Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Quantum dot (QD) based nanomaterials are very promising materials for the fabrication of optoelectronic devices like solar cells, light emitting diodes (LEDs), and photodetectors as well as as reporters for chemo- and biosensing and bioimaging. Many of These applications involve the monitoring of changes in photoluminescence intensity and energy transfer processes which can strongly depend on excitation wavelength or energy. In this work, we analyzed the excitation energy dependence (EED) of the photoluminescence quantum yields (PL QYs) and decay kinetics and the circular dichroism (CD) spectra of CdSe/CdS core/shell QDs with different thicknesses of the surface passivation shell. Our results demonstrate a strong correlation between the spectral position of local maxima observed in the EED of PL QY and the zero-crossing points of the CD profiles. Theoretical analysis of the energy band structure of the QDs with effective mass approximation suggests that these structures could correspond to exciton energy levels. This underlines the potential of CD spectroscopy for the study of electronic energy structure of chiroptically active nanocrystals which reveal quantum confinement effects.
The implementation of fluorescent methods is of outstanding importance in the field of optical chemical sensor Technology and biosciences. Their bioanalytical applications are manifold including fluorescence microscopy, fluorescence in situ hybridization, DNA sequencing, fluorescence-activated cell sorting, immunoassays, analysis of DNA and Protein microarrays, and quantitative PCR, just to name a few examples. Particularly, fluorescence microscopy is a valuable method in the versatile field of biomedical imaging methods which nowadays utilizes different fluorescence Parameters like emission wavelength/Color and lifetime for the discrimination between different targets. Sectional Images are available with confocal microscopes. Tissue, cells or single cellular compartments can be stained and visualized with fluorescent dyes and biomolecules can be selectively labeled with fluorescent dyes to Monitor biomolecular interactions inside cells or at Membrane bound receptors.
On the other hand , fluorophores can act as indicator (or "molecular probe") to visualize intrinsically colorless and non-fluorescent ionic and neutral analytes such as pH, Oxygen (pO2), metal ions, anions, hydrogen peroxide or bioactive small organic molecules such as Sugars or nucleotides. Thereby, their photoluminescent properties (fluorescence or phoporescence intensity, exitation and/or Emission wavelength, emission lifetime or anisotropy) respond to the presence of these species in their immediate Environment. In general, the use of luminescent probes has the advantage that they can be delivered directly into the sample, and detected in a contactless remote mode. By now, these probes are often encapsulated in different types of nanoparticles (NPs) made from (biodegradable) organic polymers, biopolymers or inorganic materials like silica or bound to their surface.
At the core of luminescence color and lifetime Tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the Impact of the particle architecture for commonly used sensitizer (S) and activator (A) Ions. In this respect, a series of core@Shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@..., ...@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-Shell NPs. As refealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial Distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical Impact on ther luminescence characteristics. Although the increased amount of Yb3+ Ions boosts UCNP Performance by amplifying the Absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy Migration to the surface, thereby reducing the Overall energy Transfer Efficiency to the activator ions. The results provide yet another proof that UC Phosphor chemistry combined with materials Engineering through intentional core@shell structures may help to fine-tune the luminescence Features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and Display technologies.