Microemulsion‐Mediated Synthesis and Properties of Uniform Ln:CaWO 4 (Ln = Eu, Dy) Nanophosphors with Multicolor Luminescence for Optical and CT Imaging

A new room‐temperature method has been developed that yields, for the first time in the literature, uniform and well‐dispersed CaWO 4 nanospindles. This method is based on the use of microemulsions consisting of aqueous solutions of Ca 2+ and WO 4 2– precursors, cyclohexane as the organic medium, Triton X‐100 as the surfactant, and n ‐octanol as the cosurfactant. We show that the formation of uniform nanospindles requires a restrictive set of experimental conditions. These particles crystallize into the tetragonal CaWO 4 phase and emit blue–green luminescence when excited by UV radiation. The reported method is also useful for doping the CaWO 4 spindles with Eu 3+ or Dy 3+ cations, resulting in multicolor emissions (red for Eu 3+ ; white for Dy 3+ ). The luminescence is much stronger when excited through a WO 4 2– –Ln 3+ (Ln = Eu or Dy) energy‐transfer band than through the f–f transition bands of the Ln 3+ cations. Interestingly, because of the white luminescence associated with the Dy:CaWO 4 nanophosphor, it might be useful for LED technologies. Luminescence dynamics and energy‐transfer efficiency have been analyzed to determine the optimum phosphors. Finally, the Eu‐doped CaWO 4 nanospindles also showed excellent X‐ray attenuation efficacy, which confers double functionality to this material as both a luminescence bioprobe and as a contrasting agent for X‐ray computed‐tomography.