Effects of HfO2 dopant on characteristics of Li2MgTiO4-based red phosphors: Thermal stability, photoluminescence intensity and quantum efficiency improvement

To produce natural and vivid color, the color rendering index of white light-emitting diodes (WLEDs) with single phosphors is usually lower than 70, which is problematic for LED applications. A commonly used method to resolve this issue is to enhance the red component of WLEDs. In the present study, Hf4+ and Mn4+ co-doped Li2MgTiO4 red phosphors are synthesized using a solid-state reaction method. When this red phosphor is excited at 397 and 468 nm, it exhibits weak reabsorption in the blue region and emits a broad and deep red emission band in the range of 640-750 nm, which is attributed to the E-2(g) -> (4)A(2) (g) transition. With 5 mol% HfO2 dopant, the photoluminescence intensity is enhanced by 1.45-fold and thermal stability is increased by 7.7%. Moreover, this red phosphor was applied to a red phosphor-in-glass (RPiG) optical device with a low-melting TeO2-B2O3-ZnO-Na2O-WO3 glass system. In the RPiG melting process, Li2MgTiO4:Mn4+, Hf4+ red phosphor triggered neither a chemical reaction nor severe degradation, indicating good thermal stability. Li2MgTiO4:Mn4+, Hf4+ has potential as a red emission material for warm WLED applications.