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In order to enhance the luminescent thermal stability and water resistance of K 2 SiF 6 :Mn4+, we proposed a simple hydrothermal method to synthesize K 2 SiF 6 :0.06Mn4+@GE-GQD S (6 mg/mol) (GE-GQDs: green emission graphene quantum dots) red emitting phosphor with outstanding water resistance. The emission intensity of the sample coated with the GE-GQDs still maintains 87.74% of the initial one after immersion for 360 min, while the uncoated K 2 SiF 6 :0.06Mn4+ sharply decreases to 11.26%. Another impressive phenomenon is that due to the negative thermal quenching (NTQ) effect, the luminescent thermal stability of the coated sample is also significantly improved, and the integrated photoluminescence (PL) intensity at 180 °C is 238% of that at 25 °C. In the meantime, the integrated PL intensity of the coated samples is 2.55 times that of K 2 SiF 6 :0.06Mn4+ under room temperature. Based on experimental results, it is suggested that after coating with GE-GQDs, a surface protective layer is formed on the surface of the sample, which improves the water resistance, room temperature emission intensity, and luminescent thermal stability of the coated sample. Finally, the improvement mechanism of the above multiple enhancements on luminescent properties is discussed and proposed. The above multiple enhancement effects make the sample have broad application for blue light-based warm and high-power WLEDs (white light-emitting diodes). • K 2 SiF 6 : Mn4+@GE-GQD S has been synthesized. • Sample has high water resistance, thermal stability and luminescent intensity. • Water resistance, thermal stability and emission intensity are enhanced by GE-GQDs. • The high water resistance is attributed to formation of coordination polymer. [ABSTRACT FROM AUTHOR]