Optical and thermal characterization of dye intercalated montmorillonites and rare earth doped materials Lyjo K. Joseph International School of Photonics Cochin University of Science and Technology Kochi- 682022, Kerala, India Ph. D. Thesis submitted to Cochin University of Science and Technology in partial fulfillment of the requirements for the Degree of Doctor of Philosophy November 2009 Optical and thermal characterization of dye intercalated montmorillonites and rare earth doped materials Ph. D. Thesis in the field of Photonics Author: Lyjo K. Joseph Research Fellow, International School of Photonics Cochin University of Science and Technology Kochi – 682 022, India Email: [email protected], [email protected] Research Advisors: Dr. P Radhakrishnan Professor, International School of Photonics Cochin University of Science and Technology Kochi – 682 022, India Email: [email protected] Dr. V P N Nampoori Professor, International School of Photonics Cochin University of Science and Technology Kochi – 682 022, India Email: [email protected] International School of Photonics, Cochin University of Science and Technology Kochi – 682 022, India URL:www.photonics.cusat.edu November 2009. Cover design: Manu Balakrishnan CERTIFICATE Certified that the work presented in the thesis entitled “Optical and thermal characterization of dye intercalated montmorillonites and rare earth doped materials” is based on the original work done by Mr. Lyjo K Joseph under my guidance and supervision at the International School of Photonics, Cochin University of Science and Technology, Kochi–22, India and has not been included in any other thesis submitted previously for the award of any degree. Kochi – 682022 Prof. P. Radhakrishnan 20th November 2009. (Supervising Guide) DECLARATION Certified that the work presented in the thesis entitled “Optical and thermal characterization of dye intercalated montmorillonites and rare earth doped materials” is based on the original work done by me under the guidance of Dr. P Radhakrishnan, Professor, International School of Photonics, Cochin University of Science and Technology, Kochi–22, India and the co-guidance of Dr. V P N Nampoori, Professor, International School of Photonics, Cochin University of Science and Technology, Kochi–22, India and it has not been included in any other thesis submitted previously for the award of any degree. Kochi – 682 022 20th November 2009. Lyjo K Joseph Dedicated to My parents and the Almighty God Remembering my teachers Late Dr. G V Vijayagovindan (School of Pure and Applied Physics, M G University, Kottayam), Late Smt. Susan John K (Physics Department, Baselius College, Kottayam), & Late H G Markose Mor Coorilose Metropolitan Acknowledgements First of all, I would like to express my sincere gratitude to my research supervisors Dr. P Radhakrishnan, Professor, ISP and Dr V P N Nampoori, the Director of ISP for their guidance, suggestions and support given to me in completing the thesis. Their timely help and motivation are also remembered. I also thank Dr V M Nandakumaran and Dr C P Girijavallabhan for their constant support. Thanks to all other teachers of both ISP and CELOS. I am grateful to Dr Sanjay G and Dr Suja H of Department of Applied Chemistry, CUSAT for providing me dye intercalated montmorillonite samples and to the suggestions regarding the experimental results. Dr K R Dayas, Director, C-MET, Thrissur is also thanked for providing me rare earth titanates and giving me necessary ideas for interpreting the experimental results. I am obliged to my colleagues and friends, especially Sudeesh, Thomas, Linesh, Murali, Bindu and Annieta for helping me with my experimental works and to Sajan, Sriram, Tamilarasan, Sheeba, Prabhath and Sajeev for providing me the necessary reference papers. The encouragement given by all my teachers and friends, particularly my batch-mates Litty and Dann are also remembered. I also acknowledge UGC for financial assistance and CELOS for providing experimental facilities. Thanks to all staff of ISP and CELOS and to Murali, Gopi and Joshi of Instrumentation department. Finally, I express my happiness to my parents and relatives for their support throughout my research. Thanks to my cousin Anju for proof reading. Last, but most important of all, I thank Almighty God Lyjo K Joseph General remarks regarding the thesis: The author has taken reasonable care in the preparation of the thesis. All the available information regarding the references is given including doi and URL. However, certain publishers do not have these options and hence the reader may find some references without doi and URL. Some publishers are providing articles without page numbers. In such cases the article number and the number of pages are specified. A list of abbreviations is also given at the beginning of the thesis for better readability. The division of the chapters is based on the materials used for the studies. Lyjo K Joseph (Author) Preface The photoacoustic (PA) effect was first reported by Alexander Graham Bell in 1880. Up to 1970s the applications of PA were limited and after the development of the Rosencwaig-Gersho theory, numerous inventions and detection schemes were evolved in this field. This has led to consider PA spectroscopy as one of the great rediscoveries of modern science. It is one of the classes of the photothermal phenomena in which the photothermal heating effect is detected by an indirect acoustic method. Photothermal science encompasses a wide range of non-destructive techniques and phenomena based on the conversion of absorbed optical energy into heat. It is an effective research and analytical tool for the characterization of matter in different states. The characteristics of the thermal waves generated in the sample are simply controlled by the frequency of the light source modulator. In PA, the temperature changes in the samples are monitored using a PA cell which uses a sensitive microphone. The net photothermal effect depends on both the optical and the thermal properties of the materials under investigation. As the photothermal methods monitor the non-radiative path, several material properties which are difficult to measure using the conventional spectroscopic methods can be investigated. Laser induced non- destructive PA and photothermal deflection (PTD) techniques are two common methods used for the evaluation of material parameters because of its simplicity and versatility. These methods are intrinsically non-contact in nature. The PTD approach allows point by point scanning of the sample surface and the characterization of anisotropy in thermo-physical properties of the specimens under investigation. In the thesis, the non-destructive and versatile nature of the photothermal experiments have been exploited for the characterization of the materials. The development of more complex materials necessitates a finer characterization of their physical properties and a better knowledge of the physical phenomena that determine their behaviour at the macroscopic level. Nano-composite materials, which contain organic dyes incorporated in a solid matrix, are used in various applications, such as optical sensors, devices for photo-induced switching, solid state lasers and in memory media. Clay minerals are very attractive matrices for the intercalation of dye molecules. Aqueous dispersions of swelling clay minerals are known for their colloidal and rheological properties and have several industrial applications. The increasing interest in dye/ inorganic nano-composites is focused on changes in optical and thermal properties during adsorption and / or intercalation of the dye in an inorganic matrix. Various dye-clay systems offer an interesting area of research, and Preface spectroscopic techniques have been successfully used to study such systems. Montmorillonites are used as a very convenient host structure for the intercalation of organic dyes. In this thesis, non-destructive PA and optical spectroscopic techniques have been effectively utilised to characterise the dye intercalated montmorillonites. The rare-earth doped laser crystals, glasses and ceramics, which possess trivalent rare- earth ions, are popular solid state gain media. Rare-earth based phosphors play a critical and indispensable role as luminescent materials in the display industry. Synthesis of high quality rare earth based phosphor materials is thus important. Rare earth titanates (R2Ti2O7) (RET) have interesting dielectric, piezoelectric and ferroelectric properties. Pyrochlore RETs and zirconates find numerous applications such as hosts for fluorescence centres, high temperature pigments, catalysts, thermal barrier coatings, ionic/ electronic conductors, host phase in nuclear waste control etc. The advent of high optical quality transparent nano-structured glasses, the so-called transparent glass ceramics or vitroceramics disclosed the possibility of producing nano-sized photonic devices based on rare-earth doped up-converters. Transparent glass ceramics have been investigated as hosts for lanthanide ions envisioning the production of materials that are easy to shape and with high performance for photonic applications. Rare earth doped glasses have been extensively studied due to their potential applications in optical devices such as solid state lasers and optical fibers. Various photothermal and optical techniques have been successfully applied for the thermal and optical characterization of these rare earth doped materials. In the present thesis, the effective