Controllable synthesis of uniform CaMoO4:Eu3+,M+ (M = Li, Na, K) microspheres and optimum luminescence properties

Abstract

High-quality and monodisperse CaMoO₄:Eu³⁺,M⁺ (M = Li, Na, K) microspheres have been synthesized with the assistance of poly-(diallyldimethylammonium chloride) (PDDA) via a facile coprecipitation hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), as well as photoluminescence (PL) spectroscopy are used to characterize the resulting samples. The results show that the CaMoO₄:Eu³⁺,M⁺ (M = Li, Na, K) can be directly indexed to a tetragonal CaMoO₄ phase with high purity. A series of controlled experiments indicate that PDDA as a shape modifier introduced into the reaction system plays a critical role in the morphology of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the concentration of PDDA and pH values in the initial solution. The prepared microspheres are stable at a suitable annealing temperature. The possible formation mechanism for these microspheres is presented. Additionally, the PL properties of CaMoO₄:Eu³⁺,M⁺ (M = Li, Na, K) were investigated in detail. The results reveal that the red emission peak intensities of CaMoO₄:Eu³⁺,Li⁺ and CaMoO₄:Eu³⁺,Na⁺ are higher than that of CaMoO₄:Eu³⁺,K⁺. The particle size and shape have a remarkable effect on the photoluminescence properties of the phosphor. The luminescence intensity is observably enhanced with increasing of the annealing temperature due to eliminating PDDA and/or H₂O present in the samples and to the improved crystal quality.