Alcohol-Guided Growth of Two-Dimensional Narrow-Band Red-Emitting K₂TiF₆:Mn⁴⁺ for White-Light-Emitting Diodes

The use of red phosphors with low light-scattering loss could improve the luminous efficacy and color rendering of white-light-emitting diodes (LEDs). Thus, the discovery of such phosphors is highly desired. In this work, high-efficiency two-dimensional red-emitting K₂TiF₆:Mn⁴⁺ (KTFM) were synthesized via an alcohol-assisted coprecipitation route. The synergistic effects of 1-propanol and hydrofluoric acid on the growth of KTFM microsheets (MSs) were studied through the first-principles calculations, which revealed that 1-propanol promoted the growth of KTFM MSs by preferentially adsorbing on the H-terminated K₂TiF₆ (001) surface. The photoluminescence quantum efficiency (QE) of Mn⁴⁺-activated K₂TiF₆ MSs was highly related to their size and thickness. The morphology-optimal KTFM MSs presented high internal QE (>90%), external QE (>71%), and thermal quenching temperature (102% at 150 °C relative to that at 25 °C). A prototype phosphor-converted LED with KTFM as the red-emitting component showed excellent color rendition (R_a = 91, R9 = 79) and high luminous efficacy (LE = 156 lm/w).