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Borates are well-known candidates for optical materials and, here, we are particularly interested in Ba6Bi9B79O138 (BBBO), which has an interesting layered-type structure and Bi3+-containing characteristics that has prompt us to explore its host-sensitized photoluminescence (PL). Solid solutions of BBBO: xTb3+ (0 ≤ x ≤ 1) were prepared and its host-sensitized photoluminescence was confirmed, which is a result of the efficient Bi3+-to-Tb3+ energy transfer. Furthermore, an evolution of the coordination environments of the Bi3+/Tb3+ sites was observed when increasing x. This evolution was found to correlate to the variation of the PL spectra. In particular, the value of the ratio of cyan/green [defined as I(5D4→7F6)/ I(5D4→7F5) of Tb3+] was about 0.28 when x < 0.4, and it increased to 0.71 at x = 0.9 and thereafter remained almost constant. Ba6(RE0.3- yBi yTb0.7)9B79O138 (RE = La or Y, 0 ≤ y ≤ 0.3) were also prepared for better understanding of the host-sensitization effect and in both series, Ba6(RE0.1Bi0.2Tb0.7)9B79O138 show the highest emission. [ABSTRACT FROM AUTHOR]

Scheelite compounds with Eu3+ substitution are well-known red-phosphors. We prepared and performed a detailed structural characterization of A1–1.5xEux□0.5xWO4 and A0.64–0.5yEu0.24Liy□0.12–0.5yWO4 (A = Ca, Sr; □ = vacancy) to confirm the A-site vacancy mechanism for charge balance when bivalent A cations were substituted by Eu3+. All compounds crystallize in I41/a with a disordered arrangement of A2+, Eu3+, □ at the A-site. The title compounds are all good red phosphors with a high R/O ratio (∼10), indicating that Eu3+ is located at a significantly distorted cavity. A1–1.5xEux□0.5xWO4 shows a saturation phenomenon at a high doping level, x = 0.20. With the incorporation of Li+, the emission intensity was generally enhanced compared to the Li+-free samples, moreover, an increase of the Li+ content reduces the content of vacancies, resulting in further increase of the luminescence intensity. [ABSTRACT FROM AUTHOR]

Sol–gel method was applied to prepare homogenous and highly crystalline phosphors with the formulas α-GdB5O9:xTb3+ (0 ≤x≤ 1), α-Gd1−xCexB5O9 (0 ≤x≤ 0.40), α-GdB5O9:xCe3+, 0.30Tb3+ (0 ≤x≤ 0.15) and α-GdB5O9:0.20Ce3+, xTb3+ (0 ≤x≤ 0.10). The success of the syntheses was proved by the linear shrinkage or expansion of the cell volumes against the substitution contents. In α-GdB5O9:xTb3+, an efficient energy transfer from Gd3+ to Tb3+ was observed and there was no luminescence quenching. The exceptionally high efficiency of the f–f excitations of Tb3+ implies that these phosphors may be good green-emitting UV-LED phosphors. For α-Gd1−xCexB5O9, Ce3+ absorbs the majority of the energy and transfers it to Gd3+. Therefore, the co-doping of Ce3+ and Tb3+ leads to a significant enhancement in the green emission of Tb3+. Our current results together with the study on α-GdB5O9:xEu3+ in the literature indicate that α-GdB5O9 is a good phosphor host with advantages including controllable preparation, diverse cationic doping, the absence of concentration quenching, and effective energy transfer. [ABSTRACT FROM AUTHOR]

There are very few luminescence studies for rare earth borates with hydroxyl or crystalline water molecules, which were believed to have a low luminescence efficiency because the vibrations of –OH or H2O may lead to quenching of the emission. We were motivated to study the luminescence properties of Gd1−xEux[B6O9(OH)3] (x = 0.10–1) and their dehydrated products, α-Gd1−xEuxB5O9. Efficient energy transfer from Gd3+ to Eu3+ was found in all of the studied polyborates. By TG-DSC and powder XRD experiments, we observed the dehydration of Eu[B6O9(OH)3], the re-crystallization to α-EuB5O9, and further decomposition to α-EuB3O6. During those processes, the Eu3+ luminescence spectra show interesting variations, meaning it is a good medium to understand the coordination environment evolution of Eu3+. It is observed that the symmetry of the Eu3+ coordination environment is the lowest in the amorphous state. Interestingly, this amorphous phase possesses a high efficiency of f–f transitions and a large R/O value (4.0), which implies its potential as a good red-emitting UV-LED phosphor. Anhydrous α-EuB5O9 shows the highest luminescence efficiency when excited by Eu3+ CT transition. For the first time, complete solid solutions α-Gd1−xEuxB5O9 were synthesized directly by the sol–gel method, and their luminescence properties were also studied. [ABSTRACT FROM AUTHOR]

There are limited photoluminescence (PL) studies for rare earth borates with crystalline water molecules, which are usually supposed to have low PL efficiency because the vibrations of H2O or –OH may lead to emission quenching. We investigated the PL properties of Sm1−xEux[B9O13(OH)4]·H2O (x = 0–1.00) and their dehydrated products α-Sm1−xEuxB5O9. There is no quenching effect in those studied polyborates because the large borate ionic groups isolate the Eu3+ activators very well. Sm3+ and Eu3+ are basically separated luminescent activators. Comparatively, Sm3+ shows a very small emission intensity, which can be almost ignored, therefore our interest is focused on the Eu3+ luminescence. By TG-DSC and powder XRD experiments, we defined three weight-loss steps for Eu[B9O13(OH)4]·H2O and a re-crystallization process to α-EuB5O9, during which luminescent spectra of Eu3+ are recorded. It shows an interesting variety and therefore is a good medium to understand the coordination environment evolution of Eu3+, even for the intermediate amorphous phase. In fact, the coordination symmetry of Eu3+ in the amorphous state is the lowest. The high efficiency of the f–f transitions and large R/O value (3.8) imply this amorphous phase is potentially a good red-emitting UV-LED phosphor. Anhydrous α-EuB5O9 shows the highest luminescent efficiency excited by Eu3+ CT transition. In addition, α-Sm1−xEuxB5O9 was synthesized by a sol–gel method directly for the first time, and α-EuB5O9 shows superior PL properties due to its better crystallinity. A lot of hydrated polyborates with crystalline water molecules remain unexplored and our study shows their potential as good phosphors. [ABSTRACT FROM AUTHOR]

Tb 3+ -substituted SrWO 4 Scheelite compounds are well-known green phosphors. Herein this work, we prepared three partial solid state solutions of Sr 1−1.5 x Tb x □ 0.5 x WO 4 (□ = vacancy, 0.01 ⩽ x ⩽ 0.24) and Sr 0.64− y Tb 0.24 Li 2 y □ 0.12− y WO 4 (0 ⩽ y ⩽ 0.12) and Sr 0.70−2 z Tb 0.20+ z Li z □ 0.10 WO 4 (0 ⩽ z ⩽ 0.10). Rietveld refinements on selected samples were performed to confirm the existence of A -site vacancies. In addition, the continuous variation of either Tb 3+ or vacancy concentrations offers an opportunity to study the structure–property correlation. A decrease of Sr–O average distance and an elongation of W–O bond length were detected in Sr 1-1.5 x Tb x □ 0.5 x WO 4 , which result in a slight red-shifting of WO 4 2− CT absorption band. The optimal concentration for green emission of Sr 1−1.5 x Tb x □ 0.5 x WO 4 (0.01 ⩽ x ⩽ 0.24) was found to be 0.12. The occurrence of concentration quenching effect is not only due to the increase of the Tb 3+ concentration, vacancies in the structure also play an important role. With Li + -co-doping, the emission shows a great enhancement not only due to the modification of the A -site coordination but also the diminishing of the A -site vacancy. [ABSTRACT FROM AUTHOR]

The title compounds are prepared by solid state reaction of H3BO3 (10% excess), Bi2O3, BaCO3, and Tb4O7 (staged heating, 700-850 °C, 15 h). [ABSTRACT FROM AUTHOR]

La 1− x Eu x [B 5 O 8 (OH) 2 ]·1.5H 2 O with the Eu 3+ -doping upper limit of 40 atom% were synthesized hydrothermally. Thereafter, thermal treatments at 710 °C were applied to obtain β-La 1− x Eu x B 5 O 9 . The solid solution range is even narrower, i.e. 0≤ x ≤0.15, due to the mismatch between La 3+ and Eu 3+ . The host borate system shows a typical concentration quenching effect at x =0.20 under CT excitation, and this is postponed to x =0.30 under the f − f excitation. β-La 1− x Eu x B 5 O 9 shows a very intense absorption of charge transfer, and gives strong red emissions at 615 nm with large R / O ratios (1.9–2.4). The saturation effect appears at x =0.11, which is probably due to the lattice distortion. Eu 3+ luminescence was applied as the structural probe to study the local coordination environment change during the dehydration and re-crystallization processes of La 0.93 Eu 0.07 [B 5 O 8 (OH) 2 ]·1.5H 2 O. [ABSTRACT FROM AUTHOR]

There are very few luminescence studies for rare earth borates with hydroxyl or crystalline water molecules, which were believed to have a low luminescence efficiency because the vibrations of –OH or H2O may lead to quenching of the emission. We were motivated to study the luminescence properties of Gd1−xEux[B6O9(OH)3] (x = 0.10–1) and their dehydrated products, α-Gd1−xEuxB5O9. Efficient energy transfer from Gd3+ to Eu3+ was found in all of the studied polyborates. By TG-DSC and powder XRD experiments, we observed the dehydration of Eu[B6O9(OH)3], the re-crystallization to α-EuB5O9, and further decomposition to α-EuB3O6. During those processes, the Eu3+ luminescence spectra show interesting variations, meaning it is a good medium to understand the coordination environment evolution of Eu3+. It is observed that the symmetry of the Eu3+ coordination environment is the lowest in the amorphous state. Interestingly, this amorphous phase possesses a high efficiency of f–f transitions and a large R/O value (4.0), which implies its potential as a good red-emitting UV-LED phosphor. Anhydrous α-EuB5O9 shows the highest luminescence efficiency when excited by Eu3+ CT transition. For the first time, complete solid solutions α-Gd1−xEuxB5O9 were synthesized directly by the sol–gel method, and their luminescence properties were also studied. [ABSTRACT FROM AUTHOR]

Abstract: New “114” oxides Ca1−x Eu x BaZn2+x Ga2−x O7 (x≤0.24) were synthesized by solid state reaction. Rietveld refinements were performed on high quality powder XRD data in the space group P63 mc. Zn2+ and Ga3+ co-occupy T1 and T2 positions, which are both in tetrahedral coordinated environment. Comparing the host compound, O3 moves towards T2 cation as much as 0.08Å when x=0.24. It is the most observable structural change during the substitution. By comparing the structures of CaBaZn2Ga2O7 (P63 mc) and CaBaCo4O7 (Pbn21), we find that smaller cations in tetrahedral sites would lead to a lower symmetry in “114” oxides. Luminescent spectra show the noncentrosymmetric coordination of Eu3+, and the f–f excitations are comparable to CT-excitation. No concentration quenching was observed up to x=0.24. The optical band gaps were estimated to be 3.8eV for Ca1−x Eu x BaZn2+x Ga2−x O7 (x=0, 0.16). [Copyright &y& Elsevier]

Abstract: Two Cu(II)–fluconazole supramolecular isomers 1 and 2 formulated as (flu)2Cu(SCN)2 (flu=fluconazole) have been synthesized and structurally characterized by single crystal X-ray diffraction. Different solvent media lead to the different binding modes of anion SCN− and the flexible C–C chain of fluconazole has been rotated in the two isomers. Complex 1 exhibits a two dimensional square grid-like layer and complex 2 exhibits a two dimensional framework with a parquet motif. Different H-bonds and stacking modes are observed in the two isomers. Complex 1 is nonemissive, whereas complex 2 exhibits photoluminescence property. [Copyright &y& Elsevier]

A series of rare earth polyborate with the general formula LiCa RE 5 (BO 3) 6 (RE ​= ​Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) were synthesized by high temperature solid state reactions. In literature, the Cd-analogues and LiCaTb 5 (BO 3) 6 were reported, here Rietveld refinements were performed on high quality powder X-ray diffraction data and the crystallographic parameters were obtained for the title compounds. Eu3+-luminescence in LiCa RE 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) were characterized. Eu3+ activators were doped into both the close-to-centrosymmetric and strongly-distorted coordination environments. Overall, bright orange-red emission can be observed with a slight increase of the red-to-orange (R / O) ratio with RE 3+ ionic radius increases. High quality powder samples of LiCa RE 5 (BO 3) 6 (RE ​= ​Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) were synthesized by high temperature solid state reactions. Rietveld refinements on all samples confirmed the co-occupancy of Ca2+ and RE 3+ at M1 and M3 sites, and LiCa(RE 0.95 Eu 0.05) 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) exhibits a bright red-orange emission. Image 1 • LiCa RE 5 (BO 3) 6 were synthesized by high temperature solid state reactions. • High quality powder XRD data confirm the phase purity. • Structure details were obtained by careful Rietveld refinements. • Ca2+ co-occupy with the rare earth cations at M1 and M3 sites. • LiCa(RE 0.95 Eu 0.05) 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) gives a bright red-orange emission. [ABSTRACT FROM AUTHOR]