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Highly Efficient and Stable Narrow-Band Red Phosphor Cs2SiF6:Mn4+ for High-Power Warm White LED Applications Enhai Song, Y. Y. Zhou, X. B. Yang, Z. F. Liao, Weiren Zhao, TingTing Deng, L. Y. Wang, Y. Y. Ma, Shi Ye, and Qinyuan Zhang ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.7b00852 • Publication Date (Web): 15 Sep 2017 Downloaded from http://pubs.acs.org on September 16, 2017
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ACS Photonics
Highly Efficient and Stable Narrow-Band Red Phosphor Cs2SiF6:Mn4+ for HighPower Warm White LED Applications
Enhai Song†, Yayun Zhou†, Xiao-Bao Yang*‡, Zifeng Liao§, Weiren Zhao§, Tingting Deng†, Lingyan, Wang†, Yanyan Ma†, Shi Ye† and Qinyuan Zhang*† †
State Key Laboratory of Luminescent Materials and Devices and Institute of Optical
Communication Materials, South China University of Technology, Guangzhou 510641, China ‡
Department of Physics, South China University of Technology, Guangzhou 510641,
China §
Guangdong University of Technology, School of Physics & Optoelectronic
Engineering, Guangzhou 510006, China
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ABSTRACT: Due to the unique narrow-band red emission and broadband blue light excitation, as well as milder synthesis conditions, Mn4+ ions activated fluoride red phosphors show great promising for white light emitting diodes (W-LEDs) applications. However, as the Mn4+ -emission belongs to a spin-forbidden transition (2Eg→4A2), it is a fundamental challenge to synthesize these phosphors with a high external quantum efficiency (EQE) above 60%. Herein, a highly efficient and thermally stable red fluoride phosphor Cs2SiF6:Mn4+ with a high internal quantum efficiency (IQE) of 89% and ultra-high EQE of 71% is demonstrated. Furthermore, nearly 95% of the room temperature IQE and EQE are maintained at 150 0C. The static and dynamic spectral measurements, as well as density functional theory (DFT) calculations show that the excellent performances of Cs2SiF6:Mn4+ is assigned to the Mn4+ ions tend to be evenly distributed in host lattice Cs2SiF6. By employing Cs2SiF6:Mn4+ as red light component, stable 10-W high-power warm W-LEDs with luminous efficiency of ~110 lm/W could be obtained. These findings indicate that red phosphor Cs2SiF6:Mn4+ may be highly suitable candidate for fabricating high-performance high-power warm white LEDs.
KEY WORDS: Stable, Narrow-band, Mn4+, Red phosphor, Ultra-high Quantum efficiency, Warm white LED
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ACS Photonics
White light emitting diodes (W-LEDs) has been widely applied in various fields of human’s life, due to its high efficiency, long lifetime, low energy consumption, and environmental friendliness, etc.1-6 However, the mainstream and commercialized W-LEDs based on the combination of blue InGaN chip and yellow phosphor Y3(Al,Ga)5O12:Ce3+ (YAG:Ce3+) suffers from low color rendering index (CRI, Ra4500 K) and fail to be used in indoor lighting, because of the notoriously deficient red emission from yellow phosphor YAG:Ce3+.7-11 To solve this problem, nitride phosphors such as (Ca,Sr)AlSiN3:Eu2+ and Sr2Si5N8:Eu2+ are usually used as red light component to add into the W-LEDs due to their high luminescence efficiencies and good thermal stability.12-15 However, the excessive broad absorption (~200-600 nm) and longer emission wavelength (>650 nm) of these phosphors significantly lower the luminous efficacy of the devices.2-4 Furthermore, the synthesis conditions for the nitride phosphors are usually rather harsh, leading to high cost.9, 16-19 In contrast, transition metal Mn4+ activated fluoride phosphors possess narrow-band red emission around ~630 nm and broad excitation band at ~460 nm (with a bandwidth of ~50 nm), as well as milder synthesis conditions, showing more promising for warm W-LEDs applications.20 For these characteristics, considerable attention has been focused on this field and various Mn4+ doped fluoride red phosphors such as A2BF6:Mn4+ (A = NH4, Na, K, Rb, Cs; A2 = Ba, Zn; B = Si, Ge, Ti, Zr) and H3XF6:Mn4+ (H = Li, Na, K; X = Al, Ga) have been developed.8,
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By using suitable synthesis route, nearly 100% high internal quantum
efficiency (IQE) has been achieved in fluoride phosphor K2TiF6:Mn4+.2 However, since the Mn4+ emission belongs to a spin-forbidden transition (2Eg→4A2), it is still a fundamental challenge to synthesis these Mn4+-related fluoride phosphors with external quantum efficiency (EQE) higher than 60%, which is crucial for practical applications.2, 31, 34 The ultra-high IQE value, whereas relatively low EQE in these Mn4+ doped fluoride phosphors is owing to the lower absorption efficiency (AE) of Mn4+ (usually, AE < 60%). Increasing dopant level can effectively improve the AE value, but the Mn4+ ions doped system usually shows a lower
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