Dominika Wawrzynczyk

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.

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.

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.

Tuning red-green-white up-conversion color in nano NaYF4:Er/Yb phosphor

Abstract The possibility of tuning between red, green and broadband white color of up-conversion was demonstrated in thermally 450 °C treated Yb/Er co-doped nano NaYF 4 phosphor. The color variability was studied by means of power dependence of luminescence, which exhibited unusual behavior. Large hysteresis, as well as discrepancy from a power law indicated the important role the increased heating played during the up-conversion in nano-sized materials.

Multiphoton absorption in europium(III) doped YVO4 nanoparticles

We report the synthesis and physicochemical characterization of YVO4 nanocrystals doped with Eu3+ ions. The adopted solvothermal synthesis procedure rendered YVO4 nanoparticles with tetragonal crystal structure and rod-like morphology. The absorption and excitation spectra of the studied nanoparticles showed UV bands which were attributed to the 1A1 → 1T2 and 1A1 → 1T1 electronic transitions in the vanadate group, respectively. The nonlinear optical properties of both undoped YVO4 nanocrystals and those doped with Eu3+ ions were studied by wide wavelength range (600–1600 nm) femtosecond Z-scan measurements. The experiments revealed strong multiphoton absorption in the wavelengths around 650 and 1300 nm, within the first and second biological window. This nonlinear absorption results in multiphoton excitation of red europium emission from the nanoparticles, making them potential candidates for application as markers in nonlinear microscopy imaging techniques.

Microwave-assisted synthesis and single particle spectroscopy of infrared down- and visible up-conversion in Er3+ and Yb3+ co-doped fluoride nanowires

We report a comprehensive study on the influence of solvent and organic ligands on the up-converted emission characteristics of NaYF4 nanowires. We have modified the hydrothermal reaction procedure, and used a “microwave flash heating method” to obtain 1.5 μm long and 100 nm wide up-converting NaYF4 nanowires. As-synthesized particles were dispersed in cyclohexane, and a ligand removal procedure has been performed leading to nanowires soluble in water and heavy water. The infrared emission of Er3+ ions was quenched through coupling to the vibrational modes of water molecules and the values of slopes of double logarithmic plots of power dependencies were changed. Besides the spectroscopic characterization of colloidal solutions of NaYF4 up-converting nanowires, we have also performed single particle studies of steady-state emission and luminescence kinetics. In the case of solvent-free separated particles, the ligand molecules provided the main nonradiative depopulation channels, and efficiently shortened the luminescence lifetimes. The output luminescence color also varied for colloidal solutions and single particle studies, which can be of importance for imaging and single particle tracking applications.

Third-order nonlinear optical response of CuInS2 quantum dots—Bright probes for near-infrared biodetection

Nonlinear refraction and nonlinear absorption in stoichiometric colloidal CuInS2 quantum dots, with absorption edge tuned up to the visible spectral region, were investigated. The nonlinear optical response of the quantum dots was measured in a wide range of wavelengths (700–1600 nm) using the Z-scan technique. The measurements revealed the presence of two-photon absorption in the near-infrared range and the negative nonlinear refraction in almost whole spectral range for all the investigated nanoparticles. The cubic nonlinearity of CuInS2 quantum dots is discussed in terms of defect-related optical properties of the material. The results indicate that CuInS2 quantum dots may be an interesting material for the single and multiphoton luminescence bio-detection techniques.

Optical nonlinearities and two-photon excited time-resolved luminescence in colloidal quantum-confined CuInS2/ZnS heterostructures

Comprehensive studies on the spectral dependencies of third-order nonlinear optical properties and one/two-photon excited time-resolved luminescence of quantum-confined ternary CuInS2/ZnS core/shell heterostructures with reference to their corresponding uncoated CuInS2 cores are presented in this work. Nonlinear refraction and nonlinear absorption in the quantum confined type-I core/shell CuInS2/ZnS and their corresponding CuInS2 cores were measured over a wide range of wavelengths (550–1500 nm) using the Z-scan technique. The results revealed the presence of size-dependent two-photon absorption bands in the red and near-infrared spectral range. The cubic nonlinearity of core/shell CuInS2/ZnS quantum heterostructures is discussed in terms of both the CuInS2 cores optical transitions and the impact of the wide-gap ZnS shell layer. Kinetics of recombination of the single/two-photon excited states was investigated with femtosecond time-resolved photoluminescence spectroscopy revealing the complex character of electronic relaxation. A general statistical model involving normalized discrete distribution of decay rates was used for the analysis of luminescence decay curves. Different relaxation paths including the excitonic relaxation, donor–acceptor pair recombination and free-to-bound state recombination are discussed. The results indicate that optical properties of the CuInS2/ZnS and CuInS2 quantum dots are well suited for the steady-state as well as time-resolved single/multiphoton fluorescent techniques utilized commonly for the bio-sensing issues.

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ2 for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ2Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for n...

Nonlinear absorption and nonlinear refraction: maximizing the merit factors

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications.