spectra of Eu2O3 doped calcium molybdate samples annealed at 650 °C did not show any bands attributable to carbonates or residual organic species. Finnaly, according to the UV–Vis spectra is clear that all synthesized CaMoO4:xEu3+ samples were optically active compounds at shorter wavelengths (200–310 nm) that arises from MoO42–functional groups. Reflection peaks in 360–470 nm wavelength region are attributed to the Eu3+ characteristic excitations, which are significantly influenced by both annealing temperature and dopant concentration in CaMoO4 lattice. The peak intensity of the CaMoO4:x%Eu3+ samples annealed at 750 °C reached the maximum only with doping of 5 mol% of Eu3+ ions and further increasing of dopant concentration leads to the quenching of reflectance of obtained optical materials. |
