The main objective of the dissertation is to present work describing theoretical studies of planar structures with erbium doped regions and characterization of erbium doped particles. Numerical models of erbium doped Al2O3 were formulated, taking into account the up-conversion from the metastable Er3+ levels and the cross-relaxation process as a mechanism of energy transfer between Er3+ ions. The influence of amplified spontaneous emission (ASE) is...