L.P. Sosman

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.

Structural and vibrational study of chromium doped elpasolite crystals Cs2NaAlF6

The influence of site-symmetry and electron phonon coupling in Cs2NaAlF6:Cr3+ is probed by correlation of optical and structural measurements. Based on neutron and x-ray analysis the structure is a distorted R3m¯, exhibiting a unique stacking interaction. Selection rules have been used to assign the Raman-active zone-center vibrations. Although local and bulk mode frequencies differ slightly, indicating that the guest Cr3+ ion does not significantly perturb the host structure, vibrational analysis indicates the Cr3+ ion is coupled to the first coordination sphere of the Al–F lattice.

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 properties of LiGaTiO4: Fe3+

Abstract Emission, excitation and photoacoustic absorption data are presented. The radiative decay time at room temperature and 77 K are measured. The nonradiative relaxation time and the characteristic thermal-diffusion time are obtained. The near IR fluorescence band observed in this iron doped compound is assigned to the symmetry and spin-forbidden 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transitions of tetrahedrally coordinated Fe3+ 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.

Vibrational Analysis of the Elpasolites Cs2NaAlF6 and Cs2NaGaF6 Doped with Cr3+ Ions by Fluorescence Spectroscopy

Interest in 3d transition metal impurities in ionic crystals has increased due to their important role in the laser activity of these materials. Moreover, recent advances in tunable solid-state lasers and high-power semiconductor laser diode arrays have generated a strong interest in investigating new compounds that emit in the visible and near-infrared spectral regions. In particular, many optical studies have been devoted to Cr3+-doped fluoride crystals as a consequence of the high quality of some Cr3+-based laser materials. In the present investigation, the low-temperature emission spectra of Cr3+ ions in the hexagonal elpasolites Cs2NaAlF6 and Cs2NaGaF6 have been measured. Each compound has two crystallographically inequivalent octahedral sites for the Al3+ and Ga3+ ions that can be occupied by Cr3+ ions. For both materials, the luminescence spectrum presents two zero-phonon lines accompanied by a well-defined vibrational structure. The different peaks of the emission broad band are described in terms of phonons of the lattice and normal modes of the octahedral complex [CrF6]3−. A detailed analysis of the vibrational structure observed leads to the conclusion that the 2E and 4T2 excited states of the [CrF6]3− ion are displaced along the eg and a1g and probably the t2g coordinates.

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.

Neutron Powder Diffraction Measurements of the Spinel MgGa2O4:Cr3+ - A Comparative Study between the High Flux Diffractometer D2B at the ILL and the High Resolution Powder Diffractometer Aurora at IPEN

Optical materials that emit from the visible to the near-infrared spectral region are of great interest due to their possible application as tunable radiation sources, as signal transmission, display, optoelectronics signal storage, cellulose industry as well as in dosimetry. One important family of such systems are the spinel compounds doped with Cr3+, in which the physical the properties are related to the insertion of punctual defects in the crystalline structure. The purpose of our work is two fold. First, we compare the luminescence of the MgGa2O4-Ga2O3 system with the single phase Ga2O3 and MgGa2O4 and relate structural changes observed in MgGa2O4-Ga2O3 system to the optical properties, and secondly, to compare the neutron powder diffraction results obtained using two diffractometers: D2B located at the ILL (Grenoble, France) and Aurora located at IPEN (Sao Paulo, Brazil). In the configuration chosen, Aurora shows an improved resolution, which is related to the design of its silicon focusing monochromator.

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.

Structural and photoluminescent properties of the MgGa 2 O 4 :Co 2+ ceramic compound revisited after two decades

In this work, we revisit and show how the structural and photoluminescent properties of the MgGa2O4 ceramic compound have been kept unchanged for more than two decades. The obtained results confirm the high quality, radiative efficiency, and chemical stability of this ceramic, proving that the material is a strong candidate to be used in optical device applications with relatively long useful life.