The correlation between structural and electronic order-disorder effects in understanding the optical properties of flower-like ZnO nanocrystals synthesized by the microwave-assisted hydrothermal method at low temperatures and short times is discussed. Theoretical simulations were performed at the density functional theory level to gain a better understanding of the experimental data from X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), electron paramagnetic resonance (EPR), ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy and photoluminescence (PL) measurement studies at different temperatures. The decrease in band gap values is due to the presence of intermediate states above the conduction band. These discrete levels are formed by structural and electronic disorder of tetrahedral [ZnO 4 ] clusters which enhance the electron-hole pair.
Cyanine
dye molecules, used as monomers or in aggregate form, find
interesting applications in optoelectronic devices. Among the various
aggregate species incorporating organic dyes, centrosymmetric dimers
are known as nonluminescent. They can act as exciton quenchers due
to a low-energy optically forbidden excited state. In this study,
however, we show that a dimer species in thin films exhibits efficient
and strongly red-shifted photoluminescence. When the films were excited,
a monomer emission at 590 nm along with a second emission peak at
680 nm was observed. A close relation between the dye concentration
and the emission showed that a new emission at 680 nm corresponds
to the dimer emission. Circular dichroism (CD) spectroscopy reveals
that a fraction of the dimers exist in a twisted dimer configuration.
Stable, long-lived, and quenchable fluorescence with high quantum
yield is attributed to this dimer emission.
Today numerous cyanine dyes that are soluble in organic solvents are available, driven by more than a century of research and development of the photographic industry. Several properties specific to cyanine dyes suggest that this material class can be of interest for organic solar cell applications. The main absorption wavelength can be tuned from the ultraviolet to the near-infrared. The unparalleled high absorption coefficients allow using very thin films for harvesting the solar photons. Furthermore, cyanines are cationic polymethine dyes, offering the possibility to modify the materials by defining the counteranion. We here show specifically how counterions can be utilized to tune the bulk morphology when blended with fullerenes. We compare the performance of bilayer heterojunction and bulk heterojunction solar cells for two different dyes absorbing in the visible and the nearinfrared. Light-induced Electron Spin Resonance (LESR) was used to study the charge transfers of light induced excitons between cyanine dyes and the archetype fullerene C 60. LESR results show good correlation with the cell performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.