A novel color-tunable phosphor, Na5Gd9F32:Ln3+ (Ln = Eu, Tb, Dy, Sm, Ho) sub-microcrystals: structure, luminescence and energy transfer properties

Abstract

Ln³⁺-Doped fluorides are economical and highly efficient luminescent materials, which play a crucial role in LEDs, biolabeling, and sensors. Therefore, Na₅Gd₉F₃₂:Ln³⁺ sub-microspheres with tunable multicolor emissions were successfully synthesized via a simple water bath method employing colloidal Gd(OH)CO₃ spheres as precursors. Samples were characterized by XRD, SEM, TEM, EDS and PL. It was found that the hydrolysis of BF₄⁻ ions had a dynamic effect on the retention of the morphology of the product owing to the mild reaction environment caused by the low hydrolysis rate of BF₄⁻ ions. Upon excitation by ultraviolet light, the Na₅Gd₉F₃₂:Ln³⁺ (Ln = Eu, Tb, Dy, Sm, Ho) phosphors underwent characteristic f–f transitions and gave rise to red, green, green, yellow, and pale green emissions, respectively. Moreover, various emission colors could be obtained by using different excitation wavelengths and adjusting the Eu³⁺/Tb³⁺ molar ratio owing to energy transfer between Tb³⁺ and Eu³⁺ ions in the Na₅Gd₉F₃₂ host. The energy transfer mechanism was demonstrated to be a dipole–dipole interaction. The multicolor luminescent phosphors with a certain dopant concentration based on a single host and excitation wavelength may have potential applications in the field of lighting displays.