Pavol Hronec

CdS/ZnS nanocomposites: from mechanochemical synthesis to cytotoxicity issues.

CdS/ZnS nanocomposites have been prepared by a two-step solid-state mechanochemical synthesis. CdS has been prepared from cadmium acetate and sodium sulfide precursors in the first step. The obtained cubic CdS (hawleyite, JCPDS 00-010-0454) was then mixed in the second step with the cubic ZnS (sphalerite, JCPDS 00-005-0566) synthesized mechanochemically from the analogous precursors. The crystallite sizes of the new type CdS/ZnS nanocomposite, calculated based on the XRD data, were 3-4 nm for both phases. The synthesized nanoparticles have been further characterized by high-resolution transmission electron microscopy (HRTEM) and micro-photoluminescence (μPL) spectroscopy. The PL emission peaks in the PL spectra are attributed to the recombination of holes/electrons in the nanocomposites occurring in depth associated with Cd, Zn vacancies and S interstitials. Their photocatalytic activity was also measured. In the photocatalytic activity tests to decolorize Methyl Orange dye aqueous solution, the process is faster and its effectivity is higher when using CdS/ZnS nanocomposite, compared to single phase CdS. Very low cytotoxic activity (high viability) of the cancer cell lines (selected as models of living cells) has been evidenced for CdS/ZnS in comparison with CdS alone. This fact is in a close relationship with Cd(II) ions dissolution tested in a physiological solution. The concentration of cadmium dissolved from CdS/ZnS nanocomposites with variable Cd:Zn ratio was 2.5-5.0 μg.mL(-1), whereas the concentration for pure CdS was much higher - 53 μg.ml(-1). The presence of ZnS in the nanocrystalline composite strongly reduced the release of cadmium into the physiological solution, which simulated the environment in the human body. The obtained CdS/ZnS quantum dots can serve as labeling media and co-agents in future anti-cancer drugs, because of their potential in theranostic applications.

Biodegradation of Benzo[a]Pyrene through the use of algae

AbstractIn this work for disposal of the biologically hard decomposed pollutant Benzo[a]Pyrene (BaP) photooxidation Chlorella kessleri was used. The simulation model system under the different experimental conditions (varying biomass and light intensity) was evaluated. For quantitative analysis of the decrease in BaP, GC/MS technique was used. The highest degradation efficiency was achieved in the case of biomass from the culture of live algae (29%) and light intensity at level of 13.5 W m−2. When the dry biomass was used, degradation under the same conditions was lower because of lack of enzymatic activity in the system.

PDMS membranes with 2D PhC for LEDs far-field pattern modification

In this paper we present new imprinting process for fabrication of PhC structures on surface of thin PDMS membranes. We used interference lithography in combination with imprinting technique. 2D PhC surface relief structures of period 495 nm were patterned in thin PDMS membranes with depth up to 100 nm. Patterned PDMS membranes placed on different optoelectronic device surface could modify the final optical properties.

Optical and electrical characterization of photonic crystal light emitting diodes

The paper deals with electrical and optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (MQW LED) structure including two-dimensional photonic crystals (2D PhC) patterned in the LED surface. The active region of LED consists of three quantum wells with emitting maximum at 845 nm. The effect of photonic crystal with square symmetry and 500 nm grating period on electrical and optical properties of LED was investigated. The measurements of L-I characteristics show, that app. 3 times higher optical power from LED structure was achieved using photonic crystals in comparison with structure without PhC.

LEDs with photonic crystal and quasicrystal investigated in near and far field

It was confirmed that photonic crystals (PhC) have the considerable effect on enhancement of extraction efficiency of light emitting diodes (LED) by minimizing the total internal reflection of the light escaping the LED chip. The enhancement of the extraction efficiency requires a structure design that optimizes the interaction of the guided modes with the PhCs. It strongly depends on the structure parameters as depth, period and filling factor. On the other side, choice of PhC geometry plays important role in determining of far-field radiation pattern diagram of the LED. From the point of structure shape and geometry, different PhC and photonic quasicrystals (PQC) were investigated. The PQCs with high level of symmetry produce less directional emission and it favors the PQC structure for application in LED.

Improving light extraction efficiency of PhC LED

In this work we focus on improving light extraction efficiency of PhC LED. Studied LED structure was based on GaAs/AlGaAs material system. 1D PhC was patterned on the top of the LED structure with 3 different periods (500 nm, 600 nm, 800 nm). Several studies confirm improving light extraction efficiency of studied LED structure using PhC patterning. In this work, additional thin Au or ZnO layer was deposited on the top of the patterned PhC. Additional layers improved light extraction efficiency (LEE) for PhC LED. The best results were achieved for Au deposited PhC LED sample with LEE enhancement of 59%.

Optical properties of LEDs with patterned 1D photonic crystal

In this paper we focus on the application of the one-dimensional photonic crystal (1D PhC) structures on the top of Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (MQW LED). 1D PhC structures with periods of 600 nm, 700 nm, 800 nm, and 900 nm were fabricated by the E-Beam Direct Write (EBDW) Lithography. Effect of 1D PhC period on the light extraction enhancement was studied. 1D PhC LED radiation profiles were obtained from Near Surface Light Emission Images (NSLEI). Measurements showed the strongest light extraction enhancement using 800 nm period of PhC. Investigation of PhC LED radiation profiles showed strong light decoupling when light reaches PhC structure. Achieved LEE was from 22.6% for 600 nm PhC LED to 47.0% for 800 nm PhC LED. LED with PhC structure at its surface was simulated by FDTD simulation method under excitation of appropriate launch field.

Far Field Measurements of Phc Led Prepared by E–Beam Lithography

Abstract The paper deals with optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (LED) structure with photonic crystal (2D PhC) patterned on the top of the structure using Electron Beam Direct Write Lithography (EBDWL). Light-current characteristics measured by integrating sphere shows increase of extracted light intensity as 21.1%. Additionally, extracted light intensity was studied by far-field measurements as a complementary method to light-current characteristics. The far-field measurements show increase of extracted light intensity as 31.2%. We suggest this method as more suitable for evaluation of extracted light intensity because it omits emission from edges of the LED and thus light is measured only from the area where PhC is patterned

Optical Investigation of the AlGaAs/GaAs LED with Photonic Structures Patterned by the EBDW Lithography

In this work we focus on the application of the two dimensional photonic crystal (2D PhC) embedded in the surface of Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (LED) to enable improvement of the light extraction from the LEDs. The 2D PhC structures described in this contribution were fabricated by the E-Beam Direct Write (EBDW) Lithography and consist of pillars with the period of 700 nm. In this paper a new approach is presented to measure the PhC-LEDs based on evaluating light-current characteristics from Near Surface Light Emission Image (NSLEI) measurements in comparison with standard light-current characteristics measured by integrating sphere. The measured LED emission intensity increased by 20-30% when PhC was patterned on the top of LED structure in comparison with the reference LED without PhC. In addition, it was found that the measured light extraction intensity is higher in the case of NSLEI measurements. This originates in the ability that mostly the light intensity emitted from the LED surface is measured while the edge emission effect is suppressed.

Far-field pattern modification of LEDs with 2D PhC PDMS membrane

In this paper we present results of an implementation of thin two-dimensional (2D) photonic crystal (PhC) patterned in thin polydimethylsiloxane (PDMS) membranes on the light emitting diode (LED) surface. PDMS membranes were patterned by using the interference lithography in combination with imprinting technique. 2D PhC surface relief structures of period 580 nm were patterned in thin PDMS membranes with depth up to 150 nm. Patterned PDMS membranes placed on different optoelectronic device surface could modify the final optical properties.