Morphology-controlled synthesis, characterization, and luminescence properties of KEu(MoO₄)₂ microcrystals

Large-scale one-dimensional (1D) rod-like and octagonal-like KEu(MoO ₄)₂ microcrystals were successfully synthesized by a simple, environmental friendly, and low cost molten salt method using halons (KCl or KBr) as flux. The as-prepared products were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and photoluminescence (PL) spectrometry. The results show that the reaction parameters, including reaction temperature and reaction time, played important roles on the phase structures and morphologies of the final products. The possible growth process of 1D rod-like KEu(MoO₄)₂ was proposed based on the time-dependent shape evolution and HRTEM analysis, which followed oriented aggregation and Ostwald ripening. The results of SAED and HRTEM investigations indicated an incommensurate modulated structure in the rod-like KEu(MoO₄)₂, and all the reflections can be expressed as ha* + kb* + lc* + mq, where m is an integer, and modulated vector q = 0.182b* + 0.156c*. Room temperature photoluminescence spectra of KEu(MoO₄)₂ microcrystals reveal a strong red emission via⁵D₀ → ⁷F₂ transition at 615 nm, and the 1D rod-like microcrystals own the enhanced intensity compared with the octagonal-like ones.