Photoionization of Polyvalent Ions [1 ed.] 9781617286612, 9781607410713

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Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved. Photoionization of Polyvalent Ions, Nova Science Publishers, Incorporated, 2009. ProQuest Ebook Central,

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved. Photoionization of Polyvalent Ions, Nova Science Publishers, Incorporated, 2009. ProQuest Ebook Central,

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PHOTOIONIZATION OF POLYVALENT IONS

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PHOTOIONIZATION OF POLYVALENT IONS

DORIS MÖNCKE AND

DORIS EHRT

Nova Science Publishers, Inc. New York

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The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers‟ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA

Moncke, Doris. Photoionization of polyvalent ions / Doris Moncke and Doris Ehrt. p. cm. -- (Materials science and technologies) Includes bibliographical references and index. ISBN 978-1-61728-661-2 (Ebook) 1. Glass--Effect of radiation on. 2. Glass--Additives. 3. Glass--Defects. 4. Photoionization. 5. Polyvalent molecules. I. Ehrt, Doris. II. Title. TA450.M64 2009 620.1'1--dc22 2009004636

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CONTENTS Preface

vii

Acknowledgements

ix

Chapter 1

Introduction

1

Chapter 1

Experimental Section

3

Chapter 3

Matrix Glass Types and Intrinsic Defects

7

Chapter 4

3D Ions

13

Chapter 5

4D and 5D ions

33

Chapter 6

Post Transition Metal Ions

49

Chapter 7

Photoreactions and Defect Stability

69

Chapter 8

Conclusion

73

References

75

Index

79

Photoionization of Polyvalent Ions, Nova Science Publishers, Incorporated, 2009. ProQuest Ebook Central,

Copyright © 2009. Nova Science Publishers, Incorporated. All rights reserved. Photoionization of Polyvalent Ions, Nova Science Publishers, Incorporated, 2009. ProQuest Ebook Central,

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PREFACE The effect of polyvalent dopants on photoinduced defect formation was studied in different glasses. Ionization of the glass matrix results in intrinsic defects, positively charged hole and negatively charged electron centers. Polyvalent dopants can be photooxidized or photoreduced. These extrinsic defects might replace selectively one or several intrinsic defects and / or cause an increase in the number of opposite charged defects. Photoionization can also result in unusual dopant valences otherwise not observed in glasses. The systematic comparison of different dopants and glass systems irradiated by excimer lasers helps to understand defect generation processes and might eventually help in the design of UV-resistant or UV-sensitive glasses. Defect formation occurs in the ppm range and was analyzed by optical and EPR spectroscopy. A series of polyvalent dopants such as typical trace impurities, glass or melt additives and typical dopants used for optical components like filter glasses, optical sensors, fluorophores or photochromes, were studied. Distinct melting conditions give rise to different valences of various dopants and as a consequence different photoinduced redox-reactions might be observed after irradiation. Qualitative and quantitative changes in the defect formation rates depend on the: kind and concentration of the dopant, c was varied from 50 to 5000 cation ppm. radiation parameters such as wavelength, or power density of the excimer lasers used. glass matrix; (fluoride-)phosphate and borosilicate glasses give rise to different intrinsic defects of varying stability. The matrix determines also

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viii

Doris Möncke and Doris Ehrt the initial incorporation like valence or coordination of the dopants and stabilizes or destabilizes photoionized dopant species. initial transmission of the glass sample, which also depends on the dopant (kind, valence, coordination), its concentration, and the thickness of the sample plate, d was varied from 0.5 to 2mm.

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Some dopants are photooxidized while others are photoreduced Some defects recombine easily or transform into more stable defects while others are stable for months or years.

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ACKNOWLEDGMENTS

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The authors acknowledge the financial support by SCHOTT Glass, Mainz, Germany, by the Hoschul- und Wisssenschafts-Programm HWP, and the Deutsche Forschungsgemeinschaft (No. EH 140|3-2). We thank R. Atzrodt and A. Matthai for help with the preparation of the glasses, R. Marschall for conducting the laser experiments, as well as M. Friedrich and B. Rambach for conducting the EPR-measurements.

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Chapter 1

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INTRODUCTION Solarization in glasses was first described by Faraday in 1825. The effect of irradiation induced transmission changes has been investigated since for its scientific and technological significance [1-31]. Pelouze recognized already in 1867 that a change in the oxidation state of the typical glass impurities Fe and Mn can cause strong solarization effects [2]. UV-radiation excites valence electrons in the irradiated material and complicated photoreaction processes lead subsequently to the formation of irradiation induced defects. Defects are generated in ppm concentrations and occur in pairs of negative electron centers (EC) and positive hole centers (HC). While intrinsic defects arise from the glass matrix itself are extrinsic defects connected to dopants or impurities. The formation of defects may result in transmission changes but also in changes of the refractive properties of the material. Studying the processes and mechanisms that govern defect formation requires more attention as stronger lamps and lasers, which work at increasingly shorter wavelengths, are more and more utilized. This knowledge can than be exploited in the development of photosensitive or photoresistant appliances. Because of their strong electronic transitions in the ultraviolet (UV) and visible (VIS) spectral range were, in analogy to similar absorbances in crystals, defects initially called color centers. Optical spectroscopy is the method of choice when studying defect formation; however, optical spectra of doped glasses are often dominated by transitions of the dopants that overlay the defects bands [318]. Complementary information on these defects, even regarding their detailed structure, can be derived from EPR-spectroscopy as many defects are paramagnetic [7-23, 3-18]

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Doris Möncke and Doris Ehrt

The addition of polyvalent ions often initiates or enhances considerably the formation of defects in a glass sample. Extrinsic defects can form in addition to intrinsic defects and thus cause the increased generation of reversibly charged intrinsic defects. On the other hand can extrinsic defects substitute selectively one or more intrinsic defects of like charge [3, 19-23]. Irradiation induced defects can further be classified according to their stability in transient or stable defects. Some initially formed defects transform rapidly into more stable defects, sometimes even during the irradiation process. The transformation of defects in thermodynamically more stable centers can then again be hindered kinetically. Defect formation is a dynamic process and the kind and rate of defect development depends on many factors, e.g. the glass matrix, the concentration and species of any dopants, the initial transmission of the sample, or on the radiation parameters. For example excites UV-radiation only valence electrons while X-ray radiation detaches even the inner electrons in the material. Accordingly are different defects initiated by different radiation sources [24]. This chapter intends to compare the role of a wide range of polyvalent metals in the formation of irradiation induced defects. All glass samples were irradiated with excimer lasers in the UV and the laser induced defects were characterized by optical and EPR spectroscopy. Only defects stable at room temperature are discussed. Even these relative stable defects show transformation and recombination reactions when the samples were stored at room temperature in the dark. The glass types studied were selected for their high transparency in the deep ultraviolet ( 0~160-185 nm) and consequently their application in high performance optics [25-31, 35].

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Chapter 1

EXPERIMENTAL SECTION

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Fluoridephosphate (FP) and metaphosphate glasses (NSP) were selected as primary matrix glasses for the irradiation experiments. The generated extrinsic defects were characterized by EPR and optical spectroscopy and when possible identifified yb type and charge. Additional experiments using borosilicate type samples were added later in order to study the dopants effect on defect formation in an entirely different glass matrix. All samples were prepared and irradiated under defined and comparable conditions.

2.1. SAMPLE PREPARATION The preparation of the different high purity glasses has been described in detail before [7-18, 25-31]. Only high purity reagents were used for all glasses. The iron content of the duran type borosilicate glass was < 1 ppm, of NSP ~ 5ppm and of FP10 < 10 ppm. The total iron content was analyzed by wet-chemical analysis. The Fe3+ content was also determined from the absorption of its CTtransition at 250 nm in the optical spectra [9, 27, 28-31]. The high purity dopant components were added in various amounts between 50 and 5000 ppm (cation %). The fluoroaluminate FP10 has the synthetic composition [10 P2O5 · 90 (AlF3, CaF2, SrF2, MgF2) mol%] and was melted at 1100°C under air in platinum crucibles. In order to obtain reduced dopant species were some samples also remelted under reducing melting conditions under argon atmosphere in glasscarbon crucibles. The metaphosphate glass NSP [10 Na2O · 40 SrO·50 P2O5 mol%] was melted under air at 1300°C in SiO2-crucibles. The dopants were reduced by the addition of 0.2 to 1 wt% carbon to the batch.

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Doris Möncke and Doris Ehrt

Low alkaline borosilicate samples of the duran type [82 SiO2·12 B2O3·5 (K/Na)2O·1 Al2O3 mol%] were prepared under air at 1650°C. 250 to 1000 g batches were processed for 3-5 hours. For some samples were oxidizing or reducing conditions established by using the corresponding nitrate or tartrate salts of the reagents. All melts were cast in preheated graphite moulds and annealed from 500 or 550 °C to room temperature with a cooling rate of 30 K / h.

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2.2. RADIATION SOURCES Polished samples plates of the dimensions 10 x 20 mm and a thickness of either 0.5, 1, or 2 mm were irradiated with excimer lasers. The sample thickness was chosen for each sample in accordance to the initial absorbance at the irradiation wavelength. Excimer lasers working at 193 nm (ArF-laser), 248 nm (KrF-laser), and 351 nm (XeF-laser) were used. The power density of the laser was 200 mJ/cm² per pulse by a pulse duration of ~ 20 ns. The optical spectra were taken with increasing accumulated pulse numbers (at 10, 100, 1000, 5000, and 10000 pulses). The final pulse number normally suffices to reach the saturation level. EPR spectra of the samples were taken once after the final irradiation. Further optical spectra were obtained at increasing time intervals in which the irradiated samples were stored in the dark at room temperature. Some samples were irradiated by a high pressure mercury lamp or HOK lamp with a spectral power density of 1 kW with a wide continuos spectrum from 190 nm in the UV to the NIR.

2.3. UV-VIS-SPECTROSCOPY UV-VIS-NIR spectra were taken in the range from 190 to 3000 nm. A double beam spectrophotometer (UV-3102, Shimadzu) recorded the absorbance A =lg(T0/T) with an error