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Red Mn4+-doped fluoride phosphors : why purity matters

Reinert Verstraete (UGent) , Heleen Sijbom (UGent) , Jonas Joos (UGent) , Katleen Korthout (UGent) , Dirk Poelman (UGent) , Christophe Detavernier (UGent) and Philippe Smet (UGent)
(2018) ACS APPLIED MATERIALS & INTERFACES. 10(22). p.18845-18856
Author
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Center for nano- and biophotonics (NB-Photonics)
Abstract
Traditional light sources, e.g., incandescent and fluorescent lamps, are currently being replaced by white light-emitting diodes (wLEDs) because of their improved efficiency, prolonged lifetime, and environmental friendliness. Much effort has recently been spent to the development of Mn4+-doped fluoride phosphors that can enhance the color gamut in displays and improve the color rendering index, luminous efficacy of the radiation, and correlated color temperature of wLEDs used for lighting. Purity, stability, and degradation of fluoride phosphors are, however, rarely discussed. Nevertheless, the typical wet chemical synthesis routes (involving hydrogen fluoride (HF)) and the large variety of possible Mn valence states often lead to impurities that drastically influence the performance and stability of these phosphors. In this article, the origins and consequences of impurities formed during synthesis and aging of K2SiF6:Mn4+ are revealed. Both crystalline impurities such as KHF2 and ionic impurities such as Mn3+ are found to affect the phosphor performance. While Mn3+ mainly influences the optical absorption behavior, KHF2 can affect both the optical performance and chemical stability of the phosphor. Moisture leads to decomposition of KHF2, forming HF and amorphous hydrated potassium fluoride. As a consequence of hydrate formation, significant amounts of water can be absorbed in impure phosphor powders containing KHF2, facilitating the hydrolysis of [MnF6]2− complexes and affecting the optical absorption of the phosphors. Strategies are discussed to identify impurities and to achieve pure and stable phosphors with internal quantum efficiencies of more than 90%.
Keywords
fluoride phosphors, stability, purity, transition-metal dopants, LEDs, LIGHT-EMITTING-DIODES, WARM-WHITE LEDS, THERMAL-DECOMPOSITION, PHOTOLUMINESCENCE PROPERTIES, LUMINESCENCE PROPERTIES, SYNCHROTRON-RADIATION, CONVERSION PHOSPHORS, K2SIF6MN4+ PHOSPHOR, OPTICAL-PROPERTIES, CRYSTAL-STRUCTURE

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Citation

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Chicago
Verstraete, Reinert, Heleen Sijbom, Jonas Joos, Katleen Korthout, Dirk Poelman, Christophe Detavernier, and Philippe Smet. 2018. “Red Mn4+-doped Fluoride Phosphors : Why Purity Matters.” Ed. Kirk Schanze. Acs Applied Materials & Interfaces 10 (22): 18845–18856.
APA
Verstraete, R., Sijbom, H., Joos, J., Korthout, K., Poelman, D., Detavernier, C., & Smet, P. (2018). Red Mn4+-doped fluoride phosphors : why purity matters. (K. Schanze, Ed.)ACS APPLIED MATERIALS & INTERFACES, 10(22), 18845–18856.
Vancouver
1.
Verstraete R, Sijbom H, Joos J, Korthout K, Poelman D, Detavernier C, et al. Red Mn4+-doped fluoride phosphors : why purity matters. Schanze K, editor. ACS APPLIED MATERIALS & INTERFACES. 2018;10(22):18845–56.
MLA
Verstraete, Reinert, Heleen Sijbom, Jonas Joos, et al. “Red Mn4+-doped Fluoride Phosphors : Why Purity Matters.” Ed. Kirk Schanze. ACS APPLIED MATERIALS & INTERFACES 10.22 (2018): 18845–18856. Print.
@article{8564420,
  abstract     = {Traditional light sources, e.g., incandescent and fluorescent lamps, are currently being replaced by white light-emitting diodes (wLEDs) because of their improved efficiency, prolonged lifetime, and environmental friendliness. Much effort has recently been spent to the development of Mn4+-doped fluoride phosphors that can enhance the color gamut in displays and improve the color rendering index, luminous efficacy of the radiation, and correlated color temperature of wLEDs used for lighting. Purity, stability, and degradation of fluoride phosphors are, however, rarely discussed. Nevertheless, the typical wet chemical synthesis routes (involving hydrogen fluoride (HF)) and the large variety of possible Mn valence states often lead to impurities that drastically influence the performance and stability of these phosphors. In this article, the origins and consequences of impurities formed during synthesis and aging of K2SiF6:Mn4+ are revealed. Both crystalline impurities such as KHF2 and ionic impurities such as Mn3+ are found to affect the phosphor performance. While Mn3+ mainly influences the optical absorption behavior, KHF2 can affect both the optical performance and chemical stability of the phosphor. Moisture leads to decomposition of KHF2, forming HF and amorphous hydrated potassium fluoride. As a consequence of hydrate formation, significant amounts of water can be absorbed in impure phosphor powders containing KHF2, facilitating the hydrolysis of [MnF6]2\ensuremath{-} complexes and affecting the optical absorption of the phosphors. Strategies are discussed to identify impurities and to achieve pure and stable phosphors with internal quantum efficiencies of more than 90\%.},
  author       = {Verstraete, Reinert and Sijbom, Heleen and Joos, Jonas and Korthout, Katleen and Poelman, Dirk and Detavernier, Christophe and Smet, Philippe},
  editor       = {Schanze, Kirk},
  issn         = {1944-8244},
  journal      = {ACS APPLIED MATERIALS \& INTERFACES},
  keyword      = {fluoride phosphors,stability,purity,transition-metal dopants,LEDs,LIGHT-EMITTING-DIODES,WARM-WHITE LEDS,THERMAL-DECOMPOSITION,PHOTOLUMINESCENCE PROPERTIES,LUMINESCENCE PROPERTIES,SYNCHROTRON-RADIATION,CONVERSION PHOSPHORS,K2SIF6MN4+ PHOSPHOR,OPTICAL-PROPERTIES,CRYSTAL-STRUCTURE},
  language     = {eng},
  number       = {22},
  pages        = {18845--18856},
  title        = {Red Mn4+-doped fluoride phosphors : why purity matters},
  url          = {http://dx.doi.org/10.1021/acsami.8b01269},
  volume       = {10},
  year         = {2018},
}

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