Filtern
Dokumenttyp
- Vortrag (4) (entfernen)
Sprache
- Englisch (4)
Referierte Publikation
- nein (4) (entfernen)
Schlagworte
- Quantum Yield (4) (entfernen)
Eingeladener Vortrag
- nein (4)
Hexagonal beta-NaYF₄ doped with 20 % Yb and 2 % Er is an efficient upconversion (UC) phosphor for the conversion of 976 nm to 845 nm, 655 nm and 540 nm light. The emission behavior of this material is strongly influenced by the particle size, surface chemistry, and microenvironment. Especially the design of nm-sized UC particles for bioanalytical applications requires reliable spectroscopic tools for the characterization of the optical properties of these materials like the UC quantum yield (QYUC) in aqueous media. The UC emission originates from multiphotonic absorption processes, rendering the QYUC excitation power density (P) dependent. The P-dependent absolute measurement of QYUC in aqueous media with an excitation wavelength of 976 nm presents a considerable challenge due to the low absorption coefficients of the UC materials and the absorption of water at this wavelength.
Here, we present the P-dependent QYUC of 21 nm, 26 nm and 31 nm-sized NaYF₄ UC particles dispersed in cyclohexane and aqueous solutions, in view of bioanalytical applications. To gain a better insight of the photonic nature of the upconversion mechanism and the quenching processes involved, the luminescence decay behavior as well as the P-dependent red-to-green luminescence intensity ratios and slope factors of the different emission bands are studied in both solvents. These results present an important step to the rational design of brighter upconversion nanoparticles.
The design of bright of upconversion nanoparticles requires an improved understanding of the radiationless deactivation pathways in UCNP, that are affected by their size1,2, surface chemistry,2 and microenvironment 3,4. In this respect, we discuss experimental requirements of an integrating sphere setup for absolute measurements of the excitation power density dependent quantum yield5,6 (UC(P)) in the VIS to IR spectral region. We report systematic studies of the influence of the UCNP size, surface ligands, and solvent on the UC(P), the up- and downconversion luminescence decay behavior, the power dependent intensities of the individual emission bands, and their slope factors.
Here, we report on the recent advancements in the synthesis and optical properties of novel core-shell CdSe semiconductor nanocrystals (SCNC) with either a thick monolithic shell of CdS or thin multi-shells of succeeding CdS and ZnS monolayers, characterized by steady state and time-resolved fluorescence spectroscopy at the ensemble level. SCNC samples, chosen upon the size of their photoluminescence quantum yield (PL QY), were subsequently investigated at the single particle level using a custom build confocal laser scanning microscope to obtain information on brightness, blinking behavior, and decay kinetics of single SCNCs and correlate these properties with their surface morphology. The results of this study can help to identify new synthetic routes and surface modifications to colloidally and photochemically stable SCNCs with a PL QY of close to unity.