Erbium nitride (ErN) is a rare-earth metal mononitride continuing to receive interest due to its unique electronic, magnetic, and optical properties. ErN has shown promise in the development of new functional materials for optoelectronic and spintronic devices. Here, we report on the optical properties of ErN crystals, grown by sublimation and probed by photoluminescence (PL) spectroscopy at both room temperature and 180 K. Multiple transition lines were observed between 2 and 4.5 eV. Using the PL results together with reported calculations, a coherent picture for the band structure at the Γ-point for ErN crystals was derived. PL results revealed that ErN has a minimum direct energy gap of 2.41 eV and a total of two valence bands and two conduction bands at the Γ-point separated by about 0.15 eV and 0.34 eV, respectively. These transitions reveal optical properties of ErN in the UV region and its band structure at the Γ-point.