Poor water resistance and luminescent thermal stability remain great challenges for commercial narrow red emitting Mn⁴⁺-doped fluoride phosphors for white light emitting diodes (WLEDs). In this work, a simple coating method is developed to synthesize K₂SiF₆:0.06Mn⁴⁺@0.10K₂SiF₆ red emitting composite phosphor with excellent water resistance, luminescent thermal stability and high efficiency. After immersing into water for 300 min, the optimal sample maintains 88% of the initial integrated PL intensity, whereas that of uncoated control sample steeply drops down to 1%. A remarkable negative-thermal-quenching effect is observed that the integrated PL intensities at 120, 150, 180 and 210 °C are 176, 198, 214 and 213% of that initial one at 30 °C. The mechanism of above behaviors are discussed and proposed: The K₂SiF₆ shell layer not only prevents the hydrolysis of Mn⁴⁺ by water and but also cuts off the transfer of energy to surface defects, leads to the increase of radiation transition probability faster than that of non-radiation transition with the increase of temperature. These findings not only illustrate the multiple effects of coating K₂SiF₆ on the luminescent performances of K₂SiF₆:Mn⁴⁺ red emitting phosphor, but also provide a facile strategy to improve the water resistance as well as luminescent thermal stability of Mn⁴⁺-doped fluoride phosphors for warm WLEDs in the future.

对于商业上用于白光发光二极管（WLED）的窄发射红光的Mn ⁴⁺掺杂的氟化物磷光体，差的耐水性和发光热稳定性仍然是巨大的挑战。在这项工作中，开发了一种简单的涂覆方法来合成K ₂ SiF ₆：0.06Mn ⁴⁺ @ 0.10K ₂ SiF ₆红色发光复合荧光粉，具有出色的耐水性，发光热稳定性和高效率。浸入水中300分钟后，最佳样品将保持88％的初始初始PL强度，而未涂布的对照样品的强度会急剧下降至1％。观察到显着的负热猝灭效果，在120、150、180和210°C时的积分PL强度分别是初始温度在30°C时的176、198、214和213％。讨论并提出了上述行为的机理：K ₂ SiF ₆壳层不仅防止了Mn ⁴⁺的水解由于水的作用，并且还切断了能量向表面缺陷的转移，因此随着温度的升高，辐射跃迁几率的增加要快于非辐射跃迁的几率。这些发现不仅说明了涂覆K ₂ SiF ₆对K ₂ SiF ₆：Mn ⁴⁺发射红色荧光粉的发光性能的多重影响，而且提供了一种提高Mn的耐水性和发光热稳定性的简便策略。将来会在温暖的WLED中使用⁴⁺掺杂的氟化物荧光粉。