Synthesis and optimum luminescence of doughnut-shape undoped and doped CaMoO4.

In this work, we report the size and shape-controlled synthesis of CaMoO4 nanocrystals with an aim of investigate their structural, electronic, and luminescent properties. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, and luminescence spectroscopy. It is found that when MoO4(2-) and Ca2+ were mixed at relatively low temperature (in ice salt bath), the reaction produces a uniform population of microparticles with an interesting "doughnut" shapes. Due to the low temperature, the process of crystal nucleus is slow enough to for separated growth. The intensity of the absorption band for CaMoO4 nanocrystals was greatly enhanced with the decrease reaction temperature. The as-prepared CaMoO4 doughnut phosphors reveal a broad emission with a maximum at 500 nm, which exhibit blue-green emission. We also study the luminescent property for Eu(3+)-doped CaMoO4. As for the Eu(3+)-doped samples (initial Ca2+:Eu3+ molar ratio 20:1), it is shown that Eu3+ was substituted at Ca2+ sites in the CaMoO4 host lattice, which favors energy transition between Eu3+ ions and molybdate groups that caused the decrease of strength of the peak in emission spectra.