Enhancement of emission and luminescent thermal stability of K(2)SiF(6) : Mn(4+) by synergy of co-doping with Na(+) and coating with GQDs

The luminescence properties and thermal stability of phosphors are key properties for practical applications. A series of K(2)SiF(6): Mn(4+), Na(+) @ GQDs (KSF: Mn(4+), Na(+) @ GQDs, KSF = K(2)SiF(6), GQDs = graphene quantum dots; here, Cl-contained graphene quantum dots are used) red light phosphors have been synthesized by using a combination of H(2)O(2)-free and hydrothermal coating methods. The fluorescence thermal stability and fluorescence intensity of the optimal phosphor are greatly improved by doping the matrix with Na(+) and coating it with GQDs. The strong negative thermal quenching (NTQ) effect and the color stability of the phosphor at variable temperatures result in good thermal stability. The strong NTQ effect is attributed to the phonon-induced transition mechanism. The high thermal stability makes the optimal sample ideal for high-power light LEDs (WLEDs). The test results show that the prototype WLED with the optimal sample as the red light component produces warm white light. The light has high luminescent efficiency (101.6 lm W(−1)), low correlated color temperature (CCT = 3978 K), and high color rendering index (R(a) = 92.2).