Defects in inorganic photorefractive materials and their investigations
Defects in inorganic photorefractive materials and their investigations
Defects in inorganic photorefractive materials and their investigations
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<strong>Defects</strong> <strong>in</strong> <strong>in</strong>organic <strong>photorefractive</strong> <strong>materials</strong> <strong>and</strong> <strong>their</strong> <strong>in</strong>vestigations 35<br />
hologram fix<strong>in</strong>g is the production of very-narrow-b<strong>and</strong>width <strong>in</strong>terference filters<br />
by hydrogen dop<strong>in</strong>g. This subject has been reviewed by Cabrera et al.<br />
[215].<br />
Some changes of physical properties are reflected <strong>in</strong> the position or shape<br />
of the OH absorption spectra. An example for such strong <strong>in</strong>fluence is given<br />
<strong>in</strong> Chapter 6 of this book, were the stretch mode was used to monitor changes<br />
<strong>in</strong>duced <strong>in</strong> LiNbO 3 crystals doped with damage-resistent impurities like Mg,<br />
Zn, In or Sc.<br />
9 Summary<br />
We have spread out the rich field of defects <strong>in</strong> most of the <strong>in</strong>organic <strong>photorefractive</strong><br />
<strong>materials</strong> <strong>in</strong>vestigated at present. The aim is to contribute to the<br />
improvement of <strong>their</strong> performance <strong>in</strong> <strong>their</strong> various application. Emphasis was<br />
therefore first on the elucidation of the identity of the defects <strong>and</strong> <strong>their</strong> microscopic<br />
defect structures. Studies by EPR <strong>and</strong> related methods, such as ODMR<br />
<strong>and</strong> ENDOR, are unsurpassed for this goal. Second, <strong>in</strong> order to connect these<br />
data to the <strong>photorefractive</strong> effect, close l<strong>in</strong>ks to the optical defect phenomena<br />
have been established where possible. Here a strong tool is ODMR via the<br />
MCD of a defect. Furthermore it is seen that the analysis of the changes of<br />
optical absorption, EPR <strong>and</strong> MCD <strong>in</strong> photochromic <strong>materials</strong> under vary<strong>in</strong>g<br />
pumplight illum<strong>in</strong>ations can furnish a systematic approach to the identification<br />
of defects <strong>and</strong> the paths of light-<strong>in</strong>duced charge transfers between them.<br />
Also a quantitative assessment of the <strong>photorefractive</strong> performance of a material<br />
can be derived from this method. It applies to all defects, <strong>in</strong>dependent of<br />
whether they are identified by EPR or not. While the results presented <strong>in</strong> this<br />
Chapter are more of a basic nature, it is anticipated that they will establish<br />
a foundation on which the further Chapters <strong>in</strong> the book, focuss<strong>in</strong>g on the<br />
details of the <strong>photorefractive</strong> effect <strong>in</strong> most of the <strong>materials</strong> treated here, can<br />
be l<strong>in</strong>ked to the microscopic orig<strong>in</strong>s of the phenomena.<br />
References<br />
1. Topics <strong>in</strong> applied physics, vol. 61 <strong>and</strong> 62. In P. Günter <strong>and</strong> J. P. Huignard,<br />
editor, Photorefractive Materials I <strong>and</strong> II. Spr<strong>in</strong>ger, 1988.<br />
2. K. Buse. Appl. Phys., B 64:391, 1997.<br />
3. W. Hayes <strong>and</strong> A. M. Stoneham. <strong>Defects</strong> <strong>and</strong> defect processes <strong>in</strong> nonmetallic<br />
solids. Wiley, 1985.<br />
4. K. Buse. Appl. Phys. B, 64:273, 1997.<br />
5. P. W. Atk<strong>in</strong>s. Physical Chemistry. Oxford University Press, 1986, p. 275.<br />
6. W. B. Fowler. Electronic states <strong>and</strong> optical transitions of color centers. In W. B.<br />
Fowler, editor, Physics of Color Centers, page 53. Academic Press, 1968.<br />
7. O. F. Schirmer. Z. Physik, B 24:235, 1976.<br />
8. D. Em<strong>in</strong>. Phys. Rev., B 48:13691, 1993.