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.

The three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic structure with a period of 200 nm, that exhibit photonic stopbands around 600 nm. We present measurements of the optical gain of CdS quantum dots (QDs) embedded inside the interstitials between the silica spheres. Unlike the usual gain spectra of CdS QDs in glass matrices, which display maximum gain at energies of the first quantum-confined transitions, for QDs embedded in photonic crystals the gain maximum is shifted toward the high-frequency edge of the photonic stopband (2.2 eV) far below the absorption edge of the semiconductor (2.5 eV). Studies of temperature, intensity, and orientation dependencies of the gain spectra allow one to ascribe the observed effect to gain enhancement caused by multiple coherent Bragg scattering of light in the periodic photonic crystal.

We discuss applicability of the variable stripe length method to experimental investigation of optical gain in a luminescent layer that behaves like a planar waveguide. We show that an interplay between the output direction of guided light modes and the numerical aperture of the collection optics may lead to an artifact manifesting itself as an apparent but false gain. We propose a way to circumvent this inconvenience by using a “shifting excitation spot” complementary measurement. The method is demonstrated on a layer of Si nanocrystals embedded into a synthetic silica plate.

In this paper, we discuss the validity of the band structure concept in silicon nanocrystals a few nanometers in size. We introduce a general method which allows reconstruction of a fuzzy electronic band structure of nanocrystals from ordinary real-space electronic structure calculations. A comprehensive study of the fuzzy 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 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 a diameter larger than $\approx$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. DOI: http://dx.doi.org/10.1103/PhysRevB.87.195420 ©2013 American Physical Society