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

Abstract

Understanding the origin and mechanisms of luminescence is a crucial point when it comes to the development of new phosphors with targeted luminescence properties. Herein, a new phosphor belonging to the substance class of alkali metal lithosilicates with the generalized sum formula Cs4−x−y−zRbxNayLiz[Li3SiO4]4:Eu2+ is reported. Single crystals of the cyan‐emitting UCr4C4‐type phosphor show a peculiar double‐band luminescence with one ultranarrow emission band at 473 nm and a narrow emission band at 531 nm under excitation with UV light (λexc=408 nm). Regarding occupation of the channels by the light metal ions, investigations of single‐crystal XRD data led to the assumption that domain formation with distinct lithium‐ and sodium‐filled channels occurs. Depending on which of these channels hosts the activator ion Eu2+, a green or blue emission results. The herein‐presented results shed new light on the luminescence process in the well‐studied UCr4C4‐type alkali metal lithosilicate phosphors.

Chasing Down the Eu2+ Ions: The Delicate Structure−Property Relationships in the Ultra‐Narrow Band Phosphor K1.6Na2.1Li0.3[Li3SiO4]4:Eu2+

“…Consequently, the cell parameters and the powder diffraction patterns of the compounds are hardly discernable, which makes structural elucidations by means of, for example, Rietveld refinement in these compounds somewhat ambiguous. Single‐crystal diffraction data of alkali lithosilicate phosphors are so far only provided for RbKLi 2 [Li 3 SiO 4 ] 4 , [ 21 ] CsRbNaLi[Li 3 SiO 4 ] 4 , [ 56 ] and within this work, now also for “K 2 Na 2 [Li 3 SiO 4 ] 4 “. For all the other phosphors, only powder diffraction data were used for the structural elucidation.…”

“…[ 50–55 ] Especially the groups led by Huppertz, Xia, or Liu established the material class of luminescent alkali lithosilicates by constant extension of new representatives. [ 21,51–66 ]…”

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

“…The LiÀ O distances within the tetrahedral units of the Li1, Li2, and Li5 positions vary from 191.3(2) to 216.3 (2) pm and also the SiÀ O bond lengths, which vary from 163.23 (8) to 165.52 (8) pm, are in good agreement with the sum of the ionic radii. [28,31,32,34] The LiÀ O distances within the tetrahedra of the Li6, Li7, and Li8 position range from 190.9(2) to 262.2(3) pm. The corresponding coordination polyhedra can also be described as elongated trigonal pyramids exhibiting a 3 + 1 coordination, where the Li + cations are slightly displaced from the centers of the "LiO 4 tetrahedra".…”

“…Another possibility could be that Li-rich domains are formed in the real structure, as has already been postulated for other known alkali lithosilicates such as RbKLi 2 [Li 3 SiO 4 ] 4 :Eu 2 + and CRNLLSO:Eu 2 + . [31,32] This positional disorder in LKLSO is represented in the situation that the K + cations (K2, K3, and K4) possess an eightfold coordination sphere by the O 2À anions with KÀ O bond [19,31] The K4 site is surrounded by four SiO consisting of compositely modulated structures, as is found in the compound Sr x Li 2 + x Al 2-x O 4 :Eu 2 + , [37] can be excluded, since no reflections of diffuse scattering were observed in a regular distance between the main reflections in the reciprocal space.…”

“…[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.…”