Built properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first principles beyond density functional theory. The quasi particle aspect is described in the framework of a quasi particle method (the GW approximation). The calculated band gap energy is similar to 0.8 eV whereas significance in the optical absorption occurs at similar to 1.2 eV, which are consistent with both luminescence and absorption results. The Bethe-Salpeter equation is utilized to model the two particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN. (C) 2014 Elsevier B.V. All rights reserved.