Highly Luminous N3–-Substituted Li2MSiO4−δN2/3δ:Eu2+ (M = Ca, Sr, and Ba) for White NUV Light-Emitting Diodes

• Published in: ACS omega Vol. 4; no. 5; pp. 8431 - 8440
• Main Authors: Kim, Donghyeon, Ji, Choon Woo, Lee, Jungjun, Bae, Jong-Seong, Hong, Tae Eun, Ahn, Sung Il, Chung, In, Kim, Seung-Joo, Park, Jung-Chul
• Format: Journal Article
• Language: English
• Published: American Chemical Society 31.05.2019
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.8b03489

The N3–-substituted Li2MSiO4:Eu2+ (M = Ca, Sr, and Ba) phosphors were systematically prepared and analyzed. Secondary-ion mass spectroscopy measurements revealed that the average N3– contents are 0.003 for Ca, 0.009 for Sr, and 0.032 for Ba. Furthermore, the N3– incorporation in the host lattices was corroborated by infrared and X-ray photoelectron spectroscopies. From the photoluminescence spectra of Li2MSiO4:Eu2+ (M = Ca, Sr, and Ba) phosphors before and after N3– doping, it was verified that the enhanced emission intensity of the phosphors is most likely due to the N3– doping. In Li2MSiO4:Eu2+ (M = Ca, Sr, and Ba) phosphors, the maximum wavelengths of the emission band were red-shifted in the order Ca < Ba < Sr, which is not consistent with the trend of crystal field splitting: Ba < Sr < Ca. This discrepancy was clearly explained by electron–electron repulsions among polyhedra, LiO4–MO n , SiO4–MO n , and MO n –M’O n associated with structural difference in the host lattices. Therefore, the energy levels associated with the 4f65d energy levels of Eu2+ are definitely established in the following order: Li2CaSiO4:Eu2+ > Li2BaSiO4:Eu2+ > Li2SrSiO4:Eu2+. Furthermore, using the Williamson–Hall (W–H) method, the determined structural strains of Li2MSiO4:Eu2+ (M = Ca, Sr, and Ba) phosphors revealed that the increased compressive strain after N3– doping induces the enhanced emission intensity of these phosphors. White light-emitting diodes made by three N3–-doped phosphors and a 365 nm emitting InGaN chip showed the (0.333, 0.373) color coordinate and high color-rendering index (R a = 83). These phosphor materials may provide a platform for development of new efficient phosphors in solid-state lighting field.