Luminescence Characteristics and Vibronic Coupling Behavior of a Highly Efficient Eu2+-Activated RbLi7Si2O8 Green Phosphor for Wide Color Gamut WLEDs

Hunting for a type of green phosphor with outstanding properties is of much significance for improving the performance of display backlights. In this work, a series of efficient Eu2+-activated RbLi7Si2O8 (denoted as RLSO:Eu2+) green phosphors with different doping concentrations were prepared via a low-temperature solid-state reaction approach under a reduced atmosphere. Photoluminescence (PL) measurements show that the prepared green phosphor with 8 atom % doping concentration of Eu exhibits the best internal quantum yield (IQY) of 95.8%. Besides, the phosphor delivers a good anti-thermal quenching behavior at temperatures <200 K, that is, there is no significant drop in luminescence intensity. Such thermal behavior is well consistent with the temperature dependence of measured luminescence lifetimes. The spectral analysis of the low-temperature luminescence spectrum with a semiclassical time-dependent approach reveals that three electronic levels of the Eu2+ ion coupled with a common low-frequency vibrational phonon mode with an energy of 21 meV shall be responsible for the high-efficiency luminescence of the prepared phosphor. Using the as-prepared green phosphor and K2SiF6:Mn4+ red phosphor, a white light-emitting diode (LED) device with high luminous efficacy (111.08 lm/W) and wide color gamut (112% NTSC) is fabricated on an InGaN blue chip.