Prof. Chrysochoos
Chemistry Department
2272 WO
University of Toledo


Chrysochoos Faculty Page

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John Chrysochoos
Professor
Professional Background:
Diploma of Chemistry 1957, University of Athens (Greece);
M. Sc. 1962, Ph.D. 1964, University of British Columbia (Canada);
Postdoctoral 1964-65 Harvard University (Chemistry Dept.);1965-67 Michael Reese Hospital and Medical Center (Radiation Therapy Dept.) and Illinois Institute of Technology (Physics Dept.)
Email: 
Office:		 jchryso@uoft02.utoledo.edu
WO 2272		   Phone: 
Fax:		 (419) 530-1503
(419) 530-4033
Research Synopsis:
Physical Chemistry:
Chemical kinetics; spectroscopy; molecular luminescence; lasers, photochemistry; radiation chemistry; spectroscopy of trivalent lanthanides in solution, crystals, glasses, and in the gas phase; electron transfer reactions; spectroscopy and photoreactivity of metalloporphyrins; theory of nonradiative transitions; spectroscopy of semiconductor clusters; photochemical reactions at the surface of semiconductor clusters and interfacial electron transfer.

Excitation of trivalent lanthanide ions in various environments leads to characteristic emission arising from one or more excited multiplet states. The quantum efficiency of the emission observed depends very strongly on the nature of the environment of the lanthanide ion. The highest quantum yields measured are less than unity indicating the existence of nonradiative channels via which electronic excitation energy is dissipated. Such nonradiative channels involve molecular vibrations, phonons, and other killer traps of excitation energy.

Trivalent lanthanides dissolved in POCl3:SnCl4 and other similar inorganic solvents are being used to study appropriate nonradiative transitions. Such solvent systems are characterized by low energy vibrational modes. The efficiency of nonradiative transitions of Ln3+ in such systems is similar to that in glass. In addition, dynamic interactions can be easily studied in such liquid systems. The ions Tb3+, Sm3+, Pr3+, Tm3+, and Dy3+ have been studied; Er3+ and Ho3+ are to be studied in the near future. These studies are corroborated with appropriate spectroscopic studies of Ln3+ in CaF2 and in glasses.

Substitution of Ca2+ by Ln3+ in CaF2 single crystals introduces a charge imbalance in the host which is compensated via F- or other interstitial anions. The compensation an ion gives rise to formation of distinct Ln3+ -sites (defects) such as cubic (Oh), tetragonal (C4v), trigonal (C3v), rhombic, aggregates, and others. We are studying the nature and distribution of local site symmetries in CaF2:Ln3+ using laser induced emission, IR spectroscopy, and MCD. In addition, the effect of UV light and X-rays on the distribution of such sites will be studied. The conclusions of these studies will be extended from single crystals to amorphous solids (glasses).

Incorporation of trivalent lanthanide ions into the cavity of porphyrins affects the optical, redox, and photoconducting properties of such systems in solution and in thin films. Light-induced electron transfer reactions are being studied using flash and steady state spectroscopy. We are studying dynamic interactions between excited porphyrins and Ln3+ in solution via fluorescence arising from both porphyrins and Ln3+, and interfacial electron transfer from CdS clusters to metalloporphyrins.

We are interested in the optical, redox, photocatalytic, and photoconducting properties of semiconductor particles in colloidal suspensions, thin films, and powders. At the present time we are studying the spectroscopic properties of colloidal CdS and CdS:Ln3+. Efforts are under way to correlate the band gap energy and photoredox properties of the semiconductor cluster to their size and nonstoichiometry. Both binary and ternary semiconductor nanoparticles are prepared as colloidal suspensions (30-80 ª) in nonaqueous systems and studied spectroscopically. Their potential catalytic properties are being probed. Plans are under way for their deposition as thin film on pretreated electrodes. The project is gradually evolving into spectroscopic and photocatalytic studies of thin semiconductor films.