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Li Substituent Tuning of LED Phosphors with Enhanced Efficiency, Tunable Photoluminescence, and Improved Thermal Stability
M. Zhao, Z. Xia*, X. Huang, L. Ning*, R. Gautier, M. S. Molokeev, Y. Zhou, Y.-C. Chuang, Q. Zhang, Q. Liu, K. R. Poeppelmeier*
Solid-state phosphor-converted white light-emitting diodes (pc-WLEDs) are currently revolutionizing the lighting industry. To advance the technology, phosphors with high efficiency, tunable photoluminescence, and high thermal stability are required. Here, we demonstrate that a simple lithium incorporation in NaAlSiO4:Eu system enables the simultaneous fulfillment of the three criteria. The Li substitution at Al sites beside Na sites in NaAlSiO4:Eu leads to an enhanced emission intensity/efficiency owing to an effective Eu3+ to Eu2+ reduction, an emission color tuning from yellow to green by tuning the occupation of different Eu sites, and an improvement of luminescence thermal stability as a result of the interplay with Li-related defects. A pc-WLED using the Li-codoped NaAlSiO4:Eu as a green component exhibits improved performance. The phosphors with multiple activator sites can facilitate the positive synergistic effect on luminescence properties.