An ultra-intense zero phonon line of Mn4+with the low 2E level energy in Rb2LiAlF6

Herein, Rb2LiMF6:Mn4+ (M= Al, In) phosphors were prepared by the non-equivalent doping of Mn4+. Mn4+ in Rb2LiAlF6 exhibits an ultra-intense zero phonon line (ZPL) detected at 627 nm, due to the highly-distorted symmetry. In contrast, the ZPL at 625 nm for Rb2LiInF6:Mn4+ is very weak. The 2E energy of Mn4+ in Rb2LiAlF6 (15949 cm−1) is lower than that in all reported fluoride phosphors, which may be ascribed to the stronger polarization effect of Li+. Compared with Rb2LiInF6:Mn4+ (5.07%), Rb2LiAlF6:Mn4+ (6.33%) has a high internal quantum efficiency (IQE) values of 69.8% and excellent thermal stability. The white LED packaged with Rb2LiAlF6:Mn4+ (6.33%) exhibits perfect performances with a high color render index (CRI = 92.3) and low color temperature (CCT =3875 K) as well as a high luminous efficiency (LE = 97.1 lm/W). Therefore, this work provides a promising red-emitting phosphor for high-quality white LEDs.