UTS LIBRARY
`
`11111111111111111111111111111111111111111111111111111111111111111111111111111111
`39339037982730
`
`LUMINESCENT
`MATERIALS
`
`.)
`
`Springer-Verlag
`
`LOWES 1016, Page 1
`
`VIZIO Ex. 1016 Page 0001
`
`

`

`G. Blasse, B. C. Grabmaier
`
`Luminescent
`Materials
`
`With 171 Figures and 31 Tables
`
`Springer-Verlag
`Berlin Heidelberg New York
`London Paris Tokyo
`Hong Kong Barcelona Budapest
`
`_·,j
`
`LOWES 1016, Page 2
`
`VIZIO Ex. 1016 Page 0002
`
`

`

`Prof. Dr. G. Blasse
`
`Debye Institute
`University Utrecht
`Postbox 80.000
`3508 TA Utrecht
`The Netherlands
`
`Prof .. Dr. B. C. Grabmaier
`
`Siemens Research Laboratories
`ZFE BT MR 22
`D-81730 Miinchen
`Germany
`
`ISBN 3-540-58019-0 Springer-Verlag Berlin Heidelberg New York
`ISBN 0-387-58019-0 Springer-Verlag New York Berlin Heidelberg
`
`Library of Congress Cataloging-in-Publication Data
`Blasse, G. Luminescent materials/ G. Blasse, B.C. Grabmaier. p. cm.
`Includes bibliographical references and index.
`ISBN 3-540-58019-0. -- ISBN 0-387-58019-0 (U.S.)
`I. Phosphors. 2. Luminescence. I. Grabmaier, B. C., 1935- II. Title.
`QC476.7 .853 1994 620.1' I 295--dc20 94-20336 CIP
`
`This work is subjec1 to copyrighl. All rights ore reserved whethe r the whnlc or pun of the
`mnterial is concerned, specifically the rights of iranslation, reprinting, re-u c of illusuation ,
`recitation, broadcasting, reproduction 0 11 microfilm s or in other ways. and storage in dma banks.
`Duplication or this pubUcation or parts thereof' is only permitted under the provbions of the
`German Copyright Law of September 9, I 965, in its CLJrrcnt vcr ion. and a copyright !'cc must
`always be paid.
`
`© Springer. Verlag Berlin Heidelberg 1994
`Printed in Germany
`
`The use of registered names, trademarks, etc. in this publication does not imply, even in the
`absence of a specific statement, that such names are exempt from the relevant protective laws
`and regulations and therefore free for general use.
`
`Typesetting with TEX: Data conversion by Lewis & Leins, Berlin
`SPIN: 10187460
`02/3020 - 5 4 3 2 I 0 - Printed on acid-free paper
`
`LOWES 1016, Page 3
`
`VIZIO Ex. 1016 Page 0003
`
`

`

`10 patiently typed the
`:r correction appeared
`drawing some of the
`· disposal.
`, with and inspiration
`1cts, some oral, some
`. In the preparation of
`, A. Bril, C.W.E. van
`ry useful.
`,mines.cence. We hope
`phenomena, to design
`m in doing so.
`
`G. Blasse, Utrecht
`Grabmaier, Mlinchen
`
`Table of Contents
`
`Chapter 1 A General Introduction to Luminescent Materials
`Chapter 2 How Does a Luminescent Material Absorb Its Excitation Energy?
`
`2.1 General Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
`2.2 The Influence of the Host Lattice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`16
`2.3 The Energy Level Diagrams of Individual Ions. . . . . . . . . . . . . . . . . . . . . . . . . 20
`2.3.1
`The Transition Metal Ions (d")............................. .. 20
`2.3.2
`The Transition Metal Ions with d° Configuration............ ... 25
`2.3.3
`The Rare Earth Ions (4f").................................. .. 25
`2.3.4
`The Rare Earth Ions (4f-5d and Charge-Transfer Transitions) . . . 27
`2.3.5
`Ions with s2 Configuration................................. ... 28
`Ions with d 1° Configuration............................... .... 29
`2.3.6
`2.3.7
`Other Charge-Transfer Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
`2.3.8
`Color Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
`2.4 Host Lattice Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`31
`
`Chapter 3 Radiative Return to the Ground State: Emission
`
`3.1
`3.2
`3.3
`
`3.4
`3.5
`3.6.
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
`General Discussion of Emission from a Luminescent Center . . . . . . . . . . . . . 33
`38
`Some Special Classes of Luminescent Centers ............. ...... . .... .
`38
`3.3.1
`Exciton Emission from Alkali Halides ............ .... . ....... .
`40
`Rare Earth Ions (Line Emission) ................. .... .. ...... .
`3.3.2
`45
`Rare Earth Ions (Band Emission) ................ .. .. ........ .
`3.3.3
`50
`3.3.4
`Transition Metal Ions ........................... . _ .. .. ...... .
`52
`3.3.5
`d° Complex Ions ....... • ........................ ...... ...... .
`d 10 Ions......................................... ....... ... .. 53
`3.3.6
`3.3.7
`s2 Ions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
`The U6+ ion ................................... . . ... , . . . . . . . 59
`3.3.8
`3.3.9
`Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
`3.3.10 Cross-Luminescence............................ ............. 64
`Afterglow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
`Thermoluminescence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
`Stimulated emission........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
`References ............................................. .. . .. . ... , . . . 70
`
`LOWES 1016, Page 4
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`VIZIO Ex. 1016 Page 0004
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`

`

`viii
`
`Table of Contents
`
`Chapter 4 Nonradiative Transitions
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
`4.1
`4.2 Nonradiative Transitions in an Isolated Luminescent Centre .. . . . . . . . . . . . 72
`4.2.1
`The Weak-Coupling Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
`4.2.2
`The Intermediate- and Strong-Coupling Cases. . . . . . . . . . . . . . . . . . 77
`4.3 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
`4.4 Maximum Efficiency for High Energy Excitation [13] ..... ..... .. ..... _ 85
`4.5 Photoionization and Electron-Transfer Quenching......... .............. 86
`4.6 Nonradiative Transitions in Semiconductors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
`
`Chapter 5 Energy Transfer
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
`5 .1
`5.2 Energy Transfer Between Unlike Luminescent Centers.. ............. . .. 91
`5.3 Energy Transfer Between Identical Luminescent Centers ........ . ....... 95
`5.3.1 Weak-Coupling Scheme Ions ................. .... , . . . . . . . . . . . 95
`5.3.2
`Intermediate- and strong-coupling scheme ions ................. I 03
`5.4 Energy Transfer in Semiconductors ................... ... . ............ . I 06
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 06
`
`Chapter 6 Lamp Phosphors
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 08
`6.1
`6.2 Luminescent Lighting [1-3] .............. . ................. ........... 108
`6.3 The Preparation of Lamp Phosphors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
`6.4 Photoluminescent Materials ................................ ......... . . 112
`Lamp Phosphors for Lighting ...................... .... . ...... 112
`6.4.1.
`6.4.2
`Phosphors for Other Lamp Applications . . . . . . . . . . . . . . . . . . . . . . . 126
`6.4.3
`Phosphors for High-Pressure Mercury Vapour Lamps .... . ...... 127
`6.4.4
`Phosphors with Two-Photon Emission. . . . . . . . . . . . . . . . . . . . . . . . . 130
`6.5 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
`
`Chapter 7 Cathode-Ray Phosphors
`
`7. I Cathode-Ray Tubes: Principles .ind Display. . . . . . . .. . .. . .. . . .. .. . .. . .. . 134
`7.2 Preparation of Cathode-Ray Phosphors ............. ................... 136
`7.3 Cathode-Ray Phosphors ......................... ..................... 137
`7 .3.1
`Some General Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
`Phosphors for Black-and-White Television ... . ................. 138
`7.3.2
`7.3.3
`Phosphors for Color Television.......... ..................... 138
`7.3.4
`Phosphors for Projection Television ...... .. ... ...... ..... ..... 141
`7.3.5
`Other Cathode-Ray Phosphors .......... ...................... 143
`7.4 Outlook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
`
`LOWES 1016, Page 5
`
`VIZIO Ex. 1016 Page 0005
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`

`

`.................. 71
`entre ............ . 72
`74
`........... .. . . ... 77
`84
`85
`. . . . . . . . . . . . . . . . . . 86
`. . . . . . . . . . . . . . . . . . 88
`89
`
`91
`.................. 91
`rs ............... .
`95
`95
`103
`106
`106
`
`Lump .......... .
`
`10
`108
`111
`112
`11 2
`126
`127
`130
`130
`l33
`
`134
`136
`137
`137
`138
`138
`141
`143
`145
`145
`
`Table of Contents
`
`ix
`
`Chapter 8 X-Ray Phosphors and Scintillators (Integrating Techniques)
`
`8.1
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
`8.1.1
`X-Ray Absorption....................................... .... 146
`8.1.2
`The Conventional Intensifying Screen. . . . . . . . . . . . . . . . . . . . . . . . . 148
`8.1.3
`The Photostimulable Storage Phosphor Screen . . . . . . . . . . . . . . . . . 149
`8.1.4
`Computed Tomography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
`8.2 Preparation of X-ray Phosphors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
`8.2.1
`Powder Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
`8.2.2
`Ceramic Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
`8.2.3
`Single Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
`8.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
`8.3.1
`X-Ray Phosphors for Conventional Intensifying Screens. . . . . . . . 159
`X-Ray Phosphors for Photostimulable Storage Screens ...... .... 162
`8.3.2
`8.3.3
`X-Ray Phosphors for Computed Tomography.. . . . . . . . . . . . . . . . . 165
`8.4 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
`
`Chapter 9 X-Ray Phosphors and Scintillators (Counting Techniques)
`
`9.1
`9.2
`9.3
`9.4
`9.5
`
`9.6
`
`Introduction .............................................. .. . .. . .... .
`The Interaction of Ionizing Radiation with Condensed Matter .......... .
`Applications of Scintillator Crystals ........................ .......... .
`Material Preparation (Crystal Growth) ...................... .......... .
`Scintillator Materials ...................................... .......... .
`9.5.1
`Alkali Halides .................................... .......... .
`9.5.2
`Tungstates ........................................ ......... .
`9.5.3
`Bi4Ge3O 12 (BGO) ................................ . .. .. .... . .
`Gd2SiO5 : Ce3+ and Lu2SiO5 : Ce3+ ................ ......... .
`9.5.4
`9.5.5
`CeF3 ........................................... ,, .. , ... , · ..
`9.5.6
`Other Ce3+ Scintillators and Related Materials ...... .. ... ..... .
`9.5.7
`BaF2 (Cross Luminescence; Particle Discrimination) . ......... ,
`9.5.8
`Other Materials with Cross Luminescence ........... , ........ .
`Outlook .................................................. .......... .
`References ................................. . , . . . ......... .. ..... ... .
`
`170
`170
`172
`178
`182
`182
`183
`183
`184
`186
`188
`188
`190
`191
`193
`
`Chapter 10 Other Applications
`
`IO. I Upconversion: Processes and Materials ... ............ .. . . . ............ 195
`I 0.1.1 Upconversion Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
`I 0.1.2 Upconversion Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
`10.2 The Luminescent Ion as a Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
`I 0.3 Luminescence Immuno-Assay ........... ............ , ...... . . , ... . .... 206
`Principle ....................... ............... .. . .. ....... .. 206
`10.3.1
`10.3.2 Materials ...................... ...... . .. .... ... .... .. .... .... 208
`
`Ill
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`LOWES 1016, Page 6
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`VIZIO Ex. 1016 Page 0006
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`

`

`-
`
`- - - - -
`
`X
`
`Table of Contents
`
`I 0.4 Electroluminescence ................................... . .. .... . . ..... . 210
`Introduction .................................. , ... . ....... . .. 210
`10.4.1
`10.4.2 Light-Emitting Diodes and Semiconductor Lasers . ........ . . . .. 210
`10.4.3 High-Field Electro luminescence ................ .... . ... . .. . .. . 212
`10.5 Amplifiers and Lasers with Optical Fibers ............... . . . .. .. ..... . . 214
`I 0.6 Luminescence of Very Small Particles ................... .. .. .. . . .. . , . . 216
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 218
`
`Appendix I. The Luminescence Literature ................................ , . 221
`Appendix 2. From Wavelength to Wavenumber and Some Other Conversions . 223
`Appendix 3. Luminescence, Fluorescence, Phosphoresence ................. .. 224
`Appendix 4 .. Plotting Emission Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
`
`Subject Index .. .......... . . . .... . .... . .. . ...... . ... . ........ . ...... . ...... 227
`r---.. ~
`
`LOWES 1016, Page 7
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`VIZIO Ex. 1016 Page 0007
`
`

`

`ers ............. .
`
`210
`210
`210
`212
`214
`216
`218
`
`221
`ther Conversions . 223
`224
`225
`
`....... . .... .. .... 227
`
`CHAPTER 1
`
`A General Introduction to Luminescent Materials
`
`This chapter addresses those readers for who luminescent materials are a new chal(cid:173)
`lenge. Of course you are familiar with luminescent materials: you meet them everyday
`in your laboratory and in your home. If this should come as a surprise. switch on
`your fluorescent lighting, relax in front of your television set, or take a look at the
`screen of your computer. Perhaps you would like something more specialized. Re(cid:173)
`member then your visit to the hospital for X-ray photography. Or the laser in your
`institute; the heart of this instrument consists of a luminescent material. However,
`such a high degree of specialization is not necessary. The packet of washing powder
`in your supermarket also contains luminescent material.
`Now that we have been reminded of how full of luminescent materials our society
`is, the question arises "How do we define a luminescent material'1" The answer is as
`follows: A luminescent material, also called a phosphor, is a solid which converts cer(cid:173)
`tain types of energy into electromagnetic radiation over and above thermal radiation.
`When you heat a solid to a temperature in excess of about 600°C, it emits (infra)red
`radiation. This is thermal radiation (and not luminescence). The electromagnetic ra(cid:173)
`diation emitted by a luminescent material is usually in the visible range, but can also
`be in other spectral regions, such as the ultraviolet or infrared.
`Luminescence can be excited by many types of energy. Photoluminescence is
`excited by electromagnetic (often ultraviolet) radiation, cathodoluminescence by a
`beam of energetic electrons, electroluminescence by an electric voltage, tribolumines(cid:173)
`cence by mechanical energy (e.g. grinding), X-ray luminescence by X rays, chemi(cid:173)
`luminescence by the energy of a chemical reaction. and so on. Note that thermolu(cid:173)
`minescence does not refer to thermal excitation, but to stimulation of luminescence
`which was _excited in a different way.
`
`EXC.
`
`EM .
`
`Fig. 1.1. A luminescent ion A in its host lattice. EXC: excitation; t;M: emission (radiative return
`to the ground state); HEAT: nonradiative return to the ground sta~
`
`LOWES 1016, Page 8
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`VIZIO Ex. 1016 Page 0008
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`

`

`2
`
`I. A General Introduction to Luminescent Materials
`
`R
`
`NA
`
`A _...1..-__ _,_____._ _
`
`_
`
`Fig. 1.2. Schematic energy level scheme of the luminescent ion A in Fig. 1.1. The asterisk
`indicates the excited state, R the radiative return and NR the nonradiative return to the ground
`stale
`
`In Fig. 1.1, we have drawn schematically a crystal or a grain of a photoluminescent
`material in order to illustrate the definition. Our system consists of a host lattice and
`a luminescent center, often called an activator. For example, consider the famous
`luminescent materials Ah03 : CrH (ruby) and Y 20 3 : EuH. The host lattices are
`A 1~0 3 and Y 30 3 , the activators the Crh and the Eu I
`ions.
`The luminescence processes in such a sy ' tem are ns fo llows. The exci ting radiation
`is .1bsorbcd by Lhc activator, raising it to an excited state (Fig. 1.2). The excited ·u,11e
`return
`to the ground state by emissi n of radiati on. This uggcsts rlmt every ioo and
`every material shows lumi.ncscence. This is not th case. The reason for thi
`is thn.t the
`radiative emissi n process has a c mpetitor, viz. the nonradiative return to the ground
`state . Jn that proces · the energy of the e cited state is u ed 10 excite the vibrations
`of the host lauice. i.e. to heat the host lauice. ln Clrder to creme efficient luminescent
`materials it is necessary to suppress this nonradiative process.
`The obvious characteristics to be measured on this system are the spectral energy
`distribution of the emission (the,,emission spectrum), and of the excitation (the exci(cid:173)
`tation spectrum; which in this simple case is often equal to the absorption spectrum),
`and the ratio of the radiative and the nonradiative rates of return to the ground state.
`The latter determines the conversion efficiency of our luminescent material.
`Let us for a second return to ruby (Ab03 : CrH). This is a beautiful red gem(cid:173)
`stone which shows a deeprcd luminescence under excitation with ultraviolet or visible
`radiation. Its pectroscopic properties were studiel.l as early as 1867 by the famous
`scientist Becquerel , who used sun light as the exci tat ion source. He claimed that the
`color as well as the luminescence were intrinsic properties of the host lattice. This
`time, however, Becquerel wa. wrong, 1L is the Cr1+ ion which i · responsible for the
`optical absorption of ruby in the visible and ultravi.ol.et spectrnl regions. The ho. t
`lattice Al 20J doe aol participate m all in the opticnl processes. In fact Al2 3 is col(cid:173)
`r1+ ion and t:11e host
`orle s. In the case of the ruby, the activator A in Pig. 1. 1 is rhe
`la.Hice is Al 20 3 • The host lattice or this lumine cent material has no other functiCln
`than to hold the CrH ion tightly.
`In many luminescent materials the situation is more complicated than depicted
`in Fig. I. I, because the exciting radiation is not absorbed by the activator, but else(cid:173)
`where. For example, we can add another ion to the host lattice. This ion may absorb
`
`LOWES 1016, Page 9
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`VIZIO Ex. 1016 Page 0009
`
`

`

`\ in Fig. 1.1. The asterisk
`iiative return to the ground
`
`in of a photoluminescent
`ists of a host lattice and
`le, consider the famous
`t. The host lattices are
`
`IS. The exciting radiation
`\. 1.2). The excited state
`:gests that every ion and
`reason for this is that the
`ti ve return to the ground
`to excite the vibrations
`1te efficient luminescent
`
`1 are the spectral energy
`the excitation (the exci(cid:173)
`te absorption spectrum),
`turn to the ground state.
`!scent material.
`is a beautiful red gem-
`1ith ultraviolet or visible
`as 1867 by the famous
`ce. He claimed that the
`Df the host lattice. This
`:h is responsible for the
`:ctral regions. The host
`e.s. In fact A)iO3 is col-
`1e Cr1+ ion and the host
`I has no other function
`
`nplicated than depicted
`the activator, but else(cid:173)
`:e. This ion may absorb
`
`I. A General Introduction to Luminescent Materials
`
`3
`
`Fig. 1.3. Energy transfer from a sensitiser S to an activator A. Energy transfer is indicated by
`E.T. For further notation, see Fig. 1.1
`
`s·--.----
`
`--..--- A:
`
`3: T~
`
`s -~~-
`-~- - A
`Fig. 1.4. Energy transfer from S to A. The S---,. s• transition is the absorption (or excitation),
`the A2---,. A' transition the emission. The level AT, populated by energy transfer (E.T.), decays
`nonradiatively to the slightly lower A2 level. This prevents back transfer
`
`the exciting radiation and subsequently transfer it to the activator. In this case the
`absorbing ion is called a sensitizer (see Fig. 1.3).
`Another well-known example, viz. the lamp phosphor Ca5 (PO4hF : SbH, Mn2+.
`Ultraviolet radiation is not absorbed by Mn2+, but only by Sb3+. Under ultraviolet
`irradiation, the emission consists partly of blue Sb3+ emission, and partly of yellow
`Mn2+ emission. Since the Mn2+ ion was not excited •directly, the excitation energy
`was transferred from Sb3+ to Mn2+ (see Fig. 1 ,4).' The luminescence processes can
`be written as follows, where hi, indicates radiation 'with frequency z., and the asterisk
`an excited state:
`Sb3+ + hi, -+ (Sb3+)*
`(Sb3+)* + Mn2+ -+ Sb3+ + (Mn2+)*
`
`These "equations" indicate absorption, energy transfer, and emission, respectively.
`If the Sb3+ ion has no Mn2+ ions in its vicinity, it gives its own blue emission.
`For those of you who are not familiar with solids, please realize that in general the
`concentrations of the luminescent centers· are of the order of a 1 mol.%, and that the
`centers are, in first approximation, distributed at random over the host lattice.
`Sometimes, however, the activator concentration can be I 00%. This illustrates the
`rather complicated nature of luminescent materials. Actually these high activator con(cid:173)
`centrations which occur in some cases were not understood for a long time, preventing
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`LOWES 1016, Page 10
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`VIZIO Ex. 1016 Page 0010
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`4
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`I. A General Introduction to Luminescent Materials
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`progress in our understanding of luminescent materials. A famous example of such a
`high-concentration material is CaWO4 where the tungstate group is the luminescent
`center. Simultaneously it is a building unit of the host lattice which consists of Ca2+
`and wo~- ions. This material was used for 75 years in X-ray photography, and in
`tungsten mines its luminescence is used to find CaWO4 • The miners use ultraviolet
`lamps to find the tungstate-rich ores by their visible luminescence! Chapter 5 discusses
`why a high concentration of activators is sometimes fatal for luminescence, whereas
`in other cases such high concentrations yield very high luminescence outputs.
`In stead of exciting a low concentration of sensitizers or activators, we can also
`excite the host lattice. This is, for example, what happens if we excite with X rays
`or electron beams. In many cases the host lattice transfers its excitation energy to
`the activator, so that the host lattice acts as the sensitizer. Again a few examples.
`In YVO4 : EuH ultraviolet radiation excites the vanadate groups, i.e. the host lattice.
`The emission, however, consists of Eu3+ emission. This shows that the host lattice is
`able to transfer its excitation energy to the EuH ions. Another example is ZnS : Ag+,
`the blue-emitting cathode-ray phosphor used in television tubes. Ultraviolet radiation,
`electron beams and X rays excite the sulfide host lattice which transfers this excitation
`energy rapidly to the activators (the Ag+ ions).
`In spite of the fact that we did not discuss any fundamental background (this
`will be done in Chapters 2-5), you have met by now the more important physical
`processes which play a role in a luminescent material:
`- absorption (excitation) which may take place in the activator itself, in another ion
`(the sensitizer), or in the host lattice (Chapter 2)
`emission from the activator (Chapter 3)
`- nonradiative return to the ground state, a process which reduces the luminescence
`efficiency of the material (Chapter 4)
`- energy transfer between luminescent centers (Chapter 5).
`After this short, general introduction into the operation of a luminescent material,
`we now turn to a similar introduction to the applications of luminescent materials.
`Photoluminescence is used in fluorescent lamps. This application was even used
`before the Second World War. The lamp consists of a glass tube in which a low(cid:173)
`pressure mercury discharge generates ultraviolet radiation (85% of this radiation con(cid:173)
`sists of 254 nm radiation). The lamp phosphor (or a mixture of lamp phosphors) is
`applied to the inner side of the tube. This phosphor converts the ultraviolet radiation
`into white light. The efficiency of conversion of electricity to light is in a fluorescent
`lamp considerably higher than in an incandescent lamp.
`The introduction of rare-earth activated phosphors in fluorescent lamps during the
`last decade has improved the light output and the colour rendering drastically. As a
`consequence this type of lighting is no longer restricted to shops and offices, but is
`now also suitable for living rooms. It is interesting to note that in this way chemical
`elements which for a long time have been considered as rare, peculiar, and hard to sep(cid:173)
`arate, have penetrated our houses. A modern fluorescent lamp contains the following
`rare earth ions: divalent europium, trivalent cerium, gadolinium, terbium, yttrium and
`europium. You will find more about this important application of photoluminescence
`in Chapter 6.
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`LOWES 1016, Page 11
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`VIZIO Ex. 1016 Page 0011
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`I . A General Introduction lo Luminescent Materials
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`5
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`One can han.lly imagine life today without cathode-ray tubes. Think of your tele(cid:173)
`vision set or your computer screen. In a cathode-ray tube the luminescent material is
`applied on !he inner side of !he glass tube and bombarded with fast electrons from
`the electron gun in the rear end of the tube. When the electron hits the luminescent
`material, it emits visible light. In the case of a colour television tube there are three
`electron guns , one irradiating a blue-emitting luminescent material, so that it creates
`a blue pictures, whereas two others create in a similar way a green and a red picture.
`One fast electron creates in the luminescent material many electron-hole pairs
`which recombine on the luminescent center. This multiplication is one of the factors
`which have determined the success of the cathode-ray tube as a display . It will be
`clear that the luminescent materials applied belong to the class of materials where
`excitation occurs in the host lattice. They will be discussed in Chapter 7 where we will
`also deal with materials for projection television. In this way the display screen can
`have a diameter of 2 111. This application puts rc4uirements on luminescent materials
`which are hard to satisfy.
`Let us now turn to materials which are able to conve1t X-ray irradiation into
`visible light. Rontgen discovered X rays in 1895 , and realized almost immediately
`that this type of radiation is not very efficient at exposing photographic film, because
`the film does not absorb the X rays effectively. As a consequence long irradiation
`times are required. Nowadays we know that this is bad for the patient. There is also
`a practical objection against long irradiation times: the patient is a moving object (he
`breathes and may, in addition , make other movements), so that sharp pictures can
`only be obtained if the irradiation time is short.
`Therefore Rcintgen initiated a search for luminescent materials which absorb
`X rays efficiently and convert their energy into radiation which is able to blacken
`the photographic film. Soon it was found that CaWO~ with a density of 6.06 g.cm - :i
`was able to do so. This compound was used for a very long time in the so-called X(cid:173)
`ray intensifying screens. A schematic picture of X-ray photography with this method
`is given in Fig. I .5.
`Just as in the field of lamp phosphors and (partly) cathode-ray phosphors, CaWO4
`lost its leading position to rare-earth activated X-ray phosphors (see chapter 8) . As
`a salute to this old champion, but also for your information, we give in Fig. 1.6 the
`crystal structure of CaWO.1 which illustrates the build-up of the lattice from Ca2+
`ions and luminescent wo~- groups, and in Fig. 1.7. an electron micrograph of a
`commercial CaWO,1 powder.
`A recent development in this field is the introduction of storage phosphors. These
`materials have a "memory" for the amount of X rays which has been absorbed at a
`given spot of the screen. By scanning the irradiated screen with an (infra)red laser,
`visible luminescence is stimulated. Its intensity is proportional to the amount of X rays
`absorbed. Chapter 8 discusses how to produce such materials and the physics behind
`these phenomena.
`As an example of a more specialized character, we should mention the case of X(cid:173)
`ray computed tomography. This method of medical radiology generates cross-sectional
`images of the interior of the human body (see Fig. 1.8). Besides the X-ray source,
`the key component is the detector consisting of about I 000 pieces of a luminescent
`solid (crystals or ceramics) which are connected to photodiodes or -multipliers. The
`
`I
`
`nous example of such a
`mup is the luminescent
`which consists of Ca'+
`1y photography, and in
`: miners use ultraviolet
`ice! Chapter 5 discusses
`luminescence, whereas
`escence outputs.
`activators, we can also
`we excite with X rays
`ts excitation energy to
`\gain a few examples.
`1ps, i.e . the host lattice.
`s that the host lattice is
`example is ZnS : Ag+,
`s. Ultraviolet radiation,
`transfers this excitation
`
`ental background (this
`ore important physical
`
`or itself, in another ion
`
`luces the luminescence
`
`1 luminescent material,
`minescent materials.
`ication was even used
`tube in which a low-
`0 of this radiation con(cid:173)
`of lamp phosphors) is
`Je ultraviolet radiation
`ight is in a fluorescent
`
`scent lamps during the
`ering drastically. As a
`:)ps and offices, but is
`t in this way chemical
`:uliar, and hard to sep(cid:173)
`contains the following
`1, terbium, yttrium and
`of photoluminescence
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`LOWES 1016, Page 12
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`VIZIO Ex. 1016 Page 0012
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`6
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`I. A General Introduction to Luminescent Materials
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`~ I • •
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`'- film
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`/
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`intensifying screen
`
`X-ray source
`
`patient
`
`Fig. 1.5. Schematic representation of a medical radiography system based on the use of an
`intensifying screen
`
`@:) :A
`0 . x
`Q o
`
`I
`
`I
`
`Fig. 1.6. Crystal structure of CaW04 (scheelile). The general formula is AX04 where A are the
`larger and X the smaller metal ions
`
`luminescent material has to show sharply defined properties in order to be acceptable
`for this application.
`After these examples of X-ray photography, you will not be surprised to learn that
`a and y radiation can also be detected by luminescent materials, which, in this case,
`are usually called scintillators and are often in the form of large single crystals. The
`applications range from medical diagnostics (for example positron emission tomog-
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`LOWES 1016, Page 13
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`VIZIO Ex. 1016 Page 0013
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`I. A General Introduction 10 Luminescent Materials
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`7
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`-film
`
`screen
`
`111 based on the use or an
`
`Fig. 1.7. CaWO4 powder phosphor (I000x)
`
`fan beam
`
`1 is AXO4 where A arc the
`
`Fig. 1.8. The principle of X-ray computed tomography. The patient is in the ce111cr or the picture.
`Source and detector rotate around