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The crystal structures, photoluminescence properties, and transport properties of a series of new "114" oxides CaBa1−xSrxZn2Al2O7 (x = 0–1) were investigated in detail. Careful Rietveld refinements performed on solid solution samples revealed that the structural symmetry of CaBa1−xSrxZn2Al2O7 evolves from hexagonal P63mc (x < 0.2) to trigonal P31c (0.2 ≤ x ≤ 0.6) and then to orthorhombic Pna21 (x > 0.6) with an increase of the Sr2+-content, which is cooperative with the rotation of T1O4 tetrahedra around the c-axis. Eu3+ was used as a local structural probe to gain an insight into the structure, which further corroborated the correctness of the observed structural symmetry descending sequence in CaBa1−xSrxZn2Al2O7. More importantly, the reduction of structural symmetry is also associated with a tendency from layered ordering to complete charge ordering transition for Zn2+/Al3+ cations, which was revealed to have a significant influence on the transport properties. These findings are expected to offer a route to manipulate the physical properties of "114" oxides containing magnetic cations. [ABSTRACT FROM AUTHOR]

Strecker reactions have an important application in the preparation of α-amino acids and biologically active molecules in homogeneous acid- or base-catalyzed systems. As novel solid acid catalysts, AlxGa1−x-PKU-1 (x = 0–1) solid solutions constructed by two octahedron-based molecular sieves were prepared by using a molten boric acid method and exhibited a continuously-adjustable acidity in heterogeneously-catalyzed Strecker reactions under mild conditions. AlxGa1−x-PKU-1 accommodated a large number of Brønsted acid sites in the framework, and the acidic density and strength were enhanced with the successive incorporation of Al atoms, thus the catalytic activity became superior in the formation of α-aminonitriles. Three-fold coordinated boron atoms, despite the electron-deficient configuration, seemed unable to behave as Lewis acid centers probably due to steric hindrance against the adsorption of large organic substrates. This work illustrates, for the first time, possible application in Strecker reactions using zeolite-like solid solutions, and will potentially provide an effective method and a beneficial reference to control surface acidity for porous materials. [ABSTRACT FROM AUTHOR]

Searching efficient red phosphors under near‐UV or blue light excitation is practically important to improve the current white light‐emitting diodes (WLEDs). Eu2+‐ and Mn4+‐based red phosphors have been extensively studied. Here we proposed that Eu3+ is also a promising activator when it resides on a noncentrosymmetric coordination site. We proved that Cd4GdO(BO3)3 is a good host, which has a significantly distorted coordination for Eu3+. A careful crystallographic study was performed on the solid solutions of Cd4Gd1‐xEuxO(BO3)3 (0≤x≤1) by Rietveld refinements. The as‐doped Eu3+ cations locate at the Gd3+ site and are well separated by CdO8, CdO6 and BO3 groups; thus, only a slight concentration quenching was observed at ≈80 atom % Eu3+. Most importantly, the parity‐forbidden law of 4f‐4f transitions for Eu3+ are severely depressed, thus the absorptions at ≈393 and ≈465 nm are remarkable. Cd4Gd0.2Eu0.8O(BO3)3 can be pumped by a 395 nm LED chip to give a bright red emission, and when mixed with other commercial blue and green phosphors, it can emit the proper white light (0.3657, 0.3613) with a suitable Ra≈87 and correlated colour temperature ≈4326 K. In‐situ photoluminescence study indicated the low thermal quenching of these borate phosphors, especially under 465 nm excitation. Our case proves the practicability to develop near‐UV excited red phosphors in rare‐earth‐containing borates. [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]

The crystal structures, photoluminescence properties, and transport properties of a series of new "114" oxides CaBa1−xSrxZn2Al2O7 (x = 0–1) were investigated in detail. Careful Rietveld refinements performed on solid solution samples revealed that the structural symmetry of CaBa1−xSrxZn2Al2O7 evolves from hexagonal P63mc (x < 0.2) to trigonal P31c (0.2 ≤ x ≤ 0.6) and then to orthorhombic Pna21 (x > 0.6) with an increase of the Sr2+-content, which is cooperative with the rotation of T1O4 tetrahedra around the c-axis. Eu3+ was used as a local structural probe to gain an insight into the structure, which further corroborated the correctness of the observed structural symmetry descending sequence in CaBa1−xSrxZn2Al2O7. More importantly, the reduction of structural symmetry is also associated with a tendency from layered ordering to complete charge ordering transition for Zn2+/Al3+ cations, which was revealed to have a significant influence on the transport properties. These findings are expected to offer a route to manipulate the physical properties of "114" oxides containing magnetic cations. [ABSTRACT FROM AUTHOR]

The high-pressure polymorph of β-YB 3 O 6 was stabilized by doping Bi3+ under ambient pressure, thus solid solutions of β-Y 1- m Bi m B 3 O 6 (0.10 ≤ m ≤ 0.30), β-Y 0.80- x Bi 0.20 Tb x B 3 O 6 (0.05 ≤ x ≤ 0.80), and β-Y 0.80- y Bi 0.20 Eu y B 3 O 6 (0.05 ≤ y ≤ 0.80) were prepared simply by high temperature solid state reactions. The phase purity and the successful cationic substitutions were confirmed by powder X-ray diffraction, where the linear expansion of lattice parameters was observed due to the replacement of Y3+ by lager cations. The second function of Bi3+ was to behave as a photoluminescent activator giving the blue emission, as well as a sensitizer to Tb3+ and Eu3+, which emit green and red light, respectively. Bright and color-tunable emissions from blue to green (or blue to red) were achieved by manipulating the relative ratio between Bi3+ and Tb3+ (or Eu3+). In final, a white emission was observed for the triply-doped phosphor β-Y 0.49 Bi 0.20 Tb 0.30 Eu 0.01 B 3 O 6. Since the highly efficient energy transfers from Bi3+ to Tb3+ and from Bi3+ to Eu3+, color-tunable emissions from blue to green and from blue to red can be achieved in Bi3+/Tb3+ and Bi3+/Eu3+ co-doped β-YB 3 O 6 , which is originally a high-pressure polymorph and could be stabilized at ambient pressure due to the Bi3+ substitutions. Image 1 • The high-pressure phase β-YB 3 O 6 was stabilized at ambient pressure by doping Bi3+. • Bi3+ emits the blue light and the optimal doping concentration is 20 atom%. • Bi3+, Tb3+, Eu3+ co-doped and triply-doped β-YB 3 O 6 were prepared. • Highly efficient energy transfer from Bi3+ to Tb3+/Eu3+ was proved. • Bright color-tunable emissions from blue to green (or blue to red) were achieved. [ABSTRACT FROM AUTHOR]

Completed solid solutions of Y 1- x Eu x [B 6 O 9 (OH) 3 ] were prepared by boric acid flux method and the structure of Eu[B 6 O 9 (OH) 3 ] was determined by single crystal X-ray diffraction (XRD). The successful cationic doping was supported by the linear change of unit cell parameters obtained by Le Bail fitting on powder XRD. Thermal treatments on Y 1- x Eu x [B 6 O 9 (OH) 3 ] will lead to the dehydration, re-crystallization into TD-α-Y 1- x Eu x B 5 O 9 , and decomposition to α-Y 1- x Eu x B 3 O 6 eventually. For comparison, the sol-gel method was also applied to prepare SG-α-Y 1- x Eu x B 5 O 9. Rietveld refinements on powder XRD was applied to obtain the crystallographic data for α-YB 5 O 9. PL investigation indicated that the existence of hydroxyl groups weakened the Eu3+ charge transfer (CT) in Y 1- x Eu x [B 6 O 9 (OH) 3 ]. In α-Y 1- x Eu x B 5 O 9 , an intense CT absorption was detected and a bright right emission was observed. Moreover, both series of phosphors exhibited a right shift of CT maximum wavelength due to the expansion of unit cell and the delayed concentration at x = 0.6. Complete solid solutions of α-Y 1- x Eu x B 5 O 9 were prepared by either heating the precursors Y 1- x Eu x [B 6 O 9 (OH) 3 ] or direct sol-gel method, and the purity of the borates were verified by careful analyses on powder XRD. Detailed photoluminescence property investigation proved that α-Y 1- x Eu x B 5 O 9 are good red phosphors with a delayed concentration quenching at x = 0.6. Image 1 • Y 1- x Eu x [B 6 O 9 (OH) 3 ] (0 ≤ x ≤ 1) were prepared by boric acid flux method. • Heating Y 1- x Eu x [B 6 O 9 (OH) 3 ] at 670 °C led to the formation of TD-α-Y 1- x Eu x B 5 O 9. • Sol-gel method was also applied to synthesize SG-α-Y 1- x Eu x B 5 O 9. • The CT transition of Eu3+ in Y 1- x Eu x [B 6 O 9 (OH) 3 ] was weakened by hydroxyl groups. • α-Y 1- x Eu x B 5 O 9 have a bright red emission and a concentration quenching at x = 0.6. [ABSTRACT FROM AUTHOR]

Rare earth ( RE ) borates have been extensively studied as good photoluminescent materials, however, the target hosts were limited to “ RE 3 BO 6 ”, RE BO 3 , and RE B 3 O 6 in the RE 2 O 3 -B 2 O 3 phase diagram until the recent discovery of rare earth pentaborate. For the first time, the sol-gel method was employed to synthesize β-LaB 5 O 9 doped with Eu 3+ , Tb 3+ , Ce 3+ , Sm 3+ , Dy 3+ . In comparison to the previous synthetic methods, the sol-gel method possesses superiorities including easily-controllable doping concentration, high yield and emission efficiency. Solid solutions of phosphors were prepared and carefully analyzed by powder X-ray diffraction. Concentration quenching or saturation was observed in Eu 3+ , Tb 3+ and Ce 3+ doped phosphors at round 10 at%. Eu 3+ , Tb 3+ , Sm 3+ , and Dy 3+ emit red, green, orange, and close-to-white light, respectively. The absolute emission efficiency of Ce 3+ is high and in the UV range, suggesting the function of being sensitizer once combined with other activators. [ABSTRACT FROM AUTHOR]

BiMn x Fe 3- x O 6 ( x = 1) represents a new type of oxide structure containing Bi 3+ and competing magnetic super-exchanges. In literature, multiple magnetic states were realized at low temperatures in BiMnFe 2 O 6 , and the hypothetical parent compounds (BiMn 3 O 6 , BiFe 3 O 6 ) were predicted to be different in magnetism. Herein, we performed a careful study on the syntheses of BiMn x Fe 3- x O 6 at ambient pressure, and the solid solution range was determined to be 0.9 ≤ x ≤ 1.3 by Rietveld refinements on high-quality powder X-ray diffraction data. Due to the very similar cationic size of Mn 3+ and Fe 3+ , and possibly the structural rigidity, there was no significant structure change in the whole range of solid solution. The magnetic behavior of BiMn x Fe 3- x O 6 ( x = 1.2, 1.22, 1.26, 1.28 and 1.3) was generally similar to BiMnFe 2 O 6 , while the relative higher concentration of Mn 3+ led to the decreasing of the antiferromagnetic ordering temperature. [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]

A strategy to utilize the nonlinear optical borate as the photoluminescent host is proposed in order to gain enhanced 4 f -4 f transitions because there exists a high probability of Eu3+ locating in a noncentrosymmetric coordination, serving as the near ultraviolet LED pumped red phosphor. With such a rationale, La 1- x Eu x B 4 O 6 (OH) 2 Cl have been prepared by boric acid flux method, which transfer to TD-α-La 1- x Eu x B 3 O 6 by high temperature annealing. In the meantime, HS-α-La 1- y Eu y B 3 O 6 (y ​= ​0, 0.075, 0.15, 0.3, 0.4) are synthesized directly by high temperature solid state reactions. The Eu3+-dependent cell volume is employed to obtain equation (1): V 1 ​= ​421.0(3)-26(1) y. Accordingly, the x values of TD-α-La 1- x Eu x B 3 O 6 can be deduced and the cell volume of La 1- x Eu x B 4 O 6 (OH) 2 Cl can be simulated into equation (2): V 2 ​= ​695.1(1)-37.9(8) x. In the following, all the x values for 11 samples of La 1- x Eu x B 4 O 6 (OH) 2 Cl are determined. The noncentrosymmetric coordination as well as the mix-coordination atoms lead to strong 4 f -4 f transitions of Eu3+, and only a slight concentration quenching effect is observed despite the existence of hydroxyl groups. Once combined with a 395 ​nm LED chip, it emits a bright pink light, and the thermal stability is satisfied according to the in-situ high temperature photoluminescent study. The noncentrosymmetric coordination as well as the mix-coordination atoms in La 1- x Eu x B 4 O 6 (OH) 2 Cl lead to strong 4 f -4 f transitions of Eu3+, and only a slight concentration quenching effect was observed despite the existence of hydroxyl groups, suggesting the potential as the NUV LED pumped red phosphor. Image 1 • La 1- x Eu x B 4 O 6 (OH) 2 Cl were prepared by boric acid flux method. • Eu3+-contents in La 1- x Eu x B 4 O 6 (OH) 2 Cl were determined by external standard method. • 4 f -4 f transitions of Eu3+ were enhanced due to the oxychloride coordination. • Once combined with a 395 ​nm LED chip, it emitted a bright pink light. • In-situ high temperature PL spectra proved its high thermal stability. [ABSTRACT FROM AUTHOR]