Thermal treatment of compacted GeO 2 powder under argon flow leads to the growth of a dense distribution of microwires and nanowires on the sample surface. Extended treatment causes the formation of more complex structures, including arrays of nanoneedles. Enhanced cathodoluminescence emission is associated with the wires and needles, which show a component at 2.72 eV not observed for the untreated material.

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High aspect ratio GeO 2 nano-and microwires have been grown by thermal treatment at 600 • C of compacted Ge powder under argon flow. The wires have cross-sectional dimensions from less than 100 nm to about 1 μm, depending on the duration of the treatment, and lengths of up to about 2000 μm. Waveguide behaviour of the wires was demonstrated for visible light, which shows the potential applications of these structures for optical nanodevices.

Rare earth (RE) doped gallium oxide and germanium oxide micro- and nanostructures, mostly nanowires, have been obtained and their morphological and optical properties have been characterized. Undoped oxide micro- and nanostructures were grown by a thermal evaporation method and were subsequently doped with gadolinium or europium ions by ion implantation. No significant changes in the morphologies of the nanostructures were observed after ion implantation and thermal annealing. The luminescence emission properties have been studied with cathodoluminescence (CL) in a scanning electron microscope (SEM). Both β-Ga(2)O(3) and GeO(2) structures implanted with Eu show the characteristic red luminescence peak centered at around 610 nm, due to the (5)D(0)-(7)F(2) Eu(3+) intraionic transition. Sharpening of the luminescence peaks after thermal annealing is observed in Eu implanted β-Ga(2)O(3), which is assigned to the lattice recovery. Gd(3+) as-implanted samples do not show rare earth related luminescence. After annealing, optical activation of Gd(3+) is obtained in both matrices and a sharp ultraviolet peak centered at around 315 nm, associated with the Gd(3+) (6)P(7/2)-(8)S(7/2) intraionic transition, is observed. The influence of the Gd ion implantation and the annealing temperature on the gallium oxide broad intrinsic defect band has been analyzed.

GeO2 nanowires doped with Eu, Er, or Mn, as well as codoped with each of these ions and Sn, have been grown by a catalyst-free vapor−solid process. The incorporation of Sn has been found, in all cases, to favor the formation of straight wires, which make them more appropriate for waveguiding purposes. Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the complex light emission from the nanowires. Rare earth ion emission lines and defect related bands have been observed in Eu- and Er-doped nanowires. Optical coupling and waveguiding behavior of Er-doped GeO2 nanowires have been demonstrated for green laser light and for Er excited luminescence in the wires. In Mn-doped GeO2 nanowires a band centered at 1.75 eV had been detected. X-ray photoemission measurements show the presence of GeO oxide in the surface of the GeO2 wires, which influences their native defect structure.