N. Thejo Kalyani - Principles and Applications of Organic Light Emitting Diodes (OLEDs)

1. Tables in Chapter 1
2. Tables in Chapter 2
3. Tables in Chapter 4
4. Tables in Chapter 5
5. Tables in Chapter 6
6. Tables in Chapter 7
7. Tables in Chapter 8
8. Tables in Chapter 9
9. Tables in Chapter 10

1. Figures in Chapter 1
2. Figures in Chapter 2
3. Figures in Chapter 3
4. Figures in Chapter 4
5. Figures in Chapter 5
6. Figures in Chapter 6
7. Figures in Chapter 7
8. Figures in Chapter 8
9. Figures in Chapter 9
10. Figures in Chapter 10
11. Figures in Chapter 11

N. Thejo Kalyani

Hendrik Swart

S.J. Dhoble

Woodhead Publishing Series in Electronic and Optical Materials

Woodhead Publishing is an imprint of Elsevier

The Officers Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States

The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom

Copyright 2017 Elsevier Ltd. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publishers permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

ISBN: 978-0-08-101213-0 (print)

ISBN: 978-0-08-101249-9 (online)

For information on all Woodhead Publishing publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans

Acquisition Editor: Kayla Dos Santos

Editorial Project Manager: Kattie Washington

Production Project Manager: Omer Mukthar

Designer: Mark Rogers

Typeset by MPS Limited, Chennai, India

Exploration of lighting technology is based on a solid understanding of the fundamental principles of luminescence. Luminescence refers to cool emission, caused by the movement of electrons within a substance from high energetic state to less energetic state, thereby giving off light at normal or cool temperatures without generating heat. The practical value of luminescent materials lies in their capacity to transform invisible forms of energy into visible light. Luminescence efficiency depends on the degree of transformation of excitation energy into light energy. There are relatively few materials that have sufficient luminescence efficiency to be of practical value. This chapter explores the classification of luminescence based on time lag, source of excitation, mechanism of light emission, terminology, and applications of luminescence.

Luminescence; fluorescence; phosphorescence; antenna effect; screening effect; rare earths

Since time immemorial, light emissions from glowworms, sea creatures, and the extravagant light shows of the aurora borealis have been fascinating, and a great deal of work has been done to comprehend their origins. Until the advent of quantum mechanics, the basic origins of these emissions could not be adequately understood. Later, after numerous resourceful attempts to determine the origin behind these emissions, it was finally concluded that they are due to the phenomena of luminescence, which involves the absorption of suitable energy and subsequent emission of light as ultraviolet (UV), visible light, or infrared (IR) radiation from materials. Over time, major breakthroughs in luminescence studies made this field of research a major focus of innovation.

Light has fascinated mankind since ancient times through its diverse shades and colors as it plays a vital role in almost all spheres of modern life. Various natural wonders such as the shades of sunrises and sunsets, rainbows, the blues of ocean and sky, etc., involve light. But what is light? In simple terms, it is a physical quantity that is emitted by a luminous body and when incident on the eye causes the sensation of sight through nerves. It constitutes a tiny proportion of the whole electromagnetic spectrum that is visible to the human eyes. Though our capabilities for perception of light are highly elevated, only a very narrow range of the electromagnetic spectrum, which extends from the deepest violet (400 nm) to the deepest red (750 nm), can be seen by us. According to the wavelength and frequency, the color of light also changes and hence a spectrum of VIBGYOR can be observed. In VIBGYOR, red occupies more space and hence reaches our eyes first. Red, green, and blue (RGB) occupies two-thirds of the spectrum and a specific combination thereof creates white light. The visible (VIS) spectrum and its wavelength range and bandwidth of the different colors of the VIS spectrum are shown in , respectively.

Figure 1.1 .

Table 1.1