We have investigated exciton localization in binary GaN nanorods using micro- and time-resolved photoluminescence measurements. The temperature dependence

We have observed the high-temperature $(T=300\mathrm{K})$ photoluminescence (PL) spectra from free to Mn-related acceptor pair transitions in ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{N}$ layers (where $x\approx 0.2\%–0.6\%$ ) grown on sapphire (0001) substrates using the plasma-enhanced molecular-beam epitaxy technique. Luminescence from an Mn acceptor level in ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{N}$ layer with a low Mn content was observed at around $E=3.08\mathrm{eV}$ in the PL spectra. When compared to the PL from undoped GaN, the excitation, temperature-dependent PL at $E=3.08\mathrm{eV}$ provides convincing evidence for a neutral Mn acceptor-bound hole character. The binding energy of the Mn acceptor-bound holes of $E=330\mathrm{meV}$ is in good agreement with an ionization energy of $E=402\mathrm{meV}$ obtained using effective mass theory of shallow impurity states for the hydrogen model. In addition, analysis of the PL intensities of an acceptor-bound hole in a ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{N}$ layer with $x\approx 0.6\%$ gave an activation energy of $E=310\mathrm{meV}$ , which indicates that the acceptor-bound hole with a binding energy of $E=310\mathrm{meV}$ was dissociated due to thermal quenching.