Properties of fluorescent nuclear track detectors (FNTDs) made of Al2O3:C, Mg crystals are investigated after irradiation in mono-energetic and broad spectrum neutron fields. Two types of neutron converters were investigated, high density polyethylene and natural LiF. Imaging in fluorescence contrast is performed using laser scanning confocal detection. Individual tracks induced by recoil protons, alpha particles and tritium ions are identified and counted. Two approaches to median neutron energy estimation using track density as a function of scanning depth and the ratio of track densities for two different converters are discussed.