Chasing Down the Eu²⁺ Ions: The Delicate Structure−Property Relationships in the Ultra‐Narrow Band Phosphor K_1.6Na_2.1Li_0.3[Li₃SiO₄]₄:Eu²⁺

Abstract

Eu2+‐activated phosphors of the UCr4C4 structure type have emerged as promising new (ultra‐)narrow band phosphors. Especially the UCr4C4‐type alkali lithosilicates have caused a sensation in the field of phosphor research in the recent years due to their consistent (ultra)narrow‐band luminescence in the cyan and green range that can pave the way to novel backlighting LEDs with high color gamut. The compound “K2Na2[Li3SiO4]4:Eu2+” stands out with a strikingly narrow emission in the cyan range (<0.2 eV or <30 nm full width at half maximum in the energy or wavelength scale, respectively) but the position of the Eu2+ ions within this structure has been so far controversial. High‐resolution photoluminescence spectroscopy at 10 K reveals a complex emission spectrum with seven emission bands in the violet to green range. Combination with single‐crystal X‐ray diffraction (SCXRD) demonstrates that the cation channels in the structure also contain Li+ ions. The presence of emission bands in the violet and blue spectral range reveals that the Eu2+ ions also occupy the available K sites in the structure independently confirmed by advanced ligand field calculations. This study demonstrates that a combination of SCXRD, photoluminescence spectroscopy, and theory can help elucidate advanced structural problems.

Oxidation of europium with ammonium perfluorocarboxylates in liquid ammonia: pathways to europium(ii) carboxylates and hexanuclear europium(iii) fluoridocarboxylate complexes

“…We assumed a similar stabilizing effect on the oxidation state + II of the lanthanoids (Ln) by trifluoroacetato and higher perfluorocarboxylato ligands, especially for europium and ytterbium, due to their particular electron configurations among the f-block metals (Eu: [Xe] 4f 7 6s 2 ; Yb: [Xe] 4f 14 6s 2 ). 6 Although materials containing Ln 2+ ions have been known for almost a century 7 and are still the subject of current research (especially phosphors), 8 only a very small number of simple europium( ii ) carboxylates has been reported up to date. 9 Usually, in the course of crystallization these compounds form chain and network structures to satisfy the lanthanoids’ tendency to have high coordination numbers.…”

Correlating doping with the stability and color rendition of red phosphors

“…2, [20][21][22] The broad band is due to the strong crystal field by the distorted coordination environments of the Eu 2+ emission centers. 23 The emission band is further deconvoluted into only one Gaussian profile, suggesting the presence of a single Eu 2+ center. 24 As shown in Figure 2b, the PL intensity grows at the beginning of increase the concentration of Eu 2+ , and it reaches the maximum when the concentration is equal to 0.002 in molar ratio.…”

Polymorphism and polymorph-dependent luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2+

“…22 In the past decade, a variety of phosphors belonging to this class have been discovered, particularly those related to the UCr 4 C 4 -structure type. [23][24][25] Polymorphism is a common phenomenon especially in structures, which can be described as layer-like, such as SiC. 26 In its simplest form, it appears as polytypism, where the differences lie only in the stacking pattern of the layers.…”