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

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.