Marcin Nyk

High Contrast in Vitro and in Vivo Photoluminescence Bioimaging Using Near Infrared to Near Infrared Up-Conversion in Tm3+ and Yb3+ Doped Fluoride Nanophosphors

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, Tm(3+) and Yb(3+), 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 Tm(3+) at approximately 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.

Neodymium(III) doped fluoride nanoparticles as non-contact optical temperature sensors

We report that non-contact optical temperature sensing can be achieved with the use of heavily Nd(3+) doped NaYF(4) nanoparticles. The temperature evaluation can be realized either by monitoring the absolute luminescence intensity or by measuring the intensity ratio of the two Stark components of the (4)F(3/2) multiplet in the Nd(3+) ions.

Color-coded multilayer photopatterned microstructures using lanthanide (III) ion co-doped NaYF4 nanoparticles with upconversion luminescence for possible applications in security

We report a method for fabricating predefined photopatterns of upconversion nanophosphors using a chemical amplification reaction for direct writing of films with multilayer color-coded patterning for security applications. To photopattern the nanocrystal film we have synthesized rare-earth ion (Er(3+)/Yb(3+) or Tm(3+)/Yb(3+)) co-doped sodium yttrium fluoride (alpha-NaYF(4)) nanophosphors and functionalized the nanocrystal surfaces by incorporation of a photopatternable ligand such as t-butoxycarbonyl (t-BOC). The surface modification allows photopatterning of the nanophosphor solid state film. Furthermore, upconversion nanophosphors show a nearly quadratic dependence of the upconversion photoluminescence (PL) intensity on the excitation light power, and tailoring of the PL wavelength is possible by changing the lanthanide ions. We have demonstrated the capability of anchoring nanophosphors at desirable locations by a photolithography technique. The photopatterned films exhibit fixed nanophosphor structures clearly identifiable by strong upconversion photoluminescence under IR illumination which is useful for a number of applications in security.

Spectrally resolved size-dependent third-order nonlinear optical properties of colloidal CdSe quantum dots

Nonlinear absorption and nonlinear refraction of colloidal CdSe quantum dots (QDs) of two sizes were investigated in a wide spectral range with the Z-scan technique using a tunable femtosecond laser system. The nonlinear absorption was found to be the strongest close to twice the wavelength of the second exciton absorption band of the QDs. Based on nonlinear optical parameters the exciton binding energy has been determined. The current results are compared to the nonlinear properties of CdSe QDs presented in the literature. The features of this system relevant for multiphoton fluorescence microscopy applications are discussed.

Photoluminescence from GaN nanopowder: The size effect associated with the surface-to-volume ratio

Nanosized GaN powder with the average grain size changing from ∼10to∼30nm has been obtained by combustion method with some modifications and its optical properties have been investigated by photoluminescence (PL). The GaN band-gap-related PL band at ∼3.4eV and surface-related PL bands centered at ∼2.0 and ∼2.8eV have been observed for this powder. The relative intensities between observed PL bands change in favor of the surface-related PL band with the decrease of the grain size. This phenomenon has been attributed to the change in the surface-to-volume ratio.

Giant enhancement of upconversion in ultra-small Er3+/Yb3+:NaYF4 nanoparticles via laser annealing

Most of the synthesis routes of lanthanide-doped phosphors involve thermal processing which results in nanocrystallite growth, stabilization of the crystal structure and augmentation of luminescence intensity. It is of great interest to be able to transform the sample in a spatially localized manner, which may lead to many applications like 2D and 3D data storage, anti-counterfeiting protection, novel design bio-sensors and, potentially, to fabrication of metamaterials, 3D photonic crystals or plasmonic devices. Here we demonstrate irreversible spatially confined infrared-laser-induced annealing (LIA) achieved in a thin layer of dried colloidal solution of ultra-small ∼8 nm NaYF₄ nanocrystals (NCs) co-doped with 2% Er³⁺ and 20% Yb³⁺ ions under a localized tightly focused beam from a continuous wave 976 nm medium power laser diode excitation. The LIA results from self-heating due to non-radiative relaxation accompanying the NIR laser energy upconversion in lanthanide ions. We notice that localized LIA appears at optical power densities as low as 15.5 kW cm⁻² (∼354 ± 29 mW) threshold in spots of 54 ± 3 µm diameter obtained with a 10 × microscope objective. In the course of detailed studies, a complete recrystallization to different phases and giant 2-3 order enhancement in luminescence yield is found. Our results are highly encouraging and let us conclude that the upconverting ultra-small lanthanide-doped nanophosphors are particularly promising for direct laser writing applications.

Change in photoluminescence spectra of Eu-doped GaN powders due to the aggregation of nanosized grains into micrometer-sized conglomerations

In this letter, we report a phenomenon of the aggregation of nanocrystalline grains of GaN:Eu into micrometer-sized conglomerates having optical properties different from those of the initial GaN:Eu grains. The nanocrystalline GaN:Eu powders exhibit no emission related to the GaN band gap and a very broad yellow/red PL band associated with recombination in the GaN host matrix via surface states, in addition to the strong Eu3+-related emission, i.e., the D05→FJ7 transitions with J=1, 2, 3, and 4. For the microcrystalline powders, the yellow/red photoluminescence (PL) band disappears and a strong PL band related to the GaN band gap arises. In addition, the Eu3+-related transitions start to split into individual lines typical of Eu-doped bulk-like GaN crystals. These differences in PL spectra have been correlated with the surface/volume ratio of the GaN grains. It has been concluded that, for very small grains (<50nm), surface states determine the optical properties of GaN:Eu powders. Postgrowth processing, ...

Circularly photostimulated electrogyration in europium- and terbium-doped GaN nanocrystals embedded in a silica xerogel matrix

Circularly polarized optical poling was proposed and discovered for GaN nanocrystallites embedded in a silica xerogel matrix. The method consists of the creation of screw-like polarization of the medium during the interaction of two circularly polarized coherent bicolour beams. It was shown that doping of the GaN nanocrystallites by Tb3+ and Eu3+ ions leads to substantial enhancement of the electrogyration. The effect observed is a consequence of the superposition of nanoconfined effects and the contribution of the localized rare-earth 4f levels. The role of the anharmonic electron–phonon interaction is discussed. The photoluminescence and cathodoluminescence spectra of the GaN composites were investigated. It was demonstrated that the Eu-doped nanocrystallites give a substantially higher effect of the electrogyration compared to the Tb-doped and non-doped ones.

Tip enhancement of upconversion photoluminescence from rare earth ion doped nanocrystals.

We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.

Enhanced photorefractive effect in liquid crystal structures co-doped with semiconductor quantum dots and metallic nanoparticles

In this paper, we present strong enhancement of optical properties of hybrid liquid crystal structures functionalized with metallic and semiconductor nanoparticles. Several experiments done in two wave mixing experimental set-up have reported that diffraction efficiency can be improved by up to 14 times by introducing nanoparticles of cadmium selenide or gold into the photoconducting polymer adjacent to the liquid crystal layer. Our research may open up a possible route for the development of faster and more efficient holographic materials which can be used in dynamic data processing systems.