Professor, Department of Physics, The University of Hong Kong, Hong Kong, China

Biography: S.J. Xu received his PhD degree in electronic Engineering from Xi'an Jiaotong University in 1993. Currently he is a full professor with tenure in Department of Physics, The University of Hong Kong, Hong Kong, China. S.J.X. has authored more than 160 scientific articles and 4 book chapters in the field of luminescence and photophysics of semiconductors with SCI citations >4000.

Speech Title: Boosting phonon-induced luminescence in Mn ion-activated fluoride phosphors for phosphor-converted white LEDs

Aims: Currently, hunting for anti-temperature-degradation high-efficiency phosphors has become crucial for fabricating high-brightness phosphor-converted white light-emitting diodes (pc-WLEDs). Herein, a series of (KxNa1-x)2SiF6:Mn4+ red phosphors with systematic composition variations of alkali metals were synthesized via a low-temperature full-solution approach for fabricating high-quality warm-white LEDs.

Methods: Low-temperature full-solution chemical synthesis.

Results: Phonon-induced luminescence is promoted as the most efficient and dominant light emission mechanism in cubic phosphor of K₂SiF₆:Mn⁴⁺ at room temperature and above. The best internal luminescence quantum efficiency (QE) of 97.6% (external QE=73.0%) is obtained in cubic K₂SiF₆:Mn⁴⁺ phosphor at room temperature. Finally, the K₂SiF₆:Mn⁴⁺ red phosphor, together with commercial yellow phosphor of YAG:Ce³⁺, was employed to demonstrate a pc-WLED with Ra of 82 and CCT of 2701 K.

Conclusions: A series of Mn⁴⁺-activated (K_xNa_1-x)₂SiF₆ red phosphors were prepared below 0 ^°C with a full-solution chemical route. The cubic K₂SiF₆:Mn⁴⁺ phosphor shows a high quantum efficiency of phonon-induced luminescence at room temperature. By using this red phosphor and commercial yellow phosphor together, a warm-white LED with good characteristics was demonstrated.