RbKLi₂[Li₃SiO₄]₄:Eu²⁺ an ultra narrow-band phosphor

Abstract

The new phosphor RbKLi2[Li3SiO4]4:Eu2+ was synthesized by different high-temperature solid-state reactions. It is accessible from the alkali metal carbonates, SiO2, and Eu2+ as a luminous active cation either in closed tantalum ampoules or by conventional solid-state reaction in nickel crucibles, under a constant flow of forming gas. The structure of the thereby received rod-shaped crystals was solved and refined on the basis of single crystal X-ray diffraction data. The compound crystallizes isostructurally to CsKNa2[Li3SiO4]4 and forms a highly condensed network of LiO4 and SiO4 tetrahedra [I4/m (no. 87), Z = 2, a = 10.9508(6) and c = 6.3334(3) Å]. It is a new member of the recently discovered family of alkali lithosilicate phosphors. Under excitation with UV to blue light, the compound exhibits interesting luminescence properties. Depending on the mode of synthesis, either green or blue luminescence of the samples is observed. Both emission profiles can be described as ultra-narrow-banded, since the full width at half maximum (fwhm) is below 0.2 eV. The green phosphor shows an emission maximum at 532 nm with a fwhm of 43.5 nm (0.193 eV) and the blue one at 474 nm with a fwhm of 24.8 nm (0.137 eV). Furthermore, the material presented here allows a more detailed localization of the luminescence center inside the structure, which may allow a better understanding of the luminescence properties of many other alkali lithosilicate phosphors.

A Double‐Band Emitter with Ultranarrow‐Band Blue and Narrow‐Band Green Luminescence

“…The latest publication by Dutzler et al. comes to a corresponding finding for RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2+ (RKLSO:Eu 2+ ) . In this compound, there are only Li + cations on the square‐planar position in CH2 and the green luminescence is associated with a refinement of Eu 2+ in the cube‐like eightfold‐coordinated position.…”

“…To recheck the general assumption that the activator ion migrates into CH2, as already been shown for RKLSO:Eu 2+ , a second refinement on the single‐crystal was carried out, this time involving Eu 2+ . A successful refinement was achieved with a mixed occupation of Eu 2+ on the Na + site in CH2 towards the new sum formula Cs 0.445 Rb 0.870 Na 1.628 Eu 0.06 Li 1 [Li 3 SiO 4 ] 4 .…”

“…Dutzler et al. were the first to add a sodium‐free compound, namely RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2+ (RKLSO:Eu 2+ ), to this series of alkali metal lithosilicates . All of the above‐mentioned compounds can be described by the general formula A 4 [Li 3 SiO 4 ] 4 , where A stands for the alkali metal cations (Na, K, Rb, and Cs) and the brackets enclose the lithosilicate framework.…”

“…The peculiar ultranarrow‐band blue luminescence could be observed in all UCr 4 C 4 ‐type alkali metal lithosilicates having sodium‐containing channels. The only exception so far is the recently discovered RbKLi 2 [Li 3 SiO 4 ]:Eu 2+ , which was published by Dutzler et al . Although there are no sodium‐containing channels in the structure, under certain conditions this compound shows blue luminescence at 474 nm when doped with Eu 2+ .…”

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

“…[15,16] The compound b-Si 6-z Al z O z N 8-z :Eu 2 + (b-SiAlON:Eu 2 + ) (λ max = 536 nm; fwhm = 63 nm) is often used as green phosphor. [17] From the field of alkali lithosilicates, which was already discovered by R. Hoppe in the late 1980s, [18][19][20][21] a relatively new substance class of Eu 2 + -doped luminescent materials (phosphors) emerged, containing compounds like RbLi[Li 3 SiO 4 ] 2 :Eu 2 + (RLSO:Eu 2 + ) (λ max = 530 nm; fwhm = 42 nm), [22] RbNa 3 [Li 3 SiO 4 ] 4 :Eu 2 + (λ max = 471 nm; fwhm = 22.4 nm), [19,23,24] RbNa[Li 3 SiO 4 ] 2 :Eu 2 + (λ max = 523 nm; fwhm = 41 nm), [25] RbNa 2 K[Li 3 SiO 4 ] 4 :Eu 2 + (λ max = 480 nm; fwhm = 26 nm), [26] CsNa 2 K[Li 3 SiO 4 ] 4 :Eu 2 + (λ max = 485 nm; fwhm = Na 2 K 2 [Li 3 SiO 4 ] 4 :Eu 2 + (λ max = 486 nm; fwhm = 20.7 nm), [27] (λ max = 469 nm; fwhm = 32 nm), [21,[28][29][30] RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2 + (λ max = 474 nm and 532 nm; fwhm = 24.8 nm and 43.5 nm) [18,31] 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). [32] These compounds exhibit mainly narrow band but also broad band single or double emissions in the blue and green spectral range with promising luminescence properties.…”