This thesis covers several aspects of the electronic and electromagnetic properties of doped graphene; peculiar properties of the 2D plasmon, strong quasi-particle interactions with these plasmons and finally the possibility of transforming these plasmons into radiative modes. The thesis is imbued with comparisons with available experiments and offers a solution to the longstanding problem of plasmon emission prosess seen in ARPES experiments. A graphene is a 2D single-layer hexagon crystal, with two atoms in the unit cell. The electrostatic doping fills its π∗ / π bands with the electrons / holes, enabling the well known intraband Dirac plasmon. When the graphene is doped with alkali metals, its band structure introduces a metallic σ band, which profusely fills the graphene π∗ band with the electrons. In this way, two 2D electron gases interplay, which makes the plasmonic properties of doped graphene even more interesting. Moreover, the simulated spectra of electronic excitations in the graphene intercalated with potassium [KC8 (2x2)] and caesium [CsC8 (2x2)] atoms exhibit very intensive Dirac plasmon, which dominates the IR frequency range of the electron excitations spectra. On the other hand, the acoustic plasmon also dominates the IR frequency range of the KC8 spectra, unlike in the CsC8. More precisely, the acoustic plasmon does not appear at all in the CsC8 spectra of, and a mechanism responsible for its disappearance is based on the interlayer interband screening due to the electronic excitations. In addition to plasmons in the infrared region, we shall also study interband plasmons in the ultraviolet region, in various graphene intercalates such as KC8, CsC8, LiC2 and LiC6. A comparative analysis with electrostatically doped graphene will also be done. Furthermore, when these systems are electrostatically doped with electrons / holes, their spectra of electronic excitations change drastically as a function of doping. Here we also study the intercation between electrons / holes in π / π ∗ bands in electrostatically or chemically doped graphene (KC8) with the electronic excitations (focused to the Dirac plasmon). The electron / hole spectra were calculated using a newly developed G0W0 approximation, which corrects the DFT Green’s function in terms of the induced correlation self energy, which simulates ARPES measurements. In this thesis, we shall see how the electron doping of the graphene π∗ band affects the renormalization of Fermi and Dirac group velocites, kinks at the Fermi energy and widths of the hole decays in the π and π∗ bands. Finally, we shall see that both deformation and abrupt increase in the decay width of the π band just below the Dirac point is due to the Dirac plasmon emission. These theoretical observations will be compared with the results of other theoretical and experimental studies. In this thesis, we also investigate the electromagnetic properties of doped graphene and the intensities of IR active plasmons in graphene nanoribbons. Plasmons in the doped graphene are non-radiative (evanescent) modes that cannot be excited directly by photons, but only indirectly, e.g. by scattering of the IR photon stream. In this way the photons scattered in the near-field region couple to the plasmons and excite them. Yet another way to excite plasmons is to slice the graphene into nanoribbons that support dipole-active plasmons. In the end, we shall study the IR active plasmonic resonances in the 1D array of the KC8 nanoribbons, and compare them with experimental measurements. Also, the synthesis of the KC8 nanoribbons will be discussed.