Luminescence of semiconductors is nowadays based on very firm background of solid state physics. The purpose of this book is to introduce the reader to the study of the physical principles underlying inorganic semiconductor luminescence phenomena. It guides the reader starting from the very introductory definitions over luminescence of bulk semiconductors and finishing at the up-to-date luminescence spectroscopy of individual nanocrystals. The book thus set the aim of filling the gap between general textbooks on semiconductors and dedicated advanced monographs. At the beginning, important knowledge of the solid state like lattice vibrations, exciton–phonon interaction and the concept of configurational coordinate are reviewed. Self-contained chapters are then devoted to exciton luminescence processes, effects of high optical excitation, and to an overview of the essentials of electroluminescence. Apart from spontaneous luminescence, special attention is paid to stimulated emission and investigation of optical gain. Considerable space is given also to optical processes in low-dimensional semiconductor structures. The book has been written by experimentalists and is destined primarily for experimentalists, too. Visual approach using schemes and graphs is used frequently instead of rigorous mathematical derivation. The chapter devoted to experimental techniques of luminescence spectroscopy is rich in content. Whenever it makes sense, the accent is put on how to extract from the appearance of luminescence emission spectrum (shapes of emission lines, their behaviour with varying experimental parameters) as much information on microscopic origin of luminescence as possible. The book cannot be regarded as a comprehensive monograph on semiconductor luminescence; selected examples from extremely rich literature only have been chosen to illustrate the text.

Silicon nanocrystals are an extensively studied light-emitting material due to their inherent biocompatibility and compatibility with silicon-based technology. Although they might seem to fall behind their rival, namely, direct band gap based semiconductor nanocrystals, when it comes to the emission of light, room for improvement still lies in the exploitation of various surface passivations. In this paper, we report on an original way, taking place at room temperature and ambient pressure, to replace the silicon oxide shell of luminescent Si nanocrystals with capping involving organic residues. The modification of surface passivation is evidenced by both Fourier transform infrared spectroscopy and nuclear magnetic resonance measurements. In addition, single-nanocrystal spectroscopy reveals the occurrence of a systematic fine structure in the emission single spectra, which is connected with an intrinsic property of small nanocrystals since a very similar structure has recently been observed in specially passivated semiconductor CdZnSe nanoparticles. The organic capping also dramatically changes optical properties of Si nanocrystals (resulting ensemble photoluminescence quantum efficiency 20%, does not deteriorate, radiative lifetime 10 ns at 550 nm at room temperature). Optically clear colloidal dispersion of these nanocrystals thus exhibits properties fully comparable with direct band gap semiconductor nanoparticles.

We introduce a general method which allows reconstruction of electronic band structure of nanocrystals from ordinary real-space electronic structure calculations. A comprehensive study of band structure of a realistic nanocrystal is given including full geometric and electronic relaxation with the surface passivating groups. In particular, we combine this method with large scale density functional theory calculations to obtain insight into the luminescence properties of silicon nanocrystals of up to 3 nm in size depending on the surface passivation and geometric distortion.We conclude that the band structure concept is applicable to silicon nanocrystals with diameter larger than ≈ 2 nm with certain limitations. We also show how perturbations due to polarized surface groups or geometric distortion can lead to considerable moderation of momentum space selection rules.