Enhanced luminescence of Mn4+ equivalently doped fluoride phosphors by reducing defects and impurities

The Mn ⁴⁺-equivalently doped fluoride has red emission with high color purity. Here, the luminescence of the Mn ⁴⁺-equivalently doped fluoride K ₂TiF ₆:Mn ⁴⁺ (KTF:Mn ⁴⁺) is significantly enhanced by the NH ₄ ⁺ doping strategy with a 2.27 times increase in luminescence intensity and a slight enhancement in decay time. The mechanism of luminescence enhancement is attributed to lattice distortion caused after the substitution of K ⁺ by NH ₄ ⁺, which improves the stability of Mn ⁴⁺ and reduce the number of defects and impurities. The prototype WLED with high CRI (Ra = 90.4), the high luminous efficiency of 112 lm/W and low CCT (2836 K) are obtained by using the optimal K ₂TiF ₆:Mn ⁴⁺,NH ₄ ⁺ (KTF:Mn ⁴⁺, NH ₄ ⁺) as the red light component. Some important luminous performances of the prototype WLEDs barely varied as the drive current was increased from 20 to 100 mA. These results demonstrate that the Mn ⁴⁺/ NH ₄ ⁺ co-doped KTF is well suited for the fabrication of highly stable WLEDs.