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Nd as sensitizer in NaYF4:Yb,Er,Nd tri-doped upconversion nanocrystals

  • In recent years, upconversion nanocrystals (UCNC) have shown great promise for biological and medical applications, mainly because of their excitation in the NIR region, which provides minimum fluorescence background and a rather deep penetration into biological samples, as opposed to excitation in the visible or UV region. Moreover, they show a multitude of characteristic narrow emission bands as basis for ratiometric measurements. Commonly, Yb is the sensitizer of choice, because of a comparatively high absorption cross section, simple energy scheme, and rather efficient energy transfer to the activator, mostly Er, Tm or Ho. A main disadvantage of the use of Yb as sensitizer for biological and medical applications is its absorption band at 976 nm and hence the use of an excitation wavelength at which water has a non-negligible absorption. This can lead to significant sample heating, especially at long illumination times or high excitation power densities, and thus, tissue damage orIn recent years, upconversion nanocrystals (UCNC) have shown great promise for biological and medical applications, mainly because of their excitation in the NIR region, which provides minimum fluorescence background and a rather deep penetration into biological samples, as opposed to excitation in the visible or UV region. Moreover, they show a multitude of characteristic narrow emission bands as basis for ratiometric measurements. Commonly, Yb is the sensitizer of choice, because of a comparatively high absorption cross section, simple energy scheme, and rather efficient energy transfer to the activator, mostly Er, Tm or Ho. A main disadvantage of the use of Yb as sensitizer for biological and medical applications is its absorption band at 976 nm and hence the use of an excitation wavelength at which water has a non-negligible absorption. This can lead to significant sample heating, especially at long illumination times or high excitation power densities, and thus, tissue damage or even cell death. A possible solution is the tri-doping of UCNC with Nd as sensitizer, which can be excited efficiently at around 800 nm, where water absorption is at minimum. The use of Nd as a sensitizer and Yb as a bridge between Nd and the activator Er in NaYF₄ nanocrystals is a relatively new way to overcome the problems of heating of samples in an aqueous environment. Disadvantages can arise from the tri-doping, which can favor non-radiative relaxation due to the more complicated excitation process compared to e.g., simple Yb,Er-doped UCNC, which might lower the upconversion quantum yields in these tri-doped systems. In order to quantify clear advantages, NaYF₄:Yb,Er,Nd nanoparticles were synthesized and spectroscopically studied using an 8 W 804 nm laser diode and a custom-designed Edinburgh instruments FSP980 spectrometer. Wavelength-dependent studies of the emission intensities and the decay kinetics of these tri-doped UCNC at different excitation power densities and excitation pulse widths revealed the clear advantages of preventing water absorption on measurable luminescence signals. We were able to show the influence of pulse width and excitation power density on the luminescence intensities and decay kinetics lifetimes at different emission wavelengths. Additionally, we can clearly discern power density-dependent and independent peaks in the emission spectra. In summary, we demonstrate that the tri-doping of NaYF₄:Yb,Er,Nd nanoparticles is a very promising approach to render UCNC more efficient and to make them better suitable for biological and medical applications requiring measurements in aqueous environment.zeige mehrzeige weniger

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Metadaten
Autor*innen:Bettina Grauel
Koautor*innen:Christian Würth, L. M. Wiesholler, T. Hirsch, Ute Resch-Genger
Dokumenttyp:Posterpräsentation
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2016
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:Nd-sensitizer; UCNP; excitation power density
Veranstaltung:UPCON 2016 Conference
Veranstaltungsort:Breslau, Poland
Beginndatum der Veranstaltung:23.05.2016
Enddatum der Veranstaltung:25.05.2016
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:29.08.2016
Referierte Publikation:Nein
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