$\beta \text{‐}{\mathrm{Ga}}_2{\mathrm{O}}_3$ 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 ${\mathrm{Ga}}_2{\mathrm{O}}_3$ 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 ${\mathrm{Ga}}_2{\mathrm{O}}_3$ 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.

The intensity of Eu-related luminescence from ion-implanted GaN with a $10\mathrm{nm}$ thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at $1300°\mathrm{C}$ . 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 ${}^{5}D_0\text{-}{}^{7}F_2$ $(\sim 622\mathrm{nm})$ , ${}^{5}D_0\text{-}{}^{7}F_3$ $(\sim 664\mathrm{nm})$ , and ${}^{5}D_0\text{-}{}^{7}F_1$ $(\sim 602\mathrm{nm})$ transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the ${}^{5}D_0\text{-}{}^{7}F_2$ multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at $356\mathrm{nm}$ , and a broad subedge absorption band centred at $\sim 385\mathrm{nm}$ . Marked differences in the shape of the ${}^{5}D_0\text{-}{}^{7}F_2$ 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 ${\mathrm{Eu}}^{3+}$ centers with different excitation mechanisms.

Red luminescence emission from chromium doped $\beta \text{‐}{\mathrm{Ga}}_2{\mathrm{O}}_3$ nanowires has been studied by means of photoluminescence (PL) 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 ${\mathrm{Cr}}^{3+}$ ions in the $\beta \text{‐}{\mathrm{Ga}}_2{\mathrm{O}}_3$ host, and values for the energy level separation and Huang-Rhys factor of the broad ${}^{4}T_2\text{‐}{}^{4}A_2$ emission are estimated.

Er and Cr doped $\beta \text{-}{\mathrm{Ga}}_2{\mathrm{O}}_3$ nano- and microwires have been grown by thermal treatments of ${\mathrm{Ga}}_2{\mathrm{O}}_3$ powder containing a fraction of ${\mathrm{Er}}_2{\mathrm{O}}_3$ powder or in the presence of ${\mathrm{Cr}}_2{\mathrm{O}}_3$ powder, respectively. Doping gives rise to the characteristic red photoluminescence (PL) of ${\mathrm{Cr}}^{3+}$ ions at about $700\mathrm{nm}$ and to green emission of ${\mathrm{Er}}^{3+}$ at about $555\mathrm{nm}$ . Waveguiding of the ion related PL light excited in the wires has been studied for wires with different sizes. Waveguide behavior for incident visible light of different wavelengths was demonstrated.