Ba₆(Bi_1−xEu_x)₉B₇₉O₁₃₈ (0 ≤ x ≤ 1): synergetic changing of the wavelength of Bi³⁺ absorption and the red-to-orange emission ratio of Eu³⁺

Abstract

Ba 6 (Bi 1Àx Eu x ) 9 B 79 O 138 (0 r x r 1): synergetic changing of the wavelength of Bi 3+ absorption and the red-to-orange emission ratio of Eu 3+ † Very recently, a novel barium bismuth borate Ba 6 Bi 9 B 79 O 138 (BBBO) was shown to be a new analogue of REBaB 9 O 16 (RE = rare earth), which is a family of excellent phosphor hosts, because it has two types of cationic positions suitable for bi-and tri-valent activators (or sensitizers). In this study, we prepared Eu 3+ -to-Bi 3+ substituted solid solutions Ba 6 (Bi 1Àx Eu x ) 9 B 79 O 138 (0 r x r 1) and performed a systematic UV-photoluminescence investigation. As anticipated, efficient energy transfer occurs in the whole series of compounds and the majority of the energy absorbed by Bi 3+ was transmitted to Eu 3+ , causing a great enhancement of Eu 3+ emission. More interestingly, the Eu 3+ -to-Bi 3+ substitution leads to a centrosymmetric-tononcentrosymmetric transition of the local coordination symmetry of the trivalent cations due to the size difference between Eu 3+ and Bi 3+ . This is observed in the synergetic changing of the wavelength of Bi 3+ 1 S 0 -3 P 1 absorption (excitation spectra) and the red-to-orange emission ratio (emission spectra) when changing x. BBBO is a new polyborate host with a freshly resolved structure whose interesting preliminary results suggest the further development of BBBO-based phosphors. † Electronic supplementary information (ESI) available: Unit cell parameters of Ba 6 (La 0.3Ày Bi y Eu 0.7 ) 9 B 79 O 138 (0 r y r 0.3), structural figures of Bi 3+ coordination in BBBO. See

Symmetry dependent evolution of the Tb 3+ photoluminescence in Ba 6 ( RE 1−x Tb x ) 9 B 79 O 138 ( RE = La and Y, 0 ≤ x ≤ 1) and Ce 3+ -to-Tb 3+ sensitization effect: A re-visit to RE BaB 9 O 16

“…4c along with Tb 3þ concentration (x). All these four main groups together with the total emission increase gradually, and no quenching or saturation effects were observed, which is the same with the case in Eu 3þ -doped Ba 6 Bi 9 B 79 O 138 [19]. Probably the absence of the quenching or saturation effect is the intrinsic character for this type of hosts, for example, the REO 6 octahedra are separated by BO 4 tetrahedra, which means the atomic pathways between two RE cations comprise the OeBeO three-atom bridge.…”

“…Please note that the metallic composition of BBBO is different with REBaB 9 O 16 . Indeed, it was suggested in literature that the true composition of "REBaB 9 O 16 " was likely incorrect, which was proved by the formation of Ba 6 Eu 9 B 79 O 138 , showing the same powder X-ray diffraction patterns with REBaB 9 O 16 [18,19]. We are therefore strongly motivated to re-investigate the true composition of this well-known family "REBaB 9 O 16 " and the PL property with the possible new formula, Ba 6 RE 9 B 79 O 138 .…”

“…For Eu 3þ -doped samples, the intensity ratio of R/ O ¼ I( 5 D 0 / 7 F 2 )/I( 5 D 0 / 7 F 1 ) is usually used as a probe of site symmetry of Eu 3þ [8,19,33]. Generally, a lower symmetry of the crystal field leads to a larger R/O, because 5 D 0 / 7 F 2 transition appears dominantly only when Eu 3þ locates in a noncentrosymmetric site.…”

“…When rare earth cations are used as activators, changing the surrounding crystal field will lead to an adjustment of the electron- transition selection law and the splitting of 4f levels, which therefore manifest as a variation of the emission pattern. Eu 3þ is a typical case, which is widely used as a probe for local structure investigation, because the electrical dipole transition 5 D 0 / 7 F 2 is very sensitive to the local environment, which appears dominantly only when Eu 3þ locates in a noncentrosymmetric site [8,19]. Considering the similar energy level schemes of Tb 3þ and Eu 3þ , the phosphors with Eu 3þ or Tb 3þ as activators both show fef emissions, whose relative intensities could be affected by the surrounding crystal field.…”

Strong f‐f Excitation and Bright Red Emission in Cd4Gd1‐xEuxO(BO3)3 (0≤x≤1): Near‐UV LED Pumped Red Phosphor with Low Thermal Quenching

“…Nevertheless, in those hosts where Eu 3+ is in the noncentrosymmetric coordination environment, it possibly exhibits the strong f ‐ f absorptions . Second, the Eu 3+ ‐emission contains 5 D 0 → 7 F 2 (red) and 5 D 0 → 7 F 1 (orange) transitions, and the red to orange (R/O) ratio would vary depending on the local coordination environment . Interestingly, in a noncentrosymmetric coordination, Eu 3+ could not only exhibit a strong f ‐ f transition at ≈393 nm but also mainly emit the red emission at ≈613 nm ( 5 D 0 → 7 F 2 ) .…”