C. T. M. Ribeiro

Optical spectroscopy of Er3+ and Yb3+ co-doped fluoroindate glasses

Optical absorption, Stokes, and anti-Stokes photoluminescence were performed on Er3+–Yb3+ co-doped fluoroindate glasses. For compounds prepared with a fixed 2 mol % ErF3 concentration and YbF3 contents ranging from 0 to 8 mol %, important upconversion processes were observed as a function of temperature and photon excitation energy. Based on the experimental data, two mechanisms for the upconversion (or anti-Stokes photoluminescence) processes were identified and analyzed in detail. At high Yb contents, the upconversion mechanisms are mostly determined by the population of the 2F5/2 levels of Yb3+ ions (or 4I11/2 levels of Er3+ ions, by energy transfer) regardless of the photon excitation energy and temperature of measurement. Moreover, green and red light emission have similar intensities when a large Yb3+ content is present.

Improved laser-heated pedestal growth system for crystal growth in medium and high isostatic pressure environment

A modified apparatus for single-crystal-fiber growth in an isostatic gaseous environment and for a large range of pressure (100 mbar up to 100 bar) using a floating-zone-type method known as laser-heated pedestal growth is described. The difficulties and advantages of its design are discussed through examples of crystal growth of some oxide materials.

Spectroscopic study of Nd-doped amorphous SiN films

Neodymium-doped amorphous silicon-nitrogen (a-SiN) thin films have been prepared by cosputtering a (Si+Nd) target in a nitrogen atmosphere. After deposition the films were submitted to cumulative thermal annealing treatments and investigated in detail by Raman scattering spectroscopy, optical transmission, x-ray photoelectron spectroscopy (XPS), and photoluminescence techniques. Additional information was also obtained from ion beam analyses such as Rutherford backscattering spectrometry and nuclear reaction analysis. As a result of the deposition method and conditions, the films are amorphous and contain ≈0.8 at % of neodymium. Actually, Raman scattering measurements indicate that the present films remain amorphous even after thermal anneal at 1000 °C. The electronic states at the top of the valence band of the Nd-doped a-SiN films were investigated by XPS, which indicates that most of the neodymium present in the a-SiN host stays under the trivalent (Nd3+) form. As a consequence, relatively strong and w...

Laser-induced generation of micrometer-sized luminescent patterns on rare-earth-doped amorphous films

Room-temperature photoluminescence has been achieved from rare-earth-doped amorphous (a‐) GeN films. The samples were prepared by the radio-frequency-sputtering method, and light emission from the rare-earth (RE) centers was obtained after irradiating the films with a highly focused laser beam. As a result of this laser annealing procedure, almost circular holes with approximately 1‐μm diameter were produced on the surface of the a‐GeN films. The area nearby these holes correspond to crystalline Ge and coincide with the regions, where relatively strong RE-related luminescence takes place. These laser-annealed areas can be easily and conveniently managed in order to generate different microscopic luminescent patterns. Depending on the RE ion employed, visible and near-infrared light emission were obtained from the patterns so produced. The development of these micrometer-sized luminescent centers, as well as their probable mechanisms of excitation-recombination, will be presented and discussed. The importa...

Spectroscopy of InF3 based glasses containing a large amount of GdF3

Abstract Glass formation in the pseudo ternary system ZnF 2 –GdF 3 –BaF 2 –InF 3 and other complex systems stabilized by NaF, CaF 2 , AlF 3 and YF 3 have been investigated. Samples with greater stability have been prepared and their properties measured. Optical absorption and emission spectra of Gd 3+ ions doped glasses with 2, 4, 10 and 20% concentrations have been measured. Using the Judd–Ofelt theory and the experimental oscillator strengths, the Judd–Ofelt parameters have been calculated. The emission of Gd 3+ ions from 6 I and 6 P has been detected and the lifetime has been measured.

Espectroscopia óptica de vidros fluoroindatos dopados com íons Er3+ e Yb3+

Optical spectroscopy in the 400-1700nm wavelength range was performed on rare earth doped heavy metal fluoride (HMF) glasses. In the present work In-based fluoride glasses with a fixed 2 mol % YbF3 concentration and an ErF3 content ranging from 0 to 8 mol % were investigated. According to the experimental spectroscopic data a dependence in the absorption coefficient, the photoluminescence intensity and in the radiative lifetime could be verified as a function of the ErF3 content. In addition, at liquid nitrogen temperature, light emission corresponding to indirect transitions in the infrared energy range could be easily observed as a consequence of the low phonon frequency characteristic of this class of fluoride glasses. For all the studied compositions, strong upconversion to the green and red light was observed by pumping these Er3+- and Yb3+-doped HMF glasses with 790 and 980nm photon sources.

Optoelectronic and structural properties of Er-doped sputter-deposited gallium–arsenic–nitrogen films

Erbium-doped gallium–arsenic–nitrogen thin films were prepared by cosputtering a crystalline GaAs target partially covered with small pieces of metallic erbium in an Ar+N2 atmosphere. The films were deposited near room temperature and under increasing partial pressures of nitrogen P(N2). The investigation of the films included ion beam analysis, optical spectroscopy in the infrared–visible–ultraviolet energy ranges, Raman scattering, and photoluminescence measurements. According to the experimental results, all films present an amorphous structure and nitrogen contents that scale with P(N2). Increasing amounts of nitrogen induce the widening of the optical band gap and a systematic redshift of the Raman signal of the films considered. The intensity of the Er-related light emission at ∼0.8 eV also increases at higher nitrogen contents. A detailed study of the absorption bands in the infrared region allowed the identification of different vibration modes involving gallium, arsenic, and nitrogen atoms. The c...