VNU Journal of Science Mathematics – Physics, Vol 37, No 3 (2021) 101 108 101 Original Article Synthesis and Waterproofness Improvement of K3AlF6 Mn 4+ Phosphor for Warm White Light emitting Diodes Le Quoc Dat, Duong Thanh Tung, Nguyen Duy Hung* Advanced Institute for Science and Technology, Hanoi University of Science and Technology, 1 Dai Co Viet, Hai Ba Trung, Hanoi, Vietnam Received 10 October 2020 Revised 26 November 2020; Accepted 15 December 2020 Abstract In this study, we synthesized K[.]