In this paper we performed steady-state and time-resolved near-field scanning optical spectroscopy on GaN/AlN quantum dot (QD) structures and InGaN/GaN multiple quantum wells (MQWs). The morphology of the QD sample is composed of islands in the 500-1000 nm range on the top of which dots nucleate. These islands are separated by slightly smaller structures showing less intense luminescence. Time-resolved photoluminescence mapping (spatially and spectrally resolved) of InGaN/GaN MQW structures revealed bright and dark spots with nearly constant peak energy and time decay. The results suggest that the bright and dark spots of the samples correspond to islands with higher and lower absolute number of QD-like regions where the excitons are localized.