Enhanced red emission from BaMoO₄ : Eu³⁺ by Bi³⁺ co-doping

A series of Bi³⁺ ,Eu³⁺ -doped BaMoO₄ phosphors was synthesized using a hydrothermal method. The crystal structure, morphology and optical properties of the phosphors were studied using X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) measurements. Three different particle morphologies were detected in the SEM observation. The energy dispersive spectroscopy (EDS) results indicated that the solubility of Bi³⁺ in spherical or rugby-like BaMoO₄ particles was very low and the excess Bi³⁺ element was cumulated in the irregular particles. Characteristic emissions of Eu³⁺ ions (⁵ D₀  → ⁷ F_J ; J = 0, 1, 2, 3, 4) were observed under excitation in ultraviolet (UV) light, with the most intense transition being the ⁵ D₀  → ⁷ F₂ transition. Energy transfer from MoO₄^2- and Bi³⁺ to Eu³⁺ can be readily achieved. Red emission intensity of Eu³⁺ was enhanced by a factor of two by co-doping with a small amount of Bi³⁺ . Optical properties as a function of Bi³⁺ content were studied and the optimum Bi³⁺ content in BaMoO₄ nanocrystals was determined to be 0.4 mol%.