Co-reporter:Yan Gao;Xiaorui Sun;Zhongshan Feng;Liyue Zhu;Jing Zhang;Wenliang Gao;Xianju Zhou;Tao Yang
New Journal of Chemistry (1998-Present) 2017 vol. 41(Issue 5) pp:2037-2045
Publication Date(Web):2017/02/28
DOI:10.1039/C6NJ03603A
A series of Tb3+ and Eu3+ co-doped Ba6Bi9B79O138 (BBBO) phosphors were prepared by high-temperature solid-state reactions in order to utilize the host-sensitization effect of Bi3+. Energy transfer processes from Bi3+ in the host to both Tb3+ and Eu3+, as well as from Tb3+ to Eu3+ were proved. Under UV-excitation, three emissions can be simultaneously observed in a single-phase phosphor, including a blue band attributed to Bi3+ emission in the host, green lines due to Tb3+ transitions of 5D4 → 7FJ (J = 6, 5, 4, 3), and red lines due to Eu3+ transitions of 5D0 → 7FJ (J = 1, 2, 3, 4). Thus, the total emission could be rationally tuned by varying the relative doping contents of Tb3+/Eu3+ and by selecting appropriate exciting irradiation. Thermal stability was investigated by in situ PL spectra at elevated temperatures. It is quite interesting to observe a significant enhancement of red emission in both BBBO:0.05Eu3+ and BBBO:0.05Tb3+,0.005Eu3+ excited at 279 nm. Especially in the latter case, the red emission intensity at 150 °C is roughly 3 times that at room temperature, which is explained by the increasing efficiency of Bi3+ → Eu3+ and Tb3+ → Eu3+ energy transfer upon annealing.
Co-reporter:Xiaorui Sun, Ruirui Yang, Rixiang Song, Song Leng, Pengfei Jiang, Wenliang Gao, Rihong Cong, and Tao Yang
Inorganic Chemistry 2016 Volume 55(Issue 18) pp:9276-9283
Publication Date(Web):September 1, 2016
DOI:10.1021/acs.inorgchem.6b01361
There emerge great interests in the syntheses of metastable polyborates; however, most are involved with the high-pressure technique. A facile method to synthesize metastable rare earth borates at ambient pressure is eagerly required for the large-scale production and property investigation. Here we demonstrate the critical role of Bi3+ substitutions in the stabilization of metastable β-REB3O6 (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, and Y) at ambient pressure, where the Bi3+-to-RE3+ substitutions would efficiently reduce the synthetic temperatures to 735–820 °C, well below the upper limit of thermodynamically stable window (840–980 °C). Partial solid solutions of β-RE1–xBixB3O6 were prepared, and the ranges of the solution were also studied experimentally. The thermal behaviors of β-RE0.8Bi0.2B3O6 were investigated by differential thermal analyses and powder X-ray diffraction, and they were divided into two categories; that is, β-RE0.8Bi0.2B3O6 (RE = Sm, Eu, Gd) transfers to α-RE0.8Bi0.2B3O6 with further increasing the temperature to 950 °C, while β-RE0.8Bi0.2B3O6 (RE = Tb, Dy, Ho, Er, and Y) decomposes into hexagonal REBO3 and B2O3. In particular, the allowed concentration of Bi3+ in β-Gd1–xBixB3O6 was 0.10 ≤ x ≤ 0.25, and these samples show bright blue emissions under UV excitation, which suggests the high efficiency of light absorption and high potential as phosphors with further doping of other activators.
Co-reporter:Pengfei Jiang, Zhengyang Zhou, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2016 vol. 45(Issue 9) pp:3949-3957
Publication Date(Web):22 Jan 2016
DOI:10.1039/C5DT04150C
The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO6, by selecting Zn2+ and Sb5+ with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr2+-doping-induced symmetry evolution from I2/m to P21/n was confirmed in the complete solid solutions LaBa1−xSrxZnSbO6, where the tilting system also transferred from a−a−c0 to a−a−c+. The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr–O bond distances (revealed by Rietveld refinements) motivated us to study the Eu3+ luminescence in La0.95Eu0.05Ba1−xSrxZnSbO6. Interestingly, the maximum of charge transfer absorption of Eu3+ shows a precise changing tendency with the A–O bond distances along with the Sr2+ doping, clearly revealing the structure–luminescence correlations.
Co-reporter:Qiaoqi Li, Rihong Cong, Wenliang Gao, Tao Yang
Journal of Alloys and Compounds 2016 Volume 658() pp:110-118
Publication Date(Web):15 February 2016
DOI:10.1016/j.jallcom.2015.10.197
•Ba6(RE1−xTbx)9B79O138 (RE = La, Y, 0 ≤ x ≤ 1) were prepared by solid state reaction.•XRD show a shrinkage or expansion of unit cell in La- or Y-system, respectively.•The cyan/green ratio of Tb3+ was applied to evaluate the RE-site symmetry.•The C/G value remains unchanged at ∼0.65 in Ba6(La1−xTbx)9B79O138.•The C/G increases quickly in the range of 0.50 ≤ x ≤ 0.90 in Ba6(Y1−xTbx)9B79O138.Extensive studies on photoluminescence (PL) were devoted to the well-known “REBaB9O16” family, while the structure remained unsolved until the recent work on the structure determination of its new analogue Ba6Bi9B79O138. Accordingly, a re-visit to “REBaB9O16” with the new formula was rationally performed by the syntheses and Tb3+-PL study on Ba6La9B79O138 (BLBO) and Ba6Y9B79O138 (BYBO). Powder XRD patterns of Ba6(RE1−xTbx)9B79O138 (RE = La and Y, 0 ≤ x ≤ 1) show a linear shrinkage or expansion of the unit cell in BLBO: xTb3+ and BYBO: xTb3+, respectively. The ratio of Tb3+ cyan/green (C/G) emission was proposed to evaluate the evolution principle of the RE-site symmetry in both series of phosphors. The C/G value remains unchanged in BLBO: xTb3+, while it is sensitive to the Tb3+-to-Y3+ substitution in BYBO: xTb3+. For example, C/G keeps almost constant (∼0.30) when 0.10 ≤ x ≤ 0.5; a dramatic increase of C/G (from 0.33 to 0.67) occurs in the range of 0.50 ≤ x ≤ 0.90, accompanied with a RE-site symmetry transition from centrosymmetric to noncentrosymmetric; the value of C/G remains unchanged thereafter. The Ce3+-to-Tb3+ sensitization effect is applied in Ba6(RE0.3−yCeyTb0.7)9B79O138 (RE = La or Y, 0 ≤ y ≤ 0.3), and the samples with y = 0.2 possess the strongest green emission.
Co-reporter:Kai Song, Mufei Yue, Wenliang Gao, Rihong Cong, Tao Yang
Journal of Alloys and Compounds 2016 Volume 684() pp:346-351
Publication Date(Web):5 November 2016
DOI:10.1016/j.jallcom.2016.05.194
•PbGaBO4 was prepared by conventional and solution-assisted solid state reactions.•The bandgap energy is 4.10 eV from UV–Vis reflectance spectroscopy.•Theoretical calculations were performed to analyze the electronic structure.•The intrinsic UV-light water reduction activity was observed for PbGaBO4.•The optimal H2 evolution rate achieved 41.9(9) μmol/h/g by loading cocatalysts.Metal borates are well-known optical materials while their semiconducting behavior, i.e. photocatalytic property, was less studied. Inspired by the recent publications on gallium borates with good photocatalytic performances, we investigated photocatalytic water reduction activity of another gallium borate, PbGaBO4, comprising edge-sharing GaO6-chains. Both conventional and solution assisted solid state reaction methods were employed for the preparation. Phase purity and the crystallinity of both samples were identified by powder X-ray diffraction and scanning electron microscopy. The UV–Vis reflectance spectra suggested the wide bandgap characteristic (4.10 eV) and theoretical calculations pointed out that the 6s and 5p orbitals of Pb2+ contribute to both the bottom of CB and the top of VB. However the ionic bonding of PbO in PbGaBO4 led to a slight hydrolysis during the photocatalysis process, which can be suppressed by loading cocatalysts of Pt and RuOx. In addition, such a surficial modification significantly improved the photocatalytic water reduction ability, with an optimal H2 evolution rate of 41.9(9) μmol/h/g under UV-light irradiation.
Co-reporter:Rihong Cong, Zhengyang Zhou, Qiaoqi Li, Junliang Sun, Jianhua Lin and Tao Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 17) pp:4431-4437
Publication Date(Web):24 Mar 2015
DOI:10.1039/C5TC00560D
Understanding structure–property relationships are key to the rational design of superior materials. The series of well-known photoluminescent hosts with the chemical formula REBaB9O16 (RE = La–Lu, Y) have been extensively studied but no structural details have been reported. We prepared a new analogue Ba6Bi9B79O138 (BBBO) and proved the isomorphism by X-ray diffraction studies, in spite of the fact that they possess different cationic compositions. In addition, we successfully prepared complete solid solutions of Ba6(Bi1−xEux)9B79O138 (0 ≤ x ≤ 1). Single crystal XRD characterizations on a suitable crystal of BBBO indicated an ordered structure model with the noncentrosymmetric space group R3. It possesses a layered-type structure composed of BO4–BiO6–BO4 sandwiched layers and polyborate inter-layer groups. Ba2+ atoms are located in the inter-layer cavities. There are three and two independent Bi and Ba atoms, respectively. In other words, we have taken a step forward in understanding the structure of REBaB9O16 by analysing a new analogue. We believe this will help the further interpretation and development of REBaB9O16-based optical materials.
Co-reporter:Qiaoqi Li, Rihong Cong, Xianju Zhou, Wenliang Gao and Tao Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 26) pp:6836-6843
Publication Date(Web):22 May 2015
DOI:10.1039/C5TC00923E
Very recently, a novel barium bismuth borate Ba6Bi9B79O138 (BBBO) was shown to be a new analogue of REBaB9O16 (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 Eu3+-to-Bi3+ substituted solid solutions Ba6(Bi1−xEux)9B79O138 (0 ≤ x ≤ 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 Bi3+ was transmitted to Eu3+, causing a great enhancement of Eu3+ emission. More interestingly, the Eu3+-to-Bi3+ substitution leads to a centrosymmetric-to-noncentrosymmetric transition of the local coordination symmetry of the trivalent cations due to the size difference between Eu3+ and Bi3+. This is observed in the synergetic changing of the wavelength of Bi3+ 1S0 → 3P1 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.
Co-reporter:Jia Yang, Hao Fu, Dingfeng Yang, Wenliang Gao, Rihong Cong, and Tao Yang
Inorganic Chemistry 2015 Volume 54(Issue 5) pp:2467-2473
Publication Date(Web):February 19, 2015
DOI:10.1021/ic503101s
Band structure engineering is an efficient technique to develop desired semiconductor photocatalysts, which was usually carried out through isovalent or aliovalent ionic substitutions. Starting from a UV-activated catalyst ZnGa2S4, we successfully exploited good visible light photocatalysts for H2 evolution by In3+-to-Ga3+ and (Cu+/Ga3+)-to-Zn2+ substitutions. First, the bandgap of ZnGa2–xInxS4 (0 ≤ x ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction band position. Second, Zn1–2y(CuGa)yGa1.7In0.3S4 (y = 0.1, 0.15, 0.2) provided a further and significant red-shift of the photon absorption to ∼500 nm by raising the valence band maximum and barely losing the overpotential to water reduction. Zn0.7Cu0.15Ga1.85In0.3S4 possessed the highest H2 evolution rate under pure visible light irradiation using S2– and SO32– as sacrificial reagents (386 μmol/h/g for the noble-metal-free sample and 629 μmol/h/g for the one loaded with 0.5 wt % Ru), while the binary hosts ZnGa2S4 and ZnIn2S4 (synthesized using the same procedure) show 0 and 27.9 μmol/h/g, respectively. The optimal apparent quantum yield reached to 7.9% at 500 nm by tuning the composition to Zn0.6Cu0.2Ga1.9In0.3S4 (loaded with 0.5 wt % Ru).
Co-reporter:Guangjia Wang; Yan Jing; Jing Ju; Dingfeng Yang; Jia Yang; Wenliang Gao; Rihong Cong;Tao Yang
Inorganic Chemistry 2015 Volume 54(Issue 6) pp:2945-2949
Publication Date(Web):February 25, 2015
DOI:10.1021/ic5031087
Borates are well-known candidates for optical materials, but their potentials in photocatalysis are rarely studied. Ga3+-containing oxides or sulfides are good candidates for photocatalysis applications because the unoccupied 4s orbitals of Ga usually contribute to the bottom of the conducting band. It is therefore anticipated that Ga4B2O9 might be a promising photocatalyst because of its high Ga/B ratio and three-dimensional network. Various synthetic methods, including hydrothermal (HY), sol–gel (SG), and high-temperature solid-state reaction (HTSSR), were employed to prepare crystalline Ga4B2O9. The so-obtained HY-Ga4B2O9 are micrometer single crystals but do not show any UV-light activity unless modified by Pt loading. The problem is the fast recombination of photoexcitons. Interestingly, the samples obtained by SG and HTSSR methods both possess a fine micromorphology composed of well-crystalline nanometer strips. Therefore, the excited e– and h+ can move to the surface easily. Both samples exhibit excellent intrinsic UV-light activities for pure water splitting without the assistance of any cocatalyst (47 and 118 μmol/h/g for H2 evolution and 22 and 58 μmol/h/g for O2 evolution, respectively), while there is no detectable activity for P25 (nanoparticles of TiO2 with a specific surface area of 69 m2/g) under the same conditions.
Co-reporter:Pengfei Jiang, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2015 vol. 44(Issue 13) pp:6175-6183
Publication Date(Web):19 Feb 2015
DOI:10.1039/C5DT00022J
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.
Co-reporter:Pengfei Jiang, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2015 vol. 44(Issue 13) pp:6069-6074
Publication Date(Web):11 Feb 2015
DOI:10.1039/C5DT00491H
Rietveld refinements were performed on CaBaZn2Ga2−xAlxO7 (x = 0, 1, 2) to investigate the site preference of cations in tetrahedral cavities. Tri-valent Ga3+/Al3+ preferred the tetrahedral sites (T1-sites) within the triangular layers. Moreover, a layered type cationic ordering was observed in CaBaZn2Al2O7, where all the T1-sites were occupied by Al3+. This represents the first example of a cationic ordering in “114” compounds. By substituting Al3+ into CaBaZn2Ga2O7, the major change in the structure was the shrinkage of the T1O4 tetrahedrons, especially the shortening of the T1–O2 bond distance along the c-axis, which led to an anisotropic shrinkage of the unit cell. In the literature, such an anisotropic change of unit cell would induce a structure distortion, as well as a decrease in the symmetry from P63mc to Pbn21. All the title compounds crystallized in P63mc, which is unexpected. A comparison with the selected “114” magnetic oxides help us to confirm that the strong antiferromagnetic interactions of magnetic lattices would also be beneficial for symmetry lowering. Overall, the factors affecting cationic ordering on T1-sites and symmetry lowering are discussed for the title compounds, which may also be applicable to other “114” oxides.
Co-reporter:Xiaorui Sun, Wenliang Gao, Tao Yang and Rihong Cong
Dalton Transactions 2015 vol. 44(Issue 5) pp:2276-2284
Publication Date(Web):05 Dec 2014
DOI:10.1039/C4DT03303E
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.
Co-reporter:Qiaoqi Li;Wenliang Gao ;Tao Yang
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 30) pp:5045-5052
Publication Date(Web):
DOI:10.1002/ejic.201500622
Abstract
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(5D47F6)/I(5D47F5) 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–yBiyTb0.7)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.
Co-reporter:Kai Song;Jia Yang;Pengfei Jiang;Wenliang Gao;Tao Yang
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 35) pp:5786-5792
Publication Date(Web):
DOI:10.1002/ejic.201500929
Abstract
Completely B-site-ordered Ba2InTaO6 has been prepared previously by prolonged heating at 1500 °C; here, we significantly lowered the annealing temperature to 1130 °C under H2/Ar dynamic flow and obtained a partially ordered (ca. 74 %) double perovskite, as determined by Rietveld refinement of the powder X-ray diffraction data. As a wide-band-gap semiconductor, Ba2InTaO6 possesses photocatalytic activity for overall water splitting under UV irradiation, though the gas evolution rates of 12.9 and 6.6 μmol/h/g for H2 and O2 generation, respectively, are low. With the assistance of methanol as a sacrificial reagent, the H2 evolution rate increases to 50.5 μmol/h/g, which indicates that the surficial charge recombination rate is really high. We applied the typical cocatalyst-loading method to this material, and with 1 wt.-% PtOx and NiOx, the H2 production rates in pure water were further improved to 16.0 and 18.4 μmol/h/g, respectively. Attempts to dope Ba2InTaO6 with first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) led to a general enhancement of the light-harvesting ability; however, the experimental water-splitting activity did not improve. We believe that the doped cations most likely behaved as recombination centers for photogenerated charges. Considering its structural similarity to the well-known catalyst InTaO4:Ni, Ba2InTaO6 possesses the potential to extend its photocatalytic activity to the visible-light region but needs further enhancement.
Co-reporter:Chunmei Zeng, Tao Hu, Nianjun Hou, Siyao Liu, Wenliang Gao, Rihong Cong, Tao Yang
Materials Research Bulletin 2015 61() pp: 481-485
Publication Date(Web):
DOI:10.1016/j.materresbull.2014.10.041
Co-reporter:Wenliang Gao, Yan Jing, Jia Yang, Zhengyang Zhou, Dingfeng Yang, Junliang Sun, Jianhua Lin, Rihong Cong, and Tao Yang
Inorganic Chemistry 2014 Volume 53(Issue 5) pp:2364-2366
Publication Date(Web):February 10, 2014
DOI:10.1021/ic403175w
An open-framework gallium borate with intrinsic photocatalytic activities to water splitting has been discovered. Small inorganic molecules, H3BO3 and H3B3O6, are confined inside structural channels by multiple hydrogen bonds. It is the first example to experimentally show the structural template effect of boric acid in flux synthesis.
Co-reporter:Qiaoqi Li, Cong Lin, Zhengyang Zhou, Jing Ju, Guobao Li, Jianhua Lin, Wenliang Gao, Rihong Cong, and Tao Yang
Inorganic Chemistry 2014 Volume 53(Issue 11) pp:5600-5608
Publication Date(Web):May 20, 2014
DOI:10.1021/ic500352g
Single crystals of pure aluminoborate PKU-1 (Al3B6O11(OH)5·nH2O) were obtained, and the structure was redetermined by X-ray diffraction. There are three independent Al atoms in the R3 structure model, and Al3 locates in a quite distorted octahedral environment, which was evidenced by 27Al NMR results. This distortion of Al3O6 octahedra release the strong static stress of the main framework and leads to a symmetry lowering from the previously reported R3̅ to the presently reported R3. We applied a pretreatment to prepare Al3+/Cr3+ aqueous solutions; as a consecquence, a very high Cr3+-to-Al3+ substitution content (∼50 atom %) in PKU-1 can be achieved, which is far more than enough for catalytic purposes. Additionally, the preference for Cr3+ substitution at the Al1 and Al2 sites was observed in the Rietveld refinements of the powder X-ray data of PKU-1:0.32Cr3+. We also systematically investigated the thermal behaviors of PKU-1:xCr3+ (0 ≤ x ≤ 0.50) by thermogravimetric–differential scanning calorimetry, in situ high-temperature XRD in vacuum, and postannealing experiments in furnace. The main framework of Cr3+-substituted PKU-1 could be partially retained at 1100 °C in vacuum. When 0.04 ≤ x ≤ 0.20, PKU-1:xCr3+ transferred to the PKU-5:xCr3+ (Al4B6O15:xCr3+) structure at ∼750 °C by a 5 h annealing in air. Further elevating the temperature led to a decomposition into the mullite phase, Al4B2O9:xCr3+. For x > 0.20 in PKU-1:xCr3+, the heat treatment led to a composite of Cr3+-substituted PKU-5 and Cr2O3, so the doping upper limit of Cr3+ in PKU-5 structure is around 20 atom %.
Co-reporter:Xuefang Yi, Rihong Cong, Zhengyang Zhou, Pengfei Jiang, Wenliang Gao and Tao Yang
New Journal of Chemistry 2014 vol. 38(Issue 1) pp:122-131
Publication Date(Web):30 Sep 2013
DOI:10.1039/C3NJ00925D
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.
Co-reporter:Ying Wang, Jia Yang, Wenliang Gao, Rihong Cong, Tao Yang
Materials Letters 2014 Volume 137() pp:99-101
Publication Date(Web):15 December 2014
DOI:10.1016/j.matlet.2014.08.144
•An organic-free hydrothermal method was applied to obtain chalcopyrite CuInS2.•Bulk CuInS2 was prepared by annealing Cu2S and In2S3 at 600–750 °C under vacuum.•All samples show good photocatalytic activities for nitrate reduction.•All catalysts were stable after the photocatalytic reactions.We performed a facile and organic-free hydrothermal method (thiourea-oxalic acid co-molten system) to prepare chalcopyrite CuInS2 nano-crystallite. Its intrinsic photocatalytic activities to nitrate reduction in aqueous solutions were investigated in comparison to bulk CuInS2 prepared by annealing Cu2S and In2S3 at 600–750 °C under vacuum. All samples show good and similar photocatalytic activities for nitrate reduction, for example, the conversion rate is about two times of that in a blank experiment. All CuInS2 catalysts were stable after the photocatalytic reactions, indicated by the identical XRD patterns before and after the reaction.
Co-reporter:Xuefang Yi, Rihong Cong, Mufei Yue, Yuqing Chai, Pengfei Jiang, Wenliang Gao and Tao Yang
Dalton Transactions 2013 vol. 42(Issue 46) pp:16318-16327
Publication Date(Web):05 Sep 2013
DOI:10.1039/C3DT51875B
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.
Co-reporter:Dingfeng Yang, Yan Jing, Yang Zhang, Xianming Liu, Zheshuai Lin, Rihong Cong, Wenliang Gao, Tao Yang
Materials Research Bulletin 2013 48(2) pp: 270-276
Publication Date(Web):
DOI:10.1016/j.materresbull.2012.10.054
Co-reporter:Pengfei Jiang, Zhengyang Zhou, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2016 - vol. 45(Issue 9) pp:NaN3957-3957
Publication Date(Web):2016/01/22
DOI:10.1039/C5DT04150C
The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO6, by selecting Zn2+ and Sb5+ with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr2+-doping-induced symmetry evolution from I2/m to P21/n was confirmed in the complete solid solutions LaBa1−xSrxZnSbO6, where the tilting system also transferred from a−a−c0 to a−a−c+. The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr–O bond distances (revealed by Rietveld refinements) motivated us to study the Eu3+ luminescence in La0.95Eu0.05Ba1−xSrxZnSbO6. Interestingly, the maximum of charge transfer absorption of Eu3+ shows a precise changing tendency with the A–O bond distances along with the Sr2+ doping, clearly revealing the structure–luminescence correlations.
Co-reporter:Xuefang Yi, Rihong Cong, Mufei Yue, Yuqing Chai, Pengfei Jiang, Wenliang Gao and Tao Yang
Dalton Transactions 2013 - vol. 42(Issue 46) pp:NaN16327-16327
Publication Date(Web):2013/09/05
DOI:10.1039/C3DT51875B
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.
Co-reporter:Qiaoqi Li, Rihong Cong, Xianju Zhou, Wenliang Gao and Tao Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 26) pp:NaN6843-6843
Publication Date(Web):2015/05/22
DOI:10.1039/C5TC00923E
Very recently, a novel barium bismuth borate Ba6Bi9B79O138 (BBBO) was shown to be a new analogue of REBaB9O16 (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 Eu3+-to-Bi3+ substituted solid solutions Ba6(Bi1−xEux)9B79O138 (0 ≤ x ≤ 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 Bi3+ was transmitted to Eu3+, causing a great enhancement of Eu3+ emission. More interestingly, the Eu3+-to-Bi3+ substitution leads to a centrosymmetric-to-noncentrosymmetric transition of the local coordination symmetry of the trivalent cations due to the size difference between Eu3+ and Bi3+. This is observed in the synergetic changing of the wavelength of Bi3+ 1S0 → 3P1 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.
Co-reporter:Pengfei Jiang, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2015 - vol. 44(Issue 13) pp:NaN6074-6074
Publication Date(Web):2015/02/11
DOI:10.1039/C5DT00491H
Rietveld refinements were performed on CaBaZn2Ga2−xAlxO7 (x = 0, 1, 2) to investigate the site preference of cations in tetrahedral cavities. Tri-valent Ga3+/Al3+ preferred the tetrahedral sites (T1-sites) within the triangular layers. Moreover, a layered type cationic ordering was observed in CaBaZn2Al2O7, where all the T1-sites were occupied by Al3+. This represents the first example of a cationic ordering in “114” compounds. By substituting Al3+ into CaBaZn2Ga2O7, the major change in the structure was the shrinkage of the T1O4 tetrahedrons, especially the shortening of the T1–O2 bond distance along the c-axis, which led to an anisotropic shrinkage of the unit cell. In the literature, such an anisotropic change of unit cell would induce a structure distortion, as well as a decrease in the symmetry from P63mc to Pbn21. All the title compounds crystallized in P63mc, which is unexpected. A comparison with the selected “114” magnetic oxides help us to confirm that the strong antiferromagnetic interactions of magnetic lattices would also be beneficial for symmetry lowering. Overall, the factors affecting cationic ordering on T1-sites and symmetry lowering are discussed for the title compounds, which may also be applicable to other “114” oxides.
Co-reporter:Pengfei Jiang, Wenliang Gao, Rihong Cong and Tao Yang
Dalton Transactions 2015 - vol. 44(Issue 13) pp:NaN6183-6183
Publication Date(Web):2015/02/19
DOI:10.1039/C5DT00022J
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.
Co-reporter:Rihong Cong, Zhengyang Zhou, Qiaoqi Li, Junliang Sun, Jianhua Lin and Tao Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 17) pp:NaN4437-4437
Publication Date(Web):2015/03/24
DOI:10.1039/C5TC00560D
Understanding structure–property relationships are key to the rational design of superior materials. The series of well-known photoluminescent hosts with the chemical formula REBaB9O16 (RE = La–Lu, Y) have been extensively studied but no structural details have been reported. We prepared a new analogue Ba6Bi9B79O138 (BBBO) and proved the isomorphism by X-ray diffraction studies, in spite of the fact that they possess different cationic compositions. In addition, we successfully prepared complete solid solutions of Ba6(Bi1−xEux)9B79O138 (0 ≤ x ≤ 1). Single crystal XRD characterizations on a suitable crystal of BBBO indicated an ordered structure model with the noncentrosymmetric space group R3. It possesses a layered-type structure composed of BO4–BiO6–BO4 sandwiched layers and polyborate inter-layer groups. Ba2+ atoms are located in the inter-layer cavities. There are three and two independent Bi and Ba atoms, respectively. In other words, we have taken a step forward in understanding the structure of REBaB9O16 by analysing a new analogue. We believe this will help the further interpretation and development of REBaB9O16-based optical materials.
Co-reporter:Xiaorui Sun, Wenliang Gao, Tao Yang and Rihong Cong
Dalton Transactions 2015 - vol. 44(Issue 5) pp:NaN2284-2284
Publication Date(Web):2014/12/05
DOI:10.1039/C4DT03303E
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.
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