Several hundred thousands of tons of ZnO are used by per year, e.g. as an additive to concrete or to rubber. In the field of optoelectronics, ZnO holds promises as a material for a blue/UV optoelectronics, alternatively to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits, which are transparent in the visible or for semiconductor spintronics. The main problem is presently, however, a high, reproducible and stable p-doping. We review in this contribution partly critically the material growth, fundamental properties of ZnO and of ZnO-based nanostructures, doping as well as present and future applications, with emphasis on the electronic and optical properties including stimulated emission.

ZnO is presently experiencing a research boom with more than 2000 ZnO-related publications in 2005. This phenomenon is triggered, for example, by hope to use ZnO as a material for blue/UV optoelectronics as an alternative to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits that are transparent in the visible or for semiconductor spintronics. Currently, however, the main problem is to achieve high, reproducible and stable p-doping. Herein, we critically review aspects of the material growth, fundamental properties of ZnO and ZnO-based nanostructures and doping as well as present and future applications with emphasis on the electronic and optical properties including stimulated emission.

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A weak acid selective etching strategy was put forward to fabricate oxide-based hollow nanoparticles (HNPs) using core/shell nanostructures of active metal/oxide nanoparticles as sacrificial templates. ZnO-based HNPs, including pure ZnO, Au/ZnO, Pt/ZnO, and Au/Pt/ZnO HNPs with diameter below 50 nm and shell thickness below 6 nm has been first achieved at low temperature. The diameter, thickness, and even sizes of ZnO and noble metal ultrafine crystals of HNPs can be well adjusted by the etching process. Synchronous with the formation of HNPs, the internal metal-semiconductor interfaces can be controllably eliminated (Zn-ZnO) and reconstructed (noble metal-ZnO). Excitingly, such microstructure manipulation has endued them with giant improvements in related performances, including the very strong blue luminescence with enhancement over 3 orders of magnitude for the pure ZnO HNPs and the greatly improved photocatalytic activity for the noble metal/ZnO HNPs. These give them strong potentials in relevant applications, such as blue light emitting devices, environment remediation, drug delivery and release, energy storage and conversion, and sensors. The designed fabrication procedure is simple, feasible, and universal for a series of oxide and noble metal/oxide HNPs with controlled microstructure and improved performances.

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The light emission of ZnO under high one‐ and two‐quantumexcitation is investigated in the temperature region from 4 to 300 K. Emission bands are observed which can be attributed to the interactions of free excitons with phonons, free excitons and free electrons, and of bound excitons with phonons and free and bound electrons.

The second edition, which appeared in 2005 and contains substantial updates and amendments compared to the first one and its corrected reprints, was again favourably received by the students and the scientific community worldwide.As a consequence, the present third edition became necessary. The changes introduced are, compared to the sedond edition, more limited, among others because the time elapsed between second and third edition is much shorter than the time between first and second one.The main chances concern the following points: The discussion about the density, at which an electron-hole plasma is formed, has been up-dated, in the section about photonic crystals a few comments on meta-materials have been added, several new and timely references have been included and some of the misprints have been removed.

The research on ZnO has a long history but experiences an extremely vivid revival during the last 10 years. We critically discuss in this didactical review old and new results concentrating on optical properties but presenting shortly also a few aspects of other fields like transport or magnetic properties. We start generally with the properties of bulk samples, proceed then to epitaxial layers and nanorods, which have in many respects properties identical to bulk samples and end in several cases with data on quantum wells or nano crystallites. Since it is a didactical review, we present explicitly misconceptions found frequently in submitted or published papers, with the aim to help young scientists entering this field to improve the quality of their submitted manuscripts. We finish with an appendix on quasi two-and one-dimensional exciton cavity polaritons.