 Professor
R.G. Denning
Inorganic Chemistry Laboratory
Telephone: 44 (0) 1865 272 631
My group usually consists of two or three Part II students, some
doctoral students and several post-doctoral assistants. All our
work is centred round the optical properties of condensed matter,
and makes use of laser spectroscopy as well as measurements of non-linear
optical parameters. There is considerable interaction with other
ICL groups interested in the solid state. We are at the physical
end of the spectrum of ICL activities, but usually do some straightforward
synthesis, some spectroscopy at liquid helium temperatures and some
interpretation. We grow crystals from solution and from melts, make
glasses and polymer films, all containing species with important
optical properties. Our recent industrial collaborators include
British Telecom and British Nuclear Fuels Ltd.
Our apparatus is centred round three Neodymium-YAG lasers, one
generating 40 ps pulses, another with higher power 10 ns pulses
that drives a dye laser with a tuneable output covering most of
the visible, UV and near-IR regions of the spectrum, and a third
used for the measurement of non-linear optical properties. We have
a number of optical cryostats including one with a base temperature
of 0.3°K, and another containing a superconducting magnet with
a field of 5 Tesla.
At the moment the following subject areas are being pursued:
1. Two-photon Spectroscopy of Inorganic Chromophores:
This technique has selection rules, in centrosymmetric environments,
which are complementary to those operating in ordinary one-photon
spectroscopy. For example the pure electronic transitions within
the d-shell of transition metals, as well as the f-shell of lanthanides
and actinides, which are forbidden by the one-photon electric-dipole
mechanism, can be clearly indentified in this way. Currently we
are using two-photon data to investigate how the crystalline field
in lanthanides modifies the electron-correlation interaction. This
objective is aided by extensive model calculations.
2. Materials for Non-Linear Optic Applicatons:
These have applications in switching and routing at telecommunications
nodes, as well as in all-optical computing. We are studying a variety
of compounds with large third-order non-linear optic coefficients,
using a technique known as Degenerate Four-Wave Mixing. These include
metal-dithiolene complexes, and conjugated porphyrin polymers. The
latter, made by Dr Anderson’s group in the Department, have
coefficients amongst the largest ever measured in non-absorbing
materials. We have also studied the second-order coefficients of
mixed-valence metal compounds, which have the highly direction charge
transfer transitions. For this purpose we have constructed the only
UK instrument capable of measuring Hyper-Rayleigh Scattering.
3. Photonic Bandgap Devices: These rely on an
entirely new class of materials intended to control and manipulate
photons in a manner analogous those used to control electrons in
semiconductors. Currently the properties of these devices are only
understood in theory, amongst the most striking being the suppression
of spontaneous emission, and the prospect of lasers that operate
with very low thresholds. However a satisfactory fabrication method
has not yet been found. In a collaboration with the Clarendon Laboratory
we have developed a simple three-dimensional holographic technique
for the fabrication of these devices, which we have patented. Numerous
chemical challenges occur in optimising this method.
Selected recent publications:
1. A.J. Berry, I.D. Morrison and R.G. Denning, “Energy Levels
of terbium(III) in the elpasolite Cs2NaTbF6”.
Mol. Phys., 93, 1-14 (1998)
2. S.M. Kuebler, R.G. Denning and H.L. Anderson, “Large
Third-Order Electronic Polarizability of a Conjugated Porphyrin
Polymer.” J. Am. Chem. Soc., 122,
339-347 (2000)
3. R.G. Denning, “Chromophores for Second-Order Non-linear
Optic Materials”, J. Mater. Chem., 5,
365-378 (1995)
4. M. Campbell, D.N. Sharp, M.T. Harrison, R.G. Denning and A.J.
Turberfield, " Fabrication of Photonic Crystals for the visible
spectrum by Holographic Lithography.” Nature, 404,
53, (2000)
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