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Giant Red-shifted Emission in (Sr,Ba)Y2O4:Eu2+ Phosphor Toward Broadband Near-infrared Luminescence
Z. Yang, Y. Zhao, Y. Zhou, J. Qiao, Y.-C. Chuang(莊裕鈞), M. S. Molokeev, and Z. Xia*(夏志國)
Near-infrared (NIR) light-emitting diodes (LEDs) light sources are desirable in photonic, optoelectronic, and biological applications. However, developing broadband red and NIR-emitting phosphors with good thermal stability is always a challenge. Herein, the synthesis of Eu2+-activated SrY2O4 red phosphor with high photoluminescence quantum efficiency and broad emission band ranging from 540 to 770 nm and peaking at 620 nm under 450 nm excitation is designed. Sr/Ba substitution in SrY2O4:Eu2+ has been further utilized to achieve tunable emission by modifying the local environment, which facilitates the giant red-shifted emission from 620 to 773 nm while maintaining the outstanding thermal stability of SrY2O4:Eu2+. The NIR emission is attributed to the enhanced Stokes shift and crystal field strength originated from the local structural distortions of [Y1/Eu1O6] and [Y2/Eu2O6]. The investigation in charge distribution around Y/Eu provides additional insight into increasing covalency to tune the emission toward the NIR region. As-fabricated NIR phosphor-converted LEDs demonstration shows its potential in night-vision technologies. This study reveals the NIR luminescence mechanism of Eu2+ in oxide-based hosts and provides a design principle for exploiting Eu2+-doped NIR phosphors with good thermal stability.