G.M. Cai

Crystal structure, luminescence properties and energy transfer of Eu3+/Dy3+ doped GdNbTiO6 broad band excited phosphors

GdNbTiO6 is used as a host material for phosphors for the first time. Lanthanide ion (Eu3+/Dy3+) doped GdNbTiO6 phosphors were prepared by solid-state reaction, and the crystal structure, luminescence properties, and relevant luminescence mechanisms were investigated. The crystal structure of Eu3+/Dy3+ doped GdNbTiO6 was refined from powder XRD data by the Rietveld method, which is made up of irregular (Gd/Eu/Dy)3+O813− polyhedra and slightly distorted Nb(Ti)O6 octahedra forming a layered structure. The luminescence properties of the GdNbTiO6:Eu3+/Dy3+ phosphors were studied under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The GdNbTiO6 host shows a broad emission band about the 400–650 nm region centered at 509 nm owing to the Nb(Ti)O6 octahedral groups, which has spectral overlap with f–f excitation transitions of Eu3+/Dy3+ in the doped samples. For red phosphor GdNbTiO6:Eu3+, a dominant emission peak at 614 nm was attributed to the 5D0 → 7F2 transition of Eu3+, which confirmed that Eu3+ ions are located at sites without inversion symmetry. The phosphor GdNbTiO6:Dy3+ shows bright yellow-green emission prevailing at 577 nm upon 273 nm excitation. With increasing activator concentration, the emission derived from the characteristic f–f transitions of Eu3+/Dy3+ is enhanced while the host emission is weakened, which is due to the energy transfer from the host to Eu3+/Dy3+. Considering the facile synthesis and excellent Eu3+/Dy3+ doped luminescence properties of this compound, self-activated GdNbTiO6 may be a good candidate as a host phosphor for use in various optical devices.

Synthesis, crystal structure, and thermal stability of new borates Na 3 REB 2 O 6 (RE = Pr, Sm, Eu)

Subsolidus phase equilibrium of Na 2 O–Sm 2 O 3 –B 2 O 3 system has been investigated mainly by solid-state reaction and powder X-ray diffraction method. There are nine definite three-phase regions and three ternary compounds determined under present experimental conditions. A novel compound Na 3 SmB 2 O 6 was found and confirmed in this system, along with its two homogeneous compounds Na 3 REB 2 O 6 (RE = Pr, Eu) synthesized for the first time. The indexing results showed that all three compounds crystallize in the monoclinic space group P 2 1 / c (No.14) with the same structure type as both Na 3 NdB 2 O 6 and Na 3 GdB 2 O 6 . The lattice parameters ( a, b , and c ) of new borates Na 3 REB 2 O 6 (RE = Pr, Sm, Eu) decrease linearly with a decreasing radius of RE ion, which obeys the Lanthanide-contraction rule. The existence of a trigonal BO 3 group in the Na 3 REB 2 O 6 (RE = Pr, Sm) compounds was confirmed by analysis of their infrared absorption spectra. Thermal stabilities of the three new borates have been investigated.

Phase relation, structure, and properties of borate MgYB 5 O 10 in MgO–Y 2 O 3 –B 2 O 3 system

In the investigation of MgO–Y 2 O 3 –B 2 O 3 system, six three-phase regions, five binary compounds, and one ternary compound MgYB 5 O 10 were confirmed in the subsolidus phase relations. Single-phase powder sample of MgYB 5 O 10 was successfully prepared through solution synthesis method. By using the Rietveld method from the step-scanning X-ray powder diffraction data, the crystal structure of MgYB 5 O 10 was determined. It crystallizes in the monoclinic system with the space group P 12 1 / c 1 and lattice parameters a = 8.5113(2) A, b = 7.5892(2) A, c = 12.2460(3) A, β = 130.200(1)°, and Z = 4. The infrared spectrum of MgYB 5 O 10 at room temperature demonstrates the existence of BO 3 and BO 4 groups. The UV–visible spectrum shows a wide absorption band within the range of 190–400 nm, while the absorption in the visible region is negligible. According to the electronic structure derived by first-principles calculations, MgYB 5 O 10 is an insulator with a wide indirect energy band gap of about 5.95 eV. Layered structural characteristics, existence of one-dimensional Y n O 8 n +2 chains, and the large band gap should be the immanent reason why MgYB 5 O 10 -based materials have exhibited outstanding performances in the luminescence field.

Modification of YNbO4 and YNbTiO6 photoluminescence by nitrogen doping

Niobates as multifunctional materials were of vital importance in the industry production and daily life. In present work, niobates YNbO4 and YNbTiO6 are investigated as luminescence materials. The compounds have self-activated luminescence, and it is discussed how nitrogen doping affects their electronic structure and optical properties. Various analytical techniques, including x-ray diffraction, nitrogen-content analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, UV-vis absorption spectroscopy and vacuum ultraviolet emission spectroscopy at variable temperature, were used to characterize the structure, composition, crystallinity and optical performance of these niobates. By considering the luminescence mechanisms in YNbO4 and YNbTiO6, the enhanced luminescence obtained upon nitrogen doping is attributed to the presence of oxygen vacancies and nitrogen levels, which changes the band gaps of the materials. Present work demonstrates the use of nitrogen doping for improving the photoluminescence properties of self-activated niobates.Niobates as multifunctional materials were of vital importance in the industry production and daily life. In present work, niobates YNbO4 and YNbTiO6 are investigated as luminescence materials. The compounds have self-activated luminescence, and it is discussed how nitrogen doping affects their electronic structure and optical properties. Various analytical techniques, including x-ray diffraction, nitrogen-content analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, UV-vis absorption spectroscopy and vacuum ultraviolet emission spectroscopy at variable temperature, were used to characterize the structure, composition, crystallinity and optical performance of these niobates. By considering the luminescence mechanisms in YNbO4 and YNbTiO6, the enhanced luminescence obtained upon nitrogen doping is attributed to the presence of oxygen vacancies and nitrogen levels, which changes the band gaps of the materials. Present work demonstrates the use of nitrogen doping for improving the photolu...