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author:("Nyk, marcain")
1.  Morphology- and size-dependent spectroscopic properties of Eu3+-doped Gd2O3 colloidal nanocrystals 
The synthesis, morphological characterization, and optical properties of colloidal, Eu(III) doped Gd2O3 nanoparticles with different sizes and shapes are presented. Utilizing wet chemical techniques and various synthesis routes, we were able to obtain spherical, nanodisk, nanotripod, and nanotriangle-like morphology of Gd2O3:Eu3+ nanoparticles. Various concentrations of Eu3+ ions in the crystal matrix of the nanoparticles were tested in order to establish the levels at which the concentration quenching effect is negligible. Based on the luminescence spectra, luminescence lifetimes and optical parameters, which were calculated using the simplified Judd–Ofelt theory, correlations between the Gd2O3 nanoparticles morphology and Eu3+ ions luminescence were established, and allowed to predict the theoretical maximum quantum efficiency to reach from 61 to 98 %. We have also discussed the impact of the crystal structure of Gd2O3 nanoparticles, as well as coordinating environment of luminescent ions located at the surface, on the emission spectra. With the use of a tunable femtosecond laser system and the Z-scan measurement technique, the values of the effective two-photon absorption cross-section in the wavelength range from 550 to 1,200 nm were also calculated. The nonlinear optical measurements revealed maximum multi-photon absorption in the wavelength range from 600 to 750 nm.
doi:10.1007/s11051-014-2690-x
PMCID: PMC4201743  PMID: 25346614
Oxide nanoparticles; Lanthanide luminescence; Judd–Ofelt theory; Z-scan technique; Nonlinear optics; Colloidal stability
2.  Ligand-dependent luminescence of ultra-small Eu3+-doped NaYF4 nanoparticles 
Pure cubic phase ultra-small α-NaYF4:4 % Eu3+ colloidal nanoparticles were synthesized by thermal decomposition reaction using three various capping ligands, i.e., oleic acid, trioctylphosphine oxide, and hexadecylamine. To expose as many Eu3+ ions as possible to interactions with the surface-bounded ligands, the nanoparticles were fabricated to have the diameters below 10 nm. The geometrical structure and properties of surface ligands needed for qualitative estimation of their influence on spectroscopic features of the investigated Eu3+ doped nanoparticles were obtained from DFT quantum-chemical calculations. Significant changes of luminescence spectra shapes and luminescence lifetime values were observed upon changes in the local chemical environment. We show that the ratio R = 5D0 → 7F1/5D0 → 7F2 of the intensities of the forced electric dipole (J = 2) and magnetic dipole (J = 1) transitions in the synthesized Eu3+ doped nanoparticles is highly sensitive to the type of ligand present on the nanoparticle surface. Similarly, 5D0 luminescence lifetimes are found to be sensitive to the refractive index, and also to the dielectric constant of ligands used during the synthesis to coat nanoparticles surface. We argue that the photophysical and electro-optical properties of colloidal Eu3+ doped inorganic nanoparticles show hyper-sensitive response to the chemical surroundings in the close vicinity of the nanoparticle itself. The behavior of both steady-state luminescence and its kinetics demonstrates the potential suitability of the studied nanoparticles for constructing self-referencing optical nano-sensors.
Electronic supplementary material
The online version of this article (doi:10.1007/s11051-013-1707-1) contains supplementary material, which is available to authorized users.
doi:10.1007/s11051-013-1707-1
PMCID: PMC3691485  PMID: 23807867
NaYF4 nanocrystals; Hypersensitive transitions in Eu3+ ions; Nano-scale sensing
3.  High Contrast In vitro and In vivo Photoluminescence Bioimaging Using Near Infrared to Near Infrared Up-Conversion in Tm3+ and Yb3+ Doped Fluoride Nanophosphors 
Nano letters  2008;8(11):3834-3838.
A new approach for photoluminescence imaging in vitro and in vivo has been shown, utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors. This NIR-to-NIR up-conversion process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Aqueous dispersible fluoride (NaYF4) nanocrystals (20–30 nm size) co-doped with the rare earth ions, Tm3+ and Yb3+, were synthesized and characterized by TEM, XRD and photoluminescence (PL) spectroscopy. In vitro cellular uptake was shown by the PL microscopy visualizing the characteristic emission of Tm3+ at ~ 800 nm excited with 975 nm. No apparent cytotoxicity was observed. Subsequent animal imaging studies were performed using Balb-c mice injected intravenously with up-converting nanophosphors, demonstrating the high contrast PL imaging in vivo.
doi:10.1021/nl802223f
PMCID: PMC3523349  PMID: 18928324
Nanophosphors; Energy Up-conversion; Near Infrared In vitro and In vivo imaging
4.  Zinc Oxide Nanocrystals for Non-resonant Nonlinear Optical Microscopy in Biology and Medicine 
In this paper we show that biocompatible zinc oxide (ZnO) nanocrystals (NCs) having non-centrosymmetric structure can be used as non-resonant nonlinear optical probes for targeting in bioimaging applications in vitro by use of the second order processes of second harmonic and sum frequency generation, as well as the third order process of four wave mixing. These non-resonant processes provide advantages above and beyond traditional two-photon bioimaging: (i) the probes do not photo-bleach; (ii) the input wavelength can be judiciously selected; and (iii) no heat is dissipated into the cells, ensuring longer cell viability and ultimately longer imaging times. ZnO NCs have been synthesized in organic media by using a non-hydrolytic sol-gel process, and subsequently dispersed in aqueous media using phospholipid micelles, and incorporated with the biotargeting molecule folic acid (FA). Sum Frequency, Second Harmonic and non-resonant four wave mixing non-linear signals from this stable dispersion of ZnO NCs, targeted to the live tumor (KB) cells were used for imaging. Robust intracellular accumulation of the targeted (FA incorporated) ZnO nanocrystals could be observed, without any indication of cytotoxicity.
doi:10.1021/jp801684j
PMCID: PMC2685283  PMID: 19633706

Results 1-4 (4)