Optical spectroscopy under varying temperature is used to investigate samples containing planes of self-assembled Ga1−xInxN quantum dots (0.15<x<0.20), embedded in a GaN matrix. The samples have been grown by molecular beam epitaxy on sapphire substrates and the nano-islands have been obtained by the Stranski-Krastanov growth mode transition. Half-widths at half maximum as small as 0.05 eV are obtained for photoluminescence (PL) lines at T