A spot on a layer of a 2D semiconductor material deposited on a substrate is irradiated so as to generate excitons, so that photons are emitted from the layer. The photoluminescence spectrum is recorded for different values of the charge carrier concentration in the layer. The modulation of the charge carrier concentration may be realized by modulating the output power of the light source used to irradiate the sample. The relation is recorded between the ratio of the photoluminescence intensity of a first peak in the spectrum related to radiative recombination from indirect bandgaps to the intensity of a second peak in the spectrum related to radiative recombination from direct bandgaps, and the carrier concentration. This relation is fitted to a model of the ratio that takes into account multiple recombination mechanisms, radiative and non-radiative. From this process, the trap density within the bandgap is derived.