Design of alkali-free low-Tg phosphate glass for improved luminous efficacy of (Sr,Ca)AlSiN3:Eu2+ red phosphor-in-glass

초록

Red-emitting phosphor-in-glass (PiG) color converters with high luminescence efficiency were developed for high-power LED applications using an alkali-free KFP-series phosphate glass system and commercial (Sr,Ca)AlSiN3:Eu2+ (SCASN) phosphor. Three glasses in the P2O5-ZnO-Al2O3-BaO-B2O3 system (KFP-211, KFP-212, and KFP-213) were designed to have low glass-transition temperatures of 475-477 degrees C. XRD showed that PiG processed at 550 degrees C retained an amorphous glass matrix containing the SCASN phase, whereas at 600 degrees C an additional Zn2P2O7 phase appeared, along with increased turbidity, indicating partial devitrification of the glass matrix. Among the investigated compositions, the KFP-212 (T-g = 476 degrees C) based PiG containing 3 wt% SCASN phosphor and heat-treated at 550 degrees C exhibited the highest luminous efficacy of 26.26 lm/W-rad on a blue LED chip-on-board. High-power operation was further demonstrated using an eight-chip blue LEDs, where the optimized PiG reached a luminous flux of 50 lm at 5.3 W without visible surface damage after 1 h irradiation.

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