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 ²E_g → ⁴A_{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.