Mateusz Banski

Controlled Synthesis of Tuned Bandgap Nanodimensional Alloys of PbSxSe1−x

Truly alloyed PbS(x)Se(1-x) (x = 0-1) nanocrystals (∼5 nm in size) have been prepared, and their resulting optical properties are red-shifted systematically as the sulfur content of the materials increases. Their optical properties are discussed using a modified Vegards approach and the bowing parameter for these nanoalloys is reported for the first time. The alloyed structure of the nanocrystals is supported by the energy-filtered transmission electron microscope images of the samples, which show a homogeneous distribution of sulfur and selenium within the nanocrystals. X-ray photoelectron spectroscopy studies on ligand-exchanged nanocrystals confirmed the expected stoichiometry and various oxidized species.

Selective excitation of Eu3+ in the core of small β-NaGdF4 nanocrystals

The influence of the nanocrystal matrix on the optical properties of lanthanide dopants is investigated with europium ions used as local crystal field probes. The analysis is performed on small NaYF4 and NaGdF4 nanocrystals obtained by the thermolysis of the corresponding metal trifluoroacetates. An important role in the synthesis is played by trioctylphosphine oxide which induces the crystallization of nanocrystals with small diameters (∼5 to 6 nm). In such small particles, the energy transfer from gadolinium to europium ions is studied with photoluminescence, photoluminescence excitation and time-resolved experiments. We demonstrate that excited gadolinium ions efficiently transfer their energy to europium, and their photoluminescence spectra depend on the nanocrystal size. This is contrary to the direct excitation of Eu3+ ions, which produces size-dependent emission corresponding to the surface to volume ratio of europium sites. Finally, we propose that Gd3+ ions transfer their energy mainly to the Eu3+ in the core of the nanocrystals. These observations provide a base for the optically controlled emission from only the core of the nanocrystals.

Influence of Annealing on Excitation of Terbium Luminescence in YAlO3 Films Deposited onto Porous Anodic Alumina

Terbium-doped yttrium-aluminum oxide films were synthesized by spin-on deposition on porous anodic alumina grown on a silicon wafer and annealed from 400 to 1100°C. An influence of the annealing temperature on the terbium photoluminescence (PL) was studied using two-dimensional PL excitation and time-resolved spectroscopy. Further, a comparison of thermal quenching data for the most intensive 5 D 4 → 7 F 5 luminescence band of Tb 3+ ions was performed for 10-300 K. From the resultant data, the mechanisms of Tb excitation and its dependence on the annealing conditions are proposed and discussed.

Multicolor light emitters based on energy exchange between Tb and Eu ions co-doped into ultrasmall β-NaYF4 nanocrystals

Multicolor emission is reported from ultrasmall (<10 nm) β-NaYF4:Eu,Tb nanocrystals depending on the excitation wavelengths or emission detection delay time. Detailed optical investigations of three samples (NaYF4:Eu, NaYF4:Tb and NaYF4:Eu,Tb) obtained by a co-thermolysis method have been carried out. Photoluminescence, photoluminescence excitation and emission decay time obtained at different excitation wavelengths have been measured. Excitation mechanisms of Eu and Tb ions have been explained based on the experimental results and calculations using Judd–Ofelt theory. It has been shown that efficient energy transfer from Tb to Eu ions accounts for the efficient red emission of NaYF4:Tb,Eu nanocrystals.

Excitation Mechanisms of Green Emission from Terbium Ions Embedded Inside the Sol-Gel Films Deposited onto Nanoporous Substrates

In this work we investigate the excitation mechanism of Tb ions in different inorganic sol-gel matrices (composite film of YAlO3 and Al2O3; Ba0,6Sr0,3Ca0,1:TiO3) in porous anodic alumina films. The interest in synthesis of light-emitting materials in porous anodic alumina arises from its unique tailor-made honey-comb structure, strongly enhanced Tb luminescence and great photonic density of states at direction along the channels of the anisotropic light scattering. All discussed sol-gel films were synthesized by spin-on deposition on porous anodic alumina grown on a silicon wafer and annealed at different temperatures. An influence of the annealing temperature on the terbium PL was studied using XRD, 2D photoluminescence excitation and time-resolved spectroscopy. Further, the comparison of thermal quenching data for the most intensive D4 →F5 luminescence band and excitation band of Tb 3+ ions was performed for the temperature range of 10 – 300 K. From the resultant data, mechanisms of Tb excitation and its dependence on the annealing conditions are proposed and discussed.

Hydrophobic sodium fluoride-based nanocrystals doped with lanthanide ions: assessment of in vitro toxicity to human blood lymphocytes and phagocytes.

In vitro immunotoxicity of hydrophobic sodium fluoride‐based nanocrystals (NCs) doped with lanthanide ions was examined in this study. Although there is already a significant amount of optical and structural data on NaYF4 NCs, data on safety assessment are missing. Therefore, peripheral whole blood from human volunteers was used to evaluate the effect of 25 and 30 nm hydrophobic NaYF4 NCs dissolved in cyclohexane (CH) on lymphocytes, and of 10 nm NaYF4 NCs on phagocytes. In the concentration range 0.12–75 µg cm−2 (0.17–106 µg ml−1), both 25 and 30nm NaYF4 NCs did not induce cytotoxicity when measured as incorporation of [3H]‐thymidine into DNA. Assessment of lymphocyte function showed significant suppression of the proliferative activity of T‐lymphocytes and T‐dependent B‐cell response in peripheral blood cultures (n = 7) stimulated in vitro with mitogens phytohemagglutinin (PHA) and pokeweed (PWM) (PHA > PWM). No clear dose–response effect was observed. Phagocytic activity and respiratory burst of leukocytes (n = 5–8) were generally less affected. A dose‐dependent suppression of phagocytic activity of granulocytes in cultures treated with 25 nm NCs was observed (vs. medium control). A decrease in phagocytic activity of monocytes was found in cells exposed to higher doses of 10 and 30 nm NCs. The respiratory burst of phagocytes was significantly decreased by exposure to the middle dose of 30 nm NCs only. In conclusion, our results demonstrate immunotoxic effects of hydrophobic NaYF4 NCs doped with lanthanide ions to lymphocytes and to lesser extent to phagocytes. Further research needs to be done, particularly faze transfer of hydrophobic NCs to hydrophilic ones, to eliminate the solvent effect. Copyright

Influence of neodymium concentration on excitation and emission properties of Nd doped gallium oxide nanocrystalline films

Gallium oxide and more particularly β-Ga2O3 matrix is an excellent material for new generation of devices electrically or optically driven as it is known as the widest band gap transparent conductive oxide. In this paper, the optical properties of neodymium doped gallium oxide films grown by magnetron sputtering have been analyzed. The influence of the Nd ions concentration on the excitation/emission mechanisms of Nd ions and the role of gallium oxide matrix have been investigated. The grain size reduction into gallium oxide films have been observed when concentration of Nd increases. It has been found for all samples that the charge transfer is the main excitation mechanism for Nd ions where defect states play an important role as intermediate states. As a consequence Nd emission efficiency increases with temperature giving rise to most intensive emission at 1087 nm at room temperature.

Visualization of melanoma tumor with lectin-conjugated rare-earth doped fluoride nanocrystals.

Aim To develop specific fluorescent markers for melanoma tumor visualization, which would provide high selectivity and reversible binding pattern, by the use of carbohydrate-recognizing proteins, lectins, combined with the physical ability for imaging deep in the living tissues by utilizing red and near infrared fluorescent properties of specific rare-earth doped nanocrystals (NC). Methods B10F16 melanoma cells were inoculated to C57BL/6 mice for inducing experimental melanoma tumor. Tumors were removed and analyzed by lectin-histochemistry using LABA, PFA, PNA, HPA, SNA, GNA, and NPL lectins and stained with hematoxylin and eosin. NPL lectin was conjugated to fluorescent NaGdF4:Eu3+-COOH nanoparticles (5 nm) via zero length cross-linking reaction, and the conjugates were purified from unbound substances and then used for further visualization of histological samples. Fluorescent microscopy was used to visualize NPL-NaGdF4:Eu3+ with the fluorescent emission at 600-720 nm range. Results NPL lectin selectively recognized regions of undifferentiated melanoblasts surrounding neoangiogenic foci inside melanoma tumor, PNA lectin recognized differentiated melanoblasts, and LCA and WGA were bound to tumor stroma regions. NPL-NaGdF4:Eu3+ conjugated NC were efficiently detecting newly formed regions of melanoma tumor, confirmed by fluorescent microscopy in visible and near infrared mode. These conjugates possessed high photostability and were compatible with convenient xylene-based mounting systems and preserved intensive fluorescent signal at samples storage for at least 6 months. Conclusion NPL lectin-NaGdF4:Eu3+ conjugated NC permitted distinct identification of contours of the melanoma tissue on histological sections using red excitation at 590-610 nm and near infrared emission of 700-720 nm. These data are of potential practical significance for development of glycans-conjugated nanoparticles to be used for in vivo visualization of melanoma tumor.

β-NaGdF4:Eu3+ nanocrystal markers for melanoma tumor imaging

In the current paper, the strategy of tuning the optical and structural properties of Eu doped nanocrystals (NCs) is described with the emphasis on obtaining NCs with high brightness and photostability at the desired excitation and emission range. Those NCs are further chemically functionalized and covalently conjugated with lectins, providing specific (but reversible) targeting of pathological glycans on the surface of melanoma cells. Nanoconjugates are then injected intravenously into the blood stream of laboratory mice. Subsequently, histological slices were examined by fluorescence microscopy, whereas whole melanoma tumor were examined by ex vivo fluorescence imaging. Analysis revealed specific targeting, high intensity and photostability of the signal during visualization.

Crystal phase transition in LixNa1−xGdF4 solid solution nanocrystals – tuning of optical properties

The influence of precursor composition on the crystallization of LixNa1−xGdF4 is investigated and discussed. Nanocrystals are prepared from the thermal decomposition of trifluoroacetates in the presence of trioctylphosphine oxide to provide control over particle size. A crystal phase transition from hexagonal to cubic and to tetragonal is observed by increasing lithium trifluoroacetate (Li-TFA) in the solution. Controlling the composition of LixNa1−xGdF4 nanocrystals results in modified crystal field symmetry and emission properties from doped europium (Eu3+) ions. We report that for lithium (Li+) substitution <15%, the hexagonal crystal field is preferred, while the Eu3+ emission is already tuned, whereas at higher Li+ substitution, a phase change takes place and the number of crystalline matrix defects increases which is reflected in the optical properties of Eu3+. From Eu3+ emission properties, the optimum Li+ content is determined to be ∼6.2% in the prepared LixNa1−xGdF4 nanocrystals.