Publications of the Department of Physical Chemistry


Fundamental Loading-Curve Characteristics of the Persistent Phosphor SrAl2O4:Eu2+,Dy3+,B3+: The Effect of Temperature and Excitation Density
Delgado, T.; Gartmann, N.; Walfort, B.; LaMattina, F.; Pollnau, M.; Rosspeintner, A.; Afshani, J.; Olchowka, J.; Hagemann, H.
Adv. Photonics Res. 2022, in press.

The compound SrAl2O4:Eu2+,Dy3+ is currently one of the best-performing persistent phosphors and numerous studies have been performed to understand the mechanisms involved in its afterglow process. One aspect which so far has received only limited attention is the dependence of loading curve characteristics on dopant concentrations. Herein, a detailed study of the loading curves of SrAl2O4:Eu2+,Dy3+ as a function of composition, sample temperature, and pump intensity is presented, completed by emission decay and quantum yield measurements. The observed emission decays can be described using the Inokuti−Hirayama equation for a Dexter energy transfer (ET) process. As the Dexter ET rate and the electron transfer rate have a similar radial dependence, the Inokuti−Hirayama equation can also describe the electron transfer process involved for the trapping process. These observations indicate that in this persistent phosphor, the trapping process is a local process; however, different types of traps appear to present different “Dexter” critical radii R0. This electron transfer is also temperature dependent, which requires further investigations.

The excited-state dynamics of the radical anions of cyanoanthracenes
Beckwith, J. S.; Aster, A.; Vauthey, E.
Phys. Chem. Chem. Phys. 2022, 24, archive unige:157670 pdf full text [free access]

The radical anion of 9,10-dicyanoanthracene (DCA) has been suggested to be a promising chromophore for photoredox chemistry, due to its nanosecond excited-state lifetime determined from indirect measurements. Here, we investigate the excited-state dynamics of the radical anion of three cyanoanthracenes, including DCA•−, produced by photoinduced electron transfer in liquid using both pump–probe and pump–pump probe transient electronic absorption spectroscopy. All three excited radical ions are characterised by a 3–5 ps lifetime, due to efficient non-radiative deactivation to the ground state. The decay pathway most probably involves D1/D0 conical intersection(s), whose presence is favoured by the enhanced flexibility of the radical anions relative to their neutral counterparts. The origin of the discrepancy with the nanosecond lifetime of DCA•−* reported previously is discussed. These very short lifetimes limit, but do not preclude, photochemical applications of the cyanoanthracene anions.

Metal nanoclusters as versatile building blocks for hierarchical structures
Bürgi, T.; Banach, E.
Helv. Chim. Acta 2022, in press.

Atomically precise monolayer-protected metal clusters (nanoclusters) are currently in the focus of interest due to their strongly size dependent properties, which gives rise to different applications, and the possibility to study the evolution of structure as a function of size. The use of truly monodisperse metal clusters as building blocks for the preparation hierarchical structures offers exciting possibilities for the design of new materials. In this overview article we describe the current state of the art in the field of assembly of nanoclusters in one, two and three dimensions. The nanoclusters show rich chemistry that can be used for their assembly. Several reports indicate that within the assemblies of clusters their photoluminescence is enhanced. Although there is already a considerable body of reports on the assembly of nanoclusters we believe that much more exciting properties of nanocluster assemblies will be discovered in the future.