Group Leader and Professor at the RSC
The area of my interests has been, broadly, inorganic materials in the solid state as studied by optical and magnetic resonance spectroscopies. I have been involved in the development and deployment of a number of new spectroscopic techniques in chemical spectroscopy. The application of new techniques and enhancements of established spectroscopies has led to an improved understanding of the electronic structure and photophysical processes in systems of current chemical interest. In some cases, the results have been quite revolutionary with paradigms in the literature being gradually overturned. I have taken a strong interest in theory throughout my career and have been involved in a number of quite significant and long lived theoretical developments.
Ligand Field Theory & Vibronic Processes: development of "spectroscopic" models of inorganic complexes; detailed analyses of Hertzberg-Teller & Jahn-Teller processes; applications of magnetic circular dichroism and related techniques to inorganic complexes in crystals and solid solutions;
Magnetism: exchange coupling in metal dimers; magneto-optical properties of linear chain ferromagnets; magnetic circular dichrosim study of XeF radicals;
Mixed Valence: Piepho-Krausz-Schatz (PKS) theory of mixed valence; spectroscopic studies of strongly and weakly coupled mixed valence dimers; strong coupling model of osmium di-nitrogen dimer; trigonal symmetry mixed valence dimers;
Charge Transfer: "multi-technique" spectroscopic studies on prototypal metal to ligand charge transfer complexes; identification of the role of microheterogeneity in inorganic complexes; theory of electrochromism for degenerate states; ultra-high spectral resolution in a complex; direct observation of internal electron transfer processes; intramolecular "mini-exciton" features in osmium complexes;
Techniques: magnetic circular dichroism and related techniques as general tools in chemical spectroscopy; the C term saturation technique in magnetic circular dichroism, theory and practice; the matrix injection technique, transfer of vacuum deposited argon isolation films into liquid helium without warming; detector optimisation and enhancement in optical spectroscopy; magnetic circular dichroism of vibrational transitions; utilization of computer interface techniques to enhance spectrometer and laser performance; laser stabilization with controlled mode hopping as a method in high resolution spectroscopy; line narrowing and spectral hole burning applied to chemistry;
Instrumentation: development of the first GHz NQR spectrometer; design and development of pulsed Zeeman apparatus; cryogenic flow tube and cryostat development; highest performance magnetic circular dichroism spectrometer; operational from the ultraviolet to infra-red; design of high performance micro-crystal, low temperature, single crystal, Raman and polarized absorption spectrometers;
CURRENT WORK:.
We are active in what we term the "conventional" electronic spectroscopies of inorganic materials. Polarised absorption, emission, excitation, Raman, Zeeman and magnetic circular dichroism spectroscopies. This work is spread evenly between measurements on new and perhaps exotic materials such as the monovalent nickel oxides and more detailed work on inorganic systems such as chrome alums, which are, perhaps surprisingly, rather incompletely understood.
We have made great strides in the understanding of a number of systems using the laser based techniques of spectral hole burning and fluorescence line narrowing. Results in this area have been not only very informative but also quite spectacular.
We continue to make unitiatives in the area of non-linear spectroscopies including two photon absorption and the related phenomenon of harmonic generation. This work involves collaboration with Laser Physics in RSPhysS and synthetic groups that are able to "design" new materials with specific non-linear properties.
Charge Transfer: unambiguous assignments and direct measurement of excited state electric dipole moment via the stark effect; narrowest electronic feature yet observed in a coordination compound (14 MHz) via stark swept transient hole burning; theoretical analysis of electrochromism; first resonant line narrowing of charge transfer excitations in an amorphous medium; direct observation of intramolecular electron transfer using time resolved line narrowing; assignments and analysis of intramolecular mini-exciton coupling in osmium metal to ligand charge transfer excited states; vibrational coupling of spectator ligands to single ligand localized metal to ligand charge transfer processes;
Jahn-Teller Systems: complete analysis of via magnetic circular dichroism, electron paramagnetic resonance and photoluminescence of "cubic copper" in KZnF3; first observation of the weak magnetic dipole origin in a Cu(II) coordination compound; analysis of trigonal fields and tetragonal fields in a Cu(II) "cage";
Magnetism: detailed spectra of the complex vibronic structure over the entire visible to near IR, absorption and magnetic circular dichroism in Cs3Mo2(Cl,Br)9. metal-metal bonding, exchange interactions and double excitations;
Microheterogeneity: non-correlation in d-d excitations of chromium complexes, quantitative analysis of local field variations in amorphous media; non-correlation of 3p-p* excitations in an iridium tris immine complex, a quantitative explanation of the source of apparent "dual emission" in amorphous media; strong correlation of characteristic 3MLCT (spin-orbit) splittings on a single ligand, in contrast to non-correlation of charge transfer excitations on crystalographically equivalent ligands.
Matrix Isolation: measurement of metal phthalocyanines and other chromophores isolated in solid argon matrices and cooled to 1.6 K via the "injection technique", rapid photochemical and photophysical hole- burning in matrices.
Photosystem II: Identification of optical transitions associated with the Manganese cluster Oxygen Evolving system in photosystem 2. Absorption, CD, MCD, emission of active 'core' complexes of photosystem II. Structural characterisation of the pigments and redox components in the reaction centre.
Spectroscopic techniques, so important in the molecular sciences, have often been adapted from discoveries in physics and subsequently applied to a wide range of questions in molecular science. Nuclear magnetic resonance serves as an example. Although arguably the most important technique in chemistry, nmr was initially discovered and largely abandoned by physicists.
Our research group is unique in not only being able to perform a wide range of "conventional" optical spectroscopies at the highest levels, but also in having pioneered the application of a number of new laser based techniques to chemical problems. One aim is to continually evolve these capacities.
Our technical capacities and our strong links with the physics community has given us the ability to provide a far broader and more incisive "multi-technique" view of some controversial questions in inorganic spectroscopy. Many groups concentrate on a single spectroscopic technique. We have, for example, used our approach to great advantage in the subject of charge transfer excitations and excitation hopping rates.
Our research program involves the development of an understanding of the electronic structure and photophysical properties, principally of inorganic materials, at the highest level both experimentally and theoretically. Critical to this process is the application of the most appropriate spectroscopic techniques, often in parallel, targeted to each particular problem. The spectroscopic technologies themselves need to be maintained, enhanced and evolved. We see recent developments in density functional computational methods as reaching a level where theory has a more useful function in spectroscopy.
High and ultra-high resolution spectroscopy is an area in which we have excelled and broken considerable new ground. We have obtained some funding from the major equipment committee to allow us to pursue the promising area of transient hole burning. This technique has the great advantage of being "jitter free" and independent of the long term stability of a laser source. We also plan to introduce and develop high resolution optical/radio frequency methods, which will allow some of the double resonance techniques (ENDOR, COSY etc.) so useful in magnetic resonance, to be applied to optical transitions and excited states.
The relative ease in which fully computer controlled equipment can now be assembled, allows us to fabricate dedicated facilities, largely utilizing componentry already on hand, on a more permanent and user friendly basis
Non-linear processes in optical spectroscopy have become increasingly accessible with the use of high power pulse lasers. Wavelength tuneable non-linear measurements are becoming more routine with improving laser and detector technology. Our Mirage 500 optical parametric oscillator laser operates from 400 nm to 2000 nm while maintaining close to transform limited linewidth (300 MHz), is a good example of this dramatically improved capacity.
The measurement of higher order light/matter interaction processes provide an important new dimension in the understanding the electronic structure of materials. A fundamental understanding of non-linear processes in new chemical materials is a key element in the development of new, high speed optical devices and in the fabrication of systems with relevance to molecular electronics and optical computing. [Publications] for Key Publications & current papers. Email : krausz@rsc.anu.edu.au
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