A. Dias Tavares

Structure determination and a vibrational study for the hexagonal elpasolite Cs2NaGaF6:Cr3+

Single crystals of 0.5% Cr3+-doped Cs2NaGaF6 were studied by means of x-ray diffraction and polarized Raman scattering. The crystal exhibits a unique stacking interaction, with a hexagonal structure with Rm symmetry. Polarized Raman spectra recorded at 16 and 300 K reveal sidebands that are ascribed to the local vibrational of the [CrF6] coordination unit, which differ markedly from those of the Cs2NaGaF6 host lattice. The results are compared to findings for other elpasolite lattices, and the room temperature luminescence quantum yields are discussed in terms of a delicate balance between electron–phonon strength and lattice distortion.

Near infrared spectroscopy of divalent cobalt in polycrystalline magnesium and zinc gallate

Infrared luminescence of MgGa2 O4 :Co2+ and ZnGa2 O4 :Co2+ polycrystalline samples is presented. The bands observed in these cobalt compounds are assigned to the 4 T1 (4 P) 4 T1 (4 F) transition of the tetrahedrally coordinated Co2+ ions.

Optical Spectroscopy of MgGa2O4:Fe3+

Fluorescence and excitation data for MgGa 2 O 4 :Fe 3+ are presented. We have produced by solid state reactions a compound in which a near infrared emission broadband at 77 K as well as at room temperature was observed. The emission is attributed to the spin-forbidden 4 T 1 ( 4 G) → 6 A 1 ( 6 S) electronic transition of Fe 3+ ions in tetrahedral sites.

Dependence of MgGa2O4:Co2+ photoluminescence on temperature and impurity concentration

Polycrystalline samples of MgGa 2 O 4 doped with 0.1 and 1.0% of Co 2+ ions were produced by ceramic methods and investigated by x-ray diffraction and luminescence spectroscopy. Emission data at room temperature and 77 K, as well as transition lifetimes obtained by the phase-shift method, are presented. The emission is attributed to 4 T 1 ( 4 P) → 4 A 2 ( 4 F) of Co 2+ ions in tetrahedral sites. The excitation spectra are associated with 4 A 2 ( 4 F) → 2 A 1 ( 2 G), 4 A 2 ( 4 F) → 2 E( 2 G) and 4 A 2 ( 4 F) → 4 T 1 ( 4 P) electronic transitions. The crystal field Dq and Racah parameter B were obtained from the spectra and Tanabe-Sugano energy level diagram. The highlights of the present work are the relatively simple sample obtention process as well as its reproducibility and the high photoluminescence quantum efficiency (near to 1.0) together with the intense and broad emission band which make the MgGa 2 O 4 a very attractive material for use as tunable media.

Fotoluminescência em amostras policristalinas de galato de magnésio dopado com Ni2

The photoluminescence of MgGasO4:Ni2+ are presented in this article. The observed bands are attributed to the 1T2 (1D) ® 3T2 (3F) and 1T2 (1D) ® 3T1 (3F) spin-forbidden transitions and located in the visible and infrared regions, respectively. Absorption spectra obtained from diffuse reflectance measurements show bands associated with 3A2 (3F) ® 3T1 (3F) and 3A2 (3F) ® 3T2 (3F) transitions and a weak structure assigned to 3A2 (3F) ® 1E (1D) transition. All the observed transitions are identified with energy levels of Ni2+ in octahedral sites of magnesium gallate. From the Tanabe-Sugano energy diagrams for a d8 configuration, the crystal field Dq and interelectronic repulsion B and C parameters were calculated. We also present, for comparison, previous results of Cr3+ (d3 electronic configuration), Fe3+ (d5) and Co2+ (d7) ions in this host lattice for samples prepared with the same ceramic method.

Na7Li 1 1Π(B) electronic state Λ-doubling analysis

Abstract Λ-doubling for a particular vibrational energy level of the Na 7 Li 1 1 Π(B) electronic state is calculated using a simple theory. This 1 1 Π(B) state is strongly perturbed by the 3 1 Σ + (C) electronic state so that the Λ-doubling constant cannot be obtained by a direct reduction of the difference between e and f levels as a function of J ( J + 1). A comparison between experimental data and values obtained in this simple theory shows reasonable agreement.

The costa ribeiro effect and allied phenomena

Abstract This is a brief account of Costa Ribeiro Effect (CRE) and allied phenomena; it is intended to give a comprehensive and clear description of this effect and allied phenomena, and to be a guide to the study and literature of them to those that are interested in dielectric and organic semiconductors, since they influence the physical properties of such substances, causing puzzling effects when Ignored. Besides, practical applications may also attract those that are interested in such aspects.

Temperature and impurity concentration effects on Mg(1−x)CoxGa2O4 photoluminescence

Ceramic materials doped with magnetic ions that present emission in the visible and near‐infrared spectral regions are very attractive due to their inherent tunability. Possible applications include their utilization as optoelectronic and display devices, as spintronic material, in signal transmission and information storage, in the fabrication of special papers, as dosimetric materials and room temperature solid state lasers. Materials doped with tetrahedrally coordinated Co2+ present wide bands originated from electronic transitions in the ionic unfilled 3d electronic shell. The Co2+ 3d electrons are outside of the ion core and therefore their optical properties are directly affected by static and dynamic properties of ligand anions. The magnesium gallate MgGa2O4 is a partially inverted spinel described as a AB2O4 material with two possible positions for A2+ and B3+ cations. Polycrystalline MgGa2O4 : Co2+ samples were produced by solid‐state reactions between ultra‐pure raw oxides MgO, β‐Ga2O3 and the d...