An efficient rare-earth free deep red-emitting GdGeSbO₆:Mn⁴⁺ phosphor for white light-emitting diodes

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn⁴⁺-activated deep red phosphor GdGeSbO₆:x%Mn⁴⁺ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn⁴⁺ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO₆:0.3%Mn⁴⁺ produces a narrow emission peak centred at 682 nm in the range of 650-800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. Notably, the optimal phosphor GdGeSbO₆:0.3%Mn⁴⁺ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I_{423 K}/I_{303 K} ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO₆:0.3%Mn⁴⁺ phosphors with commercial phosphors on the surface of a 365 nm UV chip.