Optical excitation of MgO nanoparticles; a computational perspective

The optical absorption spectra of magnesium oxide nanoparticles, along with the atomic centres responsible for the absorption, are studied using time-dependent density functional theory.

Theoretical design study on photophysical property on oligomers based on spirobifluorene and carbazole-triphenylamine for PLED applications

The photophysical properties of five blue light-emitting polymers based on spirobifluorene applied in polymer light-emitting diodes (PLED) materials have been studied by quantum chemistry. In order to understand the intrinsic reasons for the different performances displayed by the polymers, we carried out density functional theory (DFT) and Marcus theory investigations on their oligomers in terms of structure and properties stability, absorption and emission properties, and carrier injection and transport properties. Especially, some important parameters which had not been reported to our knowledge were given in this contribution, such as the ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ), ke/kh (the ratio between the electron transfer rate (ke) and hole transfer rate (kh)), and the radiative lifetimes (τ). The main results indicate that the co-oligomers of PCC-1, PCC-2, and PCC-3 with push-pull interactions produced by the existing D-A segments have better carrier injection and transport properties than the oligomers of PSF and PCF. Especially PCC-2 co-oligomer, its large radiation lifetime (7.46 ns) and well balanced and adequate carrier transport guarantee its champion performance for PLED. The calculated results coincide with the experimental ones. Besides, PNF structurally similar to PCC-2 has similar photoelectric properties to PCC-2 in theory, and the fluorescence emission of PNF co-oligomer is superior to PCC-2 co-oligomer. Therefore, we predict that PNF is a promising candidate for PLED.

Photoluminescence in semiconductor nanoparticles: an atomistic view of excited state relaxation in nanosized ZnS

We discuss how an approach that combines global optimisation and time-dependent density functional theory (TD-DFT) calculations allows one to predict the photoluminescence (PL) signature of true nanosized semiconductor nanoparticles. As a demonstration we calculate the PL signature of both bare and water covered zinc sulfide nanoparticles and demonstrate that we can successfully reproduce their experimentally measured PL signatures. Our TD-DFT calculations suggest that the excited state, after relaxation, becomes highly localised and that the degree of localisation changes with nanoparticle size. We also show that adsorbed water molecules can strongly influence the nanoparticle's final excited state minimum and PL signature. Finally, we discuss how this approach can be used to predict the effect of doping and what the next important methodological step will be on the route to theoretically understanding processes such as photocatalysis.