Preface

Quantum dots (QDs) are semiconductor nanoparticles with numerous unique properties and appealing characteristics, such as size-dependent emission wavelength, narrow emission peak, and broad excitation range. A QD is an artificial molecule with energy gap and energy level spacing dependent on its size (radius) with an ability to confine electrons (quantum confinement). When the size of a QD approaches the size of the material's exciton Bohr radius, the quantum confinement effect becomes prominent and the electron energy levels can no longer be treated as a continuous band; they must be treated as discrete energy levels. It is possible to achieve highly tunable electrical and optical properties by adjusting the shape, the size, and the composition of a QD, and in doing so, facilitating the use of QDs in a broad range of applications. This book discusses a few theoretical aspects and applications of QDs. The first section substantiates new opportunities to use QDs in the developments and the study of both fundamental theories and applied physics. Precisely controlling the size, shape, emission of color, and band gap of QDs allows for their use in different applications from energy harvesting to biomedicine. The physical and chemical phenomenon of QDs can be explained through a theoretical model using quantum confinement behavior.

The second section discusses the potentials of QDs in biological imaging. It provides a comprehensive overview of QD applications in tumor targeting and cancer imaging. QDs attract great attention as contrast and therapeutic agents, owing to their unique properties of good light stability, low toxicity, and strong fluorescence intensity, and the ability to change emission wavelength with their size.

As the editor of this book, I would like to thank all the authors for their contributions and efforts in bringing up-to-date research and high-quality work to this volume.

Lastly, I gratefully acknowledge the IntechOpen publishing team for their support during the preparation of the book.

> **Dr. Faten Divsar** Payame Noor University, Tehran, Iran

**1**

Section 1

Introduction

Section 1 Introduction

**3**

**Figure 1.**

*Nanosys).*

**Chapter 1**

Dots

*Faten Divsar*

**1. Introduction**

are discussed in separate sections in this book.

**2. What are quantum dots?**

Introductory Chapter: Quantum

Quantum dots are small regions defined in the semiconductor materials with the same size of the distance in an electron-hole pair [1]. The physics of quantum dots has been a very active and fruitful research topic. Their unique optical, photochemical, semiconductor, and catalytic properties are due to the quantum confinement. To date, chemistry, physics, and materials science have provided methods for the production of quantum dots and allow tighter control of factors affecting, for example, particle growth and size, solubility and emission properties. This book deals with the electronic and optical properties of quantum dots as an artificially fabricated device. These dots have proven to be useful systems to study a wide range of physical phenomena. These characteristics provide the potential applications of quantum dots in photovoltaic and laser devices, thin-film transistors, light-emitting diodes, and luminescent labels in biology and medicine. Some of these applications

Quantum dots are colloidal fluorescent semiconductor nanoscale crystals that were firstly produced in the early 1980s [2]. These artificial semiconductor nanoparticles typically have unique optical, electronic, and photophysical properties that make them appealing in promising applications in fluorescent biological labeling, imaging, solar cells, composites and detection and as efficient fluorescence resonance energy transfer donors [3]. Sufficiently miniaturized semiconductor particles show quantum confinement effects, which limit the energies at which electron hole pairs are present in the particles. Based on the relationship between the energy and wavelength of light (or color), the optical properties

*Conversion of the light spectrum into different colors depends on the quantum dot size (image: RNGS Reuters/*
