Novel Narrow Band Cyan‐Green Phosphor LiK₇[Li₃SiO₄]₈:Eu²⁺ with Enhanced Suppression of Second Broad Band Emission

Abstract

Eu 2 + ) was synthesized by a hightemperature solid-state reaction. It is accessible from K 2 CO 3 , Li 2 O, SiO 2 , and an Eu-source (Eu 2 O 3 ) by conventional solid-state reaction in nickel crucibles under a constant flow of forming gas. The crystal structure of LKLSO has been determined by single-crystal X-ray diffraction and it crystallizes in the tetragonal space group I4 1 =a (no. 88) with the lattice parameters a = 1560.83(5), c = 1278.23(4) pm, and a volume of V = 0.31140(2) nm 3 . The compound is isostructural to NaK 7 [Li 3 SiO 4 ] 8 : Eu 2 + but, in contrast, features an enhanced suppression of the second broad band emission through the specific channel filling in the crystal structure. Despite the observed positional disorder in the structure, the cyan-green phosphor shows a narrow band emission with a maximum at 511 nm and a fwhm of 45 nm (0.215 eV).

The crystal structure and luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2+

“…Due to the additional tetrahedral coordination of the O 2− anions of the Li2 site, this would form a distorted octahedron with a polyhedron size of 12.52 Å 3 and, due to the short Li-O distances, there would also be an enlargement or spatial distortion of the octahedron. The incorporation of the activator ion Eu 2+ into lithium channels or domains has already been observed in other compounds known from the literature, such as 20 However, it should be considered that in these compounds the Li + cations form an approximately square planar coordination to four O 2− anions instead of a tetrahedral one.…”

“…The incorporation of the activator ion Eu 2+ into lithium channels or domains has already been observed in other compounds known from the literature, such as RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2+ , 7,23 Cs 4− x − y − z Rb x Na y Li z [Li 3 SiO 4 ]:Eu 2+ , 24 and LiK 7 [Li 3 SiO 4 ] 8 :Eu 2+ . 20 However, it should be considered that in these compounds the Li + cations form an approximately square planar coordination to four O 2− anions instead of a tetrahedral one.…”

“…The Li1 and Li2 sites form LiO 4 tetrahedra with Li1-O and Li2-O distances ranging from 188.0(2) to 196.9(2) pm and 196.7(2) to 213.8(2) pm, respectively, which are in good agreement with the sum of the ionic radii. 20,23 The Li3 site is coordinated by four N 3− and two O 2− anions and constitutes a distorted octahedral arrangement, where the Li3-O distances are 205.0(2) pm and the Li3-N distances are between 218.9(2) and 248.94 (5) pm. Since two of the Li3-N distances are slightly longer and are located opposite to each other, this can also be described as an elongated octahedron.…”

“…(LKLSO:Eu 2+ ) (𝜆 max = 511 nm; fwhm = 45 nm), 20 Na 2 K 2 [Li 3 SiO 4 ] 4 :Eu 2+ (𝜆 max = 486 nm; fwhm = 20.7 nm), 21,22 RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2+ (𝜆 max = 474 nm and 532 ; fwhm = 24.8 nm and 43.5 nm), 7,23 and Cs 4-x-y-z Rb x Na y Li z [Li 3 SiO 4 ]:Eu 2+ (CRNLLSO:Eu 2+ ) (𝜆 max = 473 nm and 531 nm; fwhm = 25.2 nm and 58 nm). 24 These compounds exhibit interesting luminescence properties and some of them are characterized by their narrow single band emission in the blue and green spectral range.…”

“…Although no luminescent lithium oxonitridolithosilicate is known yet, there are already some established phosphors in the field of alkali lithosilicates. [7][8][9][10] The best common examples are Na [Li 3 SiO 4 ]: Eu 2+ (NLSO:Eu 2+ ) (λ max = 469 nm; fwhm = 32 nm), K[Li 3 SiO 4 ]: Eu 2+ (KLSO:Eu 2+ ) (λ max = 604 nm; fwhm = 150 nm), NaK 7 [Li 3 SiO 4 ] 8 :Eu 2+ (NKLSO:Eu 2+ ) (λ max = 515 nm and 598; fwhm = 49 nm and 138 nm), [11][12][13][14] RbNa 3 [Li 3 SiO 4 ] 4 :Eu 2+ (λ max = 471 nm; fwhm = 22.4 nm), 8,15,16 RbNa[Li 3 SiO 4 ] 2 :Eu 2+ (λ max = 523 nm; fwhm = 41 nm), 17 RbLi[Li 3 SiO 4 ] 2 :Eu 2+ (RLSO:Eu 2+ ) (λ max = 530 nm; fwhm = 42 nm), 18 RbNa 2 K[Li 3 SiO 4 ] 4 :Eu 2+ (λ max = 480 nm; fwhm = 26 nm), 19 CsNa 2 K[Li 3 SiO 4 ] 4 :Eu 2+ (λ max = 485 nm; fwhm = 26 nm), 19 LiK 7 [Li 3 SiO 4 ] 8 :Eu 2+ (LKLSO:Eu 2+ ) (λ max = 511 nm; fwhm = 45 nm), 20 Na 2 K 2 [Li 3 SiO 4 ] 4 :Eu 2+ (λ max = 486 nm; fwhm = 20.7 nm), 21,22 RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2+ (λ max = 474 nm and 532; fwhm = 24.8 nm and 43.5 nm), 7,23 and Cs 4−x−y−z Rb x Na y Li z [Li 3 SiO 4 ]:Eu 2+ (CRNLLSO:Eu 2+ ) (λ max = 473 nm and 531 nm; fwhm = 25.2 nm and 58 nm). 24 These compounds exhibit interesting luminescence properties and some of them are characterized by their narrow single band emission in the blue and green spectral range.…”