Temperature-induced phase transition, luminescence and magnetic properties of Eu₂(MoO₄)₃ microcrystal red phosphors

A series of Eu₂(MoO₄)₃ crystals with different crystal structures have been successfully fabricated via a conventional ceramics process under different sintering temperatures. Using X-ray diffraction (XRD), Rietveld refinement, Fourier transform infrared (FT-IR) spectra, scanning electron microscope (SEM), differential thermal analysis (DTA), photoluminescence (PL) and vibrating sample magnetometer (VSM), the microstructures, luminescent and magnetic properties of the as-fabricated Eu₂(MoO₄)₃ crystals have been investigated in detail. XRD, FT-IR and Rietveld refinement results show that the crystal structure of the final Eu₂(MoO₄)₃ crystals can be remarkably influenced by the sintering temperature, exhibiting the phase transformation from tetragonal to monoclinic and then orthorhombic in the region of 600–1000 °C. SEM images manifest the sintering temperature has significantly influence on grain size and dispersity of the samples, although it has negligible effect on their morphology. DTA results confirm that the phase transition temperature for tetragonal to monoclinic and monoclinic to orthorhombic is 624 and 887 °C, respectively. PL results reveal that the excitation and emission intensities of the Eu₂(MoO₄)₃ crystals initially increase and then decrease with increasing sintering temperature, given the maximum at 900 °C. VSM results indicate that all the as-fabricated Eu₂(MoO₄)₃ crystals exhibit paramagnetic property. Our work can offer a simple and effective strategy to adjust the crystal structure of Eu₂(MoO₄)₃ crystals.