The gamma decay of the giant dipole resonance (including its low-energy tail region) is an important tool to probe the properties of these states, and thus to test in detail the existing predictions. This paper focuses on two main aspects concerning the electric dipole excitation in nuclei. One is the study of the isospin character of the low-energy tail of the Giant Dipole Resonance (GDR), the so-called pygmy resonance, and the other is the isospin mixing of nuclear systems at finite temperature. In the first case, the pygmy resonance was populated using the inelastic-scattering reaction induced by ¹⁷O beams at 20 MeV/u. Comparison is made with data obtained with (α, α′γ) and (γ, γ′) reactions. In the second case, the gamma decay of the GDR in thermalized nuclear systems, formed in fusion-evaporation reactions, was used to investigate the isospin mixing in ⁸⁰Zr. For this work the reactions ⁴⁰Ca + ⁴⁰Ca at 3.4 MeV/u and ³⁷Cl + ⁴⁴Ca at 2.6 MeV/u were employed.