Ga 2 O 3 nano-and microwires with diameters ranging from tens of nanometers to about one micron and lengths of up to tens of microns, have been obtained by sintering Ga 2 O 3 powder under argon flow. The structures have been investigated by cathodoluminescence in the scanning electron microscope. The samples showed the violet-blue emission characteristic of Ga 2 O 3 and a red emission at 1.73 eV dominant in the nanowires and other nano-and microstructures formed during the sintering treatment. At temperatures below 210 K, this band exhibits sharp peaks separated by 20 meV. This observation suggests the exchange of phonons in the recombination process.

Red luminescence emission from chromium doped ␤-Ga 2 O 3 nanowires has been studied by means of photoluminescence ͑PL͒ techniques. PL excitation shows several bands in the ultraviolet-visible region. Time decay values, obtained by time resolved PL, at different temperatures fit a three level model with thermal population of the upper level from the middle one. From the results, the origin of the emission is assigned to Cr 3+ ions in the ␤-Ga 2 O 3 host, and values for the energy level separation and Huang-Rhys factor of the broad 4 T 2 -4 A 2 emission are estimated.

Optical energy gaps are measured for high-quality Al 1−x In x N-on-GaN epilayers with a range of compositions around the lattice match point using photoluminescence and photoluminescence excitation spectroscopy. These data are combined with structural data to determine the compositional dependence of emission and absorption energies. The trend indicates a very large bowing parameter of Ϸ6 eV and differences with earlier reports are discussed. Very large Stokes' shifts of 0.4-0.8 eV are observed in the composition range 0.13Ͻ x Ͻ 0.24, increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric field.

The intensity of Eu-related luminescence from ion-implanted GaN with a 10nm thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at 1300°C. Photoluminescence (PL) and PL excitation (PLE) studies reveal a variety of Eu centers with different excitation mechanisms. High-resolution PL spectra at low temperature clearly show that emission lines ascribed to D05-F27 (∼622nm), D05-F37 (∼664nm), and D05-F17 (∼602nm) transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the D05-F27 multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at 356nm, and a broad subedge absorption band centred at ∼385nm. Marked differences in the shape of the D05-F27 PL multiplet are demonstrated by selective excitation via the continuum/exciton states and the below gap absorption band. The four strongest lines of the multiplet are shown to consist of two pairs due to different Eu3+ centers with different excitation mechanisms.

Cathodoluminescence and photoluminescence techniques have been used to investigate room temperature light emission from beta-Ga(2)O(3):Eu nanostructures, which were obtained by two methods. In one of them, a mixture of Ga(2)O(3)/Eu(2)O(3) powders was used as precursor material and annealed under an argon flow. In the other one, undoped beta-Ga(2)O(3) nanostructures were first obtained by thermal oxidation of metallic gallium and europium was subsequently incorporated by a diffusion process. Room temperature luminescence at 610 nm due to Eu(3+) intraionic transitions from beta-Ga(2)O(3):Eu has been observed. Waveguiding of this red emitted light through the structures was shown.