Condensed Matter Physics Seminar

Spectroscopy and fluorescence dynamics of lanthanides in nano-phosphors

Dr. Guokui Liu
Chemistry Division
Argonne National Laboratory
Tuesday, January 24, 2006
Higgins 235, 3pm

Electronic energy level structures and excited state dynamics of optical centers in nanocrystals may exhibit quite different characteristics than those in bulk materials. In addition to quantum confinement on electronic states, the density of phonon states in a nanocrystal is also discrete, and vibrational modes are eliminated in the low energy range. Therefore, for phosphors and luminescent centers (ions and molecules) in dielectric crystals, reducing the crystal size to nanometer scale may lead to interesting phenomena that are not observable in bulk crystals. For instance, the dynamics of optically-excited electronic states of ions in nanocrystals, such as non-radiative relaxation and phonon-assisted energy transfer, have been observed to vary as a function of particle size, or to exhibit anomalous temperature dependence. Results obtained from laser spectroscopic experiments on lanthanide activated luminescent nano- particles and nano-structured core-shell phosphors will be discussed with an emphasis on fundamental understanding of quantum confinement mechanisms and potential applications.