A new disodium hafnium borate Na2Hf(BO3)2: synthesis, crystal structure, DFT calculations and luminescent properties

A ternary borate Na2Hf(BO3)2 has been prepared using a high temperature molten salt method and structurally determined by single crystal X-ray diffraction analysis. It crystallizes in dolomite-type structure with trigonal space group R3̅, and features a layer structure containing [Hf(BO3)2] layers and Na atom layers perpendicular to the c-axis. Band structure calculation using the density functional theory (DFT) method indicates that Na2Hf(BO3)2 has an indirect bond gap of about 4.76 eV. The photoluminescence excitation and emission spectra, decay curve, and the color coordinates of Na2Hf(BO3)2 were investigated. The results show that it can be efficiently excited by UV light (302 nm) and presents blue-green emission (centred at 480 nm), which may be attributed to the lattice defect emission.

Structural diversities induced by cation sizes in a series of fluorogermanophosphates: A2[GeF2(HPO4)2] (A = Na, K, Rb, NH4, and Cs)

Germanophosphates, in comparison with other metal phosphates, have been less studied but potentially exhibit more diverse structural chemistry with wide applications. Herein we applied a hydro-/solvo-fluorothermal route to make use of both the "tailor effect" of fluoride for the formation of low dimensional anionic clusters and the presence of alkali cations of different sizes to align the anionic clusters to control the overall crystal symmetries of germanophosphates. The synergetic effects of fluoride and alkali cations led to structural changes from chain-like structures to layered structures in a series of five novel fluorogermanophosphates: A₂[GeF₂(HPO₄)₂] (A = Na, K, Rb, NH₄, and Cs, denoted as Na, K, Rb, NH4, and Cs). Although these fluorogermanophosphates have stoichiometrically equivalent formulas, they feature different anionic clusters, diverse structural dimensionalities, and contrasting crystal symmetries. Chain-like structures were observed for the compounds with the smaller sized alkali ions (Na⁺, K⁺, and Rb⁺), whereas layered structures were found for those containing the larger sized cations ((NH₄)⁺ and Cs⁺). Specifically, monoclinic space groups were observed for the Na, K, Rb, and NH4 compounds, whereas a tetragonal space group P4/mbm was found for the Cs compound. These compounds provide new insights into the effects of cation sizes on the anionic clusters built from GeO₄F₂ octahedra and HPO₄ tetrahedra as well as their influences on the overall structural symmetries in germanophosphates. Further characterization including IR spectroscopy and thermal analyses for all five compounds is also presented.

PbLnB7O13 (Ln = Tb or Eu): a new type of layered polyborate with multi-colour light emission properties

This work demonstrates two new polyborates PbLnB₇O₁₃ (Ln = Tb or Eu) with layer structures. Under near-UV light excitation, their solid solutions, PbTb_1−xEu_xB₇O₁₃ (x = 0–1), show a continuously changing emission color from green to red as the x value changes.

Synthesis and structural characterization of AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta) vanadates: a structural comparison of A+M5+V2O8 vanadates and A+M5+P2O8 phosphates

Three types of [MV₂O₈]⁻ anionic frame works of twelve new and known A⁺M⁵⁺V₂O₈ vanadates are built from different modes of connectivity of [M₂V₄O₁₈] ribbons.

Yellow-orange upconversion emission in Eu(3+)-Yb(3+) codoped BaTiO(3) phosphor

The Eu(3+)-Yb(3+) codoped BaTiO3 phosphor is prepared via co-precipitation method and its upconversion emission is studied by 980nm diode laser excitation. The X-ray diffraction pattern of the prepared sample showed the tetragonal BaTiO3 phase. The co-doped phosphor showed sharp upconversion emission bands peaking at ∼592, ∼614, ∼ 654, ∼704 and ∼796nm due to the (5)D0→(7)F1, (5)D0→(7)F2, (5)D0→(7)F3, (5)D0→(7)F4 and (5)D0→(7)F6 transitions, respectively of Eu(3+) ions. The sharp band at 489nm is assigned to the (2)F5/2→(2)F7/2 transition of Yb(3+) ion while the broad band around 505nm is assigned to the defect states present in the sample. Based on the available experimental data, the process involved in the UC emissions has been explored and elaborated.