Mn4+-doped organometallic hafnium hexafluoride phosphors: Achieving near-unity quantum yield to elevate LED performance

Mn4+-activated fluoride phosphors with high luminous efficacy and short decay lifetimes are essential in realizing high-quality warm white-light-emitting diode (WLED) lighting. In this work, Mn4+-activated narrow-band red (∼630 nm) phosphor [(CH3)4N]2HfF6 was successfully synthesized by introducing an organic cationic group (tetramethylammonium) into the [HfF6]2- system using a mild chemical co-precipitation method. The sample structure was confirmed using various characterization techniques such as scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Powder particles with diameters ranging from 10 to 20 um and double pyramidal structures were prepared by adjusting the anti-solvent temperature to control the crystal growth rate. The investigation of the morphology, structure and photoluminescence properties of Mn4+-doped [(CH3)4N]2HfF6 phosphors at different anti-solvent temperatures deepened our understanding of the correlation between structure and luminescence. Ultimately, phosphors with optimal performance (external quantum efficiency, ∼92.2%, and decay lifetime, ∼3.6 ms) were obtained. The samples were mixed with polydimethylsiloxane organosilicon to prepare a red light-conversion flexible film, and the (TMA)2HfF6:Mn4+ red phosphor and commercially available YAG:Ce3+ yellow-green phosphor was thoroughly mixed with transparent silica to form a stable paste, and then coated on a blue LED bead to prepare warm white LEDs, which significantly optimized the performance of the white LEDs (correlated color temperature, ∼5564 K). These experimental results indicate that the materials prepared by the mild solution method have important applications in the domains of display and lighting.