Analysis of the experimental absorption data in GaSe showed that, at low temperature (110 K), intercalation process of sodium atoms, as well as the presence of silicon impurities and native defects such as Ga vacancies and interstitials in a high concentration, result effectively in the broadening of the ground state of the direct exciton and the decrease of exciton peak intensity. On the other hand, increasing temperature leads to the increase of the broadening parameter Λ and a shift of both the position of exciton peaks E_ex, and the band gap E_g toward longer wavelength. These effects can be ascribed to exciton-phonon and exciton-imperfection interactions. Furthermore, acceptable and reasonable values of the temperature coefficient β of the above-mentioned parameters were determined and are equal to +8.64×10⁻⁴, −3.52 × 10⁻⁴ and −3.38 × 10⁻⁴ eVK⁻¹, respectively.