R.J. Wiglusz

White emission of lithium ytterbium tetraphosphate nanocrystals.

An efficient anti-Stokes white broadband emission induced by 976 nm laser diode in lithium ytterbium tetraphosphate (LiYbP4O12) nanocrystals was investigated. The emission occurs at room temperature and atmospheric pressure. Its intensity demonstrates an evident threshold dependence on the temperature and excitation density characteristic to avalanche process. The white emission is accompanied by very efficient photoconductivity characterized by microampere photocurrent which increases with the fourth order of applied incident light power (~P4). We show that this emission is critically dependent on temperature and increases significantly in vacuum. It is concluded that the anti-Stokes white emission is associated with theYb3+- CT luminescence.

Multifunctionality of GdPO4:Yb3+,Tb3+ nanocrystals – luminescence and magnetic behaviour

Multifunctional, luminescent and magnetic systems were synthesised by a co-precipitation method and broadly investigated. In our studies down- and visible up-conversion of Yb3+ and Tb3+ doped GdPO4 nanocrystals were observed. The synthesised nanomaterials were analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spectroscopic properties were determined from excitation and emission spectra together with a subsequent analysis. The build-up characteristics of luminescence decays showed the energy transfer processes that occurred. Magnetic measurements were performed by means of vibrating sample magnetometry (VSM). These nanomaterials showed intense green emission under ultraviolet (UV), 272 nm, and near infrared (NIR), 980 nm, laser excitation. The mechanism lying behind the observed spectroscopic properties was proposed. Energy transfer between Gd3+ and Tb3+ ions, as well as cooperative energy transfer from Yb3+ to Tb3+, was found to give a dual-mode luminescence. Also, quenching processes by cross-relaxation and phonon-assisted energy transfer were observed. The presence of different lanthanide ions and the influence of the finite-size effect underlie the complex behaviour observed.

The effects of down- and up-conversion on dual-mode green luminescence from Yb3+- and Tb3+-doped LaPO4 nanocrystals

Monoclinic LaPO4 nanocrystals doped with Yb3+ and Tb3+ ions were synthesised by co-precipitation followed by annealing at 900 °C. These materials exhibited intense luminescence under ultraviolet (UV) and near infrared (NIR) irradiation. The structural properties of the products were analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The obtained nanomaterials had a single phase, a spherical shape of nanocrystals and an average size of 42 ± 5 nm. The spectroscopic properties of LaPO4:Yb3+,Tb3+ nanocrystals were investigated in detail using excitation and emission spectra. Additionally, the luminescence lifetimes for both Tb3+ and Yb3+ ions were calculated from the measured decays. The optimal dopant concentrations were estimated with respect to the intensity of luminescence. A cooperative energy transfer (CET) mechanism, which causes the observed up-conversion, was proposed because of the observed dependence of integral intensity on the power of the pumping laser. The calculated efficiencies of the CET were much higher than the efficiencies of the opposing quenching processes; these parameters were measured in samples doped with high amounts of Tb3+ ions. These materials demonstrated intense green up-conversion in addition to UV-excited emission.

Synthesis, structure and luminescence properties of KEu0.01Gd0.19Yb0.8(WO4)2 powder

Abstract The synthesis of co-doped KEu 0.01 Gd 0.19 Yb 0.8 (WO 4 ) 2 was achieved by a modified Pechini method at 750 °C. The structure of obtained compound was confirmed using X-ray diffraction measurement and Raman spectroscopy. The Scherrers formula was used to confirm the grain sizes visualized by TEM technique. The grain sizes of about 100 nm of monoclinic KGW were successfully obtained by this methodology. In order to study spectroscopic properties of the prepared system the emission spectra were measured. The effective down- and up-conversion processes in non-resonant system were investigated.

An up-converting HAP@β-TCP nanocomposite activated with Er3+/Yb3+ ion pairs for bio-related applications

A HAP@β-TCP nanocomposite doped with Er3+/Yb3+ ion pairs was prepared using Pechini’s technique. The structural properties and morphology of the particles were studied by means of XRD, TEM, and DLS techniques. The cytotoxicity of the developed product was tested on canine osteosarcoma (D17) and murine macrophage (J774.E) cells. Determination of metronidazole release from the HAP@β-TCP nanocomposite was carried out using dynamic dialysis and ultracentrifugation techniques. Thorough analysis of the up-conversion properties of the prepared system was carried out, showing that the GRR depends strongly on the sample temperature induced by the optical density of excitation, and the particle size. Relatively short decay times and the behaviour of the GRR pointed towards the enhanced contribution of non-radiative processes feeding the red emission.

Synthesis and Optical Properties of Eu3+ Ion Doped Nanocrystalline Hydroxyapatites

ABSTRACT The Ca10(PO4)6(OH)2 hydroxyapatite (HA) nanopowders doped with Eu3+ ions were prepared using a wet synthesis method. Their structure and morphology were investigated. The XRD analysis has proven a single-phase of HA nanocrystallites. The average sizes of HA nanocrystallites calcinated at 400°C and 700°C were determined to be about 20 nm and 30 nm, respectively. The emission and excitation spectra as well as the fluorescence decay rates of Eu3+ ion doped HA nanocrystallites were measured. Particular attention was given to the spectroscopic properties of Eu3+ ions as a luminescent probe of nanocrystalline HA structure as a result of varying annealing temperature and dopant concentration. The Judd-Ofelt analysis of f-f transitions of Eu3+:HA nanocrystallites was performed. The effect of calcination temperatures on grain sizes and luminescence properties is noted and discussed.

Conductivity and electric properties of La1−xSrxMnO3−δ nanopowders

La0.8Sr0.2MnO3−δ was synthesized by the Pechinis method. The XRD pattern and TEM indicate the formation of the perovskite without the presence of secondary phases. It was found that La0.8Sr0.2MnO3−δ sample prepared at 1000 °C in air atmospheres, contains about 13.11% of the manganese as Mn4+ and 86.89% of the manganese as Mn3+. The electric measurements were carried out for La0.8Sr0.2MnO3–δ nanoceramics by using impedance spectroscopy methods and found to be 0.1 S/cm at 250 °C similar to the typical value of La0.8Sr0.2MnO3-δ materials. Its dependence on reciprocal temperature shows quite complicated mechanism of conduction.

Synthesis and optical properties of Eu3+ ion doped nanocrystalline hydroxya patites embedded in PMMA matrix

Abstract Transparent, luminescent and functional nanocomposites demonstrate interesting optical and mechanical properties suitable for many optoelectronic applications. Transparent polymethyl methacrylate (PMMA) polymer nanocomposites modified with thenoyltrifluoroacetonate (TAA) were fabricated by in situ polymerization and used as hosts for homogenous dispersion of 3 mol.% Eu3+: Ca10(PO4)6(OH)2 (Eu3+:HA) hydroxyapatite ∼20 nm large nanocrystals. The emission, excitation and transmission spectra as well as the fluorescence decay rates of bare Eu3+:HA nanocrystallites, Eu3+:HA embedded in the PMMA and and Eu:HA embedded in the PMMA/TTA nanocomposites were studied. The improvement of transparency was demonstrated with the addition of TTA as well as europium doped hydroxyapatites in comparison to pure PMMA matrix. The Judd-Ofelt analysis of f-f transitions of Eu3+:HA nanocrystallites, the PMMA/Eu3+:HA and the PMMA+TTA/Eu3+:HA was performed to investigate the optical behavior of the polymeric composites.

Li+ activated nanohydroxyapatite doped with Eu3+ ions enhances proliferative activity and viability of human stem progenitor cells of adipose tissue and olfactory ensheathing cells. Further perspective of nHAP:Li+, Eu3+ application in theranostics

Spinal cord injuries (SCI) often require simultaneous regeneration of nerve tissue and bone. Hydroxyapatites are described as bioresorbable materials with proper biocompatibility and osteoconductivity, therefore its application for spinal surgery is considered. In this paper, we present repeatable method for developing nanocrystalline calcium hydroxyapatites structurally modified with Li+ ions (nHAP:Li+). Obtained biomaterials were profoundly characterized in terms of their physicochemical properties. Moreover, we have shown that nHAP:Li+ doped with europium (Eu3+) may serve as a theranostic agent, what additionally extend its potential usage for SCI treatment. The biocompatibility of nHAP:Li+ was determined using human olfactory ensheathing cells (hOECs) and adipose tissue-derived multipotent stromal cells (hASCs). Both population of cells are eagerly applied for cell-based therapies in SCI, mainly due to their paracrine activity. The extensive in vitro studies showed that nHAP:Li+ promotes the cells proliferation, viability and cell-cell interactions. Obtained results provides encouraging approach that may have potential application in regenerative medicine and that could fulfil the promise of personalized medicine - important in SCI treatment.

Multifunctional nanocrystalline calcium phosphates loaded with Tetracycline antibiotic combined with human adipose derived mesenchymal stromal stem cells (hASCs).

Osteoconductive drug delivery system composed of nanocrystalline calcium phosphates (Ca10(PO4)6(OH)2/β-Ca3(PO4)2) co-doped with Yb(3+)/Er(3+) ions loaded with Tetracycline antibiotic (TC) was developed. Their effect on human adipose derived mesenchymal stromal stem cells (hASCs) as a potential reconstructive biomaterial for bone tissue regeneration was studied. The XRD and TEM measurements were used in order to determine the crystal structure and morphology of the final products. The characteristics of nanocomposites with the TC and hASCs as potential regenerative materials as well as the antimicrobial activity of the nanoparticles against: Staphylococcus aureus ATCC 25923 as a model of the Gram-positive bacteria, Escherichia coli ATCC 8739 of the Gram-negative bacteria, were shown. These combinations can be a promising material for theranostic due to its regenerative, antimicrobial and fluorescent properties.