Lukas Ondic

• PhD
• Researcher at The Czech Academy of Sciences

ZrN nanofluids may exhibit unique optoelectronic properties because of the matching of the solar spectrum with interband transitions and localized surface plasmon resonance (LSPR). Nevertheless, these nanofluids have scarcely been...

Diamond thin films can be, at a relatively low-cost, prepared with a high-density of light-emitting negatively charged silicon vacancy (SiV) centers, which opens up the possibility of their application in photonics or sensing. The films are composed of diamond grains with both the SiV centers and sp2-carbon phase, the ratio of these two components...

We report the development of a new methodology for the preparation of cyclic tetrasubstituted alkenes with π‐conjugated substituents. The synthesis of the target compounds was accomplished through the regioselective cross‐coupling reaction of diphenyl bromocyclohexenyl phosphate with organozinc reagents. The procedure succeeded in the preparation o...

The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extract...

Apart from the frequently used high-temperature annealing of detonation nanodiamonds (DNDs) in an inert environment, laser irradiation of DNDs in a liquid can be effectively used for onion-like carbon (OLC) formation. Here, we used fully de-aggregated hydrogenated DNDs (H-DNDs) dispersed in ethanol, which were irradiated for up to 60 min using a 53...

Colloidal solutions of metal nanoparticles (NPs) are typically produced by multi-step methods using a variety of chemicals. Resultant nanofluids require extra purification steps to remove the reactions by-products and modification steps to introduce anticoagulants for the solution stabilization. Here, we suggest a single-step method to produce nano...

Diamond optical centers emerged recently as promising single-photon sources for quantum photonics. Particularly, negatively charged silicon vacancy (SiV⁻) centers show great promise due to their narrow zero-phonon emission line present also at room temperature. However, due to fabrication tolerances it is challenging to prepare directly photonic st...

Time-resolved photoluminescence (PL) is commonly used to track dynamics in a broad range of materials. Thus, the search for simplification of the acquisition of PL kinetics attracts continuous attention. This paper presents a new robust and straightforward approach to the measurement of PL decay, which is based on randomly fluctuating excitation in...

Time-resolved photoluminescence (PL) is commonly used to track dynamics in a broad range of materials. Thus, the search for simplification of the acquisition of PL kinetics attracts continuous attention. This paper presents a new robust and straightforward approach to the measurement of PL decay, which is based on randomly fluctuating excitation in...

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force and light detection capabilities. Role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), u...

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force and light detection capabilities. Role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), u...

This paper reports on the observation of an electronic energy transfer channel between silicon nanocrystals and the SiO2 matrix they are embedded in. This energy transfer manifests itself by photoluminescence at 650 nm, i.e. above the indirect band gap, in superlattices formed by alternating layers of P- or B-doped as well as undoped silicon nanocr...

Optical losses of a host material together with the total internal reflection phenomenon can significantly reduce photoluminescence external quantum efficiency of embedded light-emitters. This is not only the case for light-emitting color centers in thin layers of nanocrystalline diamond, but also for silicon nanocrystals in silica dioxide matrices...

The forces acting on optically trapped particles are commonly assumed to be conservative. Nonconservative scattering forces induce toroidal currents in overdamped liquid environments, with negligible effects on position fluctuations. However, their impact in the underdamped regime remains unexplored. Here, we study the effect of nonconservative sca...

As a first approximation, the forces acting on optically trapped particles are commonly assumed to be conservative. The influence of the nonconservative force has been shown to be negligible in overdamped liquid environments. However, its impact in the underdamped regime remains unexplored. Here, we experimentally study the combined effects of grad...

We have fabricated two-dimensional photonic crystals (PhCs) on the surface of Si nanocrystal-rich SiO2 layers with the goal to maximize the photoluminescence extraction efficiency in the normal direction. The fabricated periodic structures consist of columns ordered into square and hexagonal pattern with lattice constants computed such that the red...

Additional experimental data.

Color centers in diamond have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report the optoelectronic investigation of shallow silicon vacancy (SiV) color centers in ultra-thin (7–40 nm) nanocrystalline diamond (NCD) films with variable surface chemistry. We show that hydrogenated ultr...

We demonstrate the fabrication of a polycrystalline diamond-based two-dimensional photonic crystal (PhC) slab using microsphere lithography (MSL). First, the essential issues of MSL on rough diamond surfaces are demonstrated. The peak-to-valley value of the rough surfaces is shown as the most important parameter in choosing the appropriate sphere s...

Polycrystalline diamond-based photonic crystal slabs were designed using computer simulation and fabricated employing optimized focused ion beam milling technique. Such samples could be used to control light emission from diamond optical centers.

Light extraction from a thin planar layer can be increased by introducing a two-dimensional periodic pattern on its surface. This structure, the so-called photonic crystal (PhC) slab, then not only enhances the extraction efficiency of light but can direct the extracted emission into desired angles. Careful design of the structures is important in...

Color centers in diamond have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of as thin as 5-6 nm nanocrystalline diamond (NCD) films with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4-6 nm de...

Silicon vacancy (SiV) centers are optically active defects in diamond. The SiV centers, in contrast to nitrogen vacancy (NV) centers, possess narrow and efficient luminescence spectrum (centered at ≈738 nm) even at room temperature, which can be utilized for quantum photonics and sensing applications. However, most of light generated in diamond is...

1. Fabrication Figure S1 shows SEM images of the sample in different stages of preparation process and cross-sectional SEM images of the grown diamond films on reference samples. Details are described in the Methods section of the main text. (e) Fig. S1: Preparation of samples: (a) holes in PMMA prepared by EBL; (b) metal caps on SiO 2 after PMMA r...

Photoluminescence of 5 nm detonation nanodiamonds (DNDs) is studied as a function of their surface treatment (hydrogenation/oxidation) and underlying substrate materials (silicon, gold, platinum, and nickel). The sub-strates affect DND photoluminescence emission spectrum and lifetime in the spectral range of 600–800 nm. The dependence is different...

High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterize...

Silicon, a semiconductor underpinning the vast majority of microelectronics, is an indirect-gap material and consequently is an inefficient light emitter. This hampers the ongoing worldwide effort towards the integration of optoelectronics on silicon wafers. Even though silicon nanocrystals are much better light emitters, they retain the indirect-g...

Silicon nanocrystals (SiNCs) smaller than 5 nm are a material with strong visible photoluminescence (PL). However, the physical origin of the PL, which, in the case of oxide-passivated SiNCs, is typically composed of a slow-decaying red-orange band (S-band) and of a fast-decaying blue-green band (F-band), is still not fully understood. Here we pres...

Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a prerequisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular inter...

Diamond-based materials exhibit many unique properties, one of them being a broad-band visible photoluminescence (PL) due to a variety of color centers. However, the PL extraction from the diamond layer is inefficient due to high material refractive index. One possibility of increasing the extraction efficiency is by employing a shallow two-dimensi...

A two-dimensional photonic crystal (PhC) slab was fabricated from a luminescent planar waveguide, formed by a (800 nm thick) layer of silicon nanocrystals (SiNCs) embedded in a polished silica plate. Dimensions of the PhC were designed so that light emitted by SiNCs under excitation with an external UV source can, during its propagation in the laye...

Detailed analysis of a band diagram of a photonic crystal (PhC) slab prepared on a nano-diamond layer is presented. Even though the PhC is structurally imperfect, the existence of leaky modes, determined both theoretically and experimentally in the broad spectral region, implies that an efficient light interaction with a material periodicity occurs...

Video 1

Supplementary Information

We collect a large number of experimental data from various sources to demonstrate that free-standing (FS) oxide-passivated silicon nanocrystals (SiNCs) exhibit considerably blueshifted emission, by 200 meV on average, compared to those prepared as matrix-embedded (ME) ones of the same size. This is suggested to arise from compressive strain, exert...

One of the possibilities of increasing optical gain of a light emitting source is by embedding it into a photonic crystal (PhC). If the properties of the PhC are tuned so that the emission wavelength of the light source with gain falls close to the photonic band edge of the PhC, then due to low group velocity of the light modes near the band edge c...

Raman spectroscopy is used as a tool for measuring the light trapping abilities of thin crystalline silicon films for photovoltaic applications. Comparison of samples with different scattering characteristic is reported and the significant difference in the absolute Raman intensities is explained by light trapping effects. Raman spectroscopy is pro...

Two-dimensional photonic crystal can be exploited as the top part of a light source in order to increase its extraction efficiency. Here, we report on the room-temperature intrinsic photoluminescence (PL) behavior of a nanocrystalline diamond (NCD) layer with diamond columns prepared on the top and periodically ordered into the lattice with square...

Diamond-based materials possess many unique properties, one of them being a broad-band visible photoluminescence due to a variety of color centers. However, a high material refractive index makes the extraction of photoluminescence (PL) from a diamond layer inefficient. In this paper, we show that by periodical nanopatterning of the film's surface...

In this paper, we present time-resolved optical gain spectroscopy using a combination of the variable stripe length and the shifting excitation spot techniques under pulsed nanosecond excitation at 355 nm. Optical gain measurements in the temporal detection window of 10 ns width, coincident with the excitation pulse, revealed induced absorption los...

We present a study of ultrafast carrier transfer from highly luminescent states inside the core of silicon nanocrystal (due to quasidirect transitions) to states on the nanocrystal-matrix interface. This transfer leads to a sub-picosecond luminescence decay, which is followed by a slower decay component induced by carrier relaxation to lower interf...

Intensified charge-coupled devices (ICCDs) comprise the advantages of both fast gating detectors and spectrally broad CCDs into one device that enables temporally and spectrally resolved measurements with a few nanosecond resolution. Gating of the measured signal occurs in the image intensifier tube, where a high voltage is applied between the dete...

Small oxidized silicon nanocrystals of average sizes below 3.5 nm are prepared using modified electrochemical etching of a silicon wafer. Modifications introduced in the etching procedure together with postetching treatment in H ₂ O ₂ lead to a decrease in the nanocrystalline core size and also, to some extent, to changes in t...

In this paper we present time-resolved optical gain spectroscopy using the variable stripe length technique in combination with the shifting excitation spot technique under pumping with nanosecond laser pulses. Measurements reveal positive optical gain on a nanosecond time scale at 430 nm (F-band), accompanied by spectral narrowing and a threshold...