Intro -- Populärvetenskaplig sammanfattning -- Abstract -- Preface -- Acknowledgements -- Contents -- List of Abbreviations -- 1 An Introduction to Semiconductors -- 1.1 Crystal structure -- 1.2 Electronic structure -- 1.3 Engineering of the electronic structure -- 1.4 Excitons -- 1.5 Crystal vibrations and phonons -- 1.6 Recombination processes -- 2 Dilute Nitride Semiconductors -- 2.1 N-induced modifications of the electronic structure -- 2.2 Recombination processes in dilute nitrides -- 3 Nanowires -- 3.1 Growth of nanowires -- 3.2 Crystal structure -- 3.3 Nanowire heterostructures -- 3.4 Recombination mechanisms in nanowires -- 3.5 Strain in nanowires -- 3.6 Dielectric mismatch -- 4 Quantum Dots -- 4.1 Electronic structure -- 4.2 Charge configurations -- 4.3 Quantum dots as sources of non-classical light -- 4.4 Random population model -- 5 Modelling Excitons in Quantum Dots -- 5.1 Strained quantum dots -- 5.2 Exchange interaction -- 5.3 Excitons in a magnetic field -- 6 Experimental Techniques -- 6.1 Electron microscopy -- 6.2 Spectroscopy techniques -- 6.3 Optically detected magnetic resonance -- 6.4 The Hanbury Brown and Twiss experiment -- Bibliography -- Papers -- List of publications included in the thesis -- List of publications excluded from the thesis -- Papers.