Energy Transfer Processes in NaBiF₄ Nanocrystals Co‐Doped with Tb³⁺ and Eu³⁺ Dispersed in Aqueous Solution

The synthesis of hexagonal NaBiF 4 co‐doped with Tb 3+ and Eu 3+ (NaBi 0.75−x Tb 0.25 Eu x F 4 ; with x=0, 5, 10, 20 and 30) was achieved via a facile and fast precipitation route at 35 °C. Powder X‐ray diffraction (PXRD) and luminescence spectroscopy have been employed to characterize and investigate the materials. The study of luminescence spectroscopy and decay kinetics of the 5 D 4 excited state of Tb 3+ provides the evidence of a Tb 3+ →Eu 3+ energy transfer process. Sodium citrate has been adopted as capping agent to promote a homogeneous dispersion of the materials into water and to protect the inorganic host, which is water sensitive, from direct contact with this molecule. The comparison of luminescence properties between bare and citrate‐capped samples of NaBiF 4 co‐doped with Tb 3+ and Eu 3+ reveals a marked difference in the Tb 3+ →Eu 3+ energy transfer efficiency, which has been tentatively explained on the basis of a different environment surrounding the lanthanide ions in the two families of compounds.